I’ve been reading the various floor expansion threads with amusement. It’s coming to the fore again on my current project because we have to lay floor in a kitchen we’re working on where the heat has been largely off all winter. It’s on a new plywood subfloor over a fairly damp dry-layed stone cellar.
One thing that comes up when my partner and I start debating how best to “acclimate” the flooring before laying it, is the issue of whether or not the subfloor is expanding and contracting as well, and by how much.
I assume the movement is minimal enough to be a non-issue, he feels more strongly that it is significant. Anyone have any data on plywood panel movement?
There will be much more to say as this post starts drawing in the flies, but for starters lets discuss the plywood movement question…
Steve
Edited 3/9/2008 4:28 pm by mmoogie
Replies
I've seen individual sheets of plywood grow and shrink about 1/8" max. That can cause buckling if the ply was laid too tight. We normally gapped 1/8" on the ends and 1/16 to 1/8" on the toungue and usually the house got dried in before serious swelling would affect anything.
Some species of cheaper plywood tends to swell very fast and buckle. We rarely worked for builders that used that type of material .
OSB and Advantech tended to not grow as much as plywood. The ends tend to bulge vertically though under very wet conditions.
If you've acclimated (dried out) your rough frame and intend to keep heat in the house, it probably won't move too much after that.
Bob's next test date: 12/10/07
Jim,This subfloor was installed under a roof, so it never got wet. We've reframed and sheathed the roof, floor, and two out of three exterior walls, so for all practical purposes it's a new addition on an old stone cellar that's pretty damp. It's been dried in since the fall, but only intermittent electric heat in the cellar and upstairs as we've been working.We used that waxy GP plywood t&g subfloor. We slammed it tight, and I've seen no swelling.What this is leading up to is how to best prep the flooring for laying under these temp/humidity conditions. We won't have real heat in here till after the flooring is down.My flooring is milled locally and kiln dried to 7% The mill says that since it's at the ideal MC of 7% I can just slam it down, regardless of the current conditions in the house. I guess that's under the theory that in the long run the floor will stabilize at an average MC of 7% in the house. Their argument makes sense, especially if you assume the subfloor itself doesn't move from season to season.Well, the last time I did that with their flooring at about this time of year--in a house with a dry cellar with a concrete cellar floor that was in place for over a year--come springtime I got very noticeable cupping. So I'm not inclined to do it that way again.I just hate laying floor in the winter. But I'm thinking that since this place has been only marginally heated, things won't be too dry and I won't have as much swelling trouble this summer. But then again if it's 7% when I put it down, and the place is damp right now, maybe it'll just swell up and cup right away, rather than wait till summer, so maybe I should put it in the house and let it acclimate the the current conditions. I've got a few weeks to play with before the kitchen cabinets will have to go down on top of it, so I can let acclimate if that's the better thing to do. Heating the place is not an option right now.What do you think?Steve
mmoogie,
Just for grins I'm jumping in here.. plywood shrinks and swells according to the same rules as any other wood.. however it is modified by the different plies glued to each other in opposition.. restraining to a degree some of that shrinking and swelling factors..
Frenchy,Here's a picture of a plywood cabinet side to which has been glued and nailed a 6" wide piece of kiln-dried 1/2" thick pine. It was constructed in the summer. The first winter and every winter therefter this crack has appeared because the pine shrinks and the plywood that it's glued to does not. Something has to give. I'm wondering if the APA has any charts on movement coefficients for different types of plywood. I know roof sheathing can buckle. I've seen it. I get made fun of for insisting on the spacer clips.Steve
I get made fun of for insisting on the spacer clips By your partner I suppose.
No Wait he's the one claiming plywood
shrinks and expands.
not very consistent is he? At least he's smart enough to be watching Phil and Friends.
live in the Tavern.
