What is considered flat V pitched. I have a newish large self assembly shed with a very shallow single slope and I need to replace the felt. My previous shed was a well pitched apex and the felt lasted many years. With this new one the higher (front side) is facing the prevailing wind and the timber facings are in good order, felt overlap is nearly half a metre but rain water is getting in somehow. I would like to think that your 15 year felt would do the job but maybe with a joining spread of bituminous paint – to be sure ?

Flat roofs are 10 degrees or lower in their pitch, pitched roofs can be anywhere upward of 12.5 degrees. From our range, single layer shed felts should only be used at 20 degrees and upwards, with the laps both mechanically fixed and sealed with adhesive. Flat roofing waterproofing systems within the merchant realm are multi-layer (underlay and cap sheet) which are bonded to the deck and fully sealed at laps; potentially including a preparation layer dependant on the deck, etc. Our advice is to follow the guidance of the specific product TDS (Technical Data Sheet) in each situation for guidance on bonding, sealing, etc.