Can you replace just one side of a roof?

When one slope on its own makes sense

Roofs rarely age evenly. The slope that faces the prevailing weather takes more rain, more wind and more sun, and it tends to wear out first. A slope in the shade of a taller building may stay damp and grow moss, which brings its own problems. It is common to find one side in poor shape while the opposite side has years left in it.

Renewing a single slope is a sound choice when the following hold.

• The fault is confined to that side. Slipped tiles, rotten battens and a damp underside are all on the one slope, and the timbers of the other are dry.
• The covering is the same on both sides. Then new material can be matched in kind, so the house keeps a consistent look.
• The ridge and the other slope are in good order. A worn ridge costs little to renew alongside the slope, whereas a failing opposite side argues for looking at the full roof.
• The structure is sound. A sagging rafter or a spreading wall points to a bigger job.

Our roof survey records both slopes, so the decision rests on photographs of the actual roof rather than on a guess from the ground.

When the whole roof is the better call

There are cases where a half-roof job costs more in the long run. If both slopes were laid at the same time, with the same materials, they have had the same amount of ageing. The second side may have a year or two left, or ten. A roofer who has seen the underside of both can tell you which, but you should expect the answer to be that the second slope is close behind.

Scaffolding is the other consideration. Scaffold is often a large share of the bill on a roof job, and putting it up twice means paying for it twice. MyBuilder's 2026 guide reports scaffolding adding about £1,125 to a typical roof replacement in the UK. If the other slope will need work within a few years, doing both together may spare you a second scaffold.

Shared details matter too. A hip roof has four slopes that meet at hips and a ridge, and renewing one means working into lead and ridge tiles that serve the others. A roof with a valley, the channel formed where two slopes join, may need the valley lead lifted on both sides whichever slope is being done. In those cases a single-slope price can be misleading, because the shared work has to be done anyway.

Ask your roofer to price the single slope and the full roof together. The difference, set against the condition of the second side, usually makes the answer clear.

Matching new to old

The visible join is where a part-roof job is judged. New tiles or slates sit next to a covering that has weathered for years, so the first rule is to choose the same material. Slate goes back as slate, clay as clay and stone tiles as stone. A different covering on one side changes the weight and the look, and on an older house it can look like an afterthought from the street.

Size and gauge come next. Slate, for instance, is cut in many sizes, and the new slate needs to match the old in length and width so that the courses line up at the ridge. Reclaimed material can help. Sound slates or tiles from a stripped roof, or from salvage, carry the same weathering as the originals and settle in far more quietly than new stock.

Colour will differ for a while. New material is brighter, and a few seasons of weather bring it closer to the older side. That is normal and not a sign of a poor match. Where the front of the house faces a street, a sensible plan is to put reclaimed material on the visible slope and new material where it cannot be seen from the road.

We match materials on older roofs as a matter of course, because our aim is to put right the roof the house was given originally.

How the two sides are joined

The ridge is where the new slope meets the old. The ridge tiles, which cap the apex of the roof, are lifted along the length of the work. They are bedded back and mechanically fixed, since BS 5534:2014 asks for mechanical fixing on these tiles. A dry-fix system, tested to BS 8612:2018, is one route to that.

At the ends sits the verge, the roof's sloping edge beside a gable. Where it borders the new slope it must be sealed and fixed in the same way as the old, so water cannot work its way into the wall. If the slope runs into a chimney or a higher wall, the lead flashing along that line is renewed with the covering, because a new roof sealed with a tired flashing is still a leak waiting to happen.

Underneath, new battens and underlay are carried up to the ridge and lapped so the old and new underlay shed water in the same direction. The roofer also checks the ventilation, since a changed underlay can alter how the loft breathes.

Inside the loft, a clean line of new timber beside older rafters is quite normal. The work is judged by what happens at those joints in the first wet winter, not by how neat the line looks from above.

Permission, timing and the paperwork

A single slope can fall below the Building Regulations thresholds. Under the Planning Portal guidance, jobs affecting under 25 per cent of the building envelope and under 50 per cent of the roof generally escape approval, so the share of the roof that the slope represents decides it. A change to a heavier covering, by 15 per cent or more, needs approval whatever the area. Check with your building control body if you are unsure.

Planning also matters where the property is listed or falls inside a conservation area, because the covering itself is then a consent question. In Bath, B&NES Council decides listed building consent, and starting without it is an offence, even if only one slope is involved. Ring the council first.

Timing is flexible, though settled weather helps. The reasoning behind choosing a season for the work applies equally to a half-roof job. If you are weighing this against a full renewal, strip and re-cover sets out what a whole-roof quote includes.

When the work is finished, go through it with a checklist. Our guide to the new roof handover lists what to look for at the new join. For the full picture of the service, see roof replacement. A survey comes first, and our workmanship is backed by a ten-year guarantee in writing.