Prices for replacing a flat roof, broken down the way a quote is actually built: deck, insulation, covering, trims, outlets and access.
Typical totals by roof size
A single garage roof of roughly 15 square metres, stripped and re covered with a new deck, generally comes in between £1,800 and £3,200 depending on the system chosen. A double garage or a small extension of 25 to 30 square metres is usually £2,900 to £5,200.
A larger extension or a wrap around of 40 square metres and up, with a lantern, several upstands and a parapet, commonly runs from £5,500 to £9,000. Those figures assume ground level access and no structural repair.
On a typical job, labour and stripping account for roughly a third, the deck and insulation another third, and the covering, trims, outlets and waste the rest. That is why quotes vary so much: two prices for the same roof often include very different build ups.
The covering itself is rarely the most expensive line. A roof priced only on the membrane, with no allowance for a new deck, is the sort of quote that changes once the old covering comes off.
Insulation changes the number
If the roof is being fully replaced rather than repaired, building regulations expect the thermal performance to be improved where it is reasonably practicable. A warm roof build up, with insulation boards above the deck and the membrane over the top, adds roughly £45 to £80 per square metre.
It also raises the finished roof level, which affects door thresholds, window sills and abutment flashings. Those knock on details are a real cost and should be priced, not discovered halfway through.
Extras that appear once you strip a roof
The common ones are rotten deck timbers and joist ends, an outlet that was never large enough, a fall that runs the wrong way, and lead abutments that have to be renewed because the new roof sits higher than the old one.
A good quote lists a rate for these in advance, so if two joist ends turn out to be soft you already know the figure. We put those provisional rates in writing so nobody is negotiating on a Wednesday afternoon with the roof open.
Getting value without cutting corners
The savings worth having are practical ones: combining the flat roof with other work while access is up, choosing EPDM where a walkable finish is not needed, and booking outside the autumn rush when everyone rings at once.
The savings that are not worth having are a thinner deck, no new trims, or leaving a failed fall in place. Those are the same three items that bring us back to a roof five years later.
Do I need planning permission to replace a flat roof?
Replacing like for like is normally repair and maintenance rather than development. Changing the roof shape, adding a balcony or working on a listed building is a different matter and needs checking first.
How long does a flat roof replacement take?
A garage roof is usually one to two days. A larger extension roof with a lantern and warm roof insulation is more often three to five days including deck works.
Is a warm roof worth the extra cost?
On a habitable room below, yes. It removes the condensation risk of an unventilated cold roof and cuts heat loss noticeably. On an unheated garage it is money you do not need to spend.
Can you replace half a flat roof?
It is possible where a genuine structural division exists, but joining new to old creates a seam at the weakest point. We would usually rather price the whole roof and let you decide.
Does the price include taking the old roof away?
Yes. Stripping, skip or grab hire and waste disposal are included in our written quotations rather than added afterwards.
Want a real figure for your flat roof?
Measured on site, itemised in writing, with provisional rates for anything hidden. The survey and quotation cost you nothing.
Evans Roofing & Maintenance Ltd, Witney, Oxfordshire. Call 07960 482233 for a free written quote.