Just curious with the talk about insulating inside or outside a concrete foundation, why the ‘green’ builders aren’t making PT wood foundations? What’s not to love, other than suspected carcinogens? Not concerned here with resale, just environmental aspects.
I made mine because it was lots cheaper than concrete, i could DIY every bit of it, i had 5-1/2″ cavities to insulate, studs to screw to, no big trucks to get stuck, and it’s a renewable resource.
Shelternerd? Riversong? Anyone?
Framing the floor inside a crawlspace foundation keeps a gable-end addition close to grade.
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Replies
other than suspected carcinogens .... just environmental aspects
I don't get you guys ...
I don't think there would be any environmental concerns, carcinogens or otherwise with PT foundation. In past there was some concern that PT would eventually leach arsenic into the ground water. Is arsenic a carcinogen--I don't know. Anyway, not if that is a concern with the new PT which is Ammoniated Copper Quatenary, IIRC, which is, as far as I know, a copper salt. As for as green, I don't think you could get much better, except I do remember the caulk we use to seal joints was pretty nasty and was bad to breathe. And the beauty is that even the color is green!
Well, i tossed out the "suspected carcinogens" tag a bit too lightly....but yes, the stuff they thought might perhaps be leaching out of the CCA stuff was the only drawback i could see to what otherwise would seem a very environmentally benign foundation.
I had a truck show up with a load of PT ply and 2x6's, slide them on the ground, and working by myself had a 35x42 foundation built in a week - all screwed together, not nailed - using only a miter saw and a drill. I was able to do it by making panels, then standing them up. (I had help with that part.) It seems like such an easy DIY, and waterproofing with the plastic dimple fabric is such a breeze, too, compared to the contortions people go through with tar and all that nasty stuff.
Is there any reason to waterproof them if they are buried in dirt on both sides? I dont think I did but I can't remember. Bob's next test date: 12/10/07
I can't imagine building ANY foundation without waterproofing the outside wall.
After suffering through a catastrophe in my last walk-out basement shop after getting heavy rain on a heavy snowpack, i don't ever want to deal with water in the basement again.
That one, concrete, had been treated in the traditional manner by the builder, with tar, even though everyone i talked to recognized tarring is just about useless at keeping groundwater out. Just as i started boring in on basement waterproofing JLC ran an article on the subject featuring the dimple fabric on the cover, IIRC. FHB followed with a similar article and i was off to the races phoning the guy importing the stuff, because no one locally had ever heard of such a thing.
The only thing I can think of is that the dirt "contained" within the foundation would probably stay dry and therfore wouldn't be as much of a heat sink--wouldn't suck so much heat out of the building itself.
I like the idea of wood foundations. But they don't seem to have caught on.
I did one. I wouldn't do another unless forced into it. Bob's next test date: 12/10/07
Curious as to what you didn't like about it.
I don't like working with treated lumber in general. It has poison in it that is released when we run the saws through it. It rubs off onto our skin. I'm a bit paranoid about stuff like that.I didn't like the weight of the materials. I don't like searching for special nails. I don't like answering questions about it's stability and longevity record although I did get a chuckle out of telling a know-it-all that I would get a 50 year warranty and the best he could do on his block basement was get a 1 year warranty. That's enough dislikes to move it to the "not use" column. Bob's next test date: 12/10/07
I didn't like the weight of the materials.
Still lighter than concrete, though...
I did a concrete footing with rebar bec i was on a glacial sand bar, but i'd think a gravel footing would do just as well with better soil for it. The whole house ends up being a lot (technical term) lighter without having to support all that concrete.
And sooooooooo easy to insulate and finish the basement inside....
The idea of wood foundations seems bad to me. Which is why it hasn't caught on. Wood underground will rot here, it's wet. I don't trust the treatment to be effective long term, and I don't think it would be as waterproof as concrete or as strong. If it was a dry climate, I would probably not be so concerned about failure.
The wood doesn't rot. I don't know the current standards on the ACQ wood, but with the CCA-treated stuff i used, i ordered a special grade treated for use below-ground, not just ground-contact that you can buy off the shelf. Ply, too. I had 16' 2x6s delivered bec they tend to be a better quality than the 8'-long ones; when i cut them, i put the factory-treated end on the bottom plate.
I used plastic dimple fabric on the outside of it and a socked footing drain. Even in an un-guttered valley, i've had zero moisture infiltrate, and i left that inside corner inthe utility room exposed so i could check that most-vulnerable location. If it isn't getting wet, then it's not going to rot anyway, but the CCA treatment is belt-and-suspenders, as i see it.
This is an 'official' construction method ... that the American Plywood Association has endorsed for a long time. It's bonified!! I did one in the early 80s ... full finished basement. The house is still standing. Structurally sound method. Don't know about the ramifications in extra wet areas ... you always have to provide propper drainage for any basement wall. Assuming that happens, there should be no issues. Fewer environmnental/health issues w/ the newer chemical treatments used.
Wish I'd read this before I started pouring my foundation...
Would there be any concerns about using a wood floor for a basement instead of concrete slab? I've never been a fan of concrete floors. Basically use standard floor joists (pressure treated)suspended over gravel w/vapor barrier, and EPS insulation? Joists would sit on the footings only (We have an interior footing for a shear wall anyway). Would save about 12 yards of concrete. We are in the pacific northwet, I mean northwest...
Preserved wood foundations are the norm here in the Yukon. Our dry climate, good drainage and lack of clay soils make them the cheapest option. The expansive clay soils found in other parts of the country require engineers to design and stamp the designs but it's not required here.
