Fitting a window in a cavity wall - queries

[Lobster]

"Install a separate DPC in severe exposure conditions. A Catnic Cougar Open Back or Classic Combined Box Lintel with an additional DPC membrane installed in accordance with normal practice provides the best possible protection."

Where is this DPC supposed to go? Under the steel and above the supporting brickwork piers/windowframe? Or above the steel and below the brickwork which it supports? And what happens at the two ends?!

Secondly (and thinking ahead a bit); once you've fitted a lintel in a cavity wall [2], knocked out the brickwork below, and installed the new uPVC window in the outer leaf - how do you block off the cavity (ie sides and top) to form the window reveal?

Is it just a matter of gluing bits of plasterboard over the gaps?

Thanks David

[1] for a replacment window; lintel is for the external leaf only as there's already a lintel on the inner leaf. [2] for a different window being fitted from scratch, with a cavity-wall lintel supporting both inner and outer leaves

[Michael Mcneil]

The only catnics I know of are a box section with a stepped top so that the outer leaf of the wall sits lower down on it than the inner leaf. A strip of wide DPC sits on this.

In other words, the cavity above the section is crossed with the dpc so any water poured down on it from above falls down and out.

How you go about inserting it in your case is a different matter.

[Set Square]

The traditional method is to brick up the gap, but with a vertical strip of DPC material immediately behind the outer leaf, to prevent a damp transmission path.

Having said that, I've just had a new door and window inserted in the side of my garage, and the builder glued plasterboard over the gaps!

[Jeff]

"Lobster" wrote

My builder has used plastic cavity closers

Regards Jeff