Repair or replace: when patching stops paying
A single split or a lifted edge on an otherwise sound flat roof can be repaired for a fraction of a replacement. The trouble starts when the patches multiply. If the felt is brittle all over, blistered in several places or the ceiling below has been stained more than once, every repair just moves the leak along. At that point a full replacement is usually the better use of your money.
Our page on flat roofing explains how we strip and relay a roof. This guide is about what makes one quote bigger than another.
Size, shape, upstands and edges
Area matters, but small roofs carry a fair amount of fixed work whatever their size: setting up, stripping, disposal and the edge trims. That is why a tiny porch roof does not cost a tenth of a garage roof ten times larger.
Detail adds time. Every wall the roof meets needs an upstand turned up and sealed, often with lead or a trim over the top. Roof lights, soil pipes and outlets each need careful forming around. A plain rectangle with one drip edge and one gutter is the simplest job there is.
Choosing the covering: GRP, EPDM or felt
We lay two modern systems: GRP fibreglass and EPDM rubber. GRP is built up in layers and sets hard, which suits roofs that get walked on and shapes with lots of corners. EPDM is a single rubber sheet bonded to the deck, quick to lay on simple shapes and very forgiving of movement. Traditional felt is still around, but most people replacing an old felt roof move to one of these instead.
Which one costs less depends on the roof. For the full comparison, read our guide to GRP vs EPDM flat roofs.
The deck and joists underneath
The new covering is only as good as the board it sits on. On many older garages and extensions, years of slow leaks have softened the chipboard or plywood deck. If it flexes underfoot or crumbles at the edges, it has to come out and be replaced with new boards.
Occasionally a joist has rotted too, or the roof has sagged so water ponds in the middle. Firring strips can be added to restore a fall. These are the items that can only be confirmed when the old surface is lifted, so a fair quote explains how they will be handled.
Insulation and building regulations
When a roof over a heated room is replaced, building regulations may require insulation to be brought up to current standards. In practice that can mean a warm roof build-up with insulation boards above the deck, which raises the roof level slightly and changes the edge details. A garage that is not heated is usually treated differently. Our guide to planning and building regs for a new roof covers this in more general terms, and your local building control team has the final word.
Access, skips and waste
Old felt, gravel and rotten boards all need to go somewhere. A skip on the drive is easy; a mid-terrace extension reached only through the house takes longer to clear. Roofs above conservatories or over a neighbour's boundary may need extra protection or a scaffold tower.
Getting a written quote
Lee Draper comes out from Witham, walks the roof where it is safe, checks the ceiling below and talks through GRP and EPDM for your situation. You then get a written quote covering the system, the deck, edges, waste and any insulation, with no obligation.
Curious how long a new one should keep going? See how long a flat roof lasts. If yours is already letting water in, our page on a leaking flat roof explains what to do first.
Small roofs with awkward details
Bay window tops, porch canopies and dormer roofs are small, but they are rarely simple. They usually meet tiles, render or brickwork on several sides, and each junction has to be sealed with care. That is why the price of a tiny roof can surprise people. The time goes into the edges rather than the middle.
If a dormer or bay is leaking where it meets the main roof, the fault may be in the tiles or lead above rather than the flat surface itself. Lee checks both before suggesting a new covering, so you do not pay to replace a roof that was never the problem.