Torch-on felt roofing across County Londonderry

Price per m²

£53–£92

Typical life

15–25 years

Manufacturer guarantees

10–20 year material guarantees on specified systems

Typical garage roof

£1,350–£2,300

How much does a torch-on felt roof cost in County Londonderry?

Guide prices including VAT at Northern Ireland rates. The fixed price comes after a free survey for new and replacement roofs.

Which flat roofs are common in County Londonderry?

Flat roofs in County Londonderry sit on newer estates where the first extension roofs are now being replaced, 1960s and 1970s link-detached houses with flat-roofed garages and porches and low-rise post-war blocks of flats. Northern Ireland averages roughly 1,150 mm of rain a year, spread over many wet days, so a roof that sheds water quickly to clear outlets lasts far longer than one that holds puddles. Approximate 1991–2020 regional averages based on Met Office data.

Building control in Northern Ireland

In Northern Ireland, renovating or replacing a roof over a heated room usually means meeting Technical Booklet F1, and building control should be contacted before work starts. Technical Booklet F1 sets roof insulation at 0.18 W/m²K when a roof over a heated room is renovated or newly built, where feasible. In County Londonderry the application goes to Derry City and Strabane District Council, Causeway Coast and Glens Borough Council and Mid Ulster District Council. More on the rules.

Does replacing a felt roof mean upgrading the insulation?

Usually, yes, when the roof is over a heated space and more than half of it is being re-covered. In England, Wales and Northern Ireland that is renovation of a thermal element, which should be brought towards the renovation U-value where feasible; a Scottish project goes through the council's building standards service, which confirms whether a warrant applies.

A felt replacement is a good point to switch to a warm roof, with insulation laid above the deck under the new membranes. On larger roofs, tapered insulation can also correct poor falls that have caused ponding, which a patch repair cannot fix. Raising the roof level affects upstands and door thresholds, so we check heights at survey. Any approval is arranged by us as part of the job, and the building regulations page sets out the rules by nation.

Is torch-on roofing safe, and what is the difference between two- and three-layer systems?

Yes, torch-on is safe when hot works are properly controlled, because most roof fires linked to torching start at hidden timber or debris near edges and upstands, not on the open roof. Our teams follow a hot-works routine on every job:

• check eaves, fascias, soffits and wall cavities for timber, nests and debris before lighting a torch;
• use a cold-applied or self-adhesive membrane, rather than a flame, at edges, against combustible materials and in tight details;
• keep fire extinguishers on the roof and the gas bottles secured and away from the work;
• stop torching well before the team leaves, then carry out a fire watch so smouldering is spotted while people are still on site.

As for layers, a two-layer system (underlay plus cap sheet) is common on domestic roofs such as garages and extensions. A three-layer system adds an intermediate sheet, giving more thickness and redundancy, and is often specified on larger, commercial and multi-occupied roofs. The right choice depends on the size and use of the roof and the system's requirements, so we set it out in the quote.

Near a boundary, the external fire performance of the tested build-up, such as a BROOF(t4) classification, can also matter, and we check it where it applies.

Which towns in County Londonderry do we cover?

• Derry/Londonderry
• Coleraine
• Limavady
• Magherafelt
• Portstewart

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