Cavity closures - during or after build?

[John D v2.0]

It would be hard to meet the limit for u value with returned blockwork unless you insulate the reveals afterwards on the inside or outside.
The building regs don't prescribe a way of meeting the u value, but cavity closers seems to be the traditional way to keep a continuous insulation.

 

[r896neo]

I had never heard of prefabricated cavity closers until I joined the forum. All sites I ever worked on here in N.I just use a strip of dpc and a 25mm strip of celotex sandwiched against the outer leaf by the returned blockwork.

Merchants will stare blankly at you if you asked for a closer. They all still carry 'reveal strips' which are 1" thick 4" wide strips of xtratherm