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New Build Garden Office Roof Advice Needed Please

Postby Slimat » Wed Oct 12, 2016 11:06 am

Hi All

I hope nobody minds me starting a new post on this as I would like to give specifics to my job in the hope that someone can advise.

I am building a new office in my garden (UK) and its footprint is 4.9m x 3.9m.

The floor is made of 8x2's (200mm x 47mm) with 3.9m unbanded scaffold boards (38mm thick) as the floorboards. So you can see its fairly substantial.

The roof is to be a dual pitch roof with the apex running in the middle of the two longest sides (i.e. from one 3.9m wall to the other). I have never built anything like this and have now got to the point where I am building the roof this weekend.

Originally I was advised to make the trusses out of 6x2's (150mm x 47mm) with a 35 degree pitch. This was advice from a friedn who is a professional roofer. Since being told this I have done a lot more reasearch and it seems that this was complete overkill and "old school".

I have decided to use Marley Garsdale tiles which are lightweight and can be pitched as low as 15 degrees. and to use kingpost style trusses at 600mm centres.

I sent all these details to a truss design company who drew up a design suggesting 75mm x 38mm timber would be sufficient - so I am now wondering whether 6x2's are too overkill and perhaps to use 4x2's (100x47mm)?

I am curious whether anyone on here could offer advice on what size timber would be sufficient. Also there will be 10 trusses (2 extra to allow an overhang at each end)... but, apart from the battening should I fit another length running under the apex to keep all the trusses a fixed distance apart - or are the battens and roof tiles sufficient for this? I have seen drawings with and without this final support?!?

Any advice would be gratefully received.


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