Perimeter Expansion strip?

[junglejim]

I’m a bit confused by what seems to be standard practice so must be missing something….

 

The advice is to fix the expansion strip to the perimeter prior to floor insulation. (See attached) Surely as this is much less insulating than pir it provides a potential cold route to the slab around the edge of every room?

 

 Would it not be better to fit the insulation tight to the edges and then add the expansion strip above this. Taping the ‘skirt’ to the top of the insulation / visqueen layer will ensure a good seal for the screed without the need to compromise on floor insulation? 
 

i also thought it was good practice to install a vertical strip of pir around the edges but does the expansion strip negate the need for this?

 

 I’m likely missing something so any advice greatly appreciated. Thank you

[Nickfromwales]

@junglejim

 

Does the picture depict your situation? Masonry build with a cavity?

[Nestor]

I have enclosed  a shot, it is inside a hall cupboard!

I fitted 150mm celotex tight to the walls, taped all the joints, fitted plastic sheet, taped then UFH.

The perimeter edge insulation has an adhesive strip on one side which fixes to the upstand / wall and polythene apron which lies on the floor.

Just need to make sure the screed cannot escape.

Hope that helps.

 

[saveasteading]

1 hour ago, junglejim said:

does the expansion strip negate the need for this?

I think you have a good point. If built as your first picture, then the heat is travelling from the screed horizontally through that thin isolation strip, and into a masonry wall. That block wall presumably sits directly on a footing in the ground.

So increase the heat resistance of the strip by thickness and choice of material. Eg 25mm of PIR instead of the thin strip of something as shown.

 

On the other hand, the surface area of screed to wall is minor as compared to the lower face of the screed.

And heat loss through to earth is much less than with exposed surfaces.

 

 

[Spinny]

In our build the architect included a continuous row of celcon blocks around the inner leaf at insulation and concrete slab level (your screed level) to provide some insulation in the inner leaf between foundation/footing level and wall above. I think some people also build the inner leaf entirely from celcon blocks.

 

I think our builder put the 25mm PIR around the perimeter and then used the underfloor insulation butted up to the edge of it to hold it in place - simply a matter of practicality to hold the edge insulation in place for our concrete pour.

 

Think it may help if you can say whether you are doing new build or retrofit, and to describe the makeup of your wall structure - concrete block, celcon block, stone, sipps etc.