foundation for a two floor wooden house

Hi!

I'm looking at options for a two floor wooden framed house in a cold climate. Foundations here need to be 1.4m (almost 5 medieval feet ) deep.

Current line of thinking is, from bottom to top:
- rubble trench foundation up to ground level
- gabions or car tires +- 30 cm high, filled with well draining gravel
- wooden ring beam with interior insulation

That looks as if it would be:
- fast to build
- cheap
- very durable



Kind regards,

M

Where is the project located? Foundations are usually regulated quite heavily by local building codes and (especially for larger house) will need to be signed off on by a structural engineer. You should probably contact an engineer practicing in your area and ask him for basic requirements.

There are technical requirements here too, but a structural engineer is not required.

I realise what I've described is probably overbuilding quite a bit. I also guess it's one of the only ways to build sturdily without concrete and without trying to find an engineer. Because good luck trying to find a structural engineer around here at all, let alone one that would look into non-concrete foundations. So I think I'm doing the next best thing: trying to use my own observations on soil and historical building practices in the area:
- I've done some preliminary rotary vane testing, and that comes out quite ok.
- Quite a few historical building foundations in the area were often: scrape top soil away, throw in some boulders, wooden foundation.
- There are also some really beautiful full depth natural stone cellar ruins in the area. Easy to notice the abandoned places that feature them.

lots of old farmhouses in north I believe were built on foundations of stones , I'm no expert but building on a solid base will only help to insure what is built above will stay put and insure you investment won't heave or crumble.
I know this old house I have was not built properly and it is seriously twisted because it was not built on a solid or proper foundation

Even if it is a hassle, I would definitely look for a structural engineer or builder with the necessary experience to check your plans and execution. It is easy to look at old houses and think that if they could do it 200 years ago, it can't be that hard. But those houses were built by experts, who knew what they were doing and had years of experience.

Regarding the original question:

- Your general ideas sound fine. Not sure if gabion baskets are needed/advisable. Car tires are probably harder to mess up and soil is more readily available in most places than gravel.
- I would read up on drainage, though, because if you experience periodically heavy rains/snow melt/etc and depending on your soil you might want to guard against having your foundations washed away.
- For underfloor insulation you could look at foamed glas. This is usually made from recycled material, it is chemically inert and thus very sustainable (your can reuse it almost indefinitely or dump it somewhere without ill effects).

Peter Dörrie wrote:Even if it is a hassle, I would definitely look for a structural engineer or builder with the necessary experience to check your plans and execution. It is easy to look at old houses and think that if they could do it 200 years ago, it can't be that hard. But those houses were built by experts, who knew what they were doing and had years of experience.

Definitely having this checked by an experienced builder, in fact by multiple ones. I'm just not fond of getting a stamp of approval on paper just for the sake of the paper, but I see the value in someone experienced checking the foundation(!) of my plans.

Regarding the original question:

- Your general ideas sound fine.

Thank you for your hint.

- Not sure if gabion baskets are needed/advisable.

Dear wife can accept those.

- Car tires are probably harder to mess up

Dear wife has more difficulties accepting those. Not sure how to best hide them from sight...

and soil is more readily available in most places than gravel.

We're definitely going with gravel in there instead of soil, because of the draining properties.

- I would read up on drainage, though, because if you experience periodically heavy rains/snow melt/etc and depending on your soil you might want to guard against having your foundations washed away.

The entire foundation, including the above ground pillars, is basicly one big drainage channel. The below ground part is lined with geotextile to keep out silt that might mess up the draining qualities. At the bottom of the foundation, there's a drainage tube embedded that slopes gently to daylight.

- For underfloor insulation you could look at foamed glas. This is usually made from recycled material, it is chemically inert and thus very sustainable (your can reuse it almost indefinitely or dump it somewhere without ill effects).

I've looked it up before. It looks like a great product, but one that I would rather use directly on good bearing soil. Reasons we didn't pick that:
- Our budget is severely limited, and foam glass is expensive.
- The closest producer is 600km and a trip across the sea away.

In terms of insulation, I have grouped the wet places (bathroom, toilet, kitchen) efficiently. We'll use untreated sheeps wool in the floor that limited area, and cheap local blown in cellulose fiber elsewhere.

Marcel,

I am certainly no expert, but my understanding was that in a cold climate (or any climate), a key concern was to make certain that the foundation was below the frost line, or in a really cold climate, at least get the foundation into the permafrost.  The reason is that you don’t want ground to freeze below the foundation as that ice will heave up the building.  Worse, it will never do this evenly—it will heave one part more than another and the building will lean or worse, warp.

If the foundation is in the permafrost (as I understand), the permafrost, being already frozen, won’t freeze any more and cause frost jacking.

At my grandparents farm in Minnesota, the frost line was about 6’ deep.  In central Illinois where I grew up, buried posts and such were supposed to get to 48” deep to avoid frost jacking.  In Southern Illinois where I live now, I think that 1inch would be well below the frost line and I never hear about frost jacking in the area.  In fact, people who should know about frost jacking have never heard the term (and few of my students have heard of snow drifts, but a few have traveled north in the winter and seen “snow dunes”—amazing).

At any rate, make certain that you get deep enough to avoid frost jacking, but to do so you will need to know how deep the soil freezes, also known as the frost line.

Hope this helps,

Eric

Eric Hanson wrote:I am certainly no expert, but my understanding was that in a cold climate (or any climate), a key concern was to make certain that the foundation was below the frost line,

1.4m is the safe line building regulations recommend to safeguard against frost heaving. That is what the 1.4m deep rubble trench part of the foundation is for.

