An old house is not simply an older one. Its roof has usually been repaired several times, the construction is not always what it looks like, and there are no drawings. So the usual sequence — choose a covering and lay it — does not apply. This article covers where to start, what can be learned without opening anything, which details are typical of old buildings and how to decide when part of the information will only emerge once the roof is stripped.
Why everything is different on an old building
On an old building, the unseen decides
Old roofs often have no vapour barrier, parapets too low, and unexpected layers under the covering. So the decision is made not from a catalogue but from what is revealed once the roof is opened.
In new build the design states what is in the roof. Refurbishing an old house starts from the unknown.
- The construction is unknown. It may be timber, lightweight concrete, precast units or a mixture.
- There are several layers. Each earlier repair often meant another covering over the old one.
- There is often no vapour barrier. Nobody thought about it when it was built.
- The fall is accidental. Or absent entirely.
- Parapets are low. There is little room for a new build-up.
- Details are non-standard. Chimneys, old aerials, timber eaves, out-of-square corners.
From which follows the central rule: on an old building you start with investigation, not with choosing a covering. The covering is the last decision, not the first.
What can be learned without opening up
Before any core sample, it is worth collecting what costs nothing.
- Inspection after rain. Wherever water still stands two days later, there is no fall.
- Pond marks in dry weather. Rims of settled dirt, often greenish.
- The structure from below. In the loft or top floor, staining, mould and timber condition are visible.
- Covering edges and details. At the parapets it is usually possible to see how many layers there are.
- Winter thermography. It shows damp zones and whether there is any insulation at all.
- The building’s history. When and what was done — often the best source is neighbours or previous owners.
That last point is not a joke. On an old building, people’s memory is often the only “design” that exists at all.
The core sample: the only real answer
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Everything else is assumption. Cutting a small area open reveals:
- How many layers there are and in what condition.
- Whether there is insulation and whether it is dry.
- Whether a vapour barrier exists.
- What the structural deck is and what state it is in.
- Whether water is trapped between the layers.
A core sample costs little, and the difference between “add a layer” and “strip everything” can run to several times over. On an old building it is not an optional extra but a necessary step.
It makes sense to take several samples in different places — condition on an old roof is often uneven: worse at outlets and parapets than in the field.
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the only real answer about the build-up: a core sample
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routes: overlay the old covering or strip it
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assumptions — an old roof is judged on fact, not a catalogue
Overlay or strip
The central decision, and three things determine it.
| Finding | Decision |
|---|---|
| One layer, dry, structure sound | Overlay is possible |
| Several layers but dry | Load is assessed – often already the limit |
| Wet in places | Those zones stripped, the rest left |
| Wet throughout | Everything stripped |
| Structure doubtful | Stripped so it can be assessed |
What matters most is understanding why wet insulation is never left. It will not dry — sealed between a barrier below and new covering above, it stays wet indefinitely. It also weighs more than dry insulation, and old structures have little reserve.
The second reason is practical: a new layer over an old one means the next repair will be harder still. Each generation passes the problem on, and the cost grows.
The height problem: low parapets
A typical old-building constraint that emerges late.
In older buildings parapets are often low — enough at the time, because the insulation layer was thin or absent. Add proper insulation with a fall today and the covering ends up almost at the top of the parapet, with no upstand height left.
The possible solutions:
- Strip the old layers. That often frees up exactly what is missing.
- Raise the parapet. Possible, but that is separate work with new flashings.
- Choose thinner insulation with better conductivity.
- Reduce the tapered layer thickness by replanning the outlet positions.
A practical note: levels are checked first, not after the materials are ordered. This is the commonest reason an old-building design changes mid-works.
Details that new buildings do not have
An old roof almost always carries elements for which no standard solution exists.
- Masonry chimneys. Often crumbling, unflashed, and sometimes no longer in use.
- Timber eaves and fascias. A decision is needed on whether they stay and how the covering meets them.
- Old aerial and cable mounts. Unused, but still piercing the covering.
- Out-of-square corners. The building has shifted over decades and right angles are gone.
- Differing levels. Extensions, additions, parts built at different times.
- Old outlets. Usually undersized and without leaf guards.
A useful principle in resolving these: whatever is no longer needed gets removed. An unused chimney is sealed and covered, old mounts are taken off, openings closed permanently. Every redundant detail left in place is a permanent point of risk.
The vapour barrier that isn’t there
Old roofs often simply do not have one, and that explains a great many problems.
Without a barrier, moisture from the rooms enters the construction freely. While the roof was poorly insulated and “breathed”, that caused no great trouble — moisture moved both ways. Add proper insulation without adding a barrier and the situation gets worse: the structure cools while the moisture keeps arriving.
So in refurbishment one nearly always has to be provided. The options:
- When stripping the old layers — the barrier goes onto a cleaned substrate. The simplest case.
- Without stripping — an old bituminous covering can sometimes serve as the barrier, if it is continuous and properly joined at the details. That is assessed specifically, not assumed.
- Where it cannot be assured — a ventilated build-up is considered.
The second point matters: an old covering becomes a barrier only once that has been verified, not because it happens to be there.
Timber construction in an old building
A common case, with rules of its own.
- Condition is assessed from below. Staining, white deposits and soft timber indicate prolonged damp.
- Ventilation is often essential. Timber is destroyed irreversibly by constant moisture.
- No flame directly onto timber. The first layer is mechanically fixed.
- The fall can be formed structurally — with firrings on the joists, which is cheaper than tapered boards.
We cover these questions in detail in our article on covering over a timber deck.
