I intend to build to passivhaus standards and have specced the insulation to meet those standards - but I'm not sure about how significant an effect thermal bridging of the ground floor will have on the design (and I haven't included this in the PHPP calculations). Our architects have proposed the following design for the basement and ground floor. From outside to in: Natural stone, supporting blockwork, air gap, PU insulation, internal blockwork. The entire bottom mass that comprises the basement floor, basement walls and ground floor will be solid concrete. The exterior of the basement walls (to a depth of 1m) will also be insulated as will the ceiling of the basement.
The ground floor is about 200m2 and so is the basement, simple rectangle. Is the thermal bridging between floor slab and exterior significant in a passivhaus build? If so, what are the alternatives to minimize this bridging without increasing the building costs considerably?
Tony has solved the problem by having a double basement wall with insulation in between. This looks ideal, but would mean much more concrete and higher costs. The house is in Spain, hence all the concrete and blockwork :)

Posted By: stephendvintend to build to passivhaus standards

Posted By: stephendvOur architects have proposed the following design for the basement and ground floor.

What's wrong with this picture?!

Posted By: stephendvOur architects

Tell them its no good and to do it again!

Posted By: tonyThe design idea should be to join up all the insulation without bridging it.

If you start suggesting design details then its your fault if it goes wrong...

...say it with me...

MAKE THE ARCHITECTS DO THEIR JOB...!

...all together now...

J
(James Norton RIBA)

Posted By: ralphd

How much more expensive would it be to go with a wood floor? (wood = ~R1.2/in vs R1.2/ft for concrete)

I'd lose the use of the concrete floor as thermal mass for sunny winter days.

The Passivhaus details book has details for Passivhauses! Ask to see your architects' copy, find the relevant diagram and ask why they didn't use it?

You can borrow mine if you wish.

Came across another thread about a similar situation: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1052
where crisc recommends 'foamglass Perinsul' - I remember seeing this material mentioned in the Cepheus book too. Since it can bear a load, I was thinking of using it like so (where the red bits are foamglass):
Product details: http://www.foamglas.co.uk/perinsul.htm

Posted By: James NortonSeriously, stop trying... make them do it! Then you avoid and come back if there are any problems...

If I left it entirely up to the architects I'd have the thermal bridge sorted with multifoil wrapped around the exposed edge - which I'm not happy with. Anyway, I've just come back from a meeting with them and we've agreed a solution similar to the previous image using the foamglass to support the stone wall. The insulation will now be an unbroken barrier all the way from the wall, down to the external basement insulation.

If you read the only comment about the book it says it's in both german and english.

Posted By: stephendv

Posted By: ralphd

How much more expensive would it be to go with a wood floor? (wood = ~R1.2/in vs R1.2/ft for concrete)

I'd lose the use of the concrete floor as thermal mass for sunny winter days.

A common technique on this side of the pond is a concrete topping coat (about 1.5") over a wood floor. Commonly used with in-floor radiant heating.

-Ralph

When I looked at hollow-core precast concrete, the cost was $4-5/sf. Wood-framed with 2x10, OSB subfloor, & 1.5" finished concrete topping coat was just under $2/sf.

-Ralph

Dave, ...didn't realise was a book too! is it any good?

Stephen

Posted By: stephendvHopefully there'll be more of an impact once the house is complete and I can show them the tiny amount I'm spending on heating

or perhaps when they want to use is for promoting themselves...?

J