Hi All, A customer has a rear-of-house lean-to structure (containing a bathroom) which has a leaking flat roof that needs replacing. On examination the existing roof is chipboard laying on the ceiling joists. It has zero pitch and the chipboard is now turned into Shredded Wheat. The top covering is shed felt. My plan is to turn the flat roof into a low pitched roof, by: mount a timber wall plate in order to fit hang rafters. (Max pitch is 12°due to a window) fit 12mm wbp ply sheets cover with a damp proof membrane like this: https://goo.gl/GcGUrz cover with felt or perhaps some fibre roof slates like these: https://goo.gl/9wqW25 fit guttering etc The lean-to is south facing and not too exposed due to other surrounding structures. Any thoughts and recommendations on method & roof coverings would be welcome. Many thanks.
Thanks KIAB, Can you point me at a specific product for the top covering and the pre-formed edging? Also, is the low pitch a problem?
Not a problem the low pitch, just use firrings to give you a fall. Had grp roof at a previous place,it lasted 25 years,until building was knocked down. topseal.co.uk/ roofingsuperstore.co.uk/browse/flat-roofing/fibreglass-systems.html cfsnet.co.uk/acatalog/1project-roofs.html Got a bug on this forum at the moment,adding S to http,so have remove first bit. Don't have to use grp flat, it can do any shape as well. I would get someone to do the grp for you,quicker, & they have the experience,had firm in here to do workshop roof 7 years ago,save me a lot of hassle.
Nice info, KIAB. NT, as KIAB says, the pitch ain't an issue, but as KIAB also says, DO insulate that roof properly - especially since it's gonna be a bathroom. If you don't, not only will you have contravened regs, but the customer will have hellish long term problems with condensation. Lots of info out there on how to lay a felt roof - and that will last well in excess of 20 years. Eg: https://www.diydata.com/projects/flatroof/flatroof.php Note how they use triangular fillets along the top but also down the sides so that all the run-off ends up in the guttering.
Fantastic info chaps, much appreciated.. Another thought. Does changing a flat roof to a mildly pitched roof need to go through planning permissions? Thanks again.
Rear of house, I wouldn't worry about planning. It is a structural alteration changing from flat to pitch so building application would be needed.
I'm also going to replace my roof, and I've found out that I will need to make a roof truss. And I've been suggested to use a roof truss calculator here for this purpose. If you want to convert your flat roof to a low pitched type, you will also need a truss. So, maybe this information will be useful for you.