Foundation design

[Thorfun]

1 hour ago, Kelvin said:

Exactly my thoughts. The Marmox stuff is very expensive.

Insulated slab? 

 

😂

[Kelvin]

😂 I have a couple of quotes from two companies. 

[Gus Potter]

On 07/10/2022 at 10:32, Kelvin said:

Hi

 

I have finally got the SE pack back (well 4 drawings plus details) it's only taken them 9 weeks. Long story.

 

The house is a CPS timber kit (302mm) The blockwork foundation  detail is 325mm blockwork with a compressive strength of 7N/mm2 and a minimum built density of 750kg/m3. I was hoping to use an insulated block but they all seem to have a maximum density of 730kg/m3. Any suggestions? I also have concerns about thermal bridging which I've asked them about. 

 

 

 

Hi Kelvin.

 

On 07/10/2022 at 10:57, Thorfun said:

you're having those awesome twin stud wall (I believe called Larsen truss?

Yes it looks like a Larsen type but what your drawing shows is the outer stud resting on the underbuilding. Could be a quasi Larsen? great proven concept. the Larsen truss. The true Larsen truss allows you to put the load down the inner studs only and this lets you develop a great weather proof detail at the bottom.

 

If you are going for underfloor heating in particular I would go back to basics. Thicken the perimeter insulation up to 100mm PIR and take it down to the top of the founds. This way you actually insulate the dumpling of soil inside the building. Your designers will turn various shades as it will likely be outwith their scope of experience.. but that is what we do in industrial design from time to time.

 

If you keep the floor screed slab back a bit you can carry the perimeter insulation up to the underside of the  insulated plasterboard and now you have minimal thermal bridges.

 

Yes in the round use thermalite for the underbuilding.. but check with the SE as you need to be able to prevent building uplift and sideways sliding of the house and that is hard to make work in thermalite. Often we will have holding down straps and fixings between the inner bottom rail and the underbuildings.

 

Let us know how you get on at your design meeting.

 

 

[Mr Punter]

14 hours ago, Thorfun said:

I had a few Foamglas blocks which I got from @ToughButterCup for a cheap price as he had them leftover. but to buy them new would've been eye-watering for the perimeter of a building.

 

14 hours ago, Kelvin said:

Exactly my thoughts. The Marmox stuff is very expensive.

 

I have only used it for the inner leaf of blockwork and it works out about £16 per linear metre.  I guess for a 300mm sole plate it would be triple.

[Kelvin]

I phoned Marmox and they don’t recommend them stacked or multiple rows of them. They are going to confirm it for me however.