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curlewhouse

Roofing

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So the house is up as far as SIPs are concerned, and very nice too!

Our roofer, though extremely experienced, has not done a SIPs house before and is a little unsure if the OSB gives enough of an anchor for the battens. We've been trying to get advice on the subject (he's spoken to our supplier) but he's still a little concerned.  I think they advised something like annular nails or screws.

Looking online I see 2 examples where slate is concerned - in one, a whole extra set of sheathing is  involved, HERE (this seems to relate to asphalt shingles however rather than slates), but in others, a much simpler (and thus cheaper) method is used, which is kind of how I envisaged it being done - HERE .   

His main concern is the anchorage offered by the single layer of OSB.  Can anyone recall how their SIPs roof was done if using slate? 

Edited by curlewhouse

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How thick is the OSB? Would have thought ring nails alternately gunned in at 10 o'clock and 2 o'clock and the battens are rock solid.

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I can understand the concern, as the OSB is only 10mm thick, I suspect.  Screws would seem to be a better bet than ring shank nails.  I've had lots of 75mm ring shank nails pull out of out larch waney edge cladding (which is nailed to 50 x 25 counter battens, lined up with the frame studs, under 10mm OSB)and have had to go around easing out the old nails and replacing them with decent screws.  It's important to choose the right screws, too.  I made the mistake of using some screws with thin shanks and they just sheared off from movement in the timber within a few months.  I've replaced them all with screws with shanks that are thicker than the threaded part and they are all holding up really well.

 

FWIW, I used good quality galvanised ring shank nails originally and they were all driven in properly, with their heads set just beneath the outer surface of the cladding.  There was no sign of corrosion, the damned things just pulled themselves out with repeated small movements of the timber.  I had places on some walls (the East and West facing ones only) that looked like hedgehogs, with the nails poking out maybe an inch from the cladding.

Edited by JSHarris
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I should update this - annular ring nails were used. Because of fitting a cabrio type window which we had to wait for, part of the roof facing west was unfinished for a a few months - our West aspect faces out over a valley several miles long and we get the wind directly off the moors opposite - there is nothing between the moors and our roof.  We went through 2 periods of gales like this, with a huge vee shape missing from the slates, facing directly into the gales which if I recall right were around the 60/70mph gust mark. We had some actual sleepless nights listening to this (as it nearly tipped over the caravan we were in) and imagining the roof ripping off .... but not one slate so much as budged. The roof is finished now, but that test of strength when it was at its most vulnerable has given me a lot of confidence in it.

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Our SIPs have 12mm osb on each side.

I have double battened the roof first row 400mm centers and nailed down with ringshanks from a nail gun changing the angle of each nail so that they work against each other(300mm centers)

The cross lats were screwed with 2 screws at each inter setion which went right through to the OSB.

Tip use lats when wet as they split less and are usually strighter. I kept mine covered wet as I was working in summer.  I was putting steel on after so the second row of lats were set further apart than for slates. 

You do not need to use the blue/red lats they have only been salected to cut downon wast on large building sites. 

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Curlewhouse

 

do you mind me asking the complete makeup of your roof structure

 

What I am being told by my sips supplier is

 

Slates

Membrane

Sarking (22mm whitewood)

Battens for air ventilation

membrane

Sips osb

 

is that the same as yours?

 

 

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7 minutes ago, Tin Soldier said:

 

do you mind me asking the complete makeup of your roof structure

That would be most helpful for me to if you don't mind

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If you have 15mm OSB you should be fine -- and you can always close up the spacing between the nails and also ensure a nail on each batten goes into the "wall" at the edge of each SIP.

 

Think about the logic for a minute -- a batten is only 19mm x 38mm. If you put a nail through the middle, you only have 19mm of timber (if that!) acting against the nail in each direction. So the batten itself is probably as weak or weaker than the OSB anyway.

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Posted (edited)

Sorry, just seen these requests re roof makeup.   SIate - membrane - battens - breathable membrane - SIPs osb.  

Edited by curlewhouse

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