OK to cut excess window fixing straps to help airtightness taping?

[Gaf]

Have seen these fixing straps referenced as often being a source of air leakage and reduced airtightness. Is there any reason I shouldn’t cut the strap after the affixing nails (red line) so there is less chance of them pulling up the airtight tape?

[Mr Punter]

One nail per strap looks a bit stingy.  Often see screws and plugs or masonry screws.  No issue with zipping off the surplus strap with a grinder and thin blade.

[Gaf]

56 minutes ago, Mr Punter said:

One nail per strap looks a bit stingy.  Often see screws and plugs or masonry screws.  No issue with zipping off the surplus strap with a grinder and thin blade.

Better to use screws on the last hole to both pin it flat and add extra strength to the strap? Throughout the house there’s at least one strap that has come loose.

[Mr Punter]

Yes, 50mm concrete screws are your friends here.  For a 7.5mm screw drill a 7mm hole and clear it out a bit so the screw goes in tight with an impact driver but does not lock up before it is home.

[carlos21]

1 hour ago, Mr Punter said:

Yes, 50mm concrete screws are your friends here.  For a 7.5mm screw drill a 7mm hole and clear it out a bit so the screw goes in tight with an impact driver but does not lock up before it is home.

thats what i did with mine, dont know about airtightness, but they are fixed in tight.

are you putting insulated plasterboard in the revels?

[Nickfromwales]

1 hour ago, carlos21 said:

thats what i did with mine, dont know about airtightness, but they are fixed in tight.

are you putting insulated plasterboard in the revels?

You can kill 2 birds with one stone and just use Marmox to line the reveals. It can be plastered directly, or you can PB and then plaster. Easier to do this without insulated PB as its a bit tricky to do this in straight thin strips imo.

[carlos21]

not seen that board before, looks versatile.  i was going to either render, then skim or dot n dab plasterboard then skim over the block walls, i wasnt going to add any internal insulation as the cavity has pir in. 

but maybe some insulation in the revels would be good.

[Nickfromwales]

23 minutes ago, carlos21 said:

but maybe some insulation in the revels would be good.

Essential, not just good!

[carlos21]

even in my case where from the back of the window frame, its cavity wall pir insulation then the internal block? if that makes sense.

[Nickfromwales]

10 hours ago, carlos21 said:

even in my case where from the back of the window frame, its cavity wall pir insulation then the internal block? if that makes sense.

More for the OP's situation tbh, as it shows full depth masonry.

 

Yours will still be a cold cavity, even on the inside face of the PIR (if there's any kind of gap behind it). Not life or death for you, but if the opportunity exists to make things a lot better the I guess you can choose to do it to the highest standard.

[Gaf]

13 hours ago, carlos21 said:

thats what i did with mine, dont know about airtightness, but they are fixed in tight.

are you putting insulated plasterboard in the revels?

Yes, plan is insulated plasterboard on the reveals. 

 

12 hours ago, Nickfromwales said:

You can kill 2 birds with one stone and just use Marmox to line the reveals. It can be plastered directly, or you can PB and then plaster. Easier to do this without insulated PB as its a bit tricky to do this in straight thin strips imo.

 

It’s not visible but there is a solid piece of approx 50mm PIR used as a cavity closer between the inner and outer leaf at the reveals.

 

We have the insulated plasterboard for the reveals ready to go, but that board might be useful for the head and sill. Between the builder / window installer / block layers, there wasn’t enough space left for insulated boards in the heads or sill of the windows. Those thin marmox boards might be the trick. 

 

You can plaster directly onto them?

 

[Nickfromwales]

2 hours ago, Gaf said:

You can plaster directly onto them?

 

14 hours ago, Nickfromwales said:

It can be plastered directly, or you can PB and then plaster

👍

 

You'd need to do the head and the sill first, so the plasterboard on the insulated plasterboard isn't in contact with a cold surface.