I need more information on perm. wood foundations. As we have been researching, we have come across more recommendations to build PWF.
We are relocating to northern Minnesota and most likely having a log cabin (scribed 18″-24″ logs) shell built for us. It will have a half loft (storage/guest bed/office) with 12′ x’ pitch , steel roof. We want to use the basement as a living space. I plan on living up there until they turn me into dust. The basement needs to be a 2nd living area for a 2 family situation if need be.
Based on the great advice from the forum on radiant heat … we will probably go with in concrete radiant system in the basement (not sure if this is relevant).
Replies
PWF is the way to go. Of course, being a carpenter, I'm biased towards wood.
Lots of room for insulation - perfect for MN. You don't need concrete footings, but I found it easier to build on. The only hard part is that it's just so darn heavy building them. 3/4" treated sheeting and treated 2x8 studs make for heavy walls.
tam
please look into ICF's
(insulated concrete forms) basically they are light foam blocks that you set together and pour concrete into. very easy to do for do-it-yourselfers.very strong last indefinitely,great at insulating and already well accepted by building departments.
The cost is about what a block wall will be and very nearly what a permanent wood foundation would cost..
(without the need to put a whole bunch of poison in the ground around your house)..
these wood foundations sound interesting
the icf concrete walls are great but i have found them significantly higher than conventional poured walls. they require a very large amout of steel reinforcing and the foam blocks themselves are high.
PWF is a catch word of the treated wood industry. I don't think that in reality there is any such thing as a "permanent wood foundation" because of the large number of variables encountered with the manufacturing of the wood, the fasteners used to assemble, the construction techniques, and soil and water conditions at the site.
I have seen too many bad wood basements to even consider one to be permanent.
Secondly, Have you considered the huge amount of weight that these walls must support? 18"-24" logs are VERY heavy. If you decide to go with the wood basement, I would make sure you have a structure that will support all of that weight. I certainly wouldn't feel too comfortable with logs that size sitting on a skinny wood wall.
We have built several log homes with logs that size, but we usually set them on 12" poured walls. We have also set them on 12" block walls with the cores reinforced and filled.
I think you should talk with one of the local log home builders with a lot of experience building homes like this. I can tell you from experience tho, that there are a lot of guys who are capable of constructing something like this, but may not know anything about what type of foundation it should sit upon...so do your homework!!
P.S. Good choice for the basement heat!!
Is a PWF available in CCA? What is the pressure treated wood of choice in a wood foundation now?
'Nemo me impune lacesset'No one will provoke me with impunity
I really don't know. They started building treated wood basements in our area around 1980. It was a fad for a while and there were quite a few built.
Little by little, people started having trouble with them and you rarely see one going in anymore. The main problem seemed to be leaks of some kind into the wall cavities.
I really don't see any reason to go that route. Basically you are using a low quality product to build a foundation under a home that you hope will last for a century or more.
Rez--as far as I know--being my parents lake house is on wood in northern Mn.--it is the same chem. just in a Ground Burial concentration instead of Ground Contact.I think the acual numbers are like .40 for GC and .60 for burial--i could be off with the numbers but I am fairly confident of the same chem.Wonder why more brown treat plants don't come on line to offer an alteritive to the whole arsenate issue.Now get out there and get those profiles filled in---Bump--Bye Rez--Mike" I reject your reality and substitute my own"
Adam Savage---Mythbusters
I have friends who had a 2 story log cabin constructed on a wood foundation in No. Minnesota (Brainerd area). Here's what I saw when I visited it shortly after it was completed.
Foundation walls were 2x6, 12" O.C. Outside of wall was treated plywood (not sure what thickness) with a poly vapor barrier between it and the soil. Stud bays were filled with unfaced batt insulation, and clear poly then sheeted the interior of this wall.
I can tell you this, from all the moisture in that PT wood, any shoes left in the basement (as well as other items), developed a nice green coat of mildew. And the basement smelled, too. And it was a couple of months old.
IMHO - concrete of one sort or another (insulated forms, traditional forms, etc.) is the only way to go. No way I'd ever make the investment in a home to depend on the longevity and weather-tightness of a PT foundation. I've seen too much PT lumber that has rotted in a few years.
My $0.02.
The foundation you describe has several construction defects. One, polyethylene sheet is not long lasting enough nor tear resistant enough to serve as below grade waterproofing. Two, putting poly on the outside and the inside of the wall guarantees the wall will stay wet for a long time. Vapor barriers should never be put on both sides of any wall. While I like fiberglass for many applications I would not use it below grade because there is too much chance of it coming in contact with moisture.
The high moisture content of the wood will accelerate corrosion of the fasteners. If the wrong ones were used, the'll corrode and the foundation will fail.
It's too bad for the homeowners.
