The short answer
Yes, a single slope can be stripped and re-covered alone when the opposite side is still sound. The test is whether the tiles or slates on the other side have years left, and whether the new covering will sit well beside them. Below 25 per cent of the building envelope and 50 per cent of the roof, building control is not normally involved.
When a single slope is the right job
Roofs do not age evenly. The slope that faces south-west takes the hardest rain and the longest hours of sun, and a north-facing slope stays damp and mossy for longer. It is common to find one side of a house worn out while the other still sheds water well. If the failing side is the only side with slipped tiles, flaking slates or a sagging line, re-covering that slope alone is a fair proposal.
It is less sensible when the two slopes share an age and were covered in one go, because the second side will probably need doing within a few years. Paying for scaffolding twice is the usual regret. A survey that looks at both slopes, with photographs, is how you decide, and it is a good moment to ask what the covering on the other side is likely to do next.
Look at the battens and underlay too. A slope with sound tiles can still hide a rotten batten run, and the reverse is also true: tired tiles over good timber may only need relaying. Lead flashings, valleys and verge details on the slope you are leaving alone deserve a check too, because repairs cost less while the scaffold is already up.
Making old and new covering sit together
The hardest part of a one-sided job is the look. New tiles are usually a different colour from weathered ones, and the difference shows on a house with a prominent roof. Concrete tiles fade, clay tiles pick up lichen, and slate dulls. For a few seasons the new side looks like a patch, and then the tones draw closer.
There are ways to soften it. Reclaimed tiles of the same profile blend faster than new ones. A tile of the same make and profile, in a similar colour, helps on estate houses where the manufacturer still sells it. On a pair of semi-detached houses, a join along the shared ridge is easier to live with than a join down the middle of a slope, because the ridge is a natural break. Where the two sides meet at a hip or valley, the detail has to be done properly, and our page on the eaves, fascias and gutters shows how those edges are finished.
How the 25 and 50 per cent limits are read
Two separate measures decide whether a one-sided job needs approval, and both come from the Planning Portal.
| Measure | Stays below |
|---|---|
| Total building envelope | 25 per cent |
| The roof itself | 50 per cent |
The envelope is the whole outer shell of the house, glazing and doors included, so a single slope is usually far inside the first figure. The second is the one to watch, because one side of a simple gable roof is half of it by area. A common misreading applies the quarter figure to the roof itself, which mixes the two measures up.
Pass either figure and approval comes into play, with possible extra work such as upgrading the roof insulation to current standards. That extra work is set by Part L of the Building Regulations. We explain where your job sits and handle the building control notification where work is notifiable, so the arithmetic does not fall to you.
When the new covering is heavier or different
Changing the type of covering on one side brings its own checks. The Planning Portal puts the line at a new covering weighing 15 per cent or more above the old one. Approved Document A words it as a loading increase of more than 15%. Swap light concrete tiles for natural stone or clay on one slope and you add load to rafters that were sized for something else. Our page on a heavier roof covering sets out how that check works.
Fire performance matters too, since a new covering with a different fire rating is another trigger. The easiest route is to keep the same material and weight on both slopes. If you fancy a change of look, raise it at the survey so the rafters can be checked before anyone orders tiles, and so a mismatch between the two sides is a choice rather than a surprise.
Chimneys, party walls and other awkward edges
Where the slope meets a chimney, the flashings and soakers have to come apart and go back, and the stack may deserve attention while the roof is open. Our note on chimney work during a re-roof covers the order of work. On a semi or terrace, the slope also meets the neighbour's roof along the party wall, and that abutment must be sealed so rain cannot slip through the join. Tell the neighbour before the scaffold goes up, since the boards and the noise will be right beside their loft and garden for the duration of the work. A short chat saves awkwardness later, and it is polite.
Living in the house while it happens is possible, and our guide to staying at home during a re-roof sets out what to expect. For the whole picture, see roof replacement. Our survey takes in both slopes, and the written quote that follows carries photographs of each, and the pictures show you why one side or both is the better call. A 10-year workmanship guarantee is given in writing, and the old tiles leave with us when the site is tidied.