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Hi @Aurel,
The sheeting gets attached to purlins that are attached and run perpendicular to your rafters and sheets. The max spacing of the purlins is between 1100 to 1400mm. The maximum distance between your rafters has more to do with the calibre of timber you select for them and the distances they have to span rather than the sheeting. As long as you space purlins every 1100-1400mm along them, that's all that's required. Here's the SUNTUF Beehive Installation Guide.
Spacing for the rafters could be anything from 450 mm to 1000 mm, depending on the calibre of timber you choose to span the gap of the pergola. The smaller the timber, the smaller the gap between the rafters needs to be. Once you've determined the size of your pergola roof, you can reference timber span tables and the National Construction Code to determine the required rafter spacing.
Please let me know if you have any questions.
Mitchell
Thanks @MitchellMc for the quick response.
To give you more context: the pergola size will be 8m in length x 2.7m wide. and I was exploring 3 options for the rafters 90x45, 120x35 or 140x45. All timber will be structural pine MGP10. from what I found it seems that 90x45 rafters can span 2700mm in a 900mm spacing. is that correct? If I use 120x35 rafters can i space them more than 900mm or that that the maximum allowed?
Also for the purlin what is the most commonly used timber size? is 70x35 overkill?
Hi @Aurel
I suggest referencing a span table like this - Hyne Deck Joist Span Table or similar. This will give you an idea of the limits of the timber span. My other recommendation is to ask a draftsperson to draw up a plan for you so that it will be designed to code.
I also suggest checking the rules and regulations of your local council when building a pergola attached to your house.
In regards to the purlins, 70 x 35 sounds like its overkill, but it will be very strong when you attach your roof sheeting to it. My best advice is to make sure that the timber that you do use for your purlins is treated and can be used for outdoors.
If you have any other questions we can help with, please let us know.
Eric