Hint Hint
>>not very consistent is he?<<I didn't say that... d:-p
The average coefficient of linear thermal expansion is about 3.4 x 10-6 inch/inch per degree F for a plywood panel with 60 percent of the plies or less running perpendicular to the face (0.005” per 48” per 30°). The coefficient of thermal expansion for panel thickness is approximately 16 x 10-6 inch/inch per degree F (negligible).
The average coefficient of hygroscopic expansion or contraction in length and width for plywood panels is about 0.0002 inch per inch for each 10 percent change in equilibrium relative humidity. The total change from oven dry to fiber saturation averages about 0.2 percent (1/8” in 4’).
http://www.apawood.org/perf_panels/index.cfm?content=app_pp_atr_dim2
Solar & Super-Insulated Healthy Homes
Edited 3/9/2008 9:35 pm ET by Riversong
Thanks Robert,I knew that knowledge had to be out there.I guess the key to all this is knowing how wide the RH swings in the house are going to be from season to season. Then you could quantify how much things will move from season to season.Is there any way to know what the Equalized Moisture Content will be for a given species of wood in an atmosphere of given temp and RH?Steve
Relative
Equalized Moisture Content (%) <!----><!----><!---->
Humidity <!----><!---->
Solid Wood <!----><!---->
Plywood <!----><!---->
OSB <!----><!---->
102030405060708090 <!----><!---->
2.54.56.27.79.211.013.116.020.5 <!----><!---->
1.22.84.65.87.08.411.115.319.4 <!----><!---->
0.81.02.03.65.26.38.913.117.2 <!----><!---->
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Thanks Robert,You are a font of information. Do you know if that is independent of temperature? I may have to lay this floor in a pretty cold state.That is to say, is the wood's EMC different for 50% RH @ 70 degrees than 50% RH @ 40 degrees?Also, I was under the impression that my Delmhorst pin-style moisture meter cannot measure actual MC of plywood, only relative. Do you know anything about that?Steve
The difference in equilibrium MC at 50% RH between 70° and 40° is very slight: 9.2% vs 9.5%.
from: http://www.delmhorst.com/popups/wood_faq.html#q13
Does the Glue Used in Plywood Affect Meter Accuracy?
In most cases, no. To verify this, use insulated pins to make individual tests by touching the outer ply, glue lines, and center plys. If the glue reads the same as wood, use the meter on plywood as you would any solid material and take the readings at face value, without species correction.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Robert,You are making me lazy. How am I supposed to learn how to find this stuff on my own if you keep coming up with answers?Thanks again.Where did you get that information about EMC and RH and Temp?Steve
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch03.pdf
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
slammed the t&g plywood tight, butted the ends tight, got it wet.
years later everything has gone to H. E. double Hockey sticks.
NOT.
OSB makes me more nervous though if it's gonna get wet - but then again I don't use it.
OSB is far more stable if it gets wet. Plywood makes me nervous. I've never had to replace a single sheet of it but had to replace many Plywood sheets. Bob's next test date: 12/10/07
"OSB is far more stable if it gets wet."The 7/16" sheathing we just put on is now almost 5/8", and the places where there was no gapping are now buckled. OSB sucks in the wet. Are you saying that plywood is WORSE than this?
Yes, I'm saying that plywood moves a lot more due to moisture. There are varying grades of osb. I've never seen 7/16 swell to 5/8. I have seen plywood buckle up and need replacing. ONe of the more common mistakes is that installer lay the OSB tight. Then, when a little water hits it, it trys to grow in length and width. Immediately it bumps into one another and then the edges splinter upward and downward, mushrooming the ends. That might explain the 5/8". Since we always gapped ours, we never experienced this type of mushrooming.I have seen OSB swell to a full 1/2 when laying in a pool of water for a couple weeks. Bob's next test date: 12/10/07
I'm with you ken. I dont' like OSB. I've never had problems with ply. the worst that can happen is if it gets really wet, you might see some delamination. View Image View Image
you beswt be calling your supplier. 5/8 is awful lot of swell.
sounds like the old aspinite
Ply. decking delaminatesw like crazy. Thats why most people have switched to adventech or osb.