There are import details that must be followed such as not drilling and bolting the bottom plate (use powder actuated fasteners), not drilling the studs for the wiring (up and through the top plate only) and using the floor joists or concrete slab to resist the side thrust of the back fill. The back fill must not be compacted either. Solid blocking is required along plywood seems too.
I have the code books at work if anyone has any specific questions.
John
I'd be interested in wood basement floor details, if those are included. How big should expansion gaps be with a concrete foundation wall, wood sleepers vs. beams on piers. Insulation, vapor barrier and sub floor gravel and drainage details. Also, should the joist be anchored down in center of span to resist any forces at base of foundation walls?
Thanks
Dave
I'm not sure what you mean by expansion gaps with a concrete foundation wall. Poured concrecte foundations are very rare here. Pwf foundations rely on the floor joists to resist the pressure of the backfill so there should not be any expansion gaps. Pwf sleepers are common and they lie on top of a 6 mil vapour barrier. Floor joists would have solid blocking at the center beam to prevent twisting and usually every 4', especially at the edge to resist the soil pressure.
I'll bring my copy of the code home tomorrow to add to the discussion.
Depending on the span of the joists, and whether or not there is a wall down the center of the basement, I would think it may not be a bad idea to put something in to anchor the center of the joists--if only a grade beam (sleeper?--not sure of the proper term) staked to the ground so side pressure on the joists wouldn't bow them upward. Like someone else said, twisting or sideways deflection is probably more likely though (such a beam would help with that too, but blocking would be easier and cheaper).
I'm from the Northwet, too ... you were right the first time.
Actually the APA does have an all wood foundation/floor system if I remember correctly, so sounds like you've got the idea going in the right direction. I'd think that the APA would still have a brochure/booklet dedicated to wood foundation systems, how to, structure, etc. I would follow their lead. They wouldn't be suggesting something they didn't think would work.
Let me know if you are having difficulty finding info. BTW where in the NW?
Dig a moat around your house and pour in the poison!
Think about it!
I trimmed my second floor in MDF,, made the trim myself. My entire family got sick from it for months! I still love MDF,, but there is a wild card in there for sure!
d
I happen to like concrete foundations. In fact when shopping for a home, the slab is what sold me. Lumber is dead organic material that we like to build with. No matter what we treat it with, eventually mother nature prevails and takes it back. Slabs are colder in the winter but with a built up sub-floor, you can have any type of floor you want. I need a concrete saw to get to some of my plumbing, but at least I know my floor wont rot if a leak goes undetected. As far as cost goes, concrete is (or at least was) relatively cheap, especially in the long run.
Each to his own ... I totally respect that. I've no leanings one way or another. My first house was a wood foundation wall on a concrete slab ... buried 8 ft on 3 sides. It still stands and that was 30 years ago. My recent house was all concrete foundation.
I disagree about cost. WEIGHT is proportional to cost, generally speaking. Concrete is the most expensive construction material. You pour a slab and then ALSO finish it with other flooring ... especially wood ... your cost is even higher. That is part of the reasons my new house has a radiant slab and I acid etched it for finish. My acid etching cost me 50 cents a sqft (DIY).
Long term though, I believe concrete to be cheaper. Little to no replacement costs as compared to a floor joist. I bought the house with carpet. Bad choice on the sellers part. I've gradually begun replacing the carpet with ceramic tile. I haven't decided what to do for the bedrooms, the carpet there is already starting to go. I've been thinking about laminate, at least for a short term replacement, but would really like hardwood. Your right, hardwood would be expensive. Especially the way I would like to build the subfloor. Even those new floating OSB floors basically just double the cost of a hardwood installation. I'm not a big fan of gluing plywood to the slab, especially just regular old construction grade plywood. Good plywood is about three or four times the cost. I'm getting off topic.
Green? Only in color. And "green" must also mean durable - able to at least outlive all its impacts on the environment. The long-term durability of underground PT wood is an unknown. It's effects on the environment, however, are well known.
PT foundations use 0.60 lbs/cf of CCA instead of 0.40 lbs/cf for ground contact rated.
CCA-treated wood was banned for use in zoos long before it was banned for use in residential applications.
http://www.healthybuilding.net/arsenic/hbn_wood_factsheet.html
Why is arsenic wood a problem?
Solar & Super-Insulated Healthy Homes
In the case of a foundation, however, the wood is not accessible to handling, being covered on both sides. If built properly with a water barrier, it can't leach arsenic into the soil. The part about arsenic released by a house fire is an issue, but certainly there are much more horrible things in my basement to burn in case of a fire than my foundation.
That site lists ACQ-treated wood as a 'healthy' alternative. The "Preserve Plus" that at Treatedwood.com, a link recommended on that website, shows that they have burial-rated treatments (.60 pcf) of friendlier preservative-treated wood.
I was hoping to see a comparison of a wood-foundation as it would be made today to a concrete foundation and all that it takes to make one of each. I've been thinking about embodied energy and although there are too many variables to make exact comparisons, i was looking for a place to start on an evaluation.
On the face of it...
The wood foundation has the logging, the milling, and the treating. No drying involved, so no kilns to run, and it uses relatively low-grade softwoods. One rather small flat-bed dumped all my materials in one trip and i needed only a drill and miter saw to assemble it. When it was done, it was done.
On the other hand...the concrete foundation has a truck to bring forms, a truck or two to deliver, a truck to pick up forms, metal reinforcement, quarrying of materials plus screening or crushing, baking of limestone, assembly of materials at a batch plant, and a whole lot of workers. Some curing time. An advantage is that fly ash from the electricity industry can be used up in concrete and the high temps in the cement kilns are useful for burning hazardous waste such a tires.
