Closing cavity around window opening before fitting

Curious Geroge · 01-02-2014 07:23PM #1

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 · 01-02-2014 08:33PM

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 · 01-02-2014 08:58PM

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 · 01-02-2014 10:14PM

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 · 01-02-2014 11:40PM

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 · 02-02-2014 07:51PM

pictures please so we can offer advice e

Curious Geroge · 02-02-2014 08:43PM

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 · 02-02-2014 09:02PM

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 · 02-02-2014 09:07PM

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 · 02-02-2014 10:35PM

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 · 02-02-2014 10:42PM

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 · 02-02-2014 10:44PM

can you post photos

use spray foam in a can

Curious Geroge · 02-02-2014 10:46PM

sawdoubters wrote: »

can you post photos

use spray foam in a can

Pic attached to post already (showing spray foam used)

Curious Geroge · 02-02-2014 10:48PM

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 · 02-02-2014 11:02PM

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 · 02-02-2014 11:21PM

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 · 02-02-2014 11:31PM

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 · 02-02-2014 11:34PM

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 · 02-02-2014 11:41PM

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 · 03-02-2014 01:31AM

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 · 03-02-2014 02:47AM

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

DOCARCH · 03-02-2014 07:28AM

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 · 03-02-2014 09:15AM

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 · 03-02-2014 09:17AM

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 · 03-02-2014 09:21AM

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 · 03-02-2014 09:59AM

Curious Geroge · 03-02-2014 11:21AM

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 · 03-02-2014 11:40AM

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 · 03-02-2014 12:09PM

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 · 03-02-2014 12:24PM

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

declan52 · 03-02-2014 12:29PM

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

Closing cavity around window opening before fitting

Comments