Permanent Wood Foundation (PWF)

[Renovationking]

Hey guys,

My last (and first forum post) was about frost protecting a heated floor in a pole barn. I received some very good feedback and information about my questions there, and I am hoping you guys can assist me with another build option I am considering.

I have a two story barn that is 20X50 that is in pretty good shape; just needs some straightening as it was basically built directly on the ground and there has been some rot in the posts etc. I talked with a structural barn guy today about getting a foundation under the barn and straightening it so I can then finish it off with a roof, sheathing, interior electric, plumbing and heated concrete floor. I am trying to make a place for a wood shop and a place to build my radio controlled airplanes. I have a few 107" wing projects that are tough to negotiate around the cellar!

Rather than a concrete foundation with footer at 4 foot for frost protection, he recommended a PWF. But I am not clear on his detail yet so I am trying to educate myself ahead of time so I know what the hell I am talking about!

I went to the SouthernPine.com website where they have a PWF Design and Construction Guide. In it they cover all the particular requirements for backfill with gravel, drainage etc. for just about every scenario.

In my application, I will have a stem wall where the interior space will be completely backfilled as I will have a concrete floor pour almost at grade (The PWF wall will extend 12" above grade). This, as opposed to a crawl space, full basement, stub wall etc.

The detail build section in the guide calls for plywood only on the exterior side, with crushed stone backfill into the stud bays on the interior side. In other words, the final PWF that is burried only has plywood on the exterior side. Is that how you guys understand it?

Also, for exterior foundation insulation, the detail shows rigid foam directly on the stud wall and then plywood on top of that...I'm feeling like I would want to do that the other way around because the foam creates more of a water barrier directly against the gravel/dirt fill; plus, I get a little more purchase to the studs if I don't have to go through 2" of rigid foam.

Couple other things (sorry this is so long!)...

The guide is from 2001, so, rather than using the rigid foam on the outside what do you guys think about using closed cell foam on the inside of the plywood and then backfilling the gravel against the closed cell foam? Then I could just cover the exterior of the plywood with poly, or something? I would also cover the 12" plywood that is exposed above grade on the exterior with Durock type product, parge it and paint it so it cleans up nice (maybe eliminate paint).

Last thing...the detail for concrete pour around the interior perimeter calls for the concrete slab to be keyed between the studs. Im not clear if this just means pouring concrete into the stud bays and against the back of the exterior plywood or, does it mean that there is some type of rebar through the studs to "key" the wall to the concrete pad.

Any and all comments are welcome, I appreciate it very much guys!

Thank you!

Tom

 

[ms fowler]

Treated wooden foundations have been around for decades. Don't be afraid simply because its not concrete.

 

[readhead]

If you have a building department find out if they will accept it before you get too far along.

 

[ard]

Is this cheaper or better than concrete?

It just seems WAY easier to do a concrete footing, a wall- backfill, then slab. Done, good for 100 years. Zero concerns

 

[Renovationking]

They are cheaper...but pros and cons to everything and PWF vs concrete debates are all over the internet. Google it and your computer will explode.

That aside, I'm just trying to understand the PWF option so I can evaluate it. While I know it is very possible to have full basements with PWF...for me, I would just use concrete for that. I think the issues tend to manifest more when you are creating living space etc. In this case...I won't even have a crawl space! Its completely backfilled on both sides and certainly, there are no concerns from a structural engineering and strength standpoint. Thats why I am considering PWF anyway, in addition to potential cost savings.

I will go to building department; was planning on doing that today actually.

Anyone have any other comments about my specific questions though?

Thanks,
Tom

 

[Renovationking]

Just to follow up...I met with Codes department yesterday on-site. He said I could use a PWF for the barn/shop because they are code compliant ("In the book") as he said...

In my original post, I didn't mention that I had some concerns with having to run a sanitary line all the way across my property to meet the main at the road. I thought that was code.

But what I also learned yesterday is that I can "jump" a sanitary line from the barn/shop over to my main home drain. This is excellent news given the crawl space area is only about 30' away and I can dig that myself (read: my two sons can dig it) and the elevations seem to work ok too. I would have to hire an excavation contractor if I had to run all the way to the road with it!

Codes was recommending spray foam on the inside of the plywood sheathing that is underground from backfilling. So that question is answered.

But he was more in favor of a wood pour stop all the way around the interior as opposed to having the concrete poured up against the exterior sheathing and keyed inbetween the foundation wall studs. The problem with this approach is that the base of the wall cavity above the floor and outside the pour stop will just be gravel fill...tough to poly that off and/or piece rigid foam in there and get a good airtight seal. Perhaps at the same time I spray the interior wall insulation I could spray on top of the gravel and on the back side of the pour stop to seal it all up prior to pouring concrete.