BuildingGreen.com had a paper on the energy consumption of concrete. http://www.wbcsd.org/web/projects/cement/tf2/cementconc.pdf
I'm don't know who the reliable players are in your world, but this is what those particular folks said about concrete that makes me go "hmmm...":
They show 1.7 million BTU's of embodied energy in a yard of concrete based on concrete hauled 5 miles to the building site, a relatively urban experience from mine, and 631# of CO2 produced per yard. Here's another snippet:
They talk about the dust acidifying surrounding water, that concrete is seldom recycled and yet is 67% by weight of landfill disposal, and that excess concrete after a pour is a long-standing disposal problem. It said while concrete itself is chemically inert, the admixtures, form releases and surface treatments can bother chemically sensitive individuals.
I got to thinking that perhaps all the discussion about insulation inside or outside the thermal mass was analogous to deciding whether to put Michelins or Bridgestones on the Hummer.
I found one link i could actually understand talking about embodied energy of wood vis-a-vis concrete (and steel). It says the EE of wood homes is less than half that of concrete homes. They're referencing borate-treated wood, however, and it's not clear to me if that are saying it can be used below ground.
http://www.icup.org.uk/reports%5CICUP228.pdf
Edited 2/20/2008 5:46 pm by splintergroupie
Though I've found no figures on the embodied energy of PT wood, any wood structure will have less environmental impact than an equivalent concrete one, as long as it has reasonable durability and it's not as toxic as CCA and it's disposed of properly at the end of its usable life.
Bottom line for me, though, is that the "greenest" basement is none at all. Since we should all be building homes so energy-efficient that they require only the most compact of mechanical systems and because we should all be consuming and hoarding less "stuff", it's hard to justify a basement unless the lot is suitable for a walkout which can have enough fenestration and ventilation to make it truly livable space - and by using the basement for living space, we reduce the upper level(s) proportionately.
[By the way, contrary to your assessment, PT lumber is kiln dried before treatment.]
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I guess that answers my question about relative embodied energy, but it's even more perplexing why the use of concrete is so ubiquitous in green building schemes.
Sometimes a basement is a woodshop not a junk storage facility, which parsimoniously shares a roof and foundation with the living space and enables a short commute to work. <G>
Thanks for correction on the KD process for PT wood.
...but it's even more perplexing why the use of concrete is so ubiquitous in green building schemes.
Because most "green" building ain't.
The first LEED-Gold "green" building in NYC:
View Image
Do you disagree with the facts, or that it should have been constructed at all, or something else?
Hearst Corporation ain't green. William Randolph Hearst wasn't green.
Now his castle in San Simeon might have been greenish if it wasn't quite so big.
View Image
It doesn't have a basement? <G>
I've been thinking about the previous discussion about basement-no basement talk.
A good friend of mine has been designing houses with what he calls a "Core". Basically most of the house is on grade, while a small section has a crawl space. To house the utilities, plumbing etc.
Which got me to thinking how this is so much like the old houses I work on day in day out.
Small cellar with crawl spaces every where else.
As usual the old timers had it worked out pretty well.
PT lumber is available "Kiln Dried After Treatment" the grading stamp bears the acronym "KDAT"
I'd claimed that PT lumber didn't need to be kiln-dried at all, which prompted RS to say it's kiln-dried before pressure treating. I tried to find info on kilning for PT wood BEFORE the chemicals are added, but didn't find anything, therefore didn't dispute it. Are you aware of drying before pressure-treating? I knew lumber could be dried after, though i've never personally seen any for sale that wasn't sopping wet.
The wood is dried to 19% MC before treatment (IIRC).The treated stuff is often so full of water, etc. that it is literally wet and very heavy...even 100% MC (means the weight of the water is equal to the weight of the wood) or above 100% (which is possible).This results in lots of shrinkage, twisting, and other distortions.For a premium, you can order PT lumber that is KDAT (brought back down to 19% MC)Also there is TTR (treated to refusal) PT that was not dried before treatment or was dried but did not go below 19% or was a species not desirable for treatment. That stuff has no guarantee...it is just treated til it won't absorb any more ACQ. That grade is sold for landscaping.
Thanks. I was wondering about the percentages of M.C. in each stage. I suppose the initial drying creates a sort of vacuum to suck the chemicals deeper than even the incisions and pressure might allow.
welcum...past my bedtime...nite, nite.zzzzzzzzzzzzzzzzzzzzzz
and you know that they only incise the western PT...like fir
because it doesn't take treatment as well as SYP
normal channels of distribution have SYP in the east and fir in the west, with some cross-over
i've never seen syp incised for treatment, but all of the fir i've seen isMike Smith Rhode Island : Design / Build / Repair / Restore
I got hold of a piece of gorgeous wood a few years ago, from a client, and had to put a picture up at Knots to find out what it was: SYP. Another fellow put up a picture of his house trimmed in it, clear finish. I guess you have to love that golden pine look, which i do.
