Window cavity closure

[Pocster]

Hey all,

 

Have looked online and in the forum and get the impression this is easier to do myself and cheaper.

I have timber frame, 100mm PIR ,100mm cavity, then block work.

 

Could I not foam stick some PIR in the cavity around the window reveal and then simply screw some cement board from timber frame across the cavity to the block work?

 

Sounds very simple!; but of course the internet can make things look overly complex and costly!

 

Is this ok or are there issues I'm not aware of?

 

thanks in advance!

Edited November 29, 2017 by pocster

[PeterW]

Cement board would not provide the required DPM - you have a closer for both cavity sealing purposes and for damp control. 

 

Also, as it’s a TF cavity does your design not need the closer to be a fire block ie made of fibre ..?

[Pocster]

16 hours ago, PeterW said:

Cement board would not provide the required DPM - you have a closer for both cavity sealing purposes and for damp control. 

 

Also, as it’s a TF cavity does your design not need the closer to be a fire block ie made of fibre ..?

Hmmmm ok 

can you show me the exact thing I need then ??

i was thinking of putting dpc under around the cement board .

 

Cheers

 

[Pocster]

19 hours ago, PeterW said:

Cement board would not provide the required DPM - you have a closer for both cavity sealing purposes and for damp control. 

 

Also, as it’s a TF cavity does your design not need the closer to be a fire block ie made of fibre ..?

Hmmmm ok 

can you show me the exact thing I need then ??

i was thinking of putting dpc under around the cement board .

 

once I had to shutter a large concrete run but needed holes for posts . So I fixed pir where the holes should be and did the concrete pour . My plan was to burn out the pir and have nice holes . Covered in petrol would they stay alight ? Not a chance ! . Had to rip them out with a crow bar - seemed like a good idea at the time !! Lol 

 

Cheers

 

[TerryE]

Have a look at my blog entry:

and at @Construction Channel's recent topic on the same.  You will get some movement between the blockwork skin and the TF.  A good way to do this if you haven't already done the blockwork is to mount the frames say 50mm into the cavity and to "turn the corner" on the blockwork to block up to the front edge of the frames.  You need a minimum of 30min fire protection cavity closers between the blockwork and the TF.  If you do this then you can just render right up the windows and the blockwork looks 150mm deep. 

[Pocster]

2 hours ago, TerryE said:

Have a look at my blog entry:

and at @Construction Channel's recent topic on the same.  You will get some movement between the blockwork skin and the TF.  A good way to do this if you haven't already done the blockwork is to mount the frames say 50mm into the cavity and to "turn the corner" on the blockwork to block up to the front edge of the frames.  You need a minimum of 30min fire protection cavity closers between the blockwork and the TF.  If you do this then you can just render right up the windows and the blockwork looks 150mm deep. 

Thanks.

My block work already exists. My assumption was the actual window would fit to the timber frame ; so yes a deep recess from the outside.

 

So I'm guessing if I use 'fire protection' closer within the cavity around the window I should be ok?. Then I can just clad/render etc. right up to the window frame.

 

So this type of thing:

 

http://www.wickes.co.uk/Wickes-Cavity-Closer-2-5m/p/194006

 

??

 

I don't need a load bearing one; as the blockwork has a steel lintel across it.

 

Some of the bought ones do just look like polystyrene ............. 

 

Cheers

Edited November 30, 2017 by pocster

[TerryE]

The lack of proper cavity closers was a factor in the Gredfell Tower tragedy.  They are needed for a reason.  They have to close the gap and give 30 mins fire protection.

 

Also remember that your solution needs to be weather proof as well as giving fire protection and  acting as a thermal barrier.

[Pocster]

8 minutes ago, TerryE said:

The lack of proper cavity closers was a factor in the Gredfell Tower tragedy.  They are needed for a reason.  They have to close the gap and give 30 mins fire protection.

 

Also remember that your solution needs to be weather proof as well as giving fire protection and  acting as a thermal barrier.

So the wickes solution is no good ? 

[Roundtuit]

Hi. I went through this challenge earlier this year, and my thoughts are as follows: as above, your cavity closers need to cover at least three bases; fire protection, thermal insulation and damp ingression (If your windows don't span the cavity to meet the outside skin and cover your closers, then you'll also need something aesthetically acceptable).  If your block work isn't up yet, you can diy it by fixing timber battens around openings wide enough to fill the cavity (100mm), set back to allow for say 50mm of celotex, with a layer of dpm sandwiched in between that and the blockwork (I stand to be corrected on the correct location for the dpm!)

 

I decided that was too much hassle, and used kingspan thermabate.  Not cheap, but fire rated (unlike the cheaper stuff which appears to be really only suitable for brick and block builds), damp proof, and easy to work with for a first-timer!  Prices varied widely, so shop around when you're pricing up the options.