Cavity where meets windows, can it be completely foamed?

[Beginerz]

Hi all. The cavity, where old window is fitted to outside skin, where the plaster is knocked back, is quite wide. Big gap where insulation is missing but there is insulation further back.

I suspect the brickwork is too uneven to fit cavity closers even if I try to knock bits off and repair the mortar perfectly.

Would a solution be to apply DPC tape on the inner edge of the outer skin, spray expanding foam to completely fill the remaining open part of the cavity, sand it back flat and apply a DPC tape over the top of the cavity ready for window fitting and replastering?

Total beginner as name suggests and hoped things would be neater than they are when I knocked the plaster work surrounding the old window back.

 

[Notch7]

you could wedge something into the cavity and push it back to leave say a 2" or 3" space then spray in foam -let it dry then cut it back with a saw or breadknife

you could do the DPC after, get one wide enough to go across the inner reveal then bend it 90degrees and take it across the window frame -maybe with a few staples to hold in place.

then fit plasterboard and once skimmed, cut the dpc flush with the plaster -that way no damp can get from external brickwork into plasterboard -maybe use moisture resistant plasterboard as well

 

[^woody^]

You would need to be sure that any expanding foam does not creep around the back edge of the DPC.

Fill the reveal with rigid or dense quilt insulation first, set it back 50mm, then foam.

Use150mm DPC. Leave it projecting 50mm which is then bent forward when the frames are fitted.

 

[Notch7]

You would need to be sure that any expanding foam does not creep around the back edge of the DPC.

yeah Ive been there, ended up in a right old mess.

 

[Beginerz]

you could wedge something into the cavity and push it back to leave say a 2" or 3" space then spray in foam -let it dry then cut it back with a saw or breadknife

you could do the DPC after, get one wide enough to go across the inner reveal then bend it 90degrees and take it across the window frame -maybe with a few staples to hold in place.

then fit plasterboard and once skimmed, cut the dpc flush with the plaster -that way no damp can get from external brickwork into plasterboard -maybe use moisture resistant plasterboard as well

You would need to be sure that any expanding foam does not creep around the back edge of the DPC.

Fill the reveal with rigid or dense quilt insulation first, set it back 50mm, then foam.

Use150mm DPC. Leave it projecting 50mm which is then bent forward when the frames are fitted.

Are you able to recommend a suitable insulation brand? Would the rigid polystyrene sheet stuff work? It claims to be water resistant.

So would the DPC, which I'm assuming I'd tape over the trimmed foam, then need to be trimmed after the frames are fitted?

And would I need a DPC on the inside of the outer skin where it runs adjacent to where the frame will go?

 

[^woody^]

 

[Beginerz]

I see. What is that on the diagram behind the expanding foam? Also do I need to cover the foam itself with DPC tape to seal it before plastering?

 

[^woody^]

Fill the reveal with rigid or dense quilt insulation first, set it back 50mm, then foam.

Otherwise, it's as per the drawing, no other DPC.

 

[HERTS P&D]

View attachment 331400

This picture should be put into the 'how to guides'.

Andy