roof advice needed

matbe

I don't think the pitch will be a problem my garage has these sheets put on about 10 yrs ago with a low pitch and they have been ok only problem ive had is sagging which has caused leaks and I'm waiting for decent weather to remove the old sheets and ply over the joists and re sheet it with same type of sheets

My current overlaps are about a foot in the length and four ridges wide I think and its been fine till the sagging started but that's due to the large gaps between joists which ply will cure.

I also looked at galvanised sheets not much different in price and wont need ply but noisy when it rains if your working in there.

HTH

capeverde

triathleterob wrote: »

Hi capeverde

Thanks for replying.

During the course of my workshop build I've noticed how different people use the same terms but apply them to different parts of the roof structure, which I've found very confusing.

Here's the current state of my roof as I know it-

I have one 5" x 2" purlin running across the 5m width, which supports eleven sloping 4" x 2" rafters running across the 4m width.

I have 18mm plywood boards ready to go on when weather permits to provide additional security.

Can I fit bitumen sheets to this structure (2% drop)? If not, what do I need to do to make it possible? Or should I stick with my original plan to torch-on felt it?

Many thanks

Rob

If you close board it with the ply, the bitumen sheets wont be a problem, but you have other issues. Is it a ridge design with trusses supported by the purlin or a pent design. If the latter, a 5x2 purlin 5m long supporting an 18mm close boarded roof with the potential snow loadings, isnt big enough and will end up with the whole roof sagging. Also, if it is regular ply and not 'marine' its going to take a lot of condensation underneath a dark coloured roof sheet and certainly wont last that long.

triathleterob

Its a pent roof, sloping from front down to back, 3" fall over 4m.

What are trusses? Another new term for me!

I have one 5x2 purlin and eleven 4x2 joists to support the 18mm CE2+ boards. Is that enough to prevent sagging? Looks solid to me!

Condensation is a concern. I thought about some sort of polythene layer on top of ply to collect drips and channel them to gutter. Is that an option? Any other solutions?

Thanks for your help cv

capeverde

75mm over 4m is level to some builders. I'll be honest, with that Id beef up the supports and put some epdm covering on. I wouldnt consider the size of the purlin or rafters correct, but thats upto you. All of the 18mm ply sheets and potential snow loadings are going to bow that over time.