So no, i didn't know that about the fir being the only wood incised. It sure doesn't help the looks of it at all. I'm guessing you can stain or paint the PT SYP itself instead of covering it up?
you can, but on the exterior it loves to check and splinter
we usually air dry anything that will be painted by stickering it in our garage for a couple weeks before the project start date
if we're trying to rush the process, we build a tent over it and stick a dehumidifier in the tent
we cull all the bad ones, and there will be a lot of twisters
then we Prime caulk and paint before we bring it on the jobMike Smith Rhode Island : Design / Build / Repair / Restore
It sounds like you don't buy the KDAT wood basswood mentioned. Is it available? or just too expensive?
it's probably a special order
most of the PT in this area comes out of BB&S
which is in Davisville ( Quonset ) RI, right across the bay from meMike Smith Rhode Island : Design / Build / Repair / Restore
One thing I seldom see mentioned is how much potable water concrete requires. Not only the concrete itself, but the flushing and washing of the troughs and the drum of the delivery truck must also use a lot of potable water (though for washing, it wouldn't have to be potable water, but I'll bet it is).
That pdf concrete link i plowed through talked about that as an environmental cost, but said plants are using less and less bec of pollution concerns re acidifying the water. It said some are planning a closed-loop system. Dust is a still big problem, though, and more difficult to deal with.
But the concrete itself uses up drinking water--it is chemically bonded into the concrete (water of hydration, I think it's called) as the concrete cures. That water is "used up" as far as I know, at least until the concrete is destroyed by very high temperatures.
I see what you mean, though it seems a relatively small amount of water. That reminds me of another vote for a wood foundation: it sequesters carbon.
Most of the ptw for foundations here is rated for a minimum of 60 years. I have used it when I lived in the north and the building sites were often muskeg, proper drainage, waterproofing, and construction techniques are the key. On the plus side they are warm and dry.
You're replying to a post I made last February. Let's let old discussions lie.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
oops
Why is that? Have you seen wood foundations go bad?
Having done both, i wouldn't build one out of concrete again...which is why i started this thread. I made my decision in the late 90s based on the lower $$ cost and ease of making the wood foundation, but i didn't know how 'green' it was compared to concrete.
I built mine about 30 years ago, I was the owner builder but very green so I hired a guy who was a builder to help. Still holding up great. We are on a slight hill and I have good drainage and so far the back bath and bedrooms are dry as a bone .
The entire house has wood foundation even the knee walls. Probably would not pass the seismic requirements of today but so far has worked well. The CCA stuff was nasty to work with and of course even then you better not burn the scraps.
Always wore gloves etc. With as many small earthquakes as we get each year, no cracks or leaks. I think it is much more stable than a block foundation. That being said in my next home (coming up in a few years) it will probably be a frost protected shallow foundation with ICF's to the eves.
Jim
I'm pleased to hear yours has held up well. What did you use for waterproofing? Insulation? I used XPS board insulation, sealed at the perimeter of each cavity with spray foam, to the ground line, in case anything went wrong with the drainage.
Scraps...i don't think i had enough left over to fill a five-gallon bucket.
Why are you changing to ICFs for the next house, considering your wood house worked so well? When i did my figgerin' (late 90s), ICFs were loads more expensive than wood. They were actually about equal in cost to the wood i used, then add the concrete on top of that.
I'd think with the housing market slowing, wood would be going down in price, while ICFs, based on oil, would be going up. No figures to back it up...just thinking out loud.
How large of a structure are you talking here? The whole house, or just your new addition?
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http://www.drawingwithlight.smugmug.com
New addition?? I'm not adding on...can't even get the part i've bit off chewed! <G.
The basement was 35 x 42. The wood foundation was also advantageous in that i moved a house on top of it. Houses that have been moved can change shape a bit so i figured i could bend the baement walls a bit to fit if necessary. Fortunately, the house travelled 35 miles without much movement and turned out very close to square and plumb when it sat down on the foundation.
We used what everyone else used back then, I think it was hot mopped and 30lb felt over. Not worth a damn by today's standards of course. I remember it was 2x8 on my back wall on 12" center side walls are all 2x6 on 16. Fiberglass what ever would fit in. Don't remember anymore. Large picture window in front bedroom makes it the coldest room in the house (Anderson's) gave up the ghost years ago and I need to replace all the thermopane in the place but I think I will let the new owners do it.. Back bedroom has a egress window that opens into a well, it too needs replacement. Back bedroom, is warm tho if the kids keep the window closed.
Jim
I am planning to a permanent wood foundation basement this year, based on the experience of a friend who has one, and the detailed information at: http://newstore.southernpine.com/cgi-bin/newsopine/product?;32;But I have not heard the idea of screws only for fasteners. The above guides advises hot dipped galvanized nails above grade and stainless steel nails below grade. So I am curious - why go to the extra trouble of using screws?
Just my own insecurity. I was trying something for the first time, working alone, and i wanted to be able to correct easily any errors i might make in measurement or squaring up panels. Since i come from a woodworking orientation, i'm probably a bit over-zealous in that aspect. (I made 8x8 panels, sheathed on the bottom, stood them and fastened them together, then sheathed the upper half, off-setting sheets so as to tie it all together.) I didn't have power to the site when i built the foundation, so no air to drive a gun and i couldn't face all that hand-nailing, either. Knowing what i know, with the tools i have now, i'd used SS nails in a gun and be done with it a few days sooner.Thanks for the link. I'll check out the latest info. I hope you have an inclination to take photos and do an essay for us. How are you going to waterproof yours? I really can't say enough good things about the plastic dimple fabric for simplicity, installation ease, and low cost.
No, but I think a wood foundation will be very, very difficult to detail in such a way that it survives 100 years.Also, you are going to have a hard time in resale...and Stevensville is already the toughest real estate market in the Missoula/Bitterroot area, why compound the issue by having a foundation that people will be scared of?
why compound the issue by having a foundation that people will be scared of?
