Flat roof cost runs on three things: the size of the roof, the system you pick, and how much of the deck underneath needs replacing. These are typical Hertfordshire market prices for 2026 for a full strip and re-cover. Use them to budget. They are not our price list.
Typical prices by roof
A single garage or porch roof is £1,000 to £2,500. A single-storey rear extension of 15 to 20 square metres is £2,000 to £4,500. A dormer flat roof costs more than its size suggests, because scaffold is the biggest extra. A double garage or a bigger extension is priced on its size, above those ranges.
Felt, GRP, EPDM rubber or single-ply
Torch-on felt is the most affordable and the toughest underfoot. EPDM rubber goes down in one sheet with no joints across the roof. GRP fibreglass gives a hard, jointless finish that takes foot traffic for maintenance. Single-ply membranes suit bigger and commercial roofs. On most extension roofs the difference between them is a few hundred pounds, so choose on the roof, not the price.
The deck is the big variable
If the boards underneath are wet or rotten, they come up and a new OSB3 deck goes down, priced by the square metre on top of the covering. That is the single biggest thing that moves a flat roof price, and the reason to have the deck checked before anyone quotes. A soft, springy feel underfoot or a dip where water sits are the giveaways.
Insulation and extras
Turning an old cold roof into a warm roof with insulation board adds to the price and raises the roof edge. Rooflights and lanterns, new fascias and gutters, and scaffold on taller roofs are all extras, and every quote you compare should list them separately.
Repair or replace?
If the leak is at one joint or one edge and the rest of the roof is sound, repair it: a patch costs a fraction of a new roof. If the covering is blistered and split across the roof, the deck is soft, or repairs keep failing in new places, a new roof is the better spend. Patching the surface does not fix a rotten deck.
Free written quote, no call-out fee
KR & Sons lays flat roofs in felt, GRP, EPDM rubber and single-ply, on homes and commercial buildings. Kieran comes out, checks the deck and the edges, explains the options and gives you a free written quote, with no call-out fee. Ring 01727 326610 or send the form.
Related services
- Flat roofing in Hertfordshire
- Fascias and soffits
- Roof repairs in Hertfordshire
- Roof repair cost in Hertfordshire
Get a real price for your roof
Ranges are a guide. The real number comes from someone looking at your roof. Kieran comes out, shows you what is needed and gives you a free written quote, with no call-out fee.
Questions
Which flat roof lasts longest?
Laid properly on a sound deck, felt, GRP and EPDM all last decades. GRP and EPDM have no felt laps to open up, and torch-on felt is the toughest underfoot.
Can a new flat roof go over the old one?
Only if the old covering is flat, dry and well stuck down. On most roofs it comes off so the deck can be checked. Covering over a wet roof traps the water in.
Is a new flat roof guaranteed?
Yes. All KR & Sons work is guaranteed.