Wood Foundation - Yay or Nay?

December 5, 2018 3:48 PM

So, me and my wife are in the process of buying a house, and we just had the inspection done today. In the process of said inspection, it was discovered that the house has a wood foundation, as opposed to a concrete one. The inspector said that it's a standardized construction method, and that he did not see anything wrong with it, but reading up on it has a lot of conflicting information. Is there any recommendations for information or what to look for?
posted by NoxAeternum to Home & Garden (22 answers total)

Where is this located? And when was the home built?
posted by bennett being thrown at 4:03 PM on December 5, 2018 [5 favorites]

It's certainly very normal in NZ and Australia, and CA and AK from what I've seen. Timber piles is the technical term. It results in a more living, ever-so-slightly springy floor - Concrete floors by contrast feel dead and things dropped on them tend to break, timber floors are also less tiring to stand on that concrete - Like when you go to supermarket and see all the operators standing on rubber mats because the concrete wrecks your feet.

In earthquake countries timber piles make the building more recoverable from quake damage. They also mean that the normal settling that occurs and can result in sloping concrete floors can be easily fixed - termed pile leveling.

Concrete floors are also noisier. Also unless very new will not have insulation and so are cold and prone to damp rising thru the slab. By contrast with a timber floor you can get underneath and upgrade the insulation. Underneath you'll also find all the wiring and plumbing - with a concrete floor this is usually routed thru the slab (and inaccessible).
posted by unearthed at 4:06 PM on December 5, 2018 [1 favorite]

By foundation do you mean slab or basement? Cuz a basement made of wood...I think only in a dry warm area.
posted by vrakatar at 4:14 PM on December 5, 2018

Yeah, need to know more. Here in New England I'd find a wooden foundation pretty shocking. But then, here in New England I've never even heard of such a thing—our foundations are concrete, block, or stone. Where are you located and what style of house is it?
posted by Anticipation Of A New Lover's Arrival, The at 4:38 PM on December 5, 2018 [1 favorite]

Check for termite infestation, rot, and settling (uneven floors). All are fixable, probably. Piles can be replaced (assuming access available), either with CAREFULLY SELECTED timber replacements, or with brick, steel or concrete. Termites are a bigger problem, important that there are termite barriers to prevent the termites gaining access to the floor substructure and wall framing, otherwise they will literally eat you out of house and home. Levelling usually just requires putting spacers on top of piles to account for settling. If your inspection addressed these three issues, then you are good to go. If you buy the house, you just need to keep an eye on these into the future.
posted by GeeEmm at 4:41 PM on December 5, 2018

If your house is on piles, there's nothing wrong with wood as long as it's done properly and is in good condition, same as if it was on brick, concrete, block, or steel. It's a perfectly fine and time-honored way of holding up a house. It's less popular in moist climates or areas that are affected by Formosan termites but there's nothing inherently wrong with wooden pilings. They're strong and can last a long time.
posted by Anticipation Of A New Lover's Arrival, The at 4:55 PM on December 5, 2018 [1 favorite]

If your realtor can’t explain more detail than you’ve given here, and tell you what that means in real terms: I suggest you get a new realtor.
posted by SaltySalticid at 5:08 PM on December 5, 2018

By wood foundation do they mean post and pier? Our 90 year old farmhouse in the country sits on many concrete piers sitting in the ground, with wooden posts on top of them that hold up the floor joists.
posted by MonsieurBon at 5:09 PM on December 5, 2018

Ehhh, realtors don't really know that much about evaluating houses. At least, my realtor doesn't. My home inspector was able to go into a fair amount of detail, though. I think knowing what questions to ask helped a lot, however—if I hadn't asked probing questions at the time of the inspection, I wouldn't have gotten nearly so much info.
posted by Anticipation Of A New Lover's Arrival, The at 5:11 PM on December 5, 2018 [1 favorite]

I also have a wood foundation (in an area that has earthquakes). It seemed super weird to me since I also grew up in a place where concrete is the norm but is very common here.
posted by bighappyhairydog at 5:22 PM on December 5, 2018

Response by poster: We are up in Montana, and the house was built in 1980, but has had additions added over time. The posts are on concrete footings, and the inspector saw no signs of water infiltration.
posted by NoxAeternum at 5:40 PM on December 5, 2018

Is it the whole house or just the additions? Was it a manufactured home? Check in with your mortgage broker and your home insurance to see what they say.
posted by amanda at 5:57 PM on December 5, 2018

Response by poster: It's the original part of the house (the master suite is over the garage, which is on a slab, and the three season porch is on piles that are externally visible.) And no, this isn't a trailer. (As we found out, manufactured home = trailer; modular home = built from modules built off site; pre-fabricated home = built from components (walls, etc.) built off site.)
posted by NoxAeternum at 6:03 PM on December 5, 2018

Are you describing a concrete or cinderblock basement with wooden posts holding up the ceiling which is at or near grade, or are you describing wooden pilings that hold the house proper up in the air, above grade?
posted by Anticipation Of A New Lover's Arrival, The at 6:21 PM on December 5, 2018

