Closing cavity around window opening before fitting

Curious Geroge

While waiting for the window's to arrive and be fitted I wanted to close up the cavity around the window opening. The block layers didn't use L blocks but turned the block so its not a constant gap like an L block would give. I assume this is a common problem but how are others filling this. Just spent the day cutting PIR board ti fit it but wondered if spray foam in a can might work out better.

mfceiling

I've recently worked on 2 new builds where they used a kind of plastic insulated closer. Maybe Google might help with product names etc...it was white with corrugated ribs on the external side.

Guest0000

The plastic cavity strips are very expensive for what they are, Dow Corning being a main supplier, so to are the l shaped blocks, with quite a few in each opening, the opening are commonly closed with alternative rows of brick and half blocks, as long as the vertical dpc is in place, astrip of kingspan and ex foam should be fine......

Curious Geroge

mfceiling wrote: »

I've recently worked on 2 new builds where they used a kind of plastic insulated closer. Maybe Google might help with product names etc...it was white with corrugated ribs on the external side.

This is the kingspan closer, nice job but expensive and yet another new cost to building. For this you leave the cavity open, no L block, no return. I'm not sure if there is a return for outlay on this though (although kingspan may disagree).

Corkblowin

Guest0000 wrote: »

The plastic cavity strips are very expensive for what they are, Dow Corning being a main supplier, so to are the l shaped blocks, with quite a few in each opening, the opening are commonly closed with alternative rows of brick and half blocks, as long as the vertical dpc is in place, astrip of kingspan and ex foam should be fine......

When you say a strip...........what are you talking about?

fclauson

pictures please so we can offer advice e

Curious Geroge

fclauson wrote: »

pictures please so we can offer advice e

See attached. No need for anyone to tell me the block layers should have left a consistent bigger space, I'm already aware of not been told prior to paying them. Add it to the list of self builders mishaps. Just need to make the best of the situation now and move fwd.

fclauson

ONSULT AN ENGINEER FIRST

but could you run a con saw down removing 4inches such that you have a much wider cavity gap and thus a lower thermal bridge

declan52

Curious Geroge wrote: »

See attached. No need for anyone to tell me the block layers should have left a consistent bigger space, I'm already aware of not been told prior to paying them. Add it to the list of self builders mishaps. Just need to make the best of the situation now and move fwd.

you could run a con saw down the revels. Cut it back about 35mm. Put in a 25mm revel strip and point in the rest with motar. About only option bar cutting all the returns out and starting it again. if you leave it like that the revels would be a cold spot forever. If they left the revels like that I would get somebody you know who is clued in about how to do build to have a look at your build.

Curious Geroge

declan52 wrote: »

you could run a con saw down the revels. Cut it back about 35mm. Put in a 25mm revel strip and point in the rest with motar. About only option bar cutting all the returns out and starting it again. if you leave it like that the revels would be a cold spot forever. If they left the revels like that I would get somebody you know who is clued in about how to do build to have a look at your build.

Thanks. The cavity/space on the pic is about 30mm, about 45/50mm everywhere else. Only a few year ago, it was closed in some builds, do I really need that extra 10/20mm ? I thought thermal bridging was only on where outer actually touchs inner ? thanks for the comments.

sydthebeat

Curious Geroge wrote: »

See attached. No need for anyone to tell me the block layers should have left a consistent bigger space, I'm already aware of not been told prior to paying them. Add it to the list of self builders mishaps. Just need to make the best of the situation now and move fwd.

Jesus Christ! !

As others have said, get them to con saw that reveal out of it. Get them to cut along the outer face of the inner leaf. Install hand cut pir insulation friction fitted to keep dpc to external.

sawdoubters

can you post photos

use spray foam in a can

Curious Geroge

sawdoubters wrote: »

can you post photos

use spray foam in a can

Pic attached to post already (showing spray foam used)

Curious Geroge

sydthebeat wrote: »

Jesus Christ! !

As others have said, get them to con saw that reveal out of it. Get them to cut along the outer face of the inner leaf. Install hand cut pir insulation friction fitted to keep dpc to external.

Whats the recommendation guys Its time to organise a consaw by the sounds off it 40/50/60mm between the turn and the outer block ? As I said, its not all the windows but about 6 of them have this and some of the larger windows seem tight on top so its a job but not a knock and rebuild one (luckily).

declan52

Curious Geroge wrote: »

Whats the recommendation guys Its time to organise a consaw by the sounds off it 40/50/60mm between the turn and the outer block ? As I said, its not all the windows but about 6 of them have this and some of the larger windows seem tight on top so its a job but not a knock and rebuild one (luckily).

if U nail a bit of lathe up the revel it will guide your cut and keep it straight. The insulation strips come 100mm wide 25mm deep. You could buy a sheet and cut it to increase the depth of insulation to 38mm or 50mm. Your choice. 25mm deep strips easier to use. if you cut straight and square the strip will slide in or cut it a few cm bigger and fill gap with foam or motar.not a hard job just dusty. set the guide right take your time

Curious Geroge

declan52 wrote: »

if U nail a bit of lathe up the revel it will guide your cut and keep it straight. The insulation strips come 100mm wide 25mm deep. You could buy a sheet and cut it to increase the depth of insulation to 38mm or 50mm. Your choice. 25mm deep strips easier to use. if you cut straight and square the strip will slide in or cut it a few cm bigger and fill gap with foam or motar.not a hard job just dusty.5 set the guide right take your time

Where can I buy these strips.. asked a couple of local merchants and in the end bought the board and cut it myself to the 50mm on the other windows. 100mm seems alot, is it needed and should I be looking to increase all the others currently at 50mm too 100mm ?

declan52

Curious Geroge wrote: »

Where can I buy these strips.. asked a couple of local merchants and in the end bought the board and cut it myself to the 50mm on the other windows. 100mm seems alot, is it needed and should I be looking to increase all the others currently at 50mm too 100mm ?

the 100mm is the width same as a block. So it covers the whole face of the block. 50mm deep is gd most just use the strips that are only 25mm deep. Mine I got in my local merchant kingspan make them.

Curious Geroge

Have a look at the dpc backed with mortar near the back
http://www.palgrave.com/engineering/riley1/students/chapter/chapter7_1.htm

Curious Geroge

declan52 wrote: »

the 100mm is the width same as a block. So it covers the whole face of the block. 50mm deep is gd most just use the strips that are only 25mm deep. Mine I got in my local merchant kingspan make them.

Slightly lost. Cavity is 150mm. Block currently turned in 100mm on avg leaving 50mm where I've used the kingspan 50mm board. Are you saying block turned in should only be 50mm and 100mm insulated board ? is it worth increasing the 50mm to 100mm (I can understand I need to address the 20mm that I showed in the image but unsure if I need change the 50mm to 100mm) comments welcomed

Phirstclass

We recently did something similar on our Enerphit project.
The inner leaf return blocks were con sawed back to leave 100mm inner & outer block and 100 cavity into which we fitted a 100m PIR board. We then finished the cavity off with strips of pvc. This would be the poor mans kingspan closer but worked fine, was a cheap alternative, and will reduce the thermal bridging substantially.

sawdoubters

http://www.ggf.org.uk/assets/W&D_Good_Practice_Guide-4ec42d0c5aa21.pdf

DOCARCH

Curious Geroge wrote: »

Slightly lost. Cavity is 150mm. Block currently turned in 100mm on avg leaving 50mm where I've used the kingspan 50mm board. Are you saying block turned in should only be 50mm and 100mm insulated board ?

Very simply, the blockwork, ideally, should not be returned (at all). At your reveals, ideally, you should have the same amount/thickness of insulation you have in your cavity.

Curious Geroge

DOCARCH wrote: »

Very simply, the blockwork, ideally, should not be returned (at all). At your reveals, ideally, you should have the same amount/thickness of insulation you have in your cavity.

Unfortunately its common practice to return the block, I'm just wondering what sort of problems I might see if I leave the 50mm.

4Sticks

Curious Geroge wrote: »

Unfortunately its common practice to return the block, I'm just wondering what sort of problems I might see if I leave the 50mm.

Take good advice when you get it. Rebuild the jambs unless you like black mould

hexosan

Phirstclass wrote: »

We recently did something similar on our Enerphit project.
The inner leaf return blocks were con sawed back to leave 100mm inner & outer block and 100 cavity into which we fitted a 100m PIR board. We then finished the cavity off with strips of pvc. This would be the poor mans kingspan closer but worked fine, was a cheap alternative, and will reduce the thermal bridging substantially.

When you say plastic strips, what did you use & where did you source them.

fclauson

Curious Geroge

fclauson wrote: »

Thanks fclauson, this is a thermal/cold bridge though (probably without DPC). If there is 50mm between outer block and the turn that has both DPC and insulation, is this still the case ?

fclauson

Curious Geroge wrote: »

Thanks fclauson, this is a thermal/cold bridge though (probably without DPC). If there is 50mm between outer block and the turn that has both DPC and insulation, is this still the case ?

The magic maths you have to do is called a FRSI calc - its in Part L

You have to make sure that the internal surface temp does not drop too low thus allowing condensation. If you have a well insulated wall then thermal bridges "attract" moisture as they are small but colder than the rest of the wall.

So yes - this type of mould is a potential if that temp on that surface falls too low (from memory 16.5C when modelled with 20C inside and 0C outside but check)

declan52

the image on phirstclass is what i am trying to explain!! You need to cut out the depth of what ever insulation you have. He has used 100mm deep by the looks of it. The plastic cavity closers are a load of **** just an extra expense to pay that you dont need. Way to expensive for a piece of plastic with a bit of insulation stuck to it.

fclauson

Check out https://www.facebook.com/photo.php?fbid=165903950281384&set=pb.154344008104045.-2207520000.1391426593.&type=3&theater

declan52

Yeah plywood wrapped in dpc a far better way to do it

Doingit

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

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

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

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

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

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

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

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

sydthebeat

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

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

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

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

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

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

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

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

come on FC you know better than that

adrianegan3

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

fclauson

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

see picture

adrianegan3

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