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OSB or Ply ?


Astrokev

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I used this stuff- Onduline Corrugated Bitumen Roof Sheet - Green (2000 x 930mm)

https://www.roofingmegastore.co.uk/onduline-green-corrugated-bitumen-sheet.html

Been good for the last eight years or so 1500 feet up in the Welsh mountains ans some fairly extreme conditions.....

38049361491_a423cee2d8_b.jpg

My approach was to see what the locals use to build agricultural buildings and copy that!

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2 hours ago, laser_jock99 said:

I used this stuff- Onduline Corrugated Bitumen Roof Sheet - Green (2000 x 930mm)

Been good for the last eight years or so 1500 feet up in the Welsh mountains ans some fairly extreme conditions.....

My approach was to see what the locals use to build agricultural buildings and copy that!

Fantastic looking obsy there laser_jock. The corrugated roof looks great but I don't think would fit-in with my garden setting, but thanks for the suggestion.

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10 hours ago, RayD said:

The reason it is so important to have the gap behind the foil covered products like Celotex is that the foil acts as a built in vapour barrier, and is why you don't need a separate one if you use it.  This means then that the moisture trapped between the roof board and the insulation when the outside is sealed by EPDM has absolutely nowhere to go, so will start rotting the timbers.  Rockwool type insulation doesn't form a vapour barrier so should let things breathe fine.

Think I'm nearly there with designing positions of roof rafters to help me calculate how many sheets of OSB I need.

Another question has just occurred to me. All the roof sections are larger than any single piece of OSB, so I will need to use 2-3 pieces and "jigsaw" them together. I'll ensure all joins are supported with a rafter. Are there any extra precautions I should take to ensure the OSB sticks and stays in position with use, without any risk of bubbling up at the OSB joins?

I'm sure others must have faced a similar challenge, so I'm assuming there won't be a problem?

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It is recommended to have gaps in ply to allow for expansion / contraction but I think OSB is less prone to this although it does absorb moisture, joints could be biscuit jointed and glued for bit of belt and braces overkill.

Also OSB comes in different grades with grade 1 only recommended for interior use.

Dave

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5 hours ago, Davey-T said:

It is recommended to have gaps in ply to allow for expansion / contraction but I think OSB is less prone to this although it does absorb moisture, joints could be biscuit jointed and glued for bit of belt and braces overkill.

Also OSB comes in different grades with grade 1 only recommended for interior use.

Dave

Thanks Dave - good advice which I hadn't considered ?.

I'll be using OSB3 which is more designed for external work, with supposedly a lower moisture uptake rate ? which should help.

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