I'm at the position with my project to build a lean-to extension where the cavity blockwork is in place and a window and folding doors are to be fitted soon.  Cavity closers seem to be a good way of finishing the cavities, adding insulation and another barrier aginst damp.  Is there any general advice on these that people have to offer on type, design, fitting etc?  Are they fixed in place or do they just push in?

 

My builder says why not just cut sections of 50mm insulation (Celotex type) and push it into the cavity?  Also, is there an advantage to fitting closers on top of the wall cavity?

 

Any thoughts?

I’ve used the PolyPipe ones and found them very good. They come in different thicknesses and comprise a rigid plastic liner with a rubber edge and an EPS inner. Dead easy to fit and also mean there is no DPC required. 

 

No benefit in closing the top of the cavity unless you’re using a blown insulation.