Roofer or builder: who should do your roof job?

Slate and stone are crafts, and roofers learn them on the slopes. Natural slate is laid with a headlap that depends on pitch and exposure, and the supplier Cupa Pizarras advises against hook fixings on any pitch under 25 degrees. Cotswold stone goes up in diminishing courses, big stones called cussoms at the eaves and tiny ones, the short cocks, near the top, each held by a peg. Getting a swept valley right takes specially cut slates. These are skills a roofer uses weekly.

Leadwork is another. Lead is cut and dressed to fit, laid in short lengths so it can move with the temperature, and chosen by code. Leadworx calls Code 4 the standard for general flashing. Poor leadwork around a chimney is a leak waiting to happen.

Flat roofs demand specialist knowledge too. Falls have to be right, because BS 6229 guidance is to design for 1:40 to achieve a finished 1:80. The membrane, whether EPDM, GRP or felt, has to be jointed and upturned correctly at every edge. A roofer who does flat roofs regularly will know which details fail.

Plenty of roof work is part of a bigger scheme. A builder doing an extension will often put on the roof, particularly if the covering is a common concrete or clay tile in a standard size. A builder can also fit a roof window in a straightforward position, replace a few tiles or deal with a fascia and a length of guttering.

The arrangement works when the builder is clear about who does what. Many builders bring in a roofer for the specialised parts, which is normal. If so, ask who that is, whether you will deal with them directly and whose guarantee covers the work. Our page on roofing subcontractors explains what to look for.

If your job has several trades, such as structural changes, new windows, plastering and roofing, a builder who manages them may be simpler than juggling contractors. Just make sure the roof is itemised in the quote and not buried in a lump sum.

The right trade often depends on how complicated the roof is. A plain gable with concrete tiles is within the reach of many builders. Hips, valleys, dormers and abutments need more care, and the cost climbs with them, as MyBuilder's figures for gable (£5,000 to £8,000) and hipped (£8,000 to £12,000) re-roofs show. The main roof shapes on UK homes may help you work out how complex yours is.

Age and listing matter more. If your home is old, listed or in a conservation area, the covering is usually matched like for like. Stone should stay stone and slate should stay slate, and the planning team at Stroud District Council decides what is acceptable on a listed building. A specialist who knows the material can describe what a sympathetic repair looks like.

Weight is a further point. A heavier covering, 15% or more over the old one, needs approval from building control and a structural check first. A firm should raise that before you do.

The questions are the same for a roofer or a builder. Which people will be up on the roof, and are they employed or subcontracted? What exactly is the covering, by name and size? Will you see photographs of the existing roof and a written scope? How is the work to be paid for, and when? Who gives the guarantee, and is it on paper?

Where the work is notifiable, ask who is dealing with it. Re-roofing normally needs no Building Regulations application when under 25% of the building envelope and under 50% of the roof is affected, while larger jobs need approval and may bring a thermal upgrade with them. Where work is notifiable, Supreme explains the consent and deals with the notification. Whoever you choose, ask who makes the application and who holds the certificate.

Ask for an itemised quote, not a single figure. The checklist at what a roofing quote should include is a good guide to what the answer should look like.

Roof work is weather-dependent, and a builder with several jobs on may not be able to give the roof the attention a specialist can. Ask for the expected length of the job, and what will keep the house dry if rain arrives halfway through. A specialist should also be able to say how the roof is sheeted overnight, and in what order the slopes are opened, so no more is exposed than can be closed up the same day. Our page on how long roof jobs take gives a sense of what to expect.

For choosing between firms of the same trade, see how to choose a roofer in Stroud, which sets out the questions and paperwork to ask for.

Roofing is what Supreme Roofing Stroud does, across the Five Valleys and every town within 30 road miles. We publish typical costs before a visit, survey your roof with photographs, and put an itemised quote in writing. If your project is mostly something else, ask us to deal with the roof alone and let the builder handle the rest. That split is a perfectly sensible one, and it keeps each trade doing the work it knows best. It also makes the roof quote easy to compare with any other roofing quote you receive, since the figures stand on their own rather than sitting inside a builder's lump sum.