A roof put up before the days of sarked felt, plastic underlay and mortar-free fixings follows its own logic. Slates hang on nails or pegs over battens, with nothing underneath but air and the occasional bird's nest. Timbers are hand-sawn and sometimes reused from older buildings. Walls are bedded in lime, and the lime is doing a job that cement would undo. When someone climbs a ladder to assess a roof like that, they need to know what they are looking at before they say what is wrong with it.
This guide sets out what a sensible survey of a period roof covers, which findings are normal for an old building and which are not, and how to read a report so that the repairs match the house. The wider picture sits on our roof inspections and surveys page.
What makes a period roof different to survey
Newer roofs are layered: covering, battens, underlay, rafters, ceiling. If the top layer lets a little water through, the membrane below carries it to the gutter. A period roof usually has no such second line of defence. The slates or tiles are the whole waterproofing, and the loft beneath them has been ventilated by every gap between the slates for a hundred years or more.
That changes what a defect means. One slipped slate on a modern roof is a tidy-up. On an unfelted roof it is a direct opening to the rafters, and the damage may already show as dark staining on the timber below. Equally, a few gaps of daylight seen from inside are not automatically a fault, because a lot of old roofs breathe that way and the timbers have stayed dry because of it.
Why is the age of the building a starting point, not a verdict?
Age tells a surveyor what to expect, nothing more. A terrace from the 1890s may have been re-roofed once in the 1960s with different slates, and then patched by three owners. The roof keeps its own diary: odd slate sizes, two kinds of nail, a patch in a different material. Each entry shows where it has failed before.
Unfelted slate and tile roofs
Look at the underside of a Victorian slate roof from the loft with the lights off on a bright day and you may see pinpricks of light between the courses. That is normal on a roof with no underlay. Rain that is blown through during a storm usually lands on the laths or battens and dries out again. What a surveyor looks for is the line between that harmless breathing and the point where water starts to reach structural timbers.
The checks follow a pattern. Surveyors look at the battens or laths for dark rot at the nail positions, at the rafters for staining that runs in a line below a gap, and at the wall plates, where rainwater tends to collect. They also note whether the roof was ever sprayed or lined from underneath, because a skim of insulating foam over old rafters can hide trouble that would otherwise be visible. Our guide to surveying before a re-roof explains how those findings feed into a scope of work.
What is nail sickness and why does it matter here?
Old slates were hung on iron nails, and iron rusts. After many decades the nails thin until the slate's weight shears them, and slates slide down in lines. A run of slipped slates along one course tells a surveyor the fixings are failing widely. A handful can be refixed with tingles, the small strips of copper or lead that hold a replacement slate. Dozens across a slope point to a re-slate.
Lime, mortar and the pointing question
Before the twentieth century, brickwork, stone and roof details were bedded in lime mortar. Lime is softer than cement, lets moisture out of a wall, and flexes slightly as a building moves. Modern cement-heavy repointing is harder and denser than the brick or stone around it, so water that gets in cannot leave the way it used to, and the face of the masonry flakes off instead of the joint. A roof survey notices this wherever mortar meets the roof: chimney stacks, parapets, gable copings, verges and the abutment where a slope meets a wall.
Is cement pointing on a chimney always a problem?
Not always, but it earns a note. Where a stack has been repointed in hard cement and the bricks are now spalling, the next repair should use a lime mortar that suits the masonry. Where the brickwork is a later and harder brick, the answer can differ. The survey should say which situation you have, with a photograph of the stack, and not default to either.
What about the verges and ridge on an old roof?
Ridge and verge bedding on older roofs was often lime, later patched with cement. Under the 2014 revision of BS 5534, any repair pins the ridge down with clips or screws as well, and on a period building that has to happen without altering the ridge line. Our ridge, verge and dry-fix page explains the fixings available, and a survey will note where traditional appearance matters.
Timbers: what to look at and what a roofer can and cannot say
The timbers in a period roof deserve a slow look. Old rafters are often slender by modern standards and may have shifted a little over time. A slight sag along a ridge line can be a historic settlement that stopped long ago, or it can be a sign of rot at a wall plate or a purlin that has deflected under the weight of a heavier covering fitted at some point in the past.
