Foundations and Anchoring

[Jeremiah Gärtner]

Some issues that my dad (a licensed general contractor) came up with were:

A structure must have a stable foundation to rest on (Earthquakes, soil compression), and

Walls have to be anchored to the foundation (Wind shear).

Also, Wood, by itself, cannot be used to create a foundation, as it rots when underground.

Any ideas?

[Steve Baker]

I don't know what the 'official' WikiHouse answer is.  But in the absence of poured concrete or something like that, I guess I'd use these:

   http://www.homedepot.com/catalog/productImages/400/dd/dd3f5950-6d33-42c5-9e05-b0c1ba605393_400.jpg

...I've had garden sheds sitting on these for decades without problems...the biggest hassle is getting them all at the same level.  I usually have one of them every four feet around the edges and every eight feet on the interior when I build a garden shed or temporary utility building - but that's with 2"x8" pressure-treated wood connecting them.  I have no idea what is structurally "correct" - but that seems to work well for me.  With thinner beams and stuff made from regular plywood - who knows?

I guess it would be interesting to have a mold for casting something like this included as one of the WikiHouse parts.

Even a large concrete slab with the building sitting on it could result in problems with water running beneath and puddling around the plywood supports causing them to rot.   The nice thing about those concrete blocks is that water runs off of them and under the building - so providing they are tucked away under the building so that water doesn't fall vertically onto them - the plywood shouldn't get horrendously wet.

  -- Steve

[Larry Haines]

Check out diamond piers. I'll be using these for my tiny house shipping container project. 

On Tuesday, August 19, 2014 9:55:38 AM UTC-5, Jeremiah Gärtner wrote:

[Steve Baker]

The trouble with those are that you have to truck them into the site.  If you could come up with something that could be cast on-site using a CNC-cut plywood mould - that would be much easier to replicate.   You can probably source some bags of cement anywhere you can get plywood, and if you CNC-cut the moulds, you can scale the cement block production up to whatever number you need.

Could you hammer the pins into the ground first - and then cast the concrete block around them?   That would get you the best of both worlds.

  -- Steve

[Jeremiah Gärtner]

Alright, those provide a stable foundation, but what about resistance to upward force?

We need something like an expanding anchor or dead-man anchor that is easy to manufacture and emplace.

[Steve Baker]

I'm not saying that those diamond piers are the wrong answer - only that we'd need to devise a way to cast something similar to them on-site in a plywood mould.

Whether the sheer weight alone of those concrete blocks would be enough to hold the WikiHouse down under reasonable wind-loads is an interesting question - and we'd still need to come up with a design that would allow us to pin the house to the blocks...preferably without fasteners - or with fasteners we can fabricate from plywood and pound in with mallets.

It's all about limiting the types of raw materials we need, and minimizing the number of tools you require.   Finding materials that can be locally sourced all around the world is a big part of this.

Cement is probably an OK choice...maybe also using iron plumbing pipes or rebar to pin it to the ground would be OK...but what if we're building on rocky ground and pounding anything into the ground with hand-tools isn't feasible?

WikiHouse seems to have solved the framing and structure issues - but foundations, windows and doors - and waterproofing materials seem to be absent as yet.

  -- Steve

[Jeremiah Gärtner]

If we're going to use minimal material and as few "exotic" (with a low bar for "exotic"), then there are very few things that can create a lot of downforce within those parameters.

Maybe we should just throw Force out the window and try to go for a high Moment instead?

Perhaps if we had beams extending out from the base of the house and then had relatively low force anchors on the ends of those beams, we could get the same effect.

[Steve Baker]

That's an interesting idea!

Assumes that land is easily/cheaply available - but I suppose that if you
had a lot of Wikihouses and not much space to put them in, maybe you would
just bolt them all together and get the benefit that way instead.

Also, those L-O-N-G beams would need to be really stiff to avoid the house
bouncing around in the wind as they flex.

Another thought is that the most likely reason for needing down-force is
due to the wind blowing against the side of the structure. Maybe all you
need is some clever aerodynamics to use the wind to generate
down-force...a bunch of formula-one car spoilers on the roof maybe? Or
maybe a bunch of windmills to extract energy from the wind and thereby
reduce it's ability to destroy structures? I think aerodynamics has more
hope of working.

But you still need a foundation of some kind to protect the wood from the
soil...and that's probably gotta be concrete or something like that.
It's about as un-exotic as you could imagine.

-- Steve

-- Steve

[Jeremiah Gärtner]

I was thinking it would still be supported in the middle, so you won't have to worry about bouncing, and maybe it would be anchored along the entire length instead of only on the end, so it wouldn't be so long.

