Damp and mould
Condensation and damp in a stone tenement
Condensation in a tenement flat is a sign of too much moisture in the air indoors, and Historic Environment Scotland says the most effective fix is to cut that moisture at source.
By the Pipes Up the Stair site team · how pages are checked · Updated
Streaming sash windows on a January morning are part of tenement life from Gorgie to the New Town. They are a symptom, not the fault itself, and the fixes are mostly about habits and airflow rather than new windows.
The advice below comes mainly from Historic Environment Scotland's short guides on traditional buildings, which suit thick stone walls and timber sashes far better than advice written for modern houses.
Why do tenement windows run with condensation?
Because everyday living puts water into the air. Historic Environment Scotland says breathing, drying clothes, cooking and bathing all add moisture, and that condensation on a window is a sign of excess moisture inside, not a fault with the window itself.
What is the most effective fix?
Reduce the moisture you make. The same guide says the most effective method is to reduce the internal moisture load: dry clothes outside or in a well-ventilated room, open windows after baths and showers, and run extract fans during and after cooking and bathing.
How should you air a stone flat?
Little and often. Historic Environment Scotland's guide on mould says it is healthy to cross ventilate buildings for short periods every day, and that a sash window opened slightly at top and bottom gives a gentle flow of air. Its energy advice adds that draught-proofing is fine, but you must be careful to retain adequate ventilation.
Where should an extract fan vent?
Straight outside. Historic Environment Scotland warns that a fan should vent directly outside, or it simply moves the moisture problem elsewhere in the building. On listed buildings and in conservation areas, the City of Edinburgh Council says mechanical extractor fans should be located on rear or side elevations, not in windows, fanlights or on the front. A new fan in a bathroom may be part of a wider job; see bathroom refit in a tenement flat.
What about old fireplaces?
Keep them breathing. The condensation guide says disused chimneys should be vented both within the room and at the top of the stack. A chimney stack that serves several flats is shared property under the Tenements (Scotland) Act, so work at the top is for the owners to agree and a contractor to do, never a reason to climb onto the roof.
Is mould a health risk?
It can be. Historic Environment Scotland says mould may lead to respiratory infections, allergic rhinitis and asthma, and calls it a symptom of a wider failure in how a building handles moisture through ventilation, heating and insulation. If you rent, report mould to your landlord or letting agent rather than arranging work on the building.
Should you insulate stone walls from the inside?
Carefully, and with advice first. The condensation guide says insulating a solid masonry wall internally makes the masonry behind the insulation colder, raising the risk of condensation. It also says outside renders and pointing should be lime, which lets moisture pass, rather than impervious cement.
Could heavy condensation point to something else?
Occasionally, yes. HSE lists more condensation on windows among the signs that a gas appliance may not be burning properly, alongside yellow or orange flames and soot. A damp patch on a ceiling can also be water from the flat above; see leak into the flat below.
50
Edinburgh conservation areas, where fan siting matters
Source: City of Edinburgh Council planning
| Moisture source or part | Advice |
|---|---|
| Drying clothes | Outside, or in a well-ventilated room |
| Baths and showers | Open windows afterwards, run the fan during and after |
| Extract fans | Vent directly outside |
| Disused chimneys | Vent in the room and at the stack top |
| Pointing and render | Lime rather than impervious cement |
Asked on the stair
Is a dehumidifier a substitute for airing the flat?
Historic Environment Scotland puts cutting moisture and ventilating first. A dehumidifier does not change where the moisture comes from.
Should you block an old fireplace to stop draughts?
The guide says disused chimneys should stay vented in the room and at the stack top. Sealing one completely can trap moisture.
Is cement pointing on a sandstone tenement a problem?
Historic Environment Scotland says pointing and renders should be lime-based, because lime lets moisture move through and cement does not.
Does a trickle of air through the sash really help?
Yes. The mould guide notes that sash windows opened slightly at top and bottom give trickle ventilation.
Where this comes from
- Historic Environment Scotland: Condensation guide — moisture sources, chimneys, lime, internal insulation
- Historic Environment Scotland: Mould guide — health, ventilation, extract fans
- Historic Environment Scotland: Saving energy in traditional buildings — draught-proofing and ventilation
- City of Edinburgh Council: Listed buildings and conservation areas — extract fan siting
- City of Edinburgh Council: Conservation areas — 50 in Edinburgh
- HSE: Carbon monoxide — condensation as a warning sign
- Scottish Government: Carbon monoxide alarms in private rented properties guidance — CO alarm rule applies to all houses from 1 February 2022
- SGN: Carbon monoxide — symptoms that ease away from home: go straight to hospital