I've built two pwf foundations to Canadian codes.One for myself, and one for my cousin, both on the prairies.Both were built over 20 years ago and show no sign of problems.Both had hd poly on the outside of 3/4 ply over 2x8's on 16" ctrs. Poly will never break down if protected from sunlight.Outside of that I used a couple layers of cardboard (free mattress wrapping from a shipper) to protect the poly during backfill. (Foam sheets are what are recommended)Inside, I used 6 mil poly over fibreglass. This was "supersealed" with caulk, actually acoustic sealer which is compatible with poly, and tape. As was the rest of the house(s)If you are unfamiliar with the techniques involved with properly sealing a house, try a google on R2000 Canadian standards.It's important to build consistently, with attention to detail, for these techniques to work. You will need, if in a heating climate, an air-to-air heat exchanger to limit moisture build up in a tight house like I've described.If you can't find workers or trades to do it, find another way.Alan
I must say my parents house is a totally different story--2x8 16 OC with 7/8 PT ply. I have opened several walls to move outlets etc and have seen no signs of degradation. The house is almost 20 years old and even it has some type of fiber board just below grade on the exterior.I imagine it was to protect during backfill and provides a drainage plain now--Sounds if your friends got a bum rap on the constrution of their PT foundation. I think Wayne is right on the poly--poor wall couldn't dry if it wanted to---Mike"Even a blind squirrel finds a nut once in a while" Mitremike c. 1990" I reject your reality and substitute my own"
Adam Savage---Mythbusters
I would feel better with a poured concrete foundation with a ledge for setting stone on the outside. Next would be a block foundation with rebar and concrete infill. Just my 2 cents worth. I would never have a good feeling about skinny wood studs underground holding that weigt up.
Most foundation failures around here are from lateral/horizontal stresses and other than a poured wall I'd feel better with a 2 x 8 shear wall sheathed with 3/4 " ply as oppsed to a bunch of little blocks glued together with a little mud.
I just have a bad feeling about using wood underground. Done 100% correctly it's probably OK.
You must have more confidence in pressure treated plywood than I have!
If either the fasteners that attach it, or the glue that bonds the plys fails, you will have a complete collapse of the basement.
I have two trailers with pressure treated ply sides and bottoms. The ply has been on them about 16 years and is basically completely delaminated and needs replacement. I can only imagine this happening faster in the ground. This of course, has nothing to do with the pressure treatment, it has to do with the adhesive in the plywood.
I wouldn't put a wood basement under anything, especially an extremely heavy log home.
There are a lot of other issues to consider when setting logs this size on a wall.
You have to drop the floor joists down so they are flush with the top of the foundation, you have to anchor the logs so they don't want to roll, etc. etc....
I'm an engineer, though my experience is not in the construction industry.
I seriously doubt that a wood foundation will support the weight of a log cabin. That by itself will make the decision for you unless you can get an engineer to do the calculations and tell you it can support the weight.
ICFs have much going for them including considerable insulation and a very strong wall. They need some steel, though the amount is not much. Remember they used to build concrete foundations of cinder block with no steel at all. Most cracked, but did stand up. The combination of poured concrete with a small amount of steel is considerably stronger.
There's some speed advantage as well. Forming is quick, then the insulation is already in place so all you need to do inside is screw on drywall to finish. It also produces a very quiet wall, too.
I did ICFs for my dream home in 1999 and would do it again in a heartbeat.
To perch a heavy log structure on a wood foundation, I would expect the studding in it to be about 6" OC to support it
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IMO, PT foundations are to foundations like manufactured houses are to site-built homes.
There are two treating plants in my area....supplying mostly to the sub-tropics to the tropics (Hawaii to Indonesia) in addition to locally.
Their .40 treatment comes with a 25 to 40 year warrantee; .60 treatment offers a 30 to 50 year warrantee.
Consequently, the appreciation of a home or structure suffers over the long term with a "permanent wood" foundation, just like HUD regulated manufactured housing which is substandard in construction.
Most of the homes being built today should, with basic upkeep, last well over a 100 years or more, but with PT underpinnings, I doubt the expected lifespan would even come close to one built on concrete.
By the time a permanent wood foundation is built and all the protections added to it to assist its longevity, not to mention some of the pitfalls mentioned in previous posts, any cash saved in its construction (and that is debatable) would be offset by its potentially limited life.
didnt you go to the log home show at the excel center?
Steve,
Must have been someone else. We live in So. Cal. I haven't seen any log info. around here! We do go back to Mn in the summers but stay in the sticks :) with my parents. Sounds like PWF are not a good option for what we have hopes for. I really am happy we have fallen into this discussion group, what a help!
Tamlyn
im not the expect.. nor claim anything close to it. but here's my 2 cents. Permanent wood foundations just don't sound permanent. I don't care what anyones says. I've seen pressure treated wood rot. But then i've also seen concrete foundations crack, leak, deteriorate , crumble and what have you ( but in the worse cases... its a pretty old house )
If its my money.... im buying the house with the concrete foundation. Id make sure that the general contractor has a pretty good foundation guy. ask around, do your home work. Id even spend the extra money and get something like this done>>>
http://www.okewoodsmith.com/liteform/Default.htm
Where are you going to build? Brainard area? or elsewhere? I know of one builder up there that does great work. Im sure he even travels around doing lake homes.