Old materials that cannot simply be taken away
Some old materials cannot simply be taken away
Some old roofs contain materials subject to special disposal requirements. Before stripping, it is worth establishing what lies under the covering, so a find does not become a mid-job surprise.
Stripping an old roof sometimes turns up materials subject to their own rules. It is worth knowing this in advance, because such a find during the works changes both the programme and the price.
Asbestos cement components. Older roofs may contain them as sheets, pipes, ventilation ducts or trims. This is hazardous waste that must not be broken up dry or taken away with ordinary construction debris. It is handled under separate requirements, by people equipped for it.
The practical consequences:
- The find is identified in advance where possible — during core sampling or while inspecting details.
- Disposal is priced separately and is not included in general waste costs.
- The programme lengthens. It is a separate stage, not part of the normal works.
- The contract should carry a scenario for such materials being found.
Old bituminous covering. Nor is that simple waste — depending on its age and composition it may be handled separately. So the number of layers stripped drives not only the labour but the disposal cost, which on an old building is a significant share.
The general rule is simple: if you do not know what a material is, do not break it up or take it away yourself. Identifying it costs less than dealing with the consequences.
When an old roof can still wait
Not every finding means work must start this year. It is only fair to say so, because a hurried decision sometimes costs more than waiting.
Can wait:
- Small ponds that do dry out, with sound covering.
- Loss of mineral surfacing without cracking.
- One or two details needing repair while everything else is good.
- Lack of insulation, provided there are no moisture problems.
Does not wait:
- Wet insulation — every season enlarges the affected zone.
- Timber structure showing signs of damp.
- Water entering the rooms.
- A single outlet with no overflow.
- Splits at details letting water into the build-up.
The difference between the two lists is one thing: whether the problem spreads or stays put. Worn surfacing waits; moisture in the construction does not.
If a decision is deferred, it is worth at least recording the current condition photographically and repeating the survey a year later. That shows whether the problem is growing or genuinely static.
Deciding when information is missing
On an old building, some things will only be known once the roof is open. That is a property of the building, not a shortcoming of the contractor. So the point is not to pretend everything is known but to agree in advance what will be done.
The practical method is a contract with scenarios:
- A base case based on what the core samples showed.
- A price for additional stripping if more moisture is found.
- A price for structural repair if the deck proves damaged.
- A decision procedure — who decides, and within what time, when something is found.
Such an agreement serves both sides. The client knows the limits, and the contractor is not forced to decide on their behalf with the roof open and rain coming.
What is worth doing at the same time
A roof is opened rarely, so it makes sense to deal with things that would cost incomparably more separately.
- Correcting the fall. The cheapest moment there is.
- Adding insulation, where the structure allows.
- Replacing outlets. Old ones are almost always undersized and without guards.
- Providing an overflow. Old buildings usually have none.
- Removing redundant details.
- Sorting out access and walkways.
The fourth deserves attention: an opening in the parapet costs little and answers the scenario where the only outlet blocks.
The most common mistakes
- Choosing the covering before investigating. Deciding without knowing what is in the roof.
- No core sample taken. The gap between scenarios is several times over.
- Wet insulation left in place. It will never dry.
- Another layer added. The problem is passed on at a higher price.
- Levels checked too late. It turns out there is no room for the build-up.
- No vapour barrier added. Insulation without one works against the structure.
- Redundant details left. Permanent risk points to no purpose.
- No agreement on scenarios. Decisions taken in haste with the roof open.
What drives the cost
- How many layers are stripped and how they are disposed of.
- Whether the structure needs repair.
- Whether insulation and a fall are added.
- Number and irregularity of details.
- Whether outlets and pipework are replaced.
- Access — lifting is harder in an old town centre or a dense setting.
General pricing is set out in our flat roof cost article.
An old roof with no documentation?
We survey with core samples and thermography – and tell you what genuinely needs doing and what does not.
How the refurbishment runs
Old roof refurbishment: 6 stages
Non-invasive survey
Ponding, details and the structure from below are assessed, and the building’s history collected.
Core samples
The covering is opened in several places. Layer count, moisture, barrier and structural condition are established.
Level check
Parapets and thresholds are measured. How much room remains for the new build-up is determined.
Decision with scenarios
A base case is agreed along with prices for further findings and a decision procedure.
Stripping and preparation
Old layers are removed, the structure repaired, redundant details eliminated and a barrier installed.
Fall, insulation and covering
The fall is formed, insulation and new covering laid. Outlets are replaced and an overflow provided.
Related reading
Frequently asked questions
With investigation, not with choosing a covering. In old buildings the construction is often unknown, there are several layers, no vapour barrier and an accidental fall. The covering is the last decision, not the first.
Effectively yes. Only by opening a small area can you see how many layers there are, whether the insulation is dry, whether a barrier exists and what condition the structure is in. The gap between “add a layer” and “strip everything” can be several times over, and a sample costs little.
No. Sealed between a barrier below and new covering above, it stays wet indefinitely. It also weighs more than dry insulation, and old structures have little reserve.
Stripping the old layers usually helps – it frees up just about what is missing. Other options: raise the parapet, choose thinner insulation with better conductivity, or replan the outlet positions. Above all, check levels before ordering materials.
Sometimes, if it is continuous and properly joined at the details. But that is assessed specifically rather than assumed. An old covering becomes a barrier only once that has been verified.
With scenarios: a base case from the core samples, a separate price for additional stripping, a price for structural repair, and a procedure setting out who decides and within what time when something is found. The client then knows the limits and the contractor does not decide on their behalf with the roof open.