A roofer's survey records what can be seen and handled: dark or soft areas at rafter feet, wall plates damp to the touch, old woodworm flight holes, daylight through a broken timber, and signs of past repairs such as sistered rafters. It also records which areas could not be reached. Where the readings suggest an active beetle problem or an extensive rot, the right step is to bring in a specialist timber surveyor. That is a different discipline, and our short answer on roof timber surveys covers when it is needed.
Does a sagging roof mean the structure is failing?
Not on its own. Many old roofs have a gentle undulation that is part of their character, and the framing underneath is still performing. A survey separates old movement that has settled from movement that is still happening. Fresh cracking in plaster below, gaps opening at a party wall, or a ridge that has moved since the last visit all point the second way.
Why does weight matter?
Because a period frame was designed for one kind of covering. A heavy replacement, such as swapping slate for concrete tile, loads timbers that were never sized for it. The Planning Portal puts the line at 15 per cent or more extra weight from a new covering, beyond which Building Regulations approval applies, so a surveyor flags any plan near it.
Stone slate, clay tile and the coverings of older homes
Swindon sits between several roofing traditions. Around the Railway Village, slate is the local rule, and the council's appraisal says so in as many words. To the north, in the Cotswold edge villages, stone slates are the local material. Further south and east, clay plain tiles and hand-made peg tiles appear on older farmhouses and cottages. A survey adjusts its questions to the covering in front of it.
How is a stone slate roof assessed?
Stone slate is heavy: Cotswold District Council's technical guidance puts it at about 1000 kg per 10 sq m. Big slates sit low and small ones high, in what roofers call diminishing courses, and many hang from oak pegs. The same guidance says it is common to find about 50% of the slates perished once such a roof is stripped. A surveyor watches for stone that peels in layers after frost and for rotted pegs that let slates drop.
What do clay tiles show?
Clay plain tiles are checked for flaking faces, snapped nibs and the pegs or clips that hold them to the batten. Handmade tiles have a camber and colour that belong to the look, so replacements are matched. Cost guides quote lifespans that vary widely, and the Building Conservation Directory records peg-tiled roofs several centuries into their lives, so age alone says little about what is left.
Our page on slate roofing covers the natural slate side in more detail.
Listed buildings, conservation areas and consent
A period roof is often in a protected setting, and the survey should record that early, because it decides what repairs are allowed without further steps. Relaying the same material in the same style rarely needs planning permission, yet that is not true of every old house. A listed house needs listed building consent for alterations that touch its character, and going ahead without it is an offence. In a conservation area, an Article 4 direction can take away permitted development rights.
Swindon is a useful example. The council's conservation area list includes Swindon Old Town, Wroughton, Highworth and Chiseldon among many others, and notes Article 4 directions for Bishopstone and the Railway Village. In the Railway Village the cottages were listed in 1970, and the council's own appraisal says dishes and aerials fixed to roofs or chimneys are discouraged and need planning permission.
Who do I ask before work starts?
The local planning authority decides. For addresses in the borough, check with Swindon Borough Council's planning team. The council's conservation team has a published email on its conservation areas page. If your property lies elsewhere, the relevant district or unitary council applies.
A survey does not give consent. It tells you whether consent is likely to be an issue, so you can ask the right question before work is priced.
Our guide to listed roof repairs covers the permissions side in more depth.
Reading the report and choosing the right repair
A report on a period roof should do three things. It should describe the roof as built and as altered. It should rank defects by what they threaten: active leaks and loose elements first, deterioration that will become a leak next, and cosmetic points last. And it should propose work in proportion, which on an old building usually means repair first and replacement only where the fabric has run out.
The Skyline survey follows that order. We climb or use access equipment where it is safe to, look at the loft from inside, and take photographs of your roof that come with a written quote after the visit. We would rather fix the fault than sell you a bigger job, and on a period roof that often means refixing slates, relaying one failed patch or renewing a valley while the rest stays put.
When is full replacement the better answer?
When the nails have gone across a whole slope, the battens beneath are rotten, or perished slates outnumber the sound ones. Even then, a good report suggests reusing sound slates on the most visible slope and using matched material elsewhere.
What should I do with the report afterwards?
Keep it with the house records. A dated record of the roof's condition, with photographs, helps if you later sell, apply for a home improvement grant, or need to show an insurer what the roof was like before a storm. Our page on roof reports for insurance explains how far a report can help and where it cannot, and the answer on how a roof is measured for a quote covers the sizing behind the price. For flat sections such as a rear extension or porch, see the flat roof survey guide.