We were watching a neighbour's roofing work today. I had to look at the DIY FAQ to answer a question but found that it does not cover Scottish roofing:-
Anyway, the question was - why have they added counter battens under the new battens?
Ventilation?
I wondered that - but the only things that would be ventilated are the battens?
Geo
I did this for cross-ventilation on the underside of the rafters before fitting cellotex and plasterboard. I wouldn't bother on the outside though -- tiles are far from air-tight.
The message from Geo contains these words:
the membrane being pierced by slate or tile fixing nails.
In article , Geo writes
If you just had the horizontal battens they would be tight to the felt/membrane and to the sarking boards which would trap any moisture ingress leading to rot. With counter battens there is a vertical run off path for moisture, leaving the roof dry & rot free. The whole idea is about secondary protection, moisture may get in through severe weather or mechanical failure but the roof will remain sound and well drained.
Ok - that seems reasonable - wonder why the whole estate was not built like that though? The house being reroofed is detached - but our semi-detached would look a bit weird if only half of it was re-worked with the extra thickness of the counter battens.
Geo
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