Anyways. GoodLuck
Steve
Steve,
Thanks, the site is very interesting. I think it makes more sense than any I have seen. We hope (gotta sell our place in San Diego 1st) to build about 1/2 way between Grand Rapids & Hibbing MN.
Tam
I'll put in my 2 cents as I've worked on 5 - 6 PTW foundations over the years. The ones I did plumbing on 25 years ago are still in good shape.
I had my shell framer put one in for my house in SE MN 2 years ago, and it is fine so far. The real key is plenty of pea gravel as footing and back fill. I think you need to try to find an excavation sub that has excavated for and back filled PTW before. In order to hold down on the amount of pea gravel that you will need for backfill, the excavation needs to be done more accuretly, I think, than with a normal poured or block foundation. This guy also couldn't read prints very well, so dug wider and deeper than was really needed.
You know how excavators are when it comes time to back fill. Hurry up with the skid loader...don't mind the rocks etc...just get er dun. Mine miscalculated how much pea gravel would be needed for a PTW (had never done one before) had to go get a 'couple of extra truck loads. In retrospect, I should have used the excavator sub that my framer always uses (he does lots of PTW's)
we were looking into the PWF for our cottage, there is a book that the Canadian Wood Foundation puts out that details the construction, well worth the 25.00. One of the biggest reasons we didn't go with it was we could not get insurance on it. There are only a few companies here in Ontario that would insure the cottage ,most wouldnt touch it. The second reason we didn't go with it was that it really hinders your resale if ever you needed to sell. Unfortunately not many people are educated in this type of foundation.
If you think the basement might be used for a second family, be sure you address the egress requirements now, rather than attempting a retrofit later. I don't know the details, but I'm sure every bedroom has to have a second mode of exit. The other spaces I'm not so sure of.
My wife and I are in the process of building a new home. Our permanent wood foundation was built in July 2005. The house is closed in and insulated, radiant slab in basement is heating the house and the number 1 reason that we built the wood foundation is for comfort! When you walk down the steps you do not feel any dampness or have any basement type feeling whatsoever. I think done correctly, the pwf is about the only way to go if you plan on using the basement as living space. The plastic used on the outside, rather than a waterproofer is more of a vehicle to allow moisture to get down to the rock and to tile and to a sump or to daylight. On our foundation, we went one step further...rather than plastic used we used a sheet membrane product called "Tamko TW-60". The lumber used is a higher quality foundation grade lumber which is treated to .60 retention level and then put back in and kiln dried again with all stainless steel fasteners below grade and sitting on a 8" bed of 3/8" pea rock. With no footing to trap the water and moisture underneath the walls I can't help but think this foundation will be around along time!
PWFs were out of style for awhile, but are becoming more common again in MN. I'm guessing about one in 50 new homes here has a PWF.
I know that PWFs had some problems in the past (and the organization insuring them basically went bust with claims), but apparently the main problem was improper site prep and construction. Thus, you need to be fairly picky about who engineers the foundation and how it is installed. Properly installed and maintained, however, they should live up to the claims of permanency.
However, I'm likewise skeptical of its suitability for log construction. In theory it can be done, but it seems like a mismatch of techniques.
happy?
When i developed the costs of my own foundation in western Montana, the treated wood foundation (2x6, 16" OC, with 5/8" ply, glued and screwed) came in about a third the cost of the foam block foundation, with costs of materials a bit less than the cost of a poured foundation. The advantage to me was that i assembled the walls in panels by myself, then had two friends come over for a couple hours and help me stand them up on the poured footing. Wood founds don't require a concrete footing, but i wanted concrete with rebar to be absolutely sure of level. I saved the cost of renting formwork, the labor of forming and stripping, and the cost of hired labor for a pour. Construction wasn't hampered by weather, delivery schedules or access issues for a cement truck.
I used plastic dimple fabric (Dörken/Delta MS) as my exterior waterproofing, having installed it to great effect formerly on a leaking concrete foundation. I also installed French drains to daylight on the walk-out plan. I left an area inside unfinished right under a valley that drains a large portion of the roof on the uphill side of the house to see if it would leak. It didn't, even in the worst storms.
I fit EPS foam sheets between the bays below grade in deference to possible moisture problems, but i haven't had any. If i had it to do again, i would have foam sprayed in the bays instead to further glue the walls together and save all the fitting.
Only drawback with the PT foundation is that when the wood dried out, there was as much as 3/8" variation from one stud to another in plane, so i strung and shimmed the wall to flat before rocking. Wiring, plumbing, and attaching finish materials was utterly simple. I suppose a great deal depends on how much of the work you intend to do.