After following the forums guidance on my upstairs flooring to great success I am after some advice on the best (for a basic diy-er) approach to dealing with a square cut out around a soil pipe in our downstairs loo. The hole leads down to block and beam void which I am planning on filling with EPS beads at a later date, followed by the blocking up of the air bricks.

Is it fine just to blast expanding foam around this and then cut it away level with the cement boards? The gap is 15mm at it's most narrow, 40mm at it's widest point. Nasty draught and cold emanating from the hole. Picture (hopefully) attached.

Bonus question: In the event I fill the void with roughly 300mm of EPS beads. Would this suffice as the insulation layer for a thin retrofit wet UFH system to be laid on top of the block/beam? My thought process being that you could argue the block and beam acts as a useful thermal mass or would the thermal bypass of the block and beam render this ineffective? This is a poorly built 1990's house after all!

Any help is greatly appreciated and will be acted upon!

Thank you for the sense check! I'll get cracking.

Its likely that the whole perimeter of the floor hasnt been sealed and the area of the continuous gap around the perimeter could be more than that around the waste pipe. You just can feel the same level of cold draught because its spread over a long thin strip around the room.

If youre able to do it maybe fast track the addition of the beads so you can get the air vents closed up. Its extra work but Id take out the vent in the external leaf and seal the opening in the inner leaf to make sure theres no airflow through the cavity and into the beads.

I can help with suggestions! Did one recently, no need for negative pressure, leaf blower works well and I have spare one. Where are you? I have also used a bead blower on a compressor but a bit slow. Can talk about if you like and send pics. Unsure on price but sounds high to me try e-bay

Yes, in NZ they collect bits and run hem through a garden shredder first then fill their walls with them.

That would be a great way of recycling it philedge/tony- it's a shame it's so bulky and awkward to transport but I'm struck that councils on recycling rounds/HWRCs could collect packaging and shred it/sell it. It always seems to go in the non-recyclable waste hoppers

Ps I'd especially the UFH response time to be somewhat longer than a 40mm screed, so maybe your use pattern would benefit from "set it to run permanently at low temperature" rather than have it on and off. Rest of the house will need to be well insulated for that to work properly

Posted By: cjardThat would be a great way of recycling it philedge/tony- it's a shame it's so bulky and awkward to transport but I'm struck that councils on recycling rounds/HWRCs could collect packaging and shred it/sell it. It always seems to go in the non-recyclable waste hoppers

I think they're focussed on recycling (i.e recovering raw material that can make more new material) rather than reuse, which in principle would be better. But I suspect the council has problems with not being able to control the cleanliness and quality very easily, plus the difficulty of transporting it. We have a local volunteer-run recycling centre, but it doesn't recycle/reuse EPS either AFAIK, although it does do various other things the council doesn't. Volunteers are cheaper and have more practical control over what they accept, I suspect.

I also made an error in one of my earlier comments. The price I obtained was for 300 cubic feet (8.5 cubic metres) and was £27 a 10ft3 bag (£810 total) or £35 a 10ft3 bag delivered (£1,050 total)!

Have since found EPS/polystyrene beads for £15 a 10ft3 bag (£457) total they don't claim any insulating properties rather are bean bag fill type. Am I correct to assume these will suffice?