Wooden Foundations

[Chilterns]

In remote  and / or off grid locations where there are significant logistic or environmental considerations not to employ concrete foundations I wonder what ideas or techniques could be employed to provide adequate wooden foundations for a timber-framed or log cabin ?

C.   

[Ianab]

What's the most durable local wood? Historically Totara was used for both fence posts and house piles,  and also canoes. It was good for 50+ years in the ground, and a house on piles can be re-piled. (hard work, but possible). ERC seems a similar wood?

Rock piers built from local materials is another option, and with a modern moisture barrier to the wood should last a long time.

[Don P]

The logistical excuse mostly lives between DIY'ers ears. I've never failed to get the mud in, sometimes it is not pleasant. My mixer tipped over behind the shop 6 months ago and I haven't picked the cursed thing back up yet  :D. Environmentally, concrete is a huge problem though.

I've worked on a few permanent wood foundations. This is the code language;

Wood foundations shall be designed and installed in accordance with AWC PWF.

Exception: The provisions of this chapter shall be permitted to be used for wood foundations only in the following situations:

1.In buildings that have not more than two floors and a roof.

2.Where interior basement and foundation walls are constructed at intervals not exceeding 50 feet (15 240 mm).

Wood foundations in Seismic Design Category D0, D1 or D2 shall be designed in accordance with accepted engineering practice.

Piers are a different problem. They have such a rich history of failure that they require an engineer's design. Prescriptively, braced walls are built over bracing foundation walls.

[Southside]

25 or so years ago a co-worker built a PT foundation and full basement.  I never knew all the specs but it passed inspection and he had a mortgage on the place. 

[Jeff]

Our berm House in Harrison has a wood foundation on concrete footings. Our U.P. cabin has concrete piers.

[beenthere]

Chilterns
Would help if you would put your location in your profile.  ;) ;)

Also, you can correct the spelling in your subject line, if you want.  ;) ;)

Wood can be treated for wood foundations, and there are best practices to employ that makes them durable for a good period of time.

[barbender]

 I built our house with a Permanent Wood Foundation. I used concrete footers, then framed 2x8 walls. They require a heavier treatment, .060 retention iirc.

Special consideration must be given for backfilling. I'd guess about 90% of basements are not backfilled properly, and that will cause problems with a PWF as they don't have the resistance to all the weight bearing on the wall. I get to learn this the hard way and re-excavate ours.

I would build another. I'm not a big fan of all of the concrete that is required for poured walls. If you "lean green" there is a tremendous amount of energy that goes into cement.

My BIL is building a house with ICF's. He was able to get in his frost footings this fall, and when he back filled them he had a sinking feeling when he realized he had around $40K invested already and nothing but a concrete stub wall and some rebar poking out of the ground to show for it.

[hh76]

Drainage and ground type would be my main concern.

Our remote cabin in Northern WI is/was on cedar posts, buried about 2-3' deep in sandy soil.  Built in 1942, and had an addition added in the 60s.  When they added on, they messed up the grading.  The posts near the addition must have seen a lot of water and were completely gone. Under the center of the cabin, the posts are in like new condition.

[Raider Bill]

My BIL is building a house with ICF's. He was able to get in his frost footings this fall, and when he back filled them he had a sinking feeling when he realized he had around $40K invested already and nothing but a concrete stub wall and some rebar poking out of the ground to show for it.

ICF would be great in your area!
I built one in Tennessee.

[barbender]

 I am negatively disposed towards ICF's and the mass of concrete in general, unless you actually need it for bad ground. It will take a long time to recoup the extra expense of that building method, imo.

Everyone is concerned about a PWF getting wet. It ain't gonna rot, that's not a concern as far as I'm concerned. Correct drainage should be paramount with any basement/foundation, or you are going to have problems.

[Don P]

Under log a regular stick frame wall works, the logs distribute the load along the wall uniformly. A timberframe point loads the wall and footings below it, just be aware and check it. I've had plans call out up to stud packs of 6- 2x8's bodaciously nailed together in the basement under 8x8 posts above. Then check the footing in that area.

Precast concrete foundation walls have the same detailing on the cast in place "studs". Under a heavy post above they have ganged them up in the poured wall and that crew will place a concrete cookie in the gravel footing trench under the point loaded section. I've done 2 that way on a gravel footing, one a TF the other a hybrid TF/stick. They have about 1/3 the concrete vs a poured wall and a gravel footing. A pwf can have a wider treated sole plate and set on a gravel footing.

The typical concrete sonotube or wooden pier is too poorly braced to resist the horizontal forces the sail above can produce. In seismic events the buildings just rattle off of them or they overturn. If you are going this route assume the installer is, typical. They threw some mud in the hole to brace the pier. Design the bracing as if it is all sitting up on a parking lot in a hurricane. The bracing soil will be mud when you need a brace.

Or, run the treated posts from footing to top plate, unbroken. The wall, floor and roof planes then brace the cantilevering posts... and they are designed as such, now you have something.

[barbender]

 Don, you make a good point, with the point loads of a timber frame.

I was actually building a log home in the beginning, that got scrapped. Two thumbs down👎👎🤦😂

I'm not saying that PWF is the answer to every situation. It is a completely viable one in some though, and in some cases better imo.

I've been around a lot of construction over the years, of many types. On an asphalt crew, I worked around a lot of new homes, and I also drove a mixer truck for the company to fill in. In that time I saw many hundreds and thousands of yards of concrete poured, and a lot of it was just overkill. Like my BIL's place, it will be ICF all the way up. Sure, it will be like a bomb shelter...but do you need a bomb shelter?

