Cavity closure info and problem

[nafuk]

I've just been on the phone to Building Control (BC) asking if UPVC door and window frames need cavity closures, using either:

the propriatary strips (e.g

?_dyncharset=UTF-8&q=73488&x=0&y=0&pn=1&pd=1&pi=1&cn=1&cd=1)or a run of dpc up the edge of the outer leaf of the cavity wall and then folded back into the cavity.

I was told that it is best to do this as there is a small chance of leakage to the inside edge of the frame which could then pass onto the material used to cover the reveal (e.g. plasterboard)

Another point BC made was how was the plasterboard to be supported on the outer leaf. If a small lip was left (i.e. the frame was not flush with the inner edge of the outer leaf) to fix the p/b to, this is then a cold bridge and there is then the risk of black mold growing up the inside edge of the frame.

Questions. I would like to use dpc and not cavity closures if possible, so is there a method of supporting the plasterboard in the reveal?

Is the risk of black mold growth high?

Thank you

[dg]

?_dyncharset=UTF-8&q=73488&x=0&y=0&pn=1&pd=1&pi=1&cn=1&cd=1)>> or a run of dpc up the edge of the outer leaf of the cavity wall and

The frame should cover the DPC and not be flush with it. This stops any moisture bridge.

I don't don't know what the BCO was thinking when he mentioned supporting the plasterboard on the outer leaf? The plaster goes up to the frame only and does not touch the outer leaf - it is fixed to the inner leaf and reveal only.

If using aerated blocks, then you can return these at the reveal and use nomal DPC. If the blocks are concrete, then you should use an unsulated DPC or one of the propriatary closers.

dg

[nafuk]

Thank you for your reply.

My problem is that I have a cavity wall (brick outer, aerated block innner) with no blocks turned into the cavity and so can only stick the p/b to the inner leaf. How can I offer more support?

Thank you

dg wrote:

?_dyncharset=UTF-8&q=73488&x=0&y=0&pn=1&pd=1&pi=1&cn=1&cd=1)> >

[dg]

More support to what?

The two leafs should have ties every block course at the reveal so they support each other, and if you have not returned the blocks, then you will have to use a propriatary cavity closer.

Plasterboard is just dabed or fixed to battens on the blockwork and can be fixed to eht end of the blocks in the reveal up to the frame

dg

[nafuk]

I have not returned the blocks since a BCO and a builder told me because of cold bridging this was no longer acceptable.

Door fitters say that the cavity closures make the door fixing less stable because of the strip of membrane/plastic running down the outer leaf reveal. Does anyone know if this is just like a strip of plastic DPC?

The inner leaf is thermalite expanded blocks and are very easy to saw, so I could cut some returns in that don't touch the outer leaf. This would offer additional support to the p/b in the reveal. Is this a good idea of is there something easier and quicker I could use (like drilling some screws in etc.)?

Thank you