I'm sort of addicted to trying new things. I bought a tankless water heater before anyone else, discovered the dimple fabric, used PEX and EPDM, etc. I actually had monographs on hand from when i went to college in CA in the late 70s about "all-weather-wood foundations", as they were called then. A wood foundation isn't that novel. I think i can make a good case for it to a prospective buyer if that's the sticking point. I'd hope that the quality of work that is visible would lead them to think the foundation isn't a mistake in the making. As far as bank financing goes...yeah, that might be another story....but i've put so little into this house in $$$ that i can sell for way less than a commercial builder ever could.
I've Sarah Susanka's attitude when it comes to always having an eye to resale when making choices about materials or design: who really wants to live in a big, white box that looks like every other big, white box just in order not to offend some person i might never meet at some time in the future? I like learning new things and i see a house as a labratory or play-pen just as much as i see a piggy bank.
Alright....you make a good case.If you ever need a realtor... ;-)
LOL! Long ago and far away i worked as a graphics artist on a little newspaper making display ads, then sold widgets for 23 years at art fairs. I've got propaganda in my bones!
Ping me if you're going through Stevi some time, neighbor; i'll spring for lattes and scones at The Coffee Mill.
My wife (and architect) and my engineer designed a really cool house for an owner builder with a wood foundation for the same cost / solo construction reasons you mention. For my jobs I like block, superior wall or Polysteel ICF and the block is generally least expensive of those options. We did a cast in place a while back but couldn't really justify the cost over superior wall.
no real reason, the new PT is less toxic than the old CCA but it's still not as durable as old fashioned concrete.
I'm lovin' that Polysteel ICF these days.
Be well, don't go joustin' at windbags too much y'hear?
------------------
"You cannot work hard enough to make up for a sloppy estimate."
Thanks for the response. I don't know anything about Superior Wall; i'll check that out.
And you know me...i try desperately not to ruffle feathers. <G>
Superior Wall is just a pre-cast concrete wall system that goes in fast and gets a slab floor to hold it all together. It's probably 20% cheaper than pre-cast. The glue they use to hold the panels together is nasty stuff though. Stinks up the job site for weeks after the set. That can't be healthy or green...Those boys are real good at getting things level and plumb but not so good on the square part. A prudent person would pull diagonals on them as they go or at least before they leave... Be well Michael------------------
"You cannot work hard enough to make up for a sloppy estimate."
I watched some video on that site. It looks like the walls are located on pins driven into the ground...? Any problem with the panels getting whacked out of position before you get the slab poured?
Any problem with the panels getting whacked out of position before you get the slab poured?>>No, they're pretty heavy but as I mentionned we've had a few get set out of square by the crane in this area and left that way for the framers to deal with, and I'm talking seriously out of square here not just an inch or so. m------------------
"You cannot work hard enough to make up for a sloppy estimate."
Just curious with the talk about insulating inside or outside a concrete foundation, why the 'green' builders aren't making PT wood foundations?
The engineers I've worked with would over build a wood foundation to the point it's as costly as anything else. While it's easy to build, the devil is in the details and everything has to be done well or the foundation will have a short life.
What specifications were you following?
If you have shallow frost lines and little precip it probably makes more sense, but in a deep foundation there can be a large amount of pressure from the surrounding soils requiring more gravel backfill and much more wood in the foundation structure.
How did you size the verticle studs? Did I miss how much of a gravel bed the wood was set on or did you set the pt right on the existing soil? The exact details of the drainage system, gravel bed and moisture barriers are very important.
If I had built your foundation a client could sue me for using screws, unless they are specifically structurally rated, and I'd have to pay the cost of digging up the foundation, stripping off the waterproofing, renailing the ply and putting it all back together. Not busting your chops, just stating the obvious. It also sends out a warning, that what else in your design is not up to spec.
Again, not busting your chops, but this is one area that a contractor has to do perfectly or there is a great deal of liability down the road. The only contractor I've known that's built a wood foundation broke about 5 important rules and should be sued for what will end up being over a $100k fix. Basically, concrete is more idiot proof so that's what most people use.
Having said all that, given the right situation and soil conditions, I'd use a wood foundation for my private residence. Many areas out west have soils that drain very well, little precip, and footer drainage that is a cinch.
From one perspective a wood foundation makes a lot of sense, but for average builders with average knowledge and an average attitude towards doing things right it would be a good way to go out of business in the long term. We replace a lot of foundations, but none of them are cheap fixes.
Cheers
Beer was created so carpenters wouldn't rule the world.
I used 2x6's on 16" centers, though i don't recall now whether that was from my own calculations or listening to others' advice. I did have a bit of trouble bec i had to break the top plate over the windows for the beams that carried the house as it was being set on the foundation (photo i attached previously). I had to dig out around the window areas a bit, push the lower edge of the window back to plane, and add studs around the window and some metal mending plates. Still, that was a function of the top plate being non-continous over the window bec of my particular needs; it would be continuous in normal construction and not deflect. As it is, none of the continuous-plate areas deflected from backfill, though i only buried the walls to about 4-5' because i wanted windows without window wells. If you wanted to bury the basement deeper, no doubt one would need narrower centers or beefier studs, but it's still not going to run you near what concrete does. Possibly the screws are the weak link, but there were lots and lots of 'em...every 6", as i recall. I used a concrete footer with rebar bec i had sandy soil and figured it might shift some. I didn't have an engineer...i'd rather put my *own* money into overbuilding. I agree that a contractor building for someone else should approach the job with a lot more CYA in place.I disagree completely that concrete is more idiot proof; that's 'tradition' talkin'. There was a picture Fink put up of a basement window cut-out that showed 4 rebar lined up across the section, all next to one another. Concrete has blowouts, voids from bad vibration, and develops cracks. If it's poured out of square, out-of-plane, or unlevel, you're stuck. It can be watered down and have the wrong additives. Everyone has a leaky/moldy concrete basement story bec everyone THINKS that concrete is idiot proof when it requires just as careful detailng. If you have to build a wood wall inside your concrete wall to use your basement, you must properly add that cost to your concrete wall, as well as factor in the cost in lost square footage of floor space. And if i'm the standard of idiot used in any test, i'd much sooner trust me making a wood foundation that can be fixed than a concrete one that can't! Besides, why aim for "average"? <G>I don't take your post at all as busting my chops. Bec of your concern i'll certainly look into the screws issue before i do the next one. What i DO know is that this basement is the first one i'd known that is perfectly dry and doesn't feel damp or smell musty, nine years later. I actually plumbed my dryer hose into it - which smells kinda nice actually - to keep it humid enough that i don't die of static electric shock one day.
