Structural Slab

[Russ Hellem]

Hey All,

When i was at last year's PHI conference in Austria I was exposed to a few different companies that sell components for a system where you don't have a footing or foundation, but rather an 8" structural slab. I am wondering if anyone has ever had a structural engineer look at an assembly like this? And, has anyone looked at sourcing foam for a system like this?

We are working on design and budgeting for a couple of projects, and thought this might be a good option. Any thoughts?

The attached image is a section detail from Jackodur insulation systems from Europe. 

Thanks,

Russ Hellem

Energetechs

[mike eliason]

Russ,

This approach has been used by a number of people lately. Chris Corson's apparently uncost-effective 1,160 sf TFA house in Knox, ME (7350 HDDs, built for $130/sf) had some custom fabbed. http://www.jlconline.com/cgi-local/viewnew.pdf/0/2ec24b200e71616e7e0f73693d8940a9/www.jlconline.com/cgi-bin/jlconline.storefront/4fb5306b0a78a34927180a323cb4069d

Also, an 8" Structural slab may be overkill for a raft foundation, depending on loads, soil type, etc.

Cheers,

Mike

[mike eliason]

And here's an enlarged detail:
http://straightclaw.com/corsondrawings/footingsection.png

Another firm doing this overseas is Isoquick:
http://www.isoquick.co.uk/

[Martha Rose]

Matt Schmitter, Davido Engineering Group  http://dcgengr.com/people/ 

We used a 6" structural slab, no footings, at City Cabins.

If the foam is for under the slab, I like DOW blue. Many places carry it, but thicker than 4" go with the denser. They have 4 choices of density. Most places carry the medium.

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[Dylan Lamar]

Hi Russ,

The slab technique, called a Raft or Mat foundation, has been around a long time... I studied them in my undergrad struc engineering classes, though it's not necessarily typical so any given SE may not have ever designed one.

dylan

On Mon, May 21, 2012 at 6:38 AM, Russ Hellem <russh...@gmail.com> wrote:

[Sam Hagerman]

Russ-

This works as long as you don't need any hold downs.  The deeper concrete required by holdowns quickly neutralizes the efficiency of the raft assembly.

Sam

Sam Hagerman
Hammer and Hand, 503 232-2447
s...@hammerandhand.com
Passive House Alliance United States

[Russ Hellem]

Thanks for all your input, looks like i will need to have the project engineered and budget for our seismic zone. 

Russ Hellem

Energetechs

[Katrin Klingenberg]

Hi Russ,

Sorry I am coming late to the discussion. My travel schedule puts me behind in communications.

Inspired by the European solutions I designed the first "raft slab" to my knowledge in the younger history of PH in the US in 2010 (Dylan, if you have reference articles to earlier implementations, please send them to me! We are researching passive house history and techniques used starting in the 70s, would be great to be able to include those references). We prototyped it for an affordable project in Urbana, the first one was finished in 2010, the second one followed in 2011.

It works amazingly well and you can make the foam form work yourself very cost effectively out of Geo foam. Our contractor cut the pieces in his shop. We started including the details, slab and the hybrid wall design, in the PHIUS curriculum beginning 2010 as the most cost effective solution to build passive houses using all local materials. A lot of consultants who went through our training, liked the system, it makes all good sense (and cents :) ) and started implementing it. Our houses were built around $110/sqft. Chris Corson almost exactly used the details from the training. He was exceptionally successful implementing them and it is great to see that he has such great success with it. Nice write-up and well done!

I presented the details on the wall and floating slab prototype for the first time in Portland 2010 during the 5th Annual Passive House conference. I can send you the presentation with the details if you like. It used to be on our website but it has been temporarily moved. It will be up again soon.

We are happy to consult with you on this, if you still need help! It is very straight forward and we have done a few of them by now.

Regards,

Katrin

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