I am an owner / builder constructing my own separate shop building. The building uses ICF walls (Rastra). I am getting close to installing the roof trusses and have some questions regarding the top plates.
This building is in the Arizona desert so not a lot of persistant moisture. I know it is best practice to use PT lumber for the sill plates on masonary foundations. Do I need to use PT for the top plate on the ICF wall?
My concerns are with the corrosion issues of the fasteners and hardware in contact with the PT. The anchor bolts placed in the top of the wall are not Stainless Steel. The design also calls for a bolted “L” bracket connecting every other truss to the top plate.
I can see this adding up to a lot of Stainless and a lot of cost. Do I need to isolate the anchor bolts with some sort of pvc bushing?
Your opinions are appreciated. Thanks in advance.
-dch
Replies
Well the easy answer is that if this is subject to inspection, then call your building inspector.
Someone will no doubt correct me, but it seems to me that a certain distance above grade code does not require wood in contact with concrete to be treated.
As a practical matter, I would use untreated if I could for the reasons you state. Wood does not automatically rot if it touches concrete. There needs to be a source of moisture.
A simple precaution would be to use sill sealer.
daen
I brought this issue up with my local lumber yard.
All anchor bolts in stock are bare steel, not even galv.
They gave me the deer in the headlights look. It was like "So what's the problem."
They were about a year behind the times in getting triple galv bolts and Simpson stuff.
Frustrating.
Rich
I wouldn't be too concerned about your top plate absorbing so much moisture from the concrete that it will rot. I'd use "regular" wood.
If you are leery about this, isolate the whitewood from the concrete with some 15# felt. That will make you feel a little better.
Bob's next test date: 12/10/07
Thanks folks.
I am planning on using something like felt paper or sill seal between the wood and the concrete. I'll run it by my inspector (who has been a really helpful guy and very understanding of me as an owner / builder).
-daen
daen
Here's the situation, because of the nature of concrete moisture is wicked up a very long distance.. however if it never rains or there is never any moisture where you are then you don't need to worry about it..
However if you toss a piece of wood on the ground in your area how long before it's decayed into nothing? That's how long those top plates will last..
What is that term for the log purlins used to support roofs and ceilings in true adobe construction? Is is something like "vega?"
I'll bet you can find centuries-old buildings in the SW desert areas done with logs that support loads, and the bearings of the logs are directly on the masonry.
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Then that's your answer.. (yes, I think they are called vegas)
I agree with Jim and you that she does not need to worry, but Adobe is not masonry, it is clay mud, and vegas do rot at the top edge where they are exposed to rain and sun where they stick out.two main reasons as I understand it for isolating wood/crete contact or using PT lumber, is that crete wicks moisture and that it creates a point of condensation.ICFs eliminate dew points for condensation, and this is a dry climate anyways. The elevation keeps it away from ground damp wicking up. The only source of moisture left is what is in the crete as it ages - I don't think that is enough to cause her trouble in that climate.
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Is is something like "vega?"
Si, verdad, "viga" (VEE gha)
Plural is vigas (VEE gahs or VEE gathh')
In pure adobe construction, they are really beams, if in a purlin-like instalaltion. You use abutting smaller branches to span viga-to-viga, and viga-to-wall. Over that is a thach material, then a layer of adobe soil, which might be plastered.Occupational hazard of my occupation not being around (sorry Bubba)
Maybe it is different in your area, but here, every old house not only has joists sitting right on concrete, but the joist bays above the foundation are filled with crete. I have done extensive work on my own house, and there is no sign of rot, except where a previous homeowner had attached a deck without adequate flashing. My house is 95 years old, and I live in Minnesota. My foundation is about 3 feet above grade. I think the top plate of a ICF wall in arizona is going to last a bit longer than a piece of wood tossed on the ground.
I agree with you again Marson.In MI (Metro Detroit) there are millions of houses with the joist sitting directly on top of concrete basements. The concrete top is a minimum of 15" above grade and there is no signs of rotting. There are no sill plates, no straps, no bolts and yet the houses amazingly just sit there with no rot, no problems and they never fly of f the foundation into the sky! Then, sometime in the 80's green wood was invented and the powers that be decided that we needed this poisonous stuff in our houses. They decided in the 90's that we needed hardware to hold it down. In the 2000, the decided that the poison was eating up the hardware so they upped the ante with more expensive hardware.Sigh.......The older houses without all the newfangles stuff and still sitting there pretty as can be. Bob's next test date: 12/10/07
Marson.
For every place like yours that escapes from the ravages of moisture wicked up through concrete there are plenty of houses that don't. Sill rot is too common.
A moisture barrier is a simple thing.. a sheet of poly, maybe a bit of tar paper.
Your 95 year old home was built with old growth lumber.. very little likelyhood of that ever being available in the future.. it would be a real shame if sill rot caused your house to be destroyed and thrown into a dumpster.. if it was built with douglas fir there is every chance that the trees could have been thousands of years old. growing before Christ walked on this earth.