Perhaps you might want to consult an IRC code book. As I said before, when one warning light goes off there are often more to follow.
The way I read it, wood foundations aren't compatible with concrete footers, but rather crushed stone is for drainage reasons. The code is very specific about the automatic drainage requirement for both the footer crushed stone and slab crushed stone base.
There is also a crushed stone requirment for 1' to 2' of backfill, a 2" air gap between the plywood and any insulation, a maximum backfill of 4', and a surface grade with 1/2" slope per foot for at least 6'.
The ply panel joints are required to be sealed, and the moisture barrier requirments are also specified.
I'd get sued for building the foundation like you did unless an engineer would okay the construction, which they wouldn't. If it's for your own house and there are no inspctions in your neck of the woods, it may not matter, but if you ever go to sell the house a sharp inspector will say an engineer needs to look at it. That's an awfully hard thing to fix and have the house close anytime soon.
Good building
Beer was created so carpenters wouldn't rule the world.
I found some info on concrete footing specs for wood foundations. I was pretty sure i'd picked that up in the manual i was using, which i unfortunately still have packed away since i moved in. I checked the Net, though....
Here are some HUD specs on attaching a wood foundation to a concrete footing. ("Table C-5B is based on the capacity of the anchor connection to a treated wood wall which is attached to a concrete footing.)
As far as he IRC goes (and i am by no means up on this stuff, i grant you, and it appears to be a local revision...?), i found this link that said:
Edmonton had this:
And here's another crazy woman who got an engineer's stamp for the deal.
The concrete footer is acceptable, indeed required, for at least some locations. I can't think of any reason it wouldn't be preferable. I'm sitting on pure sand here, so drainage wasn't an issue, but i was concerned about stability. As to gravel being required under the bottom plate, this tale legislates against that:
The only reference i found to a 2" air gap between insulation and wood was not to the plywood as you mentioned - i assume you mean the plywood wall - but was in reference to holding FG insulation 2" above the bottom plate. Several diagrams i found show the insulation filling the bay completely. Perhaps that's what you meant and i misunderstood.
That Minnesota-based code references the 48" maximum backfill maximum only if not designed by a structural engineer, but i read references to 7' backfill elsewhere.
Re the seams being caulked, yep, they're supposed to be and i didn't. I did a lot more that the 6 mil poly exterior barrier though. That flimsy of a material being used as a barrier just boggles my mind. As to the slope away from the foundation and the stone backfill, those aren't requirements peculiar to a wood foundation, are they?
I'm glad i got this opportunity to research your objections bec i'm rather more convinced of the efficacy of the system after reading a large number of homeowner accounts of energy savings and comfort levels. In fact, when i googled "problems"and "wood foundations" i only got returns that indicated that there were NO problems with wood foundations. The only account i found (after three pages of returns) of a wood foundation not working above expectations was the one on the gravel bed mentioned above and another one that received absolutely no exterior waterproofing and was growing mold, to which i'd say, "Well, DUH!"
There were numerous claims that a wood foundation wouldn't last 30 years, but about 200,000 homes have been built with wood foundations since the 60s, so that judgment appears to be 'unfounded'. <g> On the other hand, here's an amazing collection of problems with concrete and block foundations.
Edited 3/1/2008 6:28 am by splintergroupie
That Minnesota-based code references the 48" maximum backfill maximum only if not designed by a structural engineer, but i read references to 7' backfill elsewhere.
An engineer will design whatever you want and there isn't any reason they wouldn't design for 10' of backfill if you wanted that, but an engineered solution isn't what we're talking about here. You're trying to eliminate the engineer and skirt the more strick requirments of most engineered solutions.
Several diagrams i found show the insulation filling the bay completely.
We're governed by IRC and it's very specific about the insulation not filling the bay.
I can understand a concrete footer if there is still a gravel or very good sand base under it, but it still has to have a drainage system to meet IRC. Since you are in Ravalli county and there are no building permits you can get away with no formal drainage system if it's certain the ground will absorb any water that might make it's way down to the footers, but when following IRC a formal drainage system is still required regardless of what the soils are (unless the design is okayed by an engineer).
The HUD link is for setting premanufactured homes on a wood foundation, but there is no way their specs are all inclusive for a full depth basement wall. The footnotes state that the design has to take into account other factors.
The specs for the amendment to 401.1 in Kenai Alaska are also for a seismic zone D2, where shaking is a huge issue, so the concrete footer makes sense, but it still has to have a drainage system since it's not deleted in their amendments. Essentially they are eliminating the 2x8 under the wall and adding the concrete footer, but to have an under-footer drainage bed the construction is still the same as IRC. They have added complexity, not reduced it.
