The short answer
Yes. A pitched roof is often done in two stages, and its two halves of a pitched roof are separate surfaces that can be re-covered on different dates. The Planning Portal test looks at less than 50 per cent of the roof, so one slope of a plain gable sits near the edge of it. Matching the old half is the harder part.
Why one slope often goes first
A pitched roof is made of slopes, and each slope weathers on its own terms. The side that faces the prevailing rain, or the one that takes the afternoon sun, tends to age first. Moss, cracked tiles and slipped slates collect there while the opposite side stays sound. So a request to replace half the roof usually means one failing slope next to one that still has years left.
The roof is not one sheet that has to be done in a single go. Each slope has its own battens, the timber strips that carry the covering, and its own underlay, the membrane under the tiles. A roofer can strip one side, renew what is below, re-cover it and leave the other side untouched, with the ridge and the verges as the places where the two sides meet.
That junction needs care. The ridge is the top line where the slopes join, and the verge is the edge at a gable end. Both have to be taken apart and rebuilt where the new slope meets the old, and we photograph both before work starts so the evidence is yours to look at and nothing rests on our word.
The 50 per cent of roof threshold
The Planning Portal gives a two-part test for skipping a building control application on a re-roof: under 25 per cent of the building envelope and under 50 per cent of the roof. On a simple two-slope roof, one slope is close to 50 per cent of the roof area, so the figure needs measuring, not assuming. A slope that is a little over half the roof area can tip the job past it.
The other limb, the building envelope share, matters too. The envelope covers the walls, the floor, the roof and every window and door added together, so a single slope usually sits well inside the 25 per cent limit on a house of normal size.
The portal adds that a covering 15 per cent or more heavier, or one that behaves quite differently in a fire, brings approval into play. Putting concrete tiles on one side of a slate roof would raise exactly that point. Councils around Farnborough give no percentage of their own, so the national test is the guide for Rushmoor addresses. In Bracknell Forest, Basingstoke and Deane and Windsor and Maidenhead the council's own wording on re-covering is worth reading first.
Matching the half that stays
The practical question is how the new half will look next to the old one. Tiles fade, lichen settles in the pores and mortar goes dark. Brand new tiles beside a weathered slope will look different for several years, whatever the maker's colour reference says.
Where the existing covering is still in production, a roofer can often match the profile and the colour closely enough that the join is hard to spot from the road. Where the old tile is discontinued, there are three routes: a reclaimed tile of the same type, a close modern equivalent on one slope, or a covering chosen to suit both slopes if the whole roof will be done within a few years.
Fitting two different profiles on one roof also changes the details at the ridge, and the page on reusing old roof tiles covers the reclaimed route. Whatever the choice, a slope in a conservation area or on a listed house needs the right consent first. A front slope is the one most likely to be controlled, so we ask which slope faces the street before we price anything.
What we measure before we agree a scope
The survey decides this, not a rule of thumb. We measure both slopes, photograph the tiles, battens and underlay on the failing side, and look at the loft side of the other slope. If the sound slope has tired timber or torn underlay, replacing the first half only means paying for scaffold twice.
Scaffold is the cost that most often changes the answer. Putting it up for one slope and then again two years later for the second is a poor way to spend money, and sometimes the better value is to do both slopes in one visit. The next page on replacing roof timbers sets out what we look for in the rafters beneath.
You see the photos and hear the findings in plain words, then receive a single written price. If one slope will do, we recommend that. If the other side is close behind it, we tell you that too and leave the choice with you. Our roof replacement page covers how a job runs from the first visit to the final tidy-up, and what happens if the weather turns during the work.
