Closing cavity around window opening before fitting

Doingit · 13-03-2014 02:40PM

Is it absolutely necessary to close the cavity before installing the windows? Wondered if we could install windows, apply airtight tape to inside (between frame and black) and then pump cavity right up against the frame! Would this work? Would it just move the dpc out of position?

fclauson · 13-03-2014 03:32PM

Doingit wrote: »

Is it absolutely necessary to close the cavity before installing the windows? Wondered if we could install windows, apply airtight tape to inside (between frame and black) and then pump cavity right up against the frame! Would this work? Would it just move the dpc out of position?

the closure is needed as you need to strap the window back - you would normally do it to the inner wall - but that might be 200mm away - so you attached ply to block - window to ply

https://www.facebook.com/media/set/?set=a.165903723614740.1073741829.154344008104045&type=3

john f 4g63 · 13-03-2014 06:26PM

Doingit wrote: »

Is it absolutely necessary to close the cavity before installing the windows? Wondered if we could install windows, apply airtight tape to inside (between frame and black) and then pump cavity right up against the frame! Would this work? Would it just move the dpc out of position?

I am thinking of doing the window detail this way as at least the pumped insulation will fit nice and snug up against the window and there will be no insulation gaps.
In order to get over the problem of fitting the windows in my 200mm cavity, my window thickness is 82mm therefore leaving a gap of 118mm to the internal leaf. As this is too wide for the window straps i am fixing a 3x2 on to the internal leaf in the cavity, the straps from the window can then be fixed to the 3x2 timber and will also just make the internal leaf so can be fixed to that as well.
I will then use the air tight tape to stop the beads when pumping the cavity. This way i know the insulation will be fitted right up to my window and reveals.

Well that's the plan anyway!!

dfader · 13-03-2014 09:58PM

john f 4g63 wrote: »

I am thinking of doing the window detail this way as at least the pumped insulation will fit nice and snug up against the window and there will be no insulation gaps.
In order to get over the problem of fitting the windows in my 200mm cavity, my window thickness is 82mm therefore leaving a gap of 118mm to the internal leaf. As this is too wide for the window straps i am fixing a 3x2 on to the internal leaf in the cavity, the straps from the window can then be fixed to the 3x2 timber and will also just make the internal leaf so can be fixed to that as well.
I will then use the air tight tape to stop the beads when pumping the cavity. This way i know the insulation will be fitted right up to my window and reveals.

Well that's the plan anyway!!

John,
Interesting... seems like a reasonable low cost solution. Only thing I'd be concerned about is bead going in between the DPC and outer leaf. If you had PIR friction fitted between inner leaf and DPC on outer leaf this would not happen, but maybe I'm just coming up with a problem that does'nt exist because the DPC will be held tight enough once mortared over at cill and windows in? Would be good to see how this goes for you - post up a pic when done

sydthebeat · 13-03-2014 10:10PM

john f 4g63 wrote: »

I am thinking of doing the window detail this way as at least the pumped insulation will fit nice and snug up against the window and there will be no insulation gaps.
In order to get over the problem of fitting the windows in my 200mm cavity, my window thickness is 82mm therefore leaving a gap of 118mm to the internal leaf. As this is too wide for the window straps i am fixing a 3x2 on to the internal leaf in the cavity, the straps from the window can then be fixed to the 3x2 timber and will also just make the internal leaf so can be fixed to that as well.
I will then use the air tight tape to stop the beads when pumping the cavity. This way i know the insulation will be fitted right up to my window and reveals.

Well that's the plan anyway!!

are you sure youre allowed to provide a combustible cavity barrier in an cavity?
I dont think you are.

BryanF · 13-03-2014 10:35PM

sydthebeat wrote: »

are you sure youre allowed to provide a combustible cavity barrier in an cavity?
I dont think you are.

+1

john f 4g63 · 13-03-2014 10:43PM

sydthebeat wrote: »

are you sure youre allowed to provide a combustible cavity barrier in an cavity?
I dont think you are.

Is it the 3x2 timber you are referring to? If so do you know why?

dfader · 13-03-2014 10:53PM

How about friction fitted pir between 3x2 and dpc and doubled up plasterboard over reveal

sydthebeat · 13-03-2014 10:55PM

john f 4g63 wrote: »

Is it the 3x2 timber you are referring to? If so do you know why?

The fire regulations, the prevention of spread of fire and smoke in cavities require non combustible cavity closers.

From a personal point of view, I hope your Windows are fixed through your 3x2 into the blockwork or there is a risk of failure of fixing in the event of a fire.

If the 3x2 has been covered in non combustible material ie plasterboard with min 30mins fire rating then I think you may be ok, I'd need to check it.

But i think people should be looking at non combustible methods to close cavities in a wide cavity situation.

dfader · 13-03-2014 10:56PM

sydthebeat wrote: »

are you sure youre allowed to provide a combustible cavity barrier in an cavity?
I dont think you are.