IRC fastener requirements for the plywood below grade are stainless and all other fasteners are to be hot dipped galvanized.
Your reffernce to a gravel footer sinking has nothing to do with anything. I'll guarantee that the gravel didn't compress 4". It's a case of poor soil conditions under the foot and any footer would have sank a similar amount in that situation.
As for wood foundation problems, it makes sense that you don't find many listed since modern wood foundations are not a common building practice. If any foundation is built right they'll last and if they aren't all bets are off.
What I'm stressing is the importance of completely understanding the requirements of a wood foundation before jumping into it.
Best of luck
Beer was created so carpenters wouldn't rule the world.
It's true that i adore a DIY and less-expensive solution, but i hope i didn't give the impression that i'm trying to "get away with" or "skirt" good practices in Ravalli county or elsewhere. I was simply addressing your statements that a concrete footer isn't allowed or that 4' is the maximum allowable backfill.
I agreed that drainage - including the drainage plane, rock or sand, the footer drain, and surface slope - are necessary for a good installation, but i see no difference between a wood foundation and a concrete one for those requirements. Concrete footers for concrete foundation walls are notorious for wicking moisture into a basement, so if the aim is a DRY basement, a capillary break must also be installed under the concrete foundation as well, no?
Even if the cost of prep for wood and concrete is the same, the advantages of a wood foundation are lower material costs, one less trade to deal with, no cure time, ease of insulation, a nailing surface, and increased square footage compared to a concrete wall with auxiliary stud wall inside it.
As to the insulation being held 2" off the plywood wall, i'm scratching my head trying to figure out the rationale for that. I don't have a code book, but if you or anyone might be willing to post the regulation, i'm anxious to read it. I've come across a lot of detail drawings, some of them from contractors specializing in wood foundations, and none of them show this spacing off the wall. One specifically recommended cellulose fill to minimize convection currents. I've also discovered that you can get SIPS panels for basements. I preferred foamboard below grade "just in case", but here's a typical detail from the National Research Council of Canada:
View Image
In the case of the footer that sank 4", certainly it points to poor soil conditions, engineer-approved or now, but the story said it didn't just sink but kept moving. I think a 10x16 footer with rebar would be quite a lot more resistant, and at least give one something to brace against if using helical piers or something similar to stabilize it. I'm not anti-concrete or pro-wood, it just seems a good building practice to use both materials to their highest advantage: concrete as a footer and wood as a wall.
The stainless fasteners are code now, but i used CCA-treated material. I'd do the next one with SS nails, for sure. I'd also foam the interior of the cavities next time to glue it all together.
There haven't been many wood foundations built compared to concrete, true, but if they were that bad it stands to reason there would be a lot more tales of woe in over 40 years of common use. The 200,000 homes estimate i used earlier is apparently about half of current estimates of wood foundations. I read that the Forest Products Laboratory built the very first trial wood-foundation building in Madison in 1937 (!) and that it's still in use. It was picked up, foundation and all, and moved 15 years after it was built so it got a good inspection and no degradation was noticed. (The preservative was creosote.) http://www.pwfs.com/history.html
I'm on board with knowing the requirements before jumping in, both for wood and for concrete foundations.
I originally started this thread with a mind to exploring the "green-ness" of PWFs. I came across the following table put out by the University of Minnesota College of Design which addressed that aspect (emphasis mine):
Foundation Alternatives
alternatives
cost/sf-habitable
material/sf-habitable
IAQ
life cycle thinking
practice
slab (stem wall)
$10.54
Concrete total (C.Y.) 0.03Steel total (lbs.) 1.86Insulation A (s.f.) 1.56
better
typical
standard
shallow frost
$8.59*
Concrete total (C.Y.) 0.02Steel total (lbs.) 3.57Insulation A (s.f.) 2.08
better
good
standard
crawl space
$14.09
Concrete total (C.Y.) 0.03Steel total (lbs.) 1.86Insulation A (s.f.) 1.56lumber (bf) 0.11subfloor 1.00
good
typical
standard
garden basement
$11.85
Concrete total (C.Y.) 0.03Steel total (lbs.) 1.86Steel total (s.f.) 1.10Insulation A (s.f.) 1.56lumber (b.f.) 0.03sheathing (s.f.) 0.56sheetrock (s.f.) 0.56Insulation B (s.f.) 0.48
typical
good
standard
poured concrete basement
$16.34
Concrete total (C.Y.) 0.05Steel total (lbs.) 2.23Steel total (s.f.) 1.10Insulation A (s.f.) 2.11
typical
typical
standard
concrete masonry units (CMU)
$19.11
Concrete total (C.Y.) 0.05Steel total (lbs.) 2.23Steel total (s.f.) 1.10Insulation A (s.f.) 2.11
typical
typical
standard
insulated concrete forms (ICF)
$16-$19*
Concrete total (C.Y.) 0.05Steel total (lbs.) 2.23Steel total (s.f.) 1.10Insulation A (s.f.) 5.44
typical
better
training required
wood foundation
$7.32
lumber treated (b.f.) 0.15sheathing treated (s.f.) 1.11Insulation B (s.f.) 1.11
typical
better
training required
what's the explanation for each of those columns ?Mike Smith Rhode Island : Design / Build / Repair / Restore
They're clickable links. I had to look up "IAQ" = Indoor Air Quality. YOu can also see the table in a more readable format plus more explanation on the "University of Minnesota" link.
