How much to replace a flat roof
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How Much Does It Cost to Replace a Flat Roof?
Replacing a flat garage roof costs £800 to £3,000 depending on roof size and the covering material chosen. Felt is the cheapest option; EPDM and GRP cost more but last significantly longer.Flat roof replacement is one of the most common maintenance projects for UK garage owners. The cost varies with the size of the roof, the choice of covering material, and whether any underlying deck or structural repairs are needed at the same time.
Cost by Material
For a standard single garage roof of approximately 18 to 20 square metres (3m x 6m), the typical supply and installation costs are as follows. Three-layer bituminous felt: £800 to £1,400. EPDM rubber: £1,200 to £2,000. GRP fibreglass: £1,500 to £2,500. The felt option is the cheapest but has the shortest lifespan (10 to 15 years). EPDM and GRP cost more initially but last 25 to 50 years, giving a lower lifetime cost per year of service.
Deck Replacement
When a flat roof covering is replaced, the contractor will assess the condition of the timber deck beneath. If the deck is in good condition, it can be reused and only the covering is replaced. If the deck boards are soft, rotten, or delaminated, they must be replaced before the new covering is applied. Deck replacement typically adds £200 to £600 to the total cost depending on the extent of the damage.
Access and Scaffolding
Garage flat roofs are typically low enough to access from a ladder without scaffolding, which keeps access costs low. For roofs adjacent to the house at higher level, or where safety requirements necessitate edge protection, a scaffold tower or short scaffold run adds £200 to £500 to the project cost.
Getting Quotes
Get at least two to three quotes from local flat roofing contractors or general roofers for any replacement job. Ensure quotes include the covering material specification, the deck inspection and any necessary replacement, flashings, drainage outlets, and a guarantee period for the new covering. EPDM and GRP systems from quality suppliers come with manufacturer guarantees of 10 to 25 years when installed by approved contractors.
The best time to replace a flat roof is when it has failed but before water has had time to penetrate the deck and cause rot. If a leak has been present for more than a few months without repair, the deck condition should be closely assessed before covering replacement, as a new covering over a rotten deck will fail quickly as the deck deteriorates beneath it.
Summary
A single garage flat roof replacement costs £800 to £1,400 for felt, £1,200 to £2,000 for EPDM, and £1,500 to £2,500 for GRP. Add £200 to £600 for deck replacement if needed. Get three quotes confirming material specification, deck assessment, flashings, and guarantee. EPDM and GRP have higher upfront cost but lower lifetime cost than felt.
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