If you have a basement, with concrete or cinderblock walls (in this scenario, these walls are your "foundation" proper) and the wooden parts are the posts in the basement which hold up the basement ceiling/first floor, there's nothing wrong with that. The rest of your house's structure is also wood, after all. The posts should be plumb, appropriately sized, sitting on appropriate footings, made from an appropriate type of wood, and either undamaged or with only cosmetic damage, and there should be enough of them and they should be properly spaced. Most of that applies to any posts though. Wooden posts are more vulnerable to certain types of damage than, say, Lally columns (which are concrete-filled steel tubes, also very common as basement posts) but that's about the only drawback. I've seen wooden posts in basements that are over 150 years old and are literally just sections of old tree trunks with the bark and everything, and which are still doing their jobs just fine.
posted by Anticipation Of A New Lover's Arrival, The at 6:32 PM on December 5, 2018 [1 favorite]

You may be talking about a "permanent wood foundation". This is a stud wall constructed with pressure treated wood studs and sheathed with pressure treated plywood. This wall is constructed on a concrete footing below the frost line and then buried the same as a cinder block or solid concrete wall foundation. These are marketed as having a 100 year life but who knows for sure since they haven't been around for 100 years yet.

A couple of things to look for. Check for bowing inward of the walls. You can sometimes see this by getting your head down and sighting along the length of the wall. Even better you can stretch a string along the wall from corner to corner of the foundation.

You want to check that water is being well diverted away from the wall so it doesn't pool against it. This means gutters on the eaves and downspouts that go away from the house. The earth should be sloped slightly away from the foundation. The inspector should use a moisture probe to check for dampness. You should be able to see a plastic film water barrier that should extend down the outside wall and visible several inches above grade.

You want to have a qualified pest expert look for evidence of insect damage. Don't just rely on the general inspector.

You want to look on the inside wall for signs of moisture penetration. Again, have the inspector use a moisture probe.

To put your mind at ease, it is probably a good idea to get a second opinion from another inspector, particularly one who has a lot of experience with wood foundations. The money will be well worth it.
posted by JackFlash at 7:56 PM on December 5, 2018 [4 favorites]

Huh, permanent wood foundations. That's a new one on me! If that's what you have then yeah, I guess that's a thing. This article, which I'm sure you've already seen if you are researching PWFs, seems reputable to me. The key to having a PWF seems to be drainage and waterproofing. There should be gutters with downspouts that extend away from the foundation, the grade should slope away from the house on all sides, the soil should be well drained, and there should be an exterior moisture barrier that extends above grade. If all those conditions are in place and the foundation has been thoroughly inspected inside and out, you're probably fine.

Even so, this foundation is nearly 40 years old. Pressure-treated or not, that's a long time for wood to be sitting underground. If I were thinking about buying a house, I would consider a PWF to be a definite drawback as compared to a masonry one—even if it seemed to be in good shape. Not a dealbreaker, but in the same category as an iffy septic or an old roof.
posted by Anticipation Of A New Lover's Arrival, The at 4:07 AM on December 6, 2018

I would ask a couple of inspectors in the area for their opinion.
posted by xammerboy at 6:13 AM on December 6, 2018

So, I almost bought a 30 year old house with a permanent wood foundation.

Both my realtor and the seller’s realtor did not know anything about wood foundations and the sellers didn’t even mention it in their disclosures.

When the home inspector told me it was a wood foundation, I did a ton of research and spoke to a wood foundation installer.

What I found was, in drier climates with sandier soils, it should be fine, if the right materials were used. The rub here was that because the basement was finished, there was no way to really see whether they used the right wood graded for use as wood foundations and the right nails, screws, and other hardware. I also couldn’t see whether there was water damage or termite issues.

Based on the type of soil and climate, plus the lack of visibility and provenance of the materials, I passed on the house.
posted by msladygrey at 5:36 PM on December 6, 2018 [1 favorite]

Just to throw another data point in the mix.... if the wood foundation is significantly out of the norm for the area (1980s construction around here is pretty wonky), then you may also have a hard time selling the property later. If the price of the house is such that you're willing to take the risk of it sitting on the market while a new buyer in the future tries to wrap their mind around a wood foundation, then maybe it's worth it. Hard to say. If you'd like to consider it further, I second the suggestion to get a second opinion on the foundation from another inspector.
posted by amanda at 7:35 AM on December 7, 2018

Response by poster: I've been told that it's not uncommon here (we have a dry climate from being on the leeward side of the Rockies.)
posted by NoxAeternum at 8:43 AM on December 7, 2018

How much do you love the house otherwise? Do you have other options in your price range? Maybe this is just the New Englander in me, but I don't like the idea of a new-tech construction method (the pressure treated lumber PWFs are made from only hit the market in the 1960s or so) that was adopted solely because it is cheaper than traditional methods. Your house's foundation is a critical part of its structure and if it goes bad you're going to have capital-P Problems. Masonry foundations have been successful throughout the entire history of Western architecture; PWFs are new, and they have no advantages other than price. In fact, they are explicitly considered to have lower longevity than masonry ones. If your inspector missed something and you turn out to need a new foundation in ten years, how big of a problem do you think that will be for you? Foundations can be replaced, but it sure ain't cheap.
posted by Anticipation Of A New Lover's Arrival, The at 4:06 PM on December 8, 2018 [1 favorite]