Edge trims, outlets and drainage across County Londonderry

Guide price

£110–£310

Repair price

Confirmed once the leak or damage is found

Condition survey report

£130–£260

Coverage

England, Wales, Scotland, NI

How much does a new roof edge or outlet cost in County Londonderry?

Guide prices including VAT at Northern Ireland rates. We confirm the price once we've traced the leak or seen the damage.

Which flat roofs are common in County Londonderry?

Flat roofs in County Londonderry sit on 1960s and 1970s link-detached houses with flat-roofed garages and porches, 1930s semis with flat-roofed garages and kitchen extensions and lock-up garage blocks on estates. 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.

Why does water sit on my flat roof?

Water sits on a flat roof because it can't drain off fast enough: the falls are too shallow, part of the roof slopes the wrong way, the deck has sagged between joists, or an outlet is blocked or set too high.

Current guidance on flat roof design (BS 6229) means most roofs need to achieve a finished fall of at least 1:80, and roofs are commonly designed with a steeper fall, such as 1:60, so that building tolerances and deck deflection still leave enough slope. Many older roofs were built with less, or have settled over time.

A small amount of water that clears within a day or two of rain is often tolerable. Deeper ponding that lingers adds weight, holds dirt and debris, can shorten the life of some coverings and turns any small defect into a leak. A patch won't fix it, because the problem is the shape of the roof. The fix is to correct the falls, either with firring pieces under a new deck or with tapered insulation in a warm roof, or to add or lower outlets so water has somewhere to go. Our ponding water guide explains this in more detail.

Do flat roofs need overflows?

Roofs that drain to internal outlets or behind parapets should normally have an overflow, so that if an outlet blocks, water spills somewhere visible instead of rising over the upstands and into the building.

An overflow is usually a spout or weir set through the parapet or kerb at a level below the top of the upstands. When water runs from it, that is a sign the main outlet is blocked or overloaded. On a simple roof that drains over a drip trim into an external gutter, the open edge itself does the same job.

We look at where the water goes in heavy rain, how many outlets the roof has for its size, and whether the outlets, hoppers and downpipes are clear and properly connected. Leaf guards on outlets help on roofs near trees, as long as they are cleared regularly.

Which towns in County Londonderry do we cover?

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

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