Which breathable membrane?

[Watshot]

Hi, nearly ready to start my pitched warm roof and need to get a breathable membrane to go over the Celotex insulation. There seems to be a lot of choice at a range of prices, from your brand names, Nilvent, Tyvek etc., to the cheaper options.

Then there's the 'high performance', 'lightweight', super this that or the other. I don't mind spending the cash if it's worth the extra, but surely if it all meets some kind of British Standard marking, it all does the same job doesn't it?

What would you recommend? Buy the best you can afford, or, it's all the same save your money? Any pointers appreciated.

Also, if you lay the membrane directly over the sarking, then counter batten, how does the felt lap onto the eaves tray? Obviously I could drape it over the counter battens instead to achieve this but it's difficult to tape the joins then, is it not?

Many thanks for any help.

 

[^woody^]

Any BBA certified membrane will do

The membrane just laps over the eaves tray - which would be fixed over any rigid sarking board

 

[Mw Roofline]

Just done my house with something called 'grafter' or something like that, BBA approved £30 a roll plus vat from Brum. not amazing, just decent quality.

 

[Watshot]

Thanks for the replies.

Regarding the eaves tray, if the membrane is laid on the insulation boards, surely the counter battens prevent it from lapping onto the tray which is itself fixed over the counter battens (and below the tiling battens).

This is the bit I don't understand. Like I said, if the membrane is draped over the counter battens, then it is on the same level as the eaves tray, so there doesn't appear to be a problem. But that method makes taping the overlaps difficult. Am I missing something, as most of the pictures I have seen show the membrane under the counter battens?

Cheers guys.

 

[^woody^]

If a warm roof, the insulation would not go right to the eaves as it would then be exposed. So you would have one or a double row of timber at the eaves (which would be the same depth as the insulation, and then the tray fits on this and the membrane laps over it

Or the fascia top is fixed flush with the top of the insulation and then fit one batten further back to catch the back of the eaves tray. The insulation would butt up against this batten