Clamping down on condensation.

Clamping down on condensation.

Landlords often blame tenants’ bad habits for condensation in rental properties, but you can make your properties much less prone to it. It’s also easy to confuse extreme condensation in poorly-insulated houses for penetrating damp. The key to stopping condensation is making all the interior surfaces warm. Ventilation is important too, particularly fans in bathrooms and kitchens. A bathroom should have a 100mm fan, and a kitchen a 100mm vented cooker hood, or a 150mm fan if not directly above the hob. Opening windows on the windward side of the building won’t help as it just blows damp air into the rest of the building. Current Building regulations specify high standards of air-tightness for residential buildings, keeping occupants warm and saving power. Insisting that tenants open windows or use constant extractors in cold weather is unreasonable when the fault is poor insulation.

ondensation at edge of poorly-insulated bathroom ceiling

Keeping inside surfaces warm is not difficult or expensive compared to the cost of extra heating, and grants are often available through the council. Ceilings should be insulated with a minimum of 270mm fibreglass to meet current standards, which should not be squashed by stored junk! Even 100mm will make a massive difference. The edges of the ceiling adjacent to outside walls get cold more easily and insulation should be pushed right into the corners, without obscuring any air-vents into the attic.

Cavity walls can be filled from the outside with little disturbance to tenants. Solid outside walls can be insulated with thin insulating ‘papers’ like Sempatap. It’s not hard to apply and only 10mm thick so doesn’t require re-fitting of skirtings, door linings etc. It can make a massive difference to the surface temperature of walls, with concomitant reductions in condensation. It still falls well short of building regs standards for renovated property, which normally requires 50mm of closed-cell phenolic foam insulation for solid walls. This is MANDATORY if you’re replacing more than 25% of plaster on any outside-facing wall. It’s particularly important to insulate around the bottoms of windows as they commonly accumulate heavy condensation.

Single-glazed windows in well-insulated homes often attract massive condensation. If double glazing is too expensive, consider secondary glazing, which often gives better insulation anyway because of the larger gap. If this is still to expensive, you can improvise with clingfilm over window casements to create a gap between the glass. You’ll also need to thoroughly seal all drafts between casements and frames with brush- or foam-type draft excluders.

Condensation mould can grow where wardrobes or pictures restrict ventilation of poorly-insulated outside walls. Moving them usually sorts the problem.

The bonus of all this condensation-prevention is it keeps your tenants warm and their heating bills down. Warm tenants with low bills are less likely to leave your property!

So far I’ve given three causes of damp: rising, penetrating, and condensation. As a builder I’ve found people often confuse them, so I should identify some of the odd sources of damp which confuse people the most. Did you know that Jackdaws can cause damp in older houses – I’ll explain how next week.


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