The other thought is that the pour stop would be the spray foam, which would basically be taking the place of 2"rigid foam that would normally be installed around the perimeter of a heated concrete floor. The problem with this approach is that each stud would be a thermal bridge.

Those two perimeter options are still open open if anyone cares to comment on it I would appreciate it.

I'm still waiting on the price for the PWF foundation work and then I can go from there.

Thanks for reading!

Tom

 

[DougWil]

Permanent, wood and ground contact don't belong in the same sentence.

Even industrially treated RR ties and utility poles aren't permanent.
Doubtful any thing you could buy now, and at the consumer level would have anywhere near the lifespan of those applications.

 

[shelteredV]

Permanent, wood and ground contact don't belong in the same sentence.

Even industrially treated RR ties and utility poles aren't permanent.
Doubtful any thing you could buy now, and at the consumer level would have anywhere near the lifespan of those applications.

I agree. Where is exactly is the longterm gain? I'm all for progressive thinking, I just wouldn't substitute concrete for this. ISF, ok. PWF just seems weak.

 

[readhead]

What is the ultimate goal here? I doubt that there will be any money saved, there will be quite a bit more labor and you will still have wood buried in the ground. If this was so great concrete companies would be out of business. I'm not seeing it.

 

[slackdaddy1]

I repair house for a living,
I have only ran into 3 PWFs.
All 3 were failing and needed to be replaced.
Get that Stone, block, brick, concrete up as high as you can before starting the wood framing.
Like I always say "You can go back and change you countertops in 10 years, kinda hard to change your foundation.

Nick

 

[kj_mustang]

There is a builder in my area that builds high end homes all with wood foundations. I have never looked at one but I would not even consider him when we started getting quotes for a new home.

 

[pstnbly]

PWF design guide from 2001. Since 2001 pressure treated wood has gone from CCA Treatment to ACQ treatment. IMHO ACQ treated wood is nowhere near as rot resistant as CCA. I would never consider it for below grade use.

 

[willymakeit]

Ive built one. Full basement with 8' walls in the early 80's.We set a manufactured home on it.
To much bracing for side loads of earth. Less issues with concrete. Theres all sorts of alternates out there but for the most part everything seems to come back to concrete and masonry walls. JMHO

 

[Renovationking]

Well that settles it then...I'm going with solid titanium!

 

[readhead]

Which color and thickness?

 

[ard]

Cutting edge? or bleeding edge? Let us know in 20 years.

 

[finn]

PWF design guide from 2001. Since 2001 pressure treated wood has gone from CCA Treatment to ACQ treatment. IMHO ACQ treated wood is nowhere near as rot resistant as CCA. I would never consider it for below grade use.

I thought the same thing, but stumbled upon the fact that CCA treated wood is still available for special applications, like foundations.

Menards has CCA treated plywood available as special order, and with a price premium. The sales info has application details and limitations.

 

[bushmechanic]

Treated wooden foundations have been around for decades. Don't be afraid simply because its not concrete.

Decades? Try millennia.

Hell, in decent environments some of the oldest still survive.

There's a bar out there somewhere that's been around since the year 900 or so, and I'm pretty sure that one's resting on a wooden foundation, as well. That place still functions, but older foundations exist elsewhere in places that haven't seen a building in several thousand years.

Comes down to how it's done and where you are, in the end; but there's nothing wrong with wood.

 

[pstnbly]

I thought the same thing, but stumbled upon the fact that CCA treated wood is still available for special applications, like foundations.

Menards has CCA treated plywood available as special order, and with a price premium. The sales info has application details and limitations.

Good luck ordering in less than unit loads. By the time you purchase in units and pay shipping concrete will probably end up cheaper.

 

[WNYflyer]

Everything I see in the ICC residential code and the SouthernPine design guide for PWF's is based upon stick built platform framing construction for the main structure itself. Is your structure framed like a typical stick built house? you mentioned rotted post which leads me to believe it is not. The ICC code has prescriptive (i.e "cook book") requirements for PWF's if you meet all the qualifications/criteria etc list in the code. If not you would probably need an engineered solution for you particular structure.

 

[n20junkie]

I see no benefit to a wood foundation, and a pile of disadvantages. Moisture is obviously an issue, hence the rot damage.

I would look at concrete. A wood foundation sounds like depression era stuff to me.

 

[Renovationking]

Everything I see in the ICC residential code and the SouthernPine design guide for PWF's is based upon stick built platform framing construction for the main structure itself. Is your structure framed like a typical stick built house? you mentioned rotted post which leads me to believe it is not. The ICC code has prescriptive (i.e "cook book") requirements for PWF's if you meet all the qualifications/criteria etc list in the code. If not you would probably need an engineered solution for you particular structure.

When originally built they just laid a 2x6 flat on field stone pretty close to grade and built up from there. The gable ends have not moved much and they seem to be on a more substantial foundation. All the movement is in the long side of the 20X50 building; dipped in the middle.

