Case study: A detached house in north Yorkshire
with mould in rooms and damp roof timbers

cavity wall insulation
Damp roof timbers ... restricting ventilation encourages mould
... had caused rot in placesmould across a ceiling Internal lapvents bring fresh air
into the loft. severe mould in a bedroom
Severe mould in a bedroom
severe mould in a bedroom
Insulating a loft hatchsevere mould in a bedroom
improved extract fan


The problem

This property suffered from mould in the upstairs rooms and our survey revealed that the loft was very humid, the roof timbers showed very levels of dampness and as a result rot had set in in some places.

Our assessment

With only two occupants it is unusual to find a problem of damp and condensation in such a large house. However we found that changes had been made to the house over the years that had severely restricted ventilation.

In the upstairs rooms secondary glazing had been installed to reduce noise from low flying jet aircraft. The original window frames had been painted over so that it was not possible to open most of the windows.

The extract fan in the bathroom was ineffective and at some point the property had been re-roofed. This had included laying an impervious bitumen impregnated hessian underlay under the tiles. This had the effect of choking off all fresh air and over many years humidity levels had become so high that the roof timbers had become saturated causing rot to set in. This was not due to a leaking roof, but simply down to the lack of ventilation.

Our solution

We installed a number of internal roof vents to ventilate the loft. A return visit several weeks later showed that the moisture content of the timbers was sharply reduced as a result.

With a