Hmm forgot bout that. how about friction fitted pir between 3x2 and dpc and doubled up plasterboard over 3x2 and reveal

sydthebeat · 13-03-2014 10:58PM

dfader wrote: »

Hmm forgot bout that. how about friction fitted pir between 3x2 and dpc and doubled up plasterboard over 3x2 and reveal

Sounds good, does your frame allow for that thickness?

dfader · 13-03-2014 11:05PM

sydthebeat wrote: »

Sounds good, does your frame allow for that thickness?

he should step back the blockwork on inner leaf maybe 30mm to allow for this

john f 4g63 · 13-03-2014 11:08PM

dfader wrote: »

How about friction fitted pir between 3x2 and dpc and doubled up plasterboard over reveal

That is another option I am considering as the pir has a better u value then the bead but the only reason I didn't want to do it this way is this must be done before the windows are fitted so this might leave a small gap between both. I know they usually pump foam in here then but I am hoping a avoid this.

fclauson · 13-03-2014 11:15PM

john f 4g63 wrote: »

That is another option I am considering as the pir has a better u value then the bead but the only reason I didn't want to do it this way is this must be done before the windows are fitted so this might leave a small gap between both. I know they usually pump foam in here then but I am hoping a avoid this.

the window boys will have a spray foam - now make sure you get the really good stuff - but it has a good U-value - no idea on name - but mine is a blueish colour

john f 4g63 · 13-03-2014 11:18PM

dfader wrote: »

he should step back the blockwork on inner leaf maybe 30mm to allow for this

Hadn't mentioned on earlier post but will be finishing the internal reveals with plaster slab all around.
Do you think if I used a fire slab here it would be ok or is the problem still there over having a 3x2 in my cavity?

Just to answer the question about where the window straps will be fitted... They will be fixed to both 3x2 and the internal block work.

john f 4g63 · 13-03-2014 11:32PM

fclauson wrote: »

the window boys will have a spray foam - now make sure you get the really good stuff - but it has a good U-value - no idea on name - but mine is a blueish colour

Does the pir insulation have to be used around windows and then spray foam the gap as I know this is what most do or would it be ok just to let the beads pump right up against the window?

fclauson · 13-03-2014 11:44PM

come on FC you know better than that

adrianegan3 · 04-11-2017 10:00PM

Did you have to step back the inner block work 12mm to allow for the plywood

fclauson · 05-11-2017 05:34PM

You need to step back the inner leaf enough to get both your insulation and your ply

see picture

adrianegan3 · 05-11-2017 07:32PM

fclauson wrote: »

You need to step back the inner leaf enough to get both your insulation and your ply

see picture

Thanks for that great detail drawing any advise on where I could more detailed photos and info on passive build . Books etc

fclauson · 06-11-2017 10:33AM

Suggest you

a) join the Passive Institute Ireland
b) follow https://twitter.com/ElrondBurrell
c) google "passive house"
d) don't ever take "asha that will work probably!" as a response to any question
e) be very nerdy about detail, maths, design, and implementation

follow my 4 Ps when building
Pragmatic
Practical
Passive Certified
Price Sensitive

ExtaticFob · 25-06-2018 08:56PM

Hi all. Looking for some advice as a first time self builder who may have made a bags of cavity closing around our windows. Keeping it short, we have our cavity fully filled with 150mm insulation and windows are in. We don’t have cavity closets installed. We do have the gap filled with expandable foam. Question is, do we need to take the windows out to put the closers in? I’ve attached pics. Any help / advice greatly appreciated.

fclauson · 25-06-2018 11:10PM

can we have a pic from the outside too

expanding foam is not airtight - what air tightness are you going for

ExtaticFob · 25-06-2018 11:28PM

fclauson wrote: »

can we have a pic from the outside too

expanding foam is not airtight - what air tightness are you going for

Thanks for the reply. We’re going to be taping inside with air tightness tape. We’re also putting an insulated board on it. That might not answer your question but there’s a lot of learning as we go. Requested photo attached.

fclauson · 25-06-2018 11:37PM

ExtaticFob wrote: »

Thanks for the reply. We’re going to be taping inside with air tightness tape. We’re also putting an insulated board on it. That might not answer your question but there’s a lot of learning as we go. Requested photo attached.

Ok - see my tech arch picture further back in this post
you need to look at how you are going to make it
a) insulated correctly with no cold bridge around the window (this will require thermal modelling probably)
b) airtight

if you fail on (a) you could end up with a cold bridge (read mold) around the wind frame on the window return because the wall/frame fall below the threshold temp

read about FRSI in the (google FRSI calculations)

ExtaticFob · 26-06-2018 12:03AM

fclauson wrote: »

Ok - see my tech arch picture further back in this post
you need to look at how you are going to make it
a) insulated correctly with no cold bridge around the window (this will require thermal modelling probably)
b) airtight

if you fail on (a) you could end up with a cold bridge (read mold) around the wind frame on the window return because the wall/frame fall below the threshold temp

read about FRSI in the (google FRSI calculations)

I’ll check that out. Thanks again. In your experience is there a way around this without removing the windows? As well as the inconvenience, we are getting the external wall plastered from tomorrow.

BryanF · 26-06-2018 06:59PM

ExtaticFob wrote: »

I’ll check that out. Thanks again. In your experience is there a way around this without removing the windows? As well as the inconvenience, we are getting the external wall plastered from tomorrow.

It’s jot clear if there is a DPM/EPDM folded out over/down side of the windows etc?
Did your eng/arch do a detailed drawing done

Closing cavity around window opening before fitting

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