Chapter 1: Why does the felt roof on our Cove garage keep blistering and splitting?
What we find
Garages and porches added to Cove's post-war houses were usually covered in bitumen felt, laid in layers over a timber deck. Felt is a modest material, and it lives a hard life on a small flat roof. Sun softens the surface, so blisters rise where moisture has been trapped between the layers. Winter frost then opens those blisters into cracks. The most exposed places are the upstand, the short vertical edge where the roof meets the house wall, and the drip edge at the front.
Look for a roof that holds a puddle for more than a day after rain, felt lifting away from the wall, or a ceiling stain inside the garage or utility room. A soft patch when you press on the deck from below means the boards have absorbed water and are starting to rot.
What we fix
If the blisters are few and the deck is dry, a localised repair is often enough: we cut out the damaged felt, dry the deck, patch with new membrane and re-seal the upstand. Where the covering has failed across the whole roof, patching only buys a season or two. We strip to the deck, replace any soft boards, fit a vapour layer if the room below is heated, and re-cover.
Our usual choices are EPDM (a one-piece synthetic rubber sheet) or GRP (fibreglass resin that is brushed on liquid and sets rigid). Typical UK ranges per square metre run £80 to £120 for rubber and £100 to £160 for fibreglass, and the fixed quote is set once we have surveyed. See our flat roofing page for how each system is laid.