fitting windows and new part L

[sm_jamieson]

Re part L robust details requirement to fit windows with the frame

30mm back into the cavity / insulated cavity closer.

I'm fitting windows now (just done one) and to pre-2006 regs as it happens. Frames are 70mm. To set back 30mm as is required for post-2006 part L, leaves only 40mm against the outer leaf. Considering the design of the PVCu profile and the desire for weatherproofing and getting a firm fix, this is impractical. To drill very close to the front of the profile does not really work, and drilling too near the edge of the brick risks blowing the brick either when drilling or when the frame fixings are tightened. In the end I set back the frame by about 15mm.

Anyone fitted windows to these regs, and how did you do it to get a secure fixing in the brick ?

Simon.

[Tim W]

sm_jamieson wibbled on Saturday 16 January 2010 22:01

Easy. I ignored the regs. Or to be precise, I didn't bother reading them in the first place. Having got Part L compliant windows, egress (my requirement) and trickle vents (well, they were more or less there by default) I just went with common sense on the rest.

I placed my windows such that I got it most of the way over the cavity, but I gave far more priority to getting a good fixing in the outer leaf of the bricks.

I showed one to the BCO and he was happy.

Personally, if it's a choice between a decent fixing or a minute bit of thermal leakage, no one but God himself is going to tell me the fixing takes lower priority.

Do what is sensible, try to cover the cavity as far as is practical. It would be a mean spirited BCO who would argue about such a trivial thing. If necessary, be prepared to argue that any other method of placement was simply impractical.

If you are really paranoid or your BCO is an absolute nazi, call him up first and tell him what you are proposing and why. I'd be surprised if he cared, as long as you've considered the options.

There is one other option - which is to drill the frames at a slight angle to give your fixings advantage. Also, if you use Fischer frame fixings, there will be relatively low expansion forces (I only use Fischer so I can't answer for others) - I think my fixings went in about 20mm (didn't actually measure them) from the edge of the bricks without issue, though my frames did permit drilling quite far forward.

[sm_jamieson]

Most of the way over the cavity ? How ? What size was the cavity ?

Well I'm only 15mm into an 75mm cavity. The frame had some ridges near the front that would not have made for a very easy fixing so I fixed about 30mm from the front. If they fuss I will add some more insulation under the plasterboard on the reveal.

[Tim W]

sm_jamieson wibbled on Saturday 16 January 2010 22:31

Sorry - I have to confess to talking bollocks. I forgot one key thing which was the cavity was closed with brick (1950's house). There was a 3/4" gap where the DPC was inserted and I was concerned to cover that with the window frame.

Been too busy looking at a new doorway I had cut into the wall, and that of course is cavity closed the modern way.

Sorry - brain spas moment. But as the closure was done by bricks from the inner leaf towards the outer, I faced a similar dilemma to the OP in the I could either fix to the closure bricks or to the outer leaf.

Due to frame design and needing the frame to seal against the outer leaf, I had to bring the window outwards such that the fixings were good.

The only differece for the OP is (presumably) heel need to stuff some cavity closer in first.

I don;t think there will be a problem for the OP, if he is using cavity closers - those have a bock of insulation anyway inserted into the cavity.

[Hugo Nebula]

This requirement has been in place for at least 15 years to my recollection, but is stoutly ignored by all and sundry.

The requirement is there to prevent cold bridging. Insulated plasterboard to the reveal should suffice.

[sm_jamieson]

Not surprised, since it is impractical. I was also fitting a french door which needs a solid fix on the bottom of the frame which may be stood on. And I wanted the door and window recess to match.

That was the conclusion I had come to ! I'll also have a thick piece of celotex under the interior window board to hide the back of the exterior window sill, which should take care of that ! Cheers, Simon.