Garage roof replacement

[the_jinj]

Hi

i am going to replace an asbestos concrete corrugated roof on my garage with bitumen sheeting. The garage size is 3100mm x 5300mm. Currently there are two large rotten beams running lengthwise to support the roof but I was planning on laying it out like this using 4x2's.

the sketch doesn't represent the spacing for the joists or purlins but, in theory, is this ok to do? Will the 4x2's be ok for the span and weight? What size do you recommend for the purlins?

The roof is on a slight slope, maybe 5 degrees.

Cheers!
Neil

 

[freddiemercurystwin]

Why are you fitting the purlins? For a span of 3.1m you need to be looking at something like 2x8 joists, 2x4's are well undersized.

 

[the_jinj]

Why are you fitting the purlins? For a span of 3.1m you need to be looking at something like 2x8 joists, 2x4's are well undersized.

OK thanks, I'll use 2x8's. The purlins were for adequate fixings for the sheeting.

 

[Cumbrianroofer30yrsexp]

Plastic coated box profile sheets are the best.If you have not already purchased your sheets i would consider this.