How to lay OSB in the rafters without purlins?

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Disperse the doubts. I have two questions:

1. When installing OSB in the rafters without purlins (step 62.5 cm on the axes. 57.5 inner, 50x200), how best to lay it? Along the rafters or across?

2. Is it necessary to make a gap between the boards or place them flush?



The OSB sheets are laid across the rafters, seams apart. It is better to lay on a crate, taking into account the snow load (9 mm is enough). Take not edged board (remove the bark). Install at the same time as the OSB.

On the official website of Shinglas, OSB-3 sheets are recommended to be laid across the rafters.


When laying without purlins, the thickness of the osb should be bigger. So it is cheaper and more convenient to lay osb on the purlins.

Lay with a gap of 3 mm – summer, 5 mm – autumn, winter, spring.

Purlins are laid across the rafters, along the rafters are nailed counter-battens, which makes the air gap.


Osb boards are laid "in a row" (with an offset of the vertical joints);

Leave a gap of 3-4 mm between the boards to compensate for their expansion as the humidity in the environment changes;

fix the boards at a distance of 10 mm from the edge with 150 mm pitch using galvanized good adhesion nails (burr nails), or self-drilling screws that are 2.5 times longer than the thickness of the board;

the distance between nails / self-tapping screws along the outline of boards is 150 mm, inside the boards – 300 mm;

When installing the roofing baseboard, the boards are installed in parallel with the eaves across the supports; height differences between the boards must not exceed 2 mm.

OSB must be stored in dry conditions on a flat surface. Boards are placed horizontally on pallets or wooden pads with a spacing not exceeding 80 cm.

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