How to finish off cavity and floor heights

[Jacko994]

Good evening everyone,

 

I wonder if I can get some help/thoughts on the below -

 

I’m currently in the middle of managing an extension/renovation on our property and I’m trying to get some clarification on how to finish off the cavities at the front and rear openings and tie in the screed.

 

At the rear where we’re going to be having bifolds with a level threshold, I have filled with some celotex insulation. I was going to finish it with a cavity closer but the company installing the bifolds want to knock the course of bricks on the outer skin off to place the bifolds on. 
 

Is this normal practice?

 

It would then mean I can’t use a cavity closer so what would be the best way to close the cavity up ready for screeding? 
 

Any suggestions would be much appreciated.

 

Thanks,

 

Jack

 

[Nickfromwales]

You remove the inner course of blocks. Place insulation vertically up against the inside face of the outer course of blocks (as an upstand) and then run the insulation and screed to meet the upstand.

[Nickfromwales]

Similar to this job. 
 

[Jacko994]

Thanks Nick.

 

what about the dpc that is running across the inner course?

 

Also that inner course is 3 courses high at the moment, above the block and beam. Are you saying to remove all 3 courses, or just the top 1 or 2?

 

Thanks

[Nickfromwales]

19 minutes ago, Jacko994 said:

Thanks Nick.

 

what about the dpc that is running across the inner course?

 

Also that inner course is 3 courses high at the moment, above the block and beam. Are you saying to remove all 3 courses, or just the top 1 or 2?

 

Thanks

You delete that DPC and run the DPM up the face of the skirt insulation upstand. Basically just treat the job as if that inner leaf of masonry had never existed.

 

Remove the lot, down to the same level as the B&B deck, and fly the insulation all the way in to meet the outer leaf of masonry.

 

If UFH, don't forget the 'thermal' expansion skirting that goes on to absorb expansion of the screed.

[ETC]

Might be better with a DPC behind the outer leaf. Personally I’d have treated it in the same way an external door is - precast concrete threshold wrapped in DPC and then taken the DPM across and up the back face.

[Jacko994]

Thanks for your advice guys.

 

The extension is just getting boarded and skimmed at the moment so once that’s done I’m going to knock those 3 courses out and start prepping the floor.

 

my architect spec’d 25mm perimeter insulation to go around the edges, would this suffice to absorb the expansion in the screed with UFH or would you recommend the insulation foam around the wall edges as well?

[EdSt]

Hi Jackie, Came across your post as in a similar position and looking for clarify on perimeter insulation. I’m also on BB floor with UFH and have the inner skin removed. My take on this detail is floor insulation up to inner face of outer skin then perimeter insulation stick to block wall with spray adhesive (spray wall, sparky insulation let tack off then attach). On mine this perimeter insulation. Is 60mm high. Then bath tub  the PIR slab in DPM and then 8mm expansion perimeter insulation on top of that and tape the skirt on that to the floor with gaffa. The 25mm PIR is to eliminate cold bridge and the 8mm has some give to cope with thermal expansion. Two difference jobs. Posting hoping others will confirm this approach really, most of what you see has people only using 8mm. I’m using decoupling mat on to of liquid screed and as away carry the tiles over the 25+8mm gap.

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