Counter battens

[davejura]

Hi folks. My roofer told me to get treated 19 x 38 timber for counter battens, then graded (stamped) 25 x 50 battens. Batten size is right according to the tile manufacturer and NHBC, but the architect specified 38 x 50. There was no specification for the counter battens.

So the question is, are we OK with the non stamped 19 x 38 counter battens? And I can't see any reason not to use 25 x 50 battens, unless anyone can give me a good reason. Tiles are Northstone Donard on 45 degree pitch. Thanks!

[George]

I'd be aiming for a 50mm cavity, so two layers of 25x50mm battens.

 

If battens are spanning, then minimum size is 25x50mm up to 600mm span to reduce risk of falling through them (25x38mm can be used up to 450mm span).

 

19x38mm generally aren't used except for repair to old roofs. 

[davejura]

Sorry, should have said there is a 12mm OSB backing board below Cromar vent 3 felt.

[Temp]

7 hours ago, davejura said:

I can't see any reason not to use 25 x 50 battens

 

The counter batten is normally to raise the membrane off the insulation/osb. Not all membrane is approved for use in contact. 

 

The membrane should also drape between the rafters and not be pressed against the underside of the tile batten. This is to allow water blown under tiles to run down and not pool above a tile batten as this can cause batten rot.

 

I thought the normal drape recommended was about 25mm so I'd go for 25mm thick counter battens.

 

Edit: Counter battens can also be installed above the membrane to raise the tile battens off the membrane for same reason.

Edited September 30, 2022 by Temp

[Temp]

Actually here it says the drape can be 10-15mm so 19mm counter battens would also be OK.. 

 

https://www.roofingsuperstore.co.uk/help-and-advice/project-guides/pitched-roofing/how-to-install-breathable-roof-membrane/

 

Quote

 

Ensure draping occurs

The breathable roof membrane should drape slightly between the timber rafters or counter battens, meaning there is a dip of around 10-15mm. 

 

 

 

[Thorfun]

25mm x 50mm battens and counter battens for us. allowed us to fully fill the rafters with insulation as the 50mm air gap was above the Roofshield. all confirmed ok with the BCO.