Roof replacement in Basingstoke

What we find

From the pavement a roof looks like one surface. In fact it is a stack of layers, and the tiles are the least important of them. Under the covering sit the battens, thin timber strips the tiles hang from, and under those the underlay, a membrane meant to catch any water that gets past the tiles. Beneath that are the rafters, the sloping timbers that carry everything, and at the bottom edge the wall plate they rest on.

On roofs from the 1960s and 1970s around Basingstoke we regularly meet the original bitumen felt underlay, which has dried, split and fallen away in strips, so the tiles have been the only defence for years. Battens can be soft where nail holes have let water in, and rafter feet at the eaves are the first timbers to rot when a gutter has overflowed for a long time. We also find tiles that were laid without any underlay at all on older roofs, and loft insulation that has been pushed hard against the underside, leaving no air gap.

None of this can be judged properly until the covering is off, which is why the survey looks from the loft as well, and why the quote has to say what happens if more is found.

What we find

Most people start by asking for like for like, and often that is the right answer. A house with a plain clay tile roof in an older part of Basingstoke or Old Basing looks right with clay, and the planners will usually expect it. A 1970s estate house with concrete interlocking tiles is simply built for that weight and that appearance.

The question is whether like for like is available and sensible. Some profiles of concrete tile went out of production years ago, so a match may mean reclaimed tiles or a close modern profile. A thin, weathered concrete tile that has lost its surface coating will not match a new one for colour. Clay and natural slate cost more than concrete, but they last longer and look better on the right house. Man-made slates and lighter tiles cost less, and suit some roofs better than others.

Weight is the other factor. Building Regulations approval is needed where the new covering weighs 15% more than the old, or beyond that, and the structure may need to be checked or strengthened, under Approved Document A. People swapping a thin slate for heavy concrete tile, or the other way round, are surprised by that.

What we find

This is the question that separates a re-roof from a repair in many quotes. Sometimes the tiles are in decent condition, and a cheaper quote proposes to lift them, brush down the old felt, and put them back. It is worth understanding what you are buying.

Underlay and battens have a shorter life than the tiles above them. Felt laid in the middle of the last century dries and cracks as it ages. Battens are softwood, and where a nail has let water in they rot slowly from that point. If the tiles go back onto old underlay and battens, the roof looks new but its hidden layers are still as old as they were, and the next leak is only a matter of time. Re-using tiles has its own risks: old concrete tiles can be brittle and break when lifted, and clay tiles with spalled faces, where the surface has flaked off in frosts, will not last another winter or two.

Ventilation matters as well. A roof space with no air movement lets warm damp air from the house condense on cold timber, and over time that rots rafters and damages insulation. Many older roofs were built when felt let moisture escape through gaps, so a tight modern covering can change how the loft behaves.

What we find

A fixed price for a new roof is built from a handful of large items, and most differences between quotes come down to which of them are included. The biggest is the size and shape of the roof: a simple gable with two long slopes is far cheaper per square metre than a roof cut up with hips, valleys, dormers, chimneys and a rear extension. Each valley, the inside corner formed where two slopes meet, adds lead or a purpose-made valley tile, and extra cutting.

The covering you choose is the next factor, from concrete tile at the lower end to natural slate at the upper end. After that come scaffolding, which on a house with a lean-to or a tall side can cost a good deal, then the timber repairs the strip reveals, the fascias, soffits and gutters if they are being replaced at the same time, and the lead around chimneys, abutments and dormers.

Cost guides that publish typical UK ranges are useful as a sense check but they cover very different roofs. The reported range for a new roof on a standard semi-detached or detached house is wide for a reason. A vague quote with one number for the lot makes it impossible to see what you are paying for or to compare it with another.

What we find

Many homeowners assume that putting new tiles on an old roof is outside the Building Regulations, and a small repair usually is. A whole new roof is where the picture changes, and it is worth knowing before the work starts.

According to the Planning Portal, no building control application is normally required when the work touches under 25% of the total building envelope and under 50% of the roof. Beyond that, an application is needed. A roof is a thermal element, which means that re-covering it should include improving its insulation under Approved Document L, and where the work is above those limits the insulation of the whole roof may need upgrading.

There is a second trigger. Where the new covering weighs 15% more than the old or beyond, approval is needed and the structure may need strengthening, under Approved Document A. A third is a change to the shape or use of the roof, such as a loft conversion or a new rooflight, which has its own rules.

Homeowners are often told by builders that none of this applies, and then discover it when they sell and the buyer's solicitor asks for the paperwork.

What we find

The covering across the middle of a slope gets most of the attention, but the places a new roof tends to fail first are its edges. The ridge runs along the very top of the roof, a hip is the sloping edge where two slopes meet at an outside corner, and the verge is the edge of the roof at a gable end, where the tiles finish over the wall.

On older roofs these edges were bedded in mortar. Mortar cracks as the timbers move and frost gets into it, and ridge tiles then slip or fall. We find mortar that has crumbled to sand, ridge tiles sitting loose on top of a hollow bed, and verges where the cement has cracked away from the wall. Where a roof meets a chimney, a wall or a dormer, the junction is sealed by a flashing, a strip of lead dressed under the covering and over the upstand, and the old ones are often stuck on with mastic that has cracked.

These details are a small share of the area and a large share of the leaks.

What we find

A roof that leaks is not necessarily a roof that has failed. A single slipped tile, a failed flashing, a crumbled ridge or a blocked valley can each let water in, and each can be repaired for a fraction of the cost of a new roof. The mistake we hear about most is the roof replaced because of a leak that turned out to be one small fault.

The other mistake is the opposite one. A roof that has been repaired repeatedly, with one patch after another, is telling you something. When tiles keep slipping because the nibs on the back of them have broken, when the surface of the tiles is flaking, when the battens crumble as tiles are lifted, or when the underlay is missing from the whole slope, more repairs are money spent on a roof that will not hold.

Age alone does not settle it. A well-laid roof can last a very long time, and a poorly laid one can fail early. Moss and lichen look dramatic but are often only cosmetic. What matters is the condition of the layers you cannot see from the road.