Roof replacement, chimneys and roof structure in London

What a roof replacement costs in London, broken down

A London terrace typically has 70 to 90 square metres of roof surface once the pitch and the rear back addition are counted.

No published source gives a London-specific rate for this work, and we would rather tell you that than publish a number we cannot source.

The more useful thing is the breakdown. One homeowner priced a South London three-bed semi recode himself as skip £1,000, scaffolding £1,500, tiles and sundries £4,000, labour £2,000 and margin £2,500, giving about £10,000 all in, then received quotes of £21,000 and £23,000 and asked publicly what he was missing. Nobody answered him.

Here is what is usually missing from a self-priced estimate: leadwork to valleys, party wall abutments and around chimney stacks, dry-fix ridge and verge systems rather than mortar bedding, replacement of battens and any rotten timber found once the covering is off, a Part L insulation upgrade where triggered, a pavement licence for the scaffolding, waste disposal at London rates, and the contractor's insurance and warranty.

And here is what is usually missing from a contractor's quote: soffits, fascias and guttering. One homeowner confirmed both his quotes excluded all three and said they would be extra.

For comparison, an Edwardian terrace in the South East had quotes above £20,000 and was eventually re-roofed for £13,000 including slate, battens, felt, scaffolding, skip and site clearance.

Roof repair or roof replacement, and the Part L trigger

Patching keeps looking cheaper right up until it is not. One homeowner spent £6,000 to £7,000 over three years on repairs that mostly failed, and called it a false economy once the budget for a full re-roof finally existed.

Against that, plenty of roofs do not need replacing. Another homeowner was told she needed a new roof and was advised by others, correctly, that a few slipped and broken tiles are not a leaking roof. Get someone to look properly, from the roof rather than the ground, before accepting a replacement.

Diagnosis genuinely fails. One homeowner spent significantly on roof work and was told afterwards that a new roof might not have fixed her problem anyway, because the issue was the pitch, and nobody had mentioned it.

The Part L trigger. Stripping and re-covering more than half of a roof counts as renovating a thermal element, which brings an obligation to upgrade the insulation. That turns a like-for-like re-covering into a bigger job with a bigger price, and it is legitimate rather than a contractor adding scope. It is also the moment to do it, because the roof is open.

Sagging rooflines: spread, rot and the trussed roof question

With the covering and the stack accounted for, the third thing that goes wrong on a London roof is the structure holding it all up, and a new covering does not touch it. A dipping roofline is usually the structure spreading, not timber rotting. The two look identical from the pavement and cost very different amounts.

Roof spread is the common cause and it is structural. A pitched roof pushes outwards as well as downwards. That thrust is resisted by ties, usually the ceiling joists, and by the purlins carrying the rafters. If those ties have been cut, weakened or were never adequate, the rafter feet push the tops of the walls outwards, the ridge drops, and the roofline dips in the middle. The signs are outward: a bulge or lean at the top of the external wall, cracking below the eaves, gaps where ceilings meet walls in upstairs rooms, and doors upstairs that have stopped closing. A roof that has spread does not need new tiles. It needs the structure tying back and, sometimes, the wall restraining.

Rot is localised and starts where water gets in: rafter feet at the eaves, timbers around a chimney abutment, purlin ends built into a damp wall. It shows as soft, dark or crumbling timber rather than a dipping line.

Then the question that decides whether a loft conversion is straightforward or expensive. A cut roof is built on site from individual rafters, purlins and ceiling joists, leaving an open triangular void, and converting it is comparatively simple. Most London stock built before roughly the 1960s is a cut roof. A trussed rafter roof is prefabricated triangular frames with webbing across the void, and it is structurally dependent on that webbing, so you cannot simply remove it to make a room. Converting a trussed roof means installing a new structural frame, usually steel, before the trusses come out. That is a significant additional cost and the most common reason a loft conversion comes back more expensive than expected. You can usually tell by looking: individual timbers of different sizes with a horizontal purlin along the slope is a cut roof, repeated identical frames with diagonal webbing is trussed.

We publish no cost figure for roof structure repair, and that is deliberate. No published cost guide prices it, because it is not a job people shop for by name. Any figure we gave you would be our own arithmetic dressed up as a benchmark. What determines it is how much structure is affected, whether the walls need restraining as well, whether the covering has to come off, and whether a structural engineer's design is needed, which it usually is.

How a Beams roofing project works

Step 1: Get your estimate

Tell us the property, the covering it has now and what is going wrong: a leak, crumbling mortar, a leaning stack, or a dip in the roofline. Your planner gives you an estimate range before any commitment.

Step 2: Inspect, diagnose and specify

The roof inspected properly, from the roof and from inside rather than from the ground. Area measured, covering and leadwork specified, the Part L position established, access and any pavement licence arranged, the Party Wall position checked where a stack is shared, and a structural engineer's assessment where anything suggests spread.

Step 3: Built by your vetted builder

Under a fixed-price contract with milestone payments held securely until you approve each stage. 12-month workmanship warranty included.

We work with vetted builders and engineers across all London postcodes, in North, South, East and West London. London roofs sit close together, frequently share stacks and abutments with next door, and almost always need pavement scaffolding. Conservation areas often require natural slate rather than a cheaper covering, which is the single biggest difference between a London quote and a national cost guide. Most London stock is a cut roof, which is good news for loft conversions and also means purlin ends built into damp party walls are a common failure point.