Interior timber frame against a single skin exterior

[pertinky]

Hey,

I'm building an interior timber frame in the recess of the PVC window panels (window + lower in one piece) in my new house. The recess is about 150mm deep. I'm looking at lining it with foil backed insulation board and fixing 12.5mm plasterboard on top to create a windowsill.

I was wondering if I need to conform to any regs when doing this; mainly:

- air gap between the exterior skin and the timber frame
- batten the insulation boards to stop them moving into the air gap
- vapour barrier between the insulation board and plasterboard

Any info would be greatly appreciated!

Also, am I right in thinking the foil backed insulation board ala Kingspan act as a vapour barrier? Presumably I'd have to vapour tape around the boards/studs.

 

[Karis]

I was wondering if I need to conform to any regs when doing this;

Not entirely sure I understand what you have or are trying to achieve but as long as your not replacing the original window frame & structure, your only improving what’s already there so you can do more or less what you want. Why do you think you need insualtion, foil backed or otherwise?

Also, am I right in thinking the foil backed insulation board ala Kingspan act as a vapour barrier? Presumably I'd have to vapour tape around the boards/studs.

Well sort of but why do you think you need to go the trouble of Kingspan insulation, a vapour barrier & vapour tape? How exactly is this frame fitted into the external wall? What sort of walls do you have?

Don’t use plasterboard for a window cill, you’ll have extra work to finish it off . Fit a proprietary cill board, preferably a laminated one which doesn’t require any further finishing treatment apart from a caulk bead around the edge.

 

[pertinky]

I was wondering if I need to conform to any regs when doing this;

Not entirely sure I understand what you have or are trying to achieve but as long as your not replacing the original window frame & structure, your only improving what’s already there so you can do more or less what you want. Why do you think you need insualtion, foil backed or otherwise?

Also, am I right in thinking the foil backed insulation board ala Kingspan act as a vapour barrier? Presumably I'd have to vapour tape around the boards/studs.

Well sort of but why do you think you need to go the trouble of Kingspan insulation, a vapour barrier & vapour tape? How exactly is this frame fitted into the external wall? What sort of walls do you have?

Don’t use plasterboard for a window cill, you’ll have extra work to finish it off . Fit a proprietary cill board, preferably a laminated one which doesn’t require any further finishing treatment apart from a caulk bead around the edge.

Exterior is concrete block no cavity wall.

Not touching existing window/panel mearly constructing an interior window sill and insulating.

I should have been clearer; will be fitting a proper window board

The frame will be fixed to concrete on 2 sides and timber on the bottom.