Even some of the Northern White pine used around here could have been hundreds of years old.. Growing before this country declared it's independance.
Well, I did suggest sill sealer. And of course if I was building a new house in a similar setting to mine, I would use treated sill plates. I too have seen plenty of rot in my time, but in all cases there has been an additional source of moisture--rain splash, ground water, what have you. My point is that if you are above grade in a dry condition, the concrete will not somehow pull all available moisture out of the air and rot the wood. That I have never seen. And I've looked for it. Remember, the OP is talking about a top plate on an ICF wall in a desert in arizona. You just cannot convince me that rot is going to be an issue there.
Ditto. Bob's next test date: 12/10/07
Marson.
I understood, However I've seen rotted wood in Arizona and in other dry regions. How important is it? Well that's for the OP to decide.. Frankly with the wood grown nowdays.. the second growth or plantation wood I'm in favor of taking more steps rather than fewer steps..
Fair warning, I'm a belt and suspenders sort of person. but I wouldn't use pressure treated wood.. I'd use white oak or some other naturally decay resistant wood. that's affordable here because I buy white oak cheaper than I can buy pine..
I know white oak grows throughout the country, so I'd be tempted to find someone with a woodmiser bandsaw mill and see what the going price in the area is for mill run white oak..
If you use a sill sealer all the other questions should be moot- A green builder I know is building a house in the SF bay area (fairly damp, at times) that was ok'd by the BD with Doug. fir mudsills over that pink compressable foam roll stuff.
k
daen,
Another option is to omit the top plate altogether.
You can use truss hangers embedded into the concrete core. The trusses will have to be induvidually shimmed to get the roof plane exactly right, but that isn't such a big deal. The trusses should have a strip of tar paper under them. It does no harm. It might do a lot of good.
Without a top plate, you have to do something out of the ordinary to get bearing for the gable trusses. You want the truss to be in the same plane as the form. You have to cut scallops out of the ICF block to allow the concrete to flow almost to the face of the form. You can't have the truss bearing only on the form. You must have concrete to support it, though it does not have to be continuous. A scallop cut out of the form every 16" - 24" should allow for plenty of support.
Look at the truss hangers here: http://icfconnect.com/ Simpson probably sells something similar.
If you use a top plate, pressure treated or not, you should install a sill gasket to keep that joint draft free. It's cheap, it's easy. Why not, even in Arizona?
Ron
Ron,
Thanks for the suggestions. The embedded hangers are a moot point because the wall is already grouted with anchor bolts out the top.
There is no moisture from the curing concrete, because it has been curing for several months...
Unlike some of the other ICF systems, the Rastra I am using has cells to receive the grout instead of a continous pour. At least for the ledgers, the hangers need to be inserted at vertical grout cells for proper load bearing. I expect you would want to do the same with the truss hangers.
The rub with Rastra is that it has its origins in Europe and I think the cell spacing originated in the metric system. So you have cells on 15" centers. I had looked into the icfconnect joist hangers as a way to eliminate the ledgers. But the nightmare of working with 15" on-center floor joists wasn't something I wanted to deal with.
If it weren't for that little detail I would most likely have used the hangers.
-daen
daen,
I have never seen Rastra. I should have looked at it more closely before even thinking about offering advice. I probably won't now though. That 15" spacing thing is reason enough for me to never think about Rastra again.
Too bad the ICF connect hangers won't work for you though. I have found them to save a lot of time, money and hassle compared to installing ledgers.
The problem with wood and concrete in contact with each other is largely a problem with fresh concrete. Curing concrete can draw water from wood with enough pressure to damage the wood's cell walls. It's called preferential dessication. This leaves the wood more vulnerable to rot if the other conditions allow rot to proceed, that is, if there is enough moisture present and the temperature is right.
Having wood in contact with cured concrete is not usually a problem unless humidity and temperature conditions are such that condensation can occur on the concrete or the concrete is wicking water from somewhere else.
I have read that in an ICF wall, where the surface of the concrete is not exposed to air, moisture can travel quite a long way by capillary action.
So, you ought to install some kind of membrane under the plate. It can't hurt.
Ron
I think the benefit of Rastra is that the ICF material has cementitious matter in it, so you can stucco directly on it FWTW.
k
KFC
OK, although acrylic stucco is made to go right on to foam, I guess that being able to use portland stucco mixes on Rastra is a good thing. A lot of people prefer the old fashioned stucco and for a lot of good reasons, too.
Ron
Yep, the Rastra basically uses small styrofoam pellets as the agregate in a concrete mix. This is poured into the big blocks. Stuco can be applied directly to it supposedly in one coat.
Another advantage is that when the wall is grouted, the grout and block become monolithic. With the pure styrofoam products a small gap developes as the grout cures. This provides a termite express lane! In the desert that is a huge issue. My termite company had to review the product before agreeing to treat the project. They said they won't touch the other ICF product for the very reason I discussed.
-daen
use different pressure treated wood.
This is what our main supplier is now carrying:
http://www.osmose.com/wood/usa/preserved/microprosmartsense/
carpenter in transition