The alternative is a frost protected shallow foundation, Scandinavian style. That could be done with xps or pir foam underneath a much more shallow foundation. My first rough calculation shows that is too expensive compared to digging down 1.4m and filling with local crushed stone, both in terms of economy and ecology. Even if we need more of the local materials, they come from 15km away. The foam glass comes from 650km and a ferry trip away, plus the production requires more energy.

Marcel,

That 1.4 meter deapth sounds pretty close to the 6 foot deapth according to my highly imperfect mental standard-to-metric calculator.  The protected frost pocket sounds like the idea of resting on permafrost.

Is it ok for me to ask where/how far north we are talking?

Eric

Eric Hanson wrote:
That 1.4 meter deapth sounds pretty close to the 6 foot deapth according to my highly imperfect mental standard-to-metric calculator.

1.4m is about 4.6 medieva^^^feet :-)

The protected frost pocket sounds like the idea of resting on permafrost.

It's the reverse, actually: making sure that the soil does not freeze underneath the building. The insulation protects the soil from the freezing temperatures above.

Is it ok for me to ask where/how far north we are talking?

About 57° in northern Europe. Similar altitude to Kalmar or Vaxjö, Sweden, Riga, Latvia. Southern Alaska is at similar latitude, but due to the gulf stream, the climate in northern Europe is quite a bit more temperated...

The idea of drainage at the bottom of the rubble trench foundation is simple. You want to keep water away from the foundation. And even if it's there, it should never freeze. So you keep the drainage pipe under the worst case freezing level. Any water ending there is liquid. The drainage pipe takes it away.

In terms of insulation, I have grouped the wet places (bathroom, toilet, kitchen) efficiently. We'll use untreated sheeps wool in the floor that limited area, and cheap local blown in cellulose fiber elsewhere.

One architect we talked to about our house warned us in very stark terms about sheep wool. He said he was involved in one property where the owner insisted on using it and it turned out real bad. They had to break open the walls and pull it out, because it started to smell. Probably due to inexperience on part of the planners, but I would be careful.

Why don't you use straw bales? You can use them for both floor and walls (as long as there is no constant source of dampness). A standard bale has good enough R-value to build a passive house, it is quite conductive to amateur builders and is quite cheap (surely cheaper than sheep wool). You an use them in standard wood framed construction (just make the walls a bit wider) and it plays really nicely with a an earthen finish.

Peter Dörrie wrote:Why don't you use straw bales? You can use them for both floor and walls (as long as there is no constant source of dampness). A standard bale has good enough R-value to build a passive house, it is quite conductive to amateur builders and is quite cheap (surely cheaper than sheep wool). You an use them in standard wood framed construction (just make the walls a bit wider) and it plays really nicely with a an earthen finish.

I started off with the idea of using small straw bales, but went with cellulose fiber insulation instead, and wool in the limited wet floor areas. The reasons are roughly:
- (for cellulose) Availability. Small straw bales are very difficult to get hold of around here. Almost all balers produce large round bales. Almost all others produce large square ones.
- (for celulose) Timing. At this latitude, harvest comes in August, if we're lucky. Very late in the building season.
- (for cellulose) Fast construction. Cellulose is more expensive than bales, but not hugely so. Two people can blow in enormous amounts of cellulose in a day.
- (for wool) sealed compartments, little risk in terms of smell or moths
- (for wool) dirt cheap or free source of wool available

I'm working on the technical side of the design right now. That should clarify things a bit. Will post here eventually.

Look at what they do in Alaska to deal with frost heaving, usually putting large threaded adjusters on all the foundation posts.  Very simple to re level the house when the foundation settles.

Might stabilized earth with basalt fabric and / or rebar work as a foundation?  I've read about it, however I am not hands on familiar with either just yet.

Catherine Windrose wrote:Might stabilized earth with basalt fabric and / or rebar work as a foundation?

No, that won't work, because the material you want to use in the foundation must be anti-capillary and well draining.

I wouldn't use gabions. In practice, we normally consider gabions to have a lifespan of 15-30 years, on the lower end if we expect there to be a lot of wet/dry cycles. I assume you want your house to last longer than that.

Other than that, it really depends on your soil type and if you want a basement or not. You can usually significantly decrease the required depth of foundation by using insulation (foam).

If I were to design a rubble trench foundation, i would probably use some sort of geotextile to prevent the transportation of fines from the surrounding soil into the rubble (or clean gravel) trench, which will prevent heave long term. Another alternative to the gabions or car tires would be concrete blocks.

Catie George wrote:I wouldn't use gabions. In practice, we normally consider gabions to have a lifespan of 15-30 years, on the lower end if we expect there to be a lot of wet/dry cycles. I assume you want your house to last longer than that.

Longevity of gabions might be a problem indeed. We'll probably go with tires, find a way to protect them from direct sunlight and hide them.

You can usually significantly decrease the required depth of foundation by using insulation (foam).

It gets trickier if you don't know how inhabited the place will be during winter. xps or pir are not really environmentally friendly materials either.

If I were to design a rubble trench foundation, i would probably use some sort of geotextile to prevent the transportation of fines from the surrounding soil into the rubble (or clean gravel) trench, which will prevent heave long term.

Definitely!

Another alternative to the gabions or car tires would be concrete blocks.

We'd rather not have any cement in our building.