Anyway, this brought me to a second thought, a two part foundation-house system.

One would create a large lattice of beams that would anchored and supported through whatever means is best suited to the locality.

The house modules would then be attached to this lattice foundation, keeping a margin on the edges of the foundation to maintain a high moment per unit height or something.

The lattice foundation system would be modular to allow for outward- or upward-expansion.

Also, things other than house modules might be attached to the foundation: railing, retaining walls, weatherproofed flooring, etc.

[Mark Van den Borre]

Hey Steve!

Another lasersaur user here!

Some straw bale builders do foundations with tires filled with gravel. Barbara Jones at Strawworks (UK) has been instrumental in getting code compliance approval for this type of foundation.

Quite labour intensive but dirt cheap and easy...

Mark

Op maandag 17 november 2014 23:01:12 UTC+1 schreef Steve Baker:

[Alex Whitcroft]

Yes, the challenge with the types is they are incredibly labour intensive if going.

US self builders often use simple cardboard tube formwork with anchors set in as necessary.  If you wanted to do gravel fill you'd have to substitute any above ground portions with something that wouldn't rot away, like HPDE pipe or something.  Engineering to be checked! ;)  Or is you're looking for something temporary, the simplest solution might be a small cast concrete block (using CNC ply formwork) or 2nd-hand concrete block with an anchor bolt or M20 threaded bar fitted.

There are also (proprietary at present, but opensource-able I'm sure) screw in steel pile systems which are reusable/removable and fast to install.  A small enough loading/diameter version might be able to be designed to be installed by hand using simple leverage.

[Jeremiah Gärtner]

Haha! Compressed Earth Bricks

They have a density (1700-2200 kg/m^3 http://unesdoc.unesco.org/images/0012/001282/128236e.pdf) comparable to concrete (2400 kg/m^3 http://en.wikipedia.org/wiki/Properties_of_concrete) without any of concrete's ecological or sourcing issues.

Bury some waterproofed boxen or troughs, fill them with CEBs, and anchor the structure to the boxen/troughs.

[Alex Whitcroft]

The issue with CEBs is that if they do get wet (which foundations will do with the best will in the world) they quickly soften and loose strength.

One other rapidly renewable option (if your building has a limited lifespan requirements is simply timber.  Timber piles of the right wood, surronuding drainage and with some kind of treatment (given we are likely not using slow growth hardwoods) have historically been used for foundations.  Oak piles often lasted about 20 years in the ground in the UK, if I remember right.

The other way to look at is it that a very small amount of concrete is ok.  Not ideal, sure, but if it's a standard, removable pile/pad then why not?  the same one could be used for centuries.  Its a different way of using the material to simply pouring a monolithic foundation and jack hammering it out in 50 years when the building is demolished.  Look at the S-Haus - passive house strawbale and CLT building in Austria.  They wrapped their small concrete pads in plastic film and set licking points in the top to enable them to be pulled out of the ground at end of life.  Nifty!

[Steve Baker]

Will just *any* earth do though?

What about on sand or gravelly soil?

I honestly don't know - but it's an important question.

If you can't use the local dirt, then this might be even harder to source
than concrete.

-- Steve


Jeremiah Gärtner wrote:

-- Steve

[Jeremiah Gärtner]

I was thinking the boxen and troughs would either be made from waterproofed materials and sealed or, more likely, have waterproof lining on the inside and outside, with a sieved drainage hole at the bottom in both instances just in case.

I was also thinking the CEBs would just provide downforce/anchoring and the structure of the boxen/troughs themselves would provide the support strength.

Lastly, CEBs would be best due to their density. Any type of earth would probably work, but the boxen/troughs would need to be bigger and the holes would need to be deeper.

[Alex Whitcroft]

In crude terms, earthen structures need to be of a clay-y sub-soil.  Critically they shouldn't contain organic matter like plant roots, leaves, etc.  They also need (hence the clay-y element) to hold water to make them workable and then dry out to set.  So overly gravelly soil is also an issue.

In this day and age buying concrete is easy.  I wouldn't necessarily suggest you try doign to a DIY store and asking for bags of sub-soil.  However, a good test for your local sub-soil is whether the local vernacular buildings use earth or brick in them (brick being fired clay).  If they are all stone or timber or lime then that suggests your sub-soil may well not be good for building.

[Alex Whitcroft]

Jeremiah,

What you're talking about sounds like quite a complicated solution and with "waterproof materials" being mentioned probably uses plastics anyway (ie; a lot of effort to avoid concrete just to use plastic).

I can also almost guaranty that the CEB element will get wet eventually and then fail.  Historic earth buildings use stone and gravel foundations often - they don't try and run the earth to the ground in wet climates.