Edited 3/1/2008 7:58 pm by splintergroupie
oh, i get it .. i gotta work for the informationMike Smith Rhode Island : Design / Build / Repair / Restore
IdahoDon has made me stretch out...i can only do the same for you. <G>
This was a good conversation for me and I learned a lot of specifics that otherwise would have gone unapreciated. Again, don't want to sound like I was busting your chops.
Beer was created so carpenters wouldn't rule the world.
I learned a lot more, too, so thanks for the opposition, truly. I didn't have the Internet or BT when i built it, just a brochure from classes i took in the 70s, but i'm kind of pleased at what i learned lately.
Just a current Winter observation of Pressure Treated lumber....
I have a 4x4 PT piece of scrap lumber laying on the ground away from a shed I'm building. Fire Ants have built a dirt nest around the PT piece in the passed three months and are doing well... PT may not rot but the chemicals don't seem to hurt the Fire Ants either....
Bill
I just looked up fire ants since we don't have them in the North. Nasty critters! It looks like they don't eat dead wood, though. The PT wood will deter termites, which ARe the culprits that destroys houses. Treating the bays and/or ground with borates is a way to deter ants, though i don't know specifically if fire ants are put off with that.When i first looked at a wood foundation, i got spooked by an article in JLC about termites loving the exterior foam insulation and using it as a covered bridge to the above-ground wood structure. I called around and talked to some extension agents who told me termites aren't around my area. I would probably still be loathe to use foam on the exterior of a house on that account. The foam is treated with borates as well, but i've also heard that the treatment can leach out and make the foam vulnerable.
It sounds like your heart is in the right place and that you're actively searching for good designs, so my hat's off to you.
The presence of an air gap on the inside of the plywood is probably to allow any moisture that makes it's way to drain off uninpeaded, rather than either be dammed up with closed cell foam or be absorbed into a fiber type insulation. Often the codes are written to be as idiot proof as possible so I don't doubt that some of the requirements are a bit broad reaching for top notch construction.
I liked the chart you dug up on foundation costs. I've been a strong supporter of shallow frost protected foundations for years because of the low cost and proven designs, but they are still few and far between.
Inadequate support under footers, either due to over digging with poor compaction, or poor soil conditions, will crack a concrete foundation and it's not uncommon for houses a few months old to show major problems. Heck, a concrete footer would crack and bend under it's own weight if lifted off the ground on one end. It's definitely not going to hold a house up cantilevered over a soft spot.
You've probably had a good deal of snow up there in MT this year?
Enjoy the day!
Beer was created so carpenters wouldn't rule the world.
I've been a strong supporter of shallow frost protected foundations for years because of the low cost and proven designs, but they are still few and far between.
Frank Lloyd Wright used them in 1936 and they've been built in Scandinavia since the 1950's with more than a million structures floating on them, from detached residential to high-rise.
They've also been used extensively in northern Canada and Alaska.
The IRC only recently caught up with the system, but it has a long and very successful track record.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
During the consensus process for the NAHB-ICC national Green Building Standard in DC last summer the concrete industry had a lobbyist pushing strongly to deny green building points for FPSFs. Kind of like the power companies petitioning against energy efficient light bulbs. We prevented them from having their way but it was a very interesting discussion. Welcome back.------------------
"We DON'T build them like they used to."
The shallow frost-protected type would be my second choice. Ever since i had my first walk-out basement, which i use for my woodshop, i wouldn't have anything else. The only drawback of having my shop so close to where i live is the proximity of the tablesaw to the dang computer! Not much snow around here. I heard a report that the state is generally above average for snowpack this year, but almost all of February in the Bitterroot Valley looked like the yearly January thaw, temps in the 40's. I got into the Spirit of Spring and planted a few hundred tulips indoors.......
Wow, that's surprising given how much snow we've accumulated south of you.
Your solarium looks an awful lot a portion of the passive solar designs we've built in Wyoming.
Beer was created so carpenters wouldn't rule the world.
I oriented the house to the southwest, a compromise between the best sun to the south and the best view to the west. I'll move the glass windows to the inner wall in the summer - similar jambs are already in place - and make screens to go in their stead in the outer wall, creating a seasonal screened-in porch. The shelf standards are mounted on the windows themselves, so the plants will also move farther inside when the sun gets brutal. I used to do the 350-booth art fair at the Boise Art Museum in early September and did extremely well there. I'd stop at High Desert Hardwoods in Eagle as i was leaving town to put in my big yearly order - those guys are the best, if you haven't met them yet. One year a bunch of us artists 'discovered' the hot springs north of town an hour or so...sweet! I was online looking into RE prices in the Boise area recently, thinking to hit a little milder climate, LOL!, and was shocked to see how much lower your land prices are compared to this area.
I'd stop at High Desert Hardwoods in Eagle as i was leaving town to put in my big yearly order - those guys are the best, if you haven't met them yet.
I'm a regular and I'm always excited to see what new material they're getting in. When we get a new kitchen remodel it's really fun to cherry pick through all their stacks. I've been hoping a client will want to go with something a bit exotic for quite some time, but no luck yet. ):
Beer was created so carpenters wouldn't rule the world.
I made a lazy susan of sapele and ripple maple which Ron Worden, the owner, wanted to give his wife, so tell him Colleen Miller (Aboveboard Woodworks) says "hello" next time you see him. (And to Jim and Bill if they're still around.) It's been about five years since i got out of woodworking, but last i knew, they'd added an architectural millworks shop to their operation and were going gangbusters. He told me once that he'd gotten a SBA loan for $100K to start up the biz and paid it off in five years. He should give lessons in how to do business.