cost effective foundations - advise please

slipstream

starting a lowish energy renovation of a 1960s bungalow w/dormer soon (we hope).

we are keeping two single leaf solid block external walls from the original house. new walls will be 215mm quinnlite we will have 150mm grey eps on top of all walls.

we were planning on using a passive slab system with ufh in the 100mm concrete on top but this hasn't worked out (for non-technical reasons i'd rather not get into).

so we are back to the drawing board and our architect is looking into our foundation options at the moment. however we would like to make a decision quickly as we are going out to tender soon.

we were planning to have 200mm+ of eps in the floor.

i'd like to ask what foundation buildup have your guys found to be the most cost effective?

also, i've read about the passive strip foundation for cavity walls but am unclear on the function of the concrete slab below the insulation as here for instance there is no concrete beneath the insulation.

thanks for your help,

slip

fash

slipstream wrote: »

also, i've read about the passive strip foundation for cavity walls but am unclear on the function of the concrete slab below the insulation as here for instance there is no concrete beneath the insulation.

The passive design foundation doesn't work properly- the aerated block work must be on the dry side of a DPM- it doesn't work if it is wet.

As for the detail- the concrete slab under is a structural slab. The other is a floating screed- they are just different ways of doing a floor.

slipstream

fash wrote: »

The passive design foundation doesn't work properly- the aerated block work must be on the dry side of a DPM- it doesn't work if it is wet.

As for the detail- the concrete slab under is a structural slab. The other is a floating screed- they are just different ways of doing a floor.

Thanks Fash,

Our architect was proposing quinnlite foundation b3 blocks under the DPM.

Slip

fash

slipstream wrote: »

Thanks Fash,

Our architect was proposing quinnlite foundation b3 blocks under the DPM.

Slip

Make sure it is wrapped in DPM- and preferably open to the dry structure vertically to allow it to dry out. Wet aac is worse than useless.

See section 7.3 here

slipstream

cheers fash.

do you have a recommended cost effective insulated raft or strip foundation buildup?

DeeJunFan

I have been told if you cover the lite blocks with bitumen paint and that makes them waterproof.

Seems like a fairly budget way of getting around the problem. A bit of a boring job but if it sorts out that thermal bridge.

Sligoronan

Here is an example of the bitumen covered Quinn lites.
Really simple detail Workers perfect for us.

slipstream

Sligoronan wrote: »

Here is an example of the bitumen covered Quinn lites.
Really simple detail Workers perfect for us.

ronan,

is that bitumen paint or some sort of sheet you used?