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How should i space my rafters, 400 or 450?

I'm Working on my new single story extension vaulted roof. The pitch is approx 20deg and I'm using 8x2 rafters on a 3m span. I could do with advice on spacing the rafters as even the building inspectors seem to be confused. I was thinking of 400 spacing and then discovered that the Kingspan or similar insulation comes in a 450 width. In which case, should I consider 450 spacing and save a bit on timber?

5 Answers from MyBuilder Roofers

The best is to space every 400


Answered 14th Nov 2017

Your rafters should be spaced 16 inches or 400 on center, starting from right to left, the longer the span,, the closer to each other the rafters should be


Answered 15th Nov 2017

Rafters should be ideally every 400 with jack supports every third truss.


Answered 15th Nov 2017

I would suggest 400mm centres. You can check with the related span tables in building controls approval document. You'll need to check which one.
Best Regards


Answered 17th Nov 2017

King span, celotex etc also comes in 2400 x1200 and is probably cheaper than the diy stuff per metre square so 400 would be better if your going along that route. Plasterboard also comes in the same size and works out cheaper than 1800 X 900 sheets. Personally 8x2 at 3 metres long I would put in at 600 centres. This is a standard size


Answered 19th Nov 2017

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