[Chilterns]

Hi,

I observe that the Forestry Forum spell checker has beat me to having to edit the title. Thank you.

I had not expected to see so many replies however many of these do tend to include the mention of concrete and / or mud.

A few years ago I was able to examine 1700 year old Roman foundations that are nothing more than a trench dug 24" wide x 18" deep backfilled with interlocked flint stone. The buildings that stood upon these foundations are now long gone but it's likely that these were of timber construction employing timber sills. This kind of foundation would be very flexible although the foundations observed are not in a frost heave area. I agree that good drainage would be key to ensuring a longer wooden foundation life although oak buried in completely wet ground has survived for close to 10,000 years (bog oak) and alder piles (not durable) completley submerged in water have survived for 1000's of years. Venice is built on larch piles. Some early Australian buildings stand on tree stumps.

I tried to upload pics but this failed.

C.

[Hilltop366]

Photo posting help.

https://forestryforum.com/board/index.php?topic=100194.0

[Joe Hillmann]

Hi,

I observe that the Forestry Forum spell checker has beat me to having to edit the title. Thank you.

I had not expected to see so many replies however many of these do tend to include the mention of concrete and / or mud.

A few years ago I was able to examine 1700 year old Roman foundations that are nothing more than a trench dug 24" wide x 18" deep backfilled with interlocked flint stone. The buildings that stood upon these foundations are now long gone but it's likely that these were of timber construction employing timber sills. This kind of foundation would be very flexible although the foundations observed are not in a frost heave area. I agree that good drainage would be key to ensuring a longer wooden foundation life although oak buried in completely wet ground has survived for close to 10,000 years (bog oak) and alder piles (not durable) completley submerged in water have survived for 1000's of years. Venice is built on larch piles. Some early Australian buildings stand on tree stumps.

I tried to upload pics but this failed.

C.

Wood will last a long time underground.  The problem is often worst right at the surface where it is wet and can still get air.  Often posts rot off right at ground level.  The wood in the ground  and the wood up higher can be just fine but at or just below the surface rotting takes place the quickest.

I am currently building a log home on a pier foundation made of a combination of old power poles and old highway guard rail posts.  I wouldn't necessary recommend it but time will tell if it works or not.

[trees_are_good]

In remote  and / or off grid locations where there are significant logistic or environmental considerations not to employ concrete foundations I wonder what ideas or techniques could be employed to provide adequate wooden foundations for a timber-framed or log cabin ?

C.

You might try a post-on-rock foundation as described here: https://theyearofmud.com/2019/07/12/scribing-wood-to-stone/ - no concrete required. The link uses rocks on concrete but that's not required. Each rock can sit directly on a deep gravel bed for drainage (to prevent frost issues).

[Don P]

Keeping this in mind;

R401.2 Requirements.
Foundation construction shall be capable of accommodating all loads in accordance with Section R301 and of transmitting the resulting loads to the supporting soil.

R301.1 Application.
Buildings and structures, and parts thereof, shall be constructed to safely support all loads, including dead loads, live loads, roof loads, flood loads, snow loads, wind loads and seismic loads as prescribed by this code. The construction of buildings and structures in accordance with the provisions of this code shall result in a system that provides a complete load path that meets the requirements for the transfer of loads from their point of origin through the load-resisting elements to the foundation.

[TW]

The Roman stone foundation mentioned would be what we call a "steinbäddo" (stone bed) in my dialect of Swedish. A trench bankfilled with stones the size a man can move around. In frost prone areas the size a man can carry. Larger stones are more likely to be heaved by frost. Above ground a row of boulders and on top of that a log house or a post and beam building with the post right above the boulders.
An adequate foundation if a couple of centimetres (or an inch) of settlement or frost heave doesn't matter. As traditional as anything can be. I made one last summer.

Orn firm sand or gravel one can just lay the boulders on the natural subsoil if it is a smallish building like a cabin or shed. I made one such foundation last autumn.

In moist clay the oldtimers in the Nordic countries often dug a trench a couple of metres deep. They bailed or pumped the trench dry as they dug. On the bottom well below groundwater they built a raft from round unbarked logs laid crosswise. On top of them large boulders up to just under ground level. Around the boulders they backfilled with clay very thoroughly ensuring that no cavities were left. Above ground they built a plinth from cut stone. The ground surface was graded with a good slopa away from the building. The building always settled a bit when new so it had to be high up to start with. Thanks to the raft and the rather stiff log walls it settled evenly. The raft is protected from oxygen and does never rot as long as the groundwater level doesn't drop.
This would be an adequate foundation even today under a log building.

The story goes that back in the 17th century and before it was common in Finland to just lay the first course of the lof wall on birchbark on the ground in a sandy or gravely and well drained place. A few such houses survive but they have all been taken apart and reassembled on top of several courses of new logs and a stone foundation. There is nothing but hearsay to go by. Anyway I doubt those houses lasted more than 50 years at the very most before they had to be rebuilt.
In the Aunus region of Russia this type of no foundation was still fairly common when my grandfather was there during the continuation war. The floor was usually high up and supported by beams notched into the log walls. The oven was carried by huge beams. That way a few log courses could rot away at ground level with no other damage to the building than the oversize crawlspace becoming lower. My grandfather never understood the reason for that oversize crawlspace but a Russian carpenter explained it to me a few months ago. 24 years to late to tell grandfather that the mystey is solved.