hi just brought a house and it needs a new felt flat roof above our spare bedroom. i know nothing about this but i need to decide between three layers and two layers of felt and osb? or ply. i want the best regardless of cost but i dont know what is better and i need to choose between two roofing guys.
many thanks

The three layer i would imagine will be using hot tar and 3 layers of felt.The two layers should be one underlay felt with a caping sheet (felt) of mineral felt.The OSB is a decking board that is put down first,ply is better but more expensive.I have always used the two layer system with OSB board.With the two layer using mineral felt top sheet,thats the finished job,where as a lot of blokes paint on silver reflective paint(3 layer) to finish the job.This paint always fades aways and gets dirty,then not doing what its supposed to do,that is reflect the sun.
As long as the three layer has a top mineral felt,they are much the same.

Why didnt you consider grp materials more expensive but ihas a 50 year life expectency and looks good too. mineral felt only has a 12-15 year life expectency I d go with GRP everytime and I never lay the old fashioned mineral felt

Hi Jasmine

Have you considered EPDM Rubber roofing membranes. They are relatively cheap and very easy to install unlike GRP and will also last 50+ years. Most good builders/roofs will be able to install this for you. The EPDM membrane wont Crack, Blister or Peal unlike felt systems which as Robo says only lasts 12-15 yrs (Less on a South facing roof)

Check out www.rubber4roofs.co.uk They sell three systems. I think the "One-Piece" system would be perfect for a simple flat roof extension.

All the Best
Tom