They tend to lye flat, and much easier to pound them together.
Anyone used the adventech with the elephant on it?
3/4 sheet has to weigh 100lbs. Try lifting that up to second floor by hand. Better eat your wheatties
Anyone used the adventech with the elephant on it?
3/4 sheet has to weigh 100lbs. Try lifting that up to second floor by hand. Better eat your wheatties
I used 1 1/8" Advantech in my home when I built my addition.
Forget Wheatties...go with the steak!
J. D. Reynolds
Home Improvements
Pp, Qq
jaybird,
100# sheets of flooring? can you say telehandler? <grin>
That's fer sissys.
I didn't cry....much.
J. D. Reynolds
Home Improvements
Pp, Qq
jaybird,
or smart men who realize their back has limitations and once ruined remains ruined!
Yeah....that's what I said...sissys.
{BIG FAT GRIN}
J. D. Reynolds
Home Improvements
Pp, Qq
I used 1 1/8" Advantech
4' OC framing?
That was probably heavier than the 1-1/8" double tongue-and-groove plywood I used on 4' oc floor trusses for a home I built in TN that was a prototype designed by the TVA for affordable housing.
The on-site TVA engineer bragged how this floor system was designed strong enough to hold an elephant. Maybe so, but when the occupants moved in and their clothes drier was on spin cycle (and probably a bit out of balance), the whole house did the shimmy.
The 2' deep floor trusses were top cord hung and the bottom cords weren't braced so they wiggled with any significant "seismic" loading. Braced off the bottom cords and took care of the problem.
Even weirder, the roof trusses were on 8' centers and were covered with site-built 3/4" T&G plywood with lateral 2x10 purlins on top to create insulation cavities, and then covered with Onduline corrugated asphalt roofing panels. And the sidewalls were framed, well... sideways (prefabbed).
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Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 3/13/2008 1:59 pm ET by Riversong
No....16" centers. A combination of overkill and the need to match existing floor heights.
The project you describe sounds interesting.
Were you happy with the finished product?
J. D. Reynolds
Home Improvements
Pp, Qq
The project you describe sounds interesting. Were you happy with the finished product?
Not really. Everyone who worked on it, including two of us from New England and three local carpenters, all thought it was poorly designed.
When the TVA engineer and architect showed up on site, the first thing they did was nail a big sign to a tree that listed Murphy's Laws - and it seemed every one of them came true.
The first house we built on the Woodlands Community Land Trust was a locally-designed double stud wall superinsulated house. Just 640 sf for 3 bedrooms on one floor. It was small, but we all thought it was a much better design.
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Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 3/13/2008 3:09 pm ET by Riversong
Murphy's Laws - and it seemed every one of them came true.
Seems that's often the case when the archy shows up...LOL
I understand the premise that abundance of resources would lessen the concern when using a double stud wall....but would metal studs for the interior (presumably non-structural) walls have been that cost prohibitive?
J. D. Reynolds
Home Improvements
Pp, Qq
Why metal studs? Nobody down there even considered it. And one problem with double-stud walls is that they both tend to share some of the load, regardless of which one you insist is the load-bearing one (unless you build the interior wall with a gap to the trusses and attach with sliding clips.
For the local carpenters, it was a stretch to build with KD lumber - they're used to rough and green.
As I said, this "Warm & Dry" house was designed by the Federation of Appalachian Housing Enterprises, a consortium of low-cost builders in Kentucky and Tennessee. They build with wood.
It was hard enough to get TNers to consider leasing the land from the Community Land Trust (they own the house), since many generations suffered from arbitrary leasing policies of Big Coal which owned all the land. No one there would have been interested in a house made of steel.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Why metal studs?
Conservation purposes. As I said....I'm sure in areas where wood is of an abundance, it's probably not considered practical...but this nation once had an abundance of wood seemingly everywhere. Obviously, that is no longer the case.
J. D. Reynolds
Home Improvements
Pp, Qq
Jaybird,
I don't know about the harvest practices of your state. I do know that in Minnesota we have more trees now (by a factor of 5) then we had 50 years ago. These are mature trees with diameters over I think it's 20 inches..
Many states have serious reforestration programs and have been doing them as long or longer.
I do know that we are down to about 2% old growth forests which may be what you are thinking of. I also am well aware of the deforestattion of tropical/rain forests. Good news is that Brazil and a few other countriesare now starting to be active in preserving those forest lands.. while they are not completely successful at least attempts are being made to limit more and more deforestration.
.. while they are not completely successful at least attempts are being made to limit more and more deforestration.
I understand that....none the less, conservation of resources should always be a concern.
I aplaud the type of building practices Riversong has described (double wall), which should certainly lead to the conservation of other such resources, depending upon what type of heating/cooling systems are employed.
I don't get much opportunity for such in this neck of the wood (excuse the pun).....but if I did, I would look into complementing the idea in such a way as to conserve even more of our natural resources.
J. D. Reynolds
Home Improvements
Pp, Qq
Conservation purposes.
I don't get that. How is taking non-renewable minerals out of the ground and using lots of non-renewable fossil fuel energy to form it into steel and then into a finished product - an act of conservation?
Here in VT, 100 years ago 90% of the state was cleared of trees for herding and farming. Today, 90% of the state is forested. Trees, harvested responsibly, are a renewable resource and their use is carbon neutral (beyond the small amount of energy required to mill and transport).
Using renewable resources is always more "conservative" than using finite non-renewable minerals and fuels that have to be mined from the earth.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I'm not looking to get into a pizzing match over this.
It's great that Vermont has been able to re-forest itself. Unfortunately, the rest of the nation has not been able to do the same.
I'm not advocating you build entirely out of steel. Only suggesting that perhaps there are compromises available.
J. D. Reynolds
Home Improvements
Pp, Qq
Riversong,
I applaud your intent, I question some of your conclusions.. Building a home is a series of trade offs.. Double walled building practices are one of them.. The intent is to reduce heat/energy loss with superior insulation. However doing so makes compromises which will end to lead towards shorter durability of the structure itself.
We can sit here and question greater wall thermal efficiency to death while ignoring that often it is used to gain enough to offset the addition of more and more energy robbing windows.. (why is it those of us with wonderful views all want to live in glass houses?) <weak grin>
I do happen to agree that light gauge steel is a poor building material both because of the nonrenewable nature of it and also it's inherent flaws and weaknesses..
I don't believe that use of all nonrenewable resources should automatically be cause for rejection.
For example the Cathedral Du Notre Dam is made from nearly 100% non renewable resources and yet it's durability and functionality justify it's existence.
On the other hand a log home is a poor choice of materials even though logs are renewable.. The simple fact is few log homes have survived long enough to grow their own replacements. So in effect log homes are not renewable..
Timberframes on the other hand have survived for many centuries past the point where the replacement trees have matured to reusable sizes..
Hence Timberframes are renewable log homes aren't.. same basic material different method of construction..
And I'll have to question some of your conclusions:
wall thermal efficiency ...is used to gain enough to offset the addition of more and more energy robbing windows..
Given the importance of not only natural daylighting and natural ventilation but also a perceptual connection to the outdoors (not to mention solar gain), appropriately-sized and located windows ARE one of the wonderful trade-offs of a highly-insulated envelope.
I've talked several homeowners out of building earth-bermed or underground homes in favor of a superinsulated home with good fenestration on all sides - and it STILL uses less operating energy than what they had in mind.
I don't believe that use of all nonrenewable resources should automatically be cause for rejection.
I've never stated this. I use all kinds of non-renewables in my homes, just in the appropriate places and in limited amounts. I use either copper or PEX plumbing, and if I can't get a plumber to use ABS DWV piping (it's hardly available any more), then it's PVC. I use XPS under and around foundations, and plastic sub-slab vapor barriers. I use a foam gun to seal around doors and windows and butyl acoustical sealant for the air-tight-drywall system. I even use aluminum-clad wood windows and aluminum gutters and asphalt shingle roofs.
But for the bulk of the house structure, that's where the real impacts are: foundation, frame, and insulation.
For example the Cathedral Du Notre Dam is made from nearly 100% non renewable resources and yet it's durability and functionality justify it's existence.
I've never heard anyone suggest that native stone was a non-renewable resource, though its true it has to be "mined" from the earth. Indigenous cultures, living sustainably on Earth, have long used stone for construction. It's a material that's universally considered sustainable.
On the other hand a log home is a poor choice of materials even though logs are renewable.. The simple fact is few log homes have survived long enough to grow their own replacements. So in effect log homes are not renewable..
I'd like to see any data on this. There's no reason a log home can't last for a hundred years, and there should be no log home that can't last the 30 years it would take for the forest to replenish what was used.
Logs were used as a building material specifically because of their easy availability and the minimum amount of embodied (mostly human) energy required to utilize them. A scribed log home can be as much a work of art as a traditional timber frame, but at far less cost.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Riversong,
Oh. the log home debate.. Well for proof I suggest that you show me 100 year old log homes.. those that do exist as homes and not as exhibits have had major repairs or renovation.. While 100 year old timberframed, ballon framed or even stick framed abound.
The weakness of logs is the log ends.. .. they tend to wick moisture in which causes decay. Too often modern log homes do not realize just how much moisture modern living puts into the air.. Logs check.. that's what they do.. it's natural and doesn't weaken the logs at all,, however, those checks become the intake site of vapor which must go someplace.. since there is no insulation the vapor point moves back and forth based on temps and pressures.. soaking those logs more and more.. Eventually they rot out.. usually at the ends first..
It is not uncommon for 10 year old log hoomes to need major repairs..
That's too bad because there certainly is real charm and romance to log home living.. Well except for the light issue. Either you accept a lot of lights on during the day , or a lot of windows or a dark an gloomy interior.. those are your choices.. wood is extremely poor at reflecting light..
That was hard for me to arrive at since I am such a fan of wood.. Look at the pictures of my house or what's better look at the stacks and stacks of wood yet to be put up!
I love wood in all it's nuances and character.. I enjoy working with it and I love the feeling it imparts.. A nice highly polished piece of burl or a interesting grain just tickles me pink.. The joy I feel as I sweeten a tenon to slide into it's mortice pocket with a soft thunk is as close to heaven as a mere mortal is allowed to get..
I looked at the fine old houses of Europe and here in America and studied them well.. the one thing they've all got in common is a low maintinace exterior of some sort.. either stone or some extremely decay resistant wood.
While it's true there is a finite amount of stone,, long before the use of that material approaches critical we will have expoilted everything else beyond it's ability to sustain us..
I do note you agree that homes are a compromise and that windows are part and parcel to that level of compromise..
I'd love to go ranting here about the advantages of ICF's and SIPs but SIP's only have about a 60 year window of experiance and ICF's are only about 25 years old or so.. neither meet the 100 year durability tests altough priliminary data indicates they should achieve both in a walk..
Based on that data I have concluded they are superior to double wall construction..
I would be FAR more concerned with what the hardwood is going to do once you get the house air conditioned than that of the plywood. regardless of its current moisture content.
J. D. Reynolds
Home Improvements
Pp, Qq
W don't do much A/C in this neck of the woods. That's why we put up with the winters. So we get nice comfortable summers. Plus these are city people who shut thehouse down for the winter. I'm more afraid of swelling in august and in the middle of the unheated, damp winter.I've been taking moisture readings and the subfloor is at 11-12 percent right now. 185-year-old pine flooring in the rest of the house is at aobut 10-11 percent, and I've been keeping it above freezing all winter. Though just.Steve
Sorry....I meant conditioned air, as opposed to "air conditioning". Meaning the homes heating and any possible humidifying system(s).
J. D. Reynolds
Home Improvements
Pp, Qq