Window opening details

[Crofter]

I'm about to start installing the breather membrane onto my timber frame. This will be hung vertically and then fixed via battens every 600.

Question- do I fix a horizontal batten at the top and bottom of each window opening?

[thomas]

Depends on your cladding, if you can have water penetration the top of the window must be allowed to drain.
Bottoms are windows are normally closed by the cill.

[Mikey_1980]

Ours our open with stainless steel insect mesh across the top to stop bug ingress but allow free draining of any water that gets behind the cladding. Also we went 400 centres on the battens because it can get quite windy where our site is so might be worth considering.

[Jeremy Harris]

On 31/05/2016 at 08:43, Crofter said:

I'm about to start installing the breather membrane onto my timber frame. This will be hung vertically and then fixed via battens every 600.

Question- do I fix a horizontal batten at the top and bottom of each window opening?

There's a TRADA detail for this.  What Trada suggest is that you don't fit a batten across the head but that there be a bent aluminium flashing fitted behind the counter battens at the window or door opening head, to direct any water ingress that might get through the cladding and out over the timber fitted across the head of the window as a part of the cladding.  I did a drawing of how we did this as it came up on Ebuild, and this is what our's looks like:

After some debate, I chose not to have solid aluminium flashing bent up, mainly because I wanted it to be black, so it didn't stand out and the cost of getting black anodised or powder coated flashing was a bit high.  There was also the potential problem that the flashing would spring away from the timber at the head, and so would probably need to be bonded down.

What I did was fit lead substitute flashing, as this was sufficiently malleable to stay bent without being at all springy and could be neatly trimmed so that it doesn't show at all in practice.  I can't remember the brand, but it was 150mm wide, with a black external finish.  The head board in that sketch is 70mm x 20mm thick, with a planed bevel where it meets the ends of the counter battens.  It is skew nailed in place, through the end of the counter battens and into the underlying house frame.  The gaps between the battens were filled with stretched out stainless steel industrial pan scourers, available from large catering suppliers very cheaply and ideal for allowing ventilation whilst keeping insects out, and a lot cheaper than insect mesh.

 

[Crofter]

Thanks for the details.

I probably don't need to overthink this- the windows go up to within about 60mm of the soffet, which will be about 160mm past the cladding. So it's very hard to see how any water is going to get in from above.