In an attic almost every problem is caused by condensation on the underside of the roof — and that is not the same thing as a leak through a hole.
The attic is the part of a building almost nobody looks into, and that is exactly why problems there develop for years before anyone notices. When they are noticed, they usually show up as dark patches on the rafters, grey bloom on the boarding, or a heavy, fungal smell coming down through the hatch.
The mechanism is this. Warm, humid air from the living space rises — through the floor structure, through the hatch, through ventilation and cable penetrations. In the attic it meets the underside of the roof covering, which in winter is close to the outside temperature. If that surface is colder than the dew point, moisture condenses on it. In cold weather it can freeze and later, in a thaw, drip onto the insulation.
| What you see in the attic | What it usually means |
|---|---|
| An even grey bloom on the boarding | Condensation and inadequate roof ventilation |
| Dark patches on the rafters | Prolonged high moisture in the timber surface |
| A local stain in one place by the chimney | A leak, not condensation |
| Compressed, heavy insulation | The wool has got wet and no longer insulates |
| Frost on the underside of the roof in winter | Warm room air is getting into the attic |
| A fungal smell through the hatch | Active mould in the attic space |
To that should be added another common cause that is not looked for in the roof itself. If a bathroom or kitchen extract discharges into the attic rather than outside the building, it is delivering exactly the humid air everything else is trying to keep out. An attic hatch that does not seal, and unsealed cable or pipe penetrations through the floor, do the same. These are cheap to fix, but only if somebody notices them.
This is the most important question in an attic, because the answer is completely different in each case. A leak is a roofer's job; condensation is a ventilation and building physics question. Treatment is not a solution to the cause in either case — it clears the effect.
A practical technique you can use yourself: tape a small piece of clear film over the suspect area with the edges sealed, and leave it for a few days. If moisture appears between the film and the surface, the moisture is coming from the material or from outside. If moisture collects on the room side of the film, it is condensation from the attic air. It is not a laboratory measurement, but in most cases it points the right way.
Treating mould under an active leak is money thrown away — establish the cause before treating.
If the signs are mixed, we say so openly at the inspection and do not claim more than we can see.
Another question people often ask: does mould in the attic affect the living space? In practice the effect is indirect and depends on how well the floor structure seals. If the attic hatch does not seal, or there are unsealed service penetrations through the floor, air from the attic gets down — and that is how the characteristic smell shows up, noticeably stronger upstairs than below. So on attic work we always look at the hatch and the penetrations too, not just the roof structure.
We look at the rafters, the boarding, the insulation and the ventilation openings across the whole attic.
We measure moisture in the timber and the insulation at several points, not only at the visible spot.
We establish whether it is condensation or a leak — what happens next depends on it.
We clear access to the affected surfaces and cover what must not be treated.
We remove the layer of mould from the timber surfaces and identify damaged insulation for replacement.
We treat the timber structures and the boarding, observing the contact time.
We set out what needs addressing in the roof ventilation or the floor structure so the problem does not recur.
An important distinction. We work with mould fungus on timber structures — the kind that grows on the surface and causes patches and smells. Wood-destroying organisms, which eat into the material and change its strength, are a different field and a different service; timber structure specialists assess and deal with those. If we see signs of it at the inspection, we say so and do not take on work that is not ours.
Attics also have practical working conditions that affect timing and planning:
More on how mould arises and what is done about it: mould removal. If a persistent smell comes down from the attic, ozone treatment also helps, because it acts on the air and on porous surfaces; on the causes — odour removal. An attic is rarely the only problem in a building, so we often look at it together with the basement and the other zones: private house disinfection, all property types.
For smaller buildings and a limited zone — from €55. By area: up to 100 m² — €1.20/m², 100–300 m² — €0.90/m², 300–1000 m² — €0.70/m². Ozone treatment for odour removal €1.20/m², minimum €60. If damp in the attic recurs every season, scheduled treatment sometimes makes more sense than a one-off job.
A leak is local, recurs in the same place and appears during rain. Condensation is broad, even, and appears in cold weather or in thaws even without rain. We establish which it is on site at the inspection.
Mould fungus on timber — yes. Wood-destroying organisms, which eat into the material and change the strength of the structure, are a different field and a different service.
Usually not. Damp wool no longer insulates and holds moisture for a long time. At the inspection we identify which areas ought to be replaced — the replacement itself is building work, not treatment.
Describe the situation — we will tell you whether treatment is needed at all, and which one.
Fill in the form — we will call you on the number you provide, ask a few clarifying questions and propose a solution.
Thank you! We will contact you on the phone number you provided shortly.