Each 50' dimension has two posts supporting beams with floor joists sistered on top of the beam. The movement was mostly at the post locations (where most of the load is).

One gable has a large beam supporting floor joists while the other gable has a ribbon strip (balloon framed basically).

Your comment about platform builds on all the PWF's in the guide is interesting. I'll look at that. Not that it makes it correct and certainly not to minimize your observation, but this contractor specializes in structural barn and foundation work. In fact, my barn is really small compared to some of the other stuff they have worked on.

Thank you for your comments and taking time to reply about my situation!

Tom

 

[Renovationking]

I see no benefit to a wood foundation, and a pile of disadvantages. Moisture is obviously an issue, hence the rot damage.

I would look at concrete. A wood foundation sounds like depression era stuff to me.

There are clear benefits and clear drawbacks...like everything I guess.

The pressure treatment basically eliminates wood fiber as a food source and thereby eliminates one of the big contributors of deterioration.

As to moisture...what about reclaimed logs that have been at the bottom of rivers for years and years. There isn't any rot in them, mostly because of the lack of oxygen and so forth.

To me it is interesting stuff to read about and I happen to be learning quite a bit as I have researched this idea of a PWF. If it is substantially cheaper than concrete, I'll probably go with it...if not, I would be more inclined to go with concrete.

I'm supposed to get my quote this afternoon...and I have to read up on this platform build idea now that WNYflyer has alerted me to that...thank you!

Tom

 

[n20junkie]

I have never pulled a piece of pressure treated wood out of dirt that wasn't rotted. There is a big difference between wood submerged in water, and wood in dirt that is moist with air pockets.

The old pressure treatment didn't protect wood from decay or insects for extended periods of time, and the new enviro safe stuff is laughable as a protectant.

 

[pstnbly]

As to moisture...what about reclaimed logs that have been at the bottom of rivers for years and years. There isn't any rot in them, mostly because of the lack of oxygen and so forth.

Tom

In this case you are talking about old growth, tight grained logs preserved in a near oxygen free environment. That's a far cry from the fast growth, SWP grown on tree farms and utilized in modern day PTL to be used in below grade applications.

 

[joes169]

As a masonry/concrete contractor, I tend to have an obvious bias. That said, in the right scenario, treated wood foundations can be much simpler and cheaper. It sounds like it may work well for your scenario.

We worked on a home about 7-8 years ago that had a treated wood foundation, going strong after 35+ years, and it was retaining 7' of dirt as well.

For those who think that underpinning and using concrete is cheaper than a wood foundation, I take it you've never actually gotten your hands dirty on an underpinning job. It's not as easy in reality as it is on paper or the internet........

 

[padroo]

I have been catching up on this thread and have a couple of questions. Are you planning on doing the work yourself? A lot of times people tend to stick with what they know best, a carpenter builds a wood house, a bricklayer builds a masonry house. Are you capable of doing the wood and concrete work?

 

[Renovationking]

Sorry I have been out of commission with my damn day job! I'm disappointed in my conversations with the PWF contractor and I'm not so sure I can use him as a result. For starters, he opened up by telling me they usually only go down two feet...and it just was hard to pin him down on his approach. Im not trying to put constraints on his work, but I think I have enough general understanding to know when something doesn't smell right. Last he left it he was going to check with the owner of the company and get back to me on some of the open items that I have with him.

In terms of doing the work myself, I am limited by equipment and time. I have been thinking it would be good to have a contractor lift the building and get it back down on a stable foundation (concrete, PWF, posts with bracing etc.) and then I would be able to finish everything else on my own. I'd pull all the exterior clap boards and interior T&G walls, create my new window and door openings and put a new roof on...then try to get everything closed back up and insulated so I can nibble away at it this winter.

I can also do most of the electric work and am comfortable doing all the prep work for the concrete floor, hydronic heating, plumbing etc. and then I would have a mason come pour the floor.

In my 20's I could do more grunt work but I'm not interested in that anymore. I'm just trying to find the right combination of getting help from a contractor on those things that I am not equipped to do so I can finish up on my own.

I have another contractor coming that specializes in building jacking and I am interested in hearing what he has to say/offer. At that point I am going to have to fish or cut bait on something!

I appreciate the comments you guys have made and certainly I respect the time you took to comment and the expertise you offer.

Tom

 

[bczygan]

How permanent is permanent?

Will they provide a 100 year replacement warranty backed by insurance to cover actual costs to R&R?

Bill

 

[joes169]

How permanent is permanent?

Will they provide a 100 year replacement warranty backed by insurance to cover actual costs to R&R?

Bill

If you've actually spent any time around the construction trades, you'd realize that no material is permanent. If concrete was permanent, I'd have a heck of a time making the living I do...........