Block/cavity floor slab thermal-bridge problem

[Tim2021]

I've poured foundation strips and am just about to start building the wall on my cottage extension.

 

The plan was to have 100mm dense block - 100mm full-fill cavity - 100mm dense block construction. Inside would be a 100mm floorslab containing UFH heating pipe over 75mm insulation, and edge insulation around the slab. Radon barrier below and up the sides of the slab.

 

BC have just told me that, in this high Radon area, I must use a 100mm slab with rebar, supported on the inner wall, radon barrier below, continuous, out to the cavity. I understand the construction of that but it will make an obvious thermal bridge. I think I need to minimise this?

 

Can I / should I use lightweight blocks on the innerwall supporting the slab to reduce the thermal bridge?  Can I still use dense blocks above? (for cost and more thermal mass).

 

I can't easily put insulation above the slab and UFH in a screed on top of that as it ends up too far out of the ground.

 

Any other ideas for this construction?

 

Thanks.

Tim

 

 

 

 

 

[Dave Jones]

you could look at using a 300mm trenchblock with a block and beam floor. 

[Tim2021]

Thanks for the reply.

 

BC just told me that if I use (at least) one course of thermalite blocks supporting the slab and bring the insulation down below the slab they will be happy.:-)

 

Sorted ?