new extension, how to construct window opening properly

[diydad888]

In Edinburgh, building new single storey extension, I would lik some help on how to deal with the block/brick around window/door openings.
I need to make sure it is insulated and properly sealed.
Best to use cavity closers? or return the block with some insulation to close cavity ?
Do I use DPC around the window/door area? eg under cills?

Thanks for reading

 

[noseall]

When using aerated blocks on the inner skin it is possible to return the blocks at reveals using a dpc at the abutment.

Alternatively, you can leave the cavity masonry open, bring the cavity insulation almost flush to the reveals, leaving enough room for a proprietary cav closer.

 

[Blagard]

Do I use DPC around the window/door area? eg under cills?

Methods of closing cavity as Noseall has advised - Applies all around except to the head.

 

[r896neo]

using normal concrete fellows a strip of dpc and a strip of insulation between the returned block and outer skin will do.

 

[jeds]

Just bear in mind that returning blocks to close a cavity is not an accredited detail. It's still commonly used in England because English inspectors are very slow to implement changes. It might be different in Scotland though (apparently it's a bit cooler up there) so if I were you I would check to make sure your inspector is happy. Otherwise build in accordance with accredited construction details (Scotland in your case) which you can find online. You can't go wrong then.

 

[stuart45]

I'm not 100% certain, but I think you need rebated jambs at the windows and doors in Scotland.

 

[landyandy]

In England.

Open cavity on jamb and cill with cavity closures. Brick ties every block course adjacent to opening. insulated lintel at head.

 

[geraint]

i was under the understanding, with the new regs, that you cannot now close off a cavity in blockwork... must be the useless cavity closers.

 

[diydad888]

Thanks to all for the advice.
I will be using dense block both sides for rear ext and dense block with facing brick for the porch.
Yes in Scotland the windows must be rebated, not sure if is best to return the inner leaf with insulation. If I left the walls open at the ends with the insulation flush will it be ok to fit the window frames like that?
How to fit the window frames securely ?wedged? screwed? I have no experience of fitting a window and frame (Upvc) how to seal the window frame?
Thanks

 

[r896neo]

leaving it open or full filling with insulation makes fitting the windows more troublesome, as does using closers. The easiest way is to return the blocks with a strip of dpc and a stip of insulation. Then you have a nice secure block to fix your window to.

PVC windows will be fitted with lugs like thishttp://www.thermaframe.co.uk/images/upvc-windows/sash/fixing-lugs.png

and they clip onto the frame and then are hilti'ed into the reveals. They usually wedge the frame into place then attach the lugs with a nail gun then foam around it. Cut the foam back flush and plaster the reveal.

On the outside all you need is to silicone between the frame and reveal. Some people use mastic putty under the window as it can make levelling it easier. Or if its a good tight fit some frame sealant in there.