NorDan window positioning in timber frame + cill depth

[eros_poli]

Hi forum

 

I've searched around and can't find anything that explicitly helps my situation so here we go!

 

We're building a timber framed extension, with NorDan windows and doors. What I want to know is the best place to put the windows when mounting them to the timber structure; closest to the external face, or further into the frame? Bigger/smaller external/internal reveals etc. 

 

But while figuring this out, I realise the largest cill that NorDan provide is 107.9mm, with 20mm of that extending under the window frame to connect to the unit.

 

My build up equates to (outside > in)

 

50mm larch cladding (board-on-board 25mm)

25mm horizontal battens

25mm vertical battens

9mm OSB

150mm frame. 

 

If I want the windows within that frame, that's 109mm minimum that the cill has to cover, excluding any overlap I'd like. 

 

Surely this is a relatively simple/regular building make up? Just surprised that I'd need "bespoke" cills....

 

Any thoughts welcome, attached is my drawing. 

 

Joe

[Mr Punter]

That doesn't seem like a particularly large cill.  It must come up all the time.  What have NorDan suggested?

[eros_poli]

@Mr Punter The response has been the following:

 

Quote

 

The largest cill I can offer is 107.9mm with 20mm sitting under the frame.

 

If you need larger than this, we will need to look at bespoke cills and outsource them.

 

 

I'm trying to figure out if that 20mm is included or excluded in that 107.9mm. 

 

Perhaps I can move the window out-bound by 20mm, so the cill attachment is protruding from the timber frame, but the main window frame is still within the frame/insulated area. 

 

Joe

[Kelvin]

You’ll need to have cills made up. Nordan don’t do them deep enough. Caused us a huge amount of grief. All our windows are flush with the kit. The French doors and sliding door have a few mm overhang but our walls are pretty wide for a timber kit so we have a deep interior and exterior reveal. 
 

I can post some pictures if it’ll help. 

Edited Tuesday at 14:25 by Kelvin

[Mr Punter]

I have used Finish Architectural in the past for ali cills.  Good firm.

[eros_poli]

@Kelvin photos would be great thanks - any context is great. 

[Kelvin]

The cill is 170mm deep to give us the recommended drip over the edge of the cladding. These are 3G windows so quite deep themselves. A standard timber kit SIP wall build and 3G windows fitted flush would give you a very shallow internal reveal. 
 

 

Edited Tuesday at 15:54 by Kelvin

[eros_poli]

Thanks @Kelvin, looks good. 

 

Yes as it stands if I placed the windows inline with the outer edge of the timber frame, we’d have 135mm internally to the edge of the plasterboard, so not a massive space for a windowsill.

 

The windows themselves are 105mm, so not enormously deep, and we're not going passivhaus standard or anything, so our frame isn't the thickest in the world either. 

 

Are your frames flush with the outside edge of your frame, or do they protrude slightly with the cill connection being in line? If that makes sense... If not I've attached a marked up drawing.

 

Cill connection in red, edge of frame in green, blue is outer edge of timber frame.

 

Joe

 

[Kelvin]

Frames are flush which made fitting the Nordan cill on the full length windows  difficult as it has a crimped edge that needs some force to make fit. The custom made cills were easier to fit but less secure so I glued them in place. Because they are flush it does make sealing around them easier. I used Wigluv tape on the outside and Pro Clima on the inside. Our walls are a space frame system with a 302mm stud depth. From outside face to inside face it’s almost 500mm. Consequently, even with the windows flush, our internal reveal is 245mm. It means we get all the performance benefit of the windows being inside the thermal envelope of the building and the deep reveal look we wanted. 

Edited Tuesday at 21:02 by Kelvin