hi there i just moved into a new property with a 20 ft by 9ft garage, the roof needs redoing as the previous owners let it fall to pieces,the chipboards are all wet like soggy weetabix so i'm planning on ripping of all the old mineral felt and the boards and replacing with 8x4s but was wondering how many 8x4 boards should i need and what would be the best and cheapest boards to use,should i use the OSB boards or ply.Thanks..
OSB and go to diydata.com for how to lay cold adhesive felt. Look for 3 layer felt roofing using cold applied adhesive.
Or enquire at builders merchants about the hot laid felt [two layers] undercoat pitch both sides. One side adhers as its softened, to the board the other amalgamates with the top layer pitched oneside mineral top coat, entails hire of a propane lance, and need for thick work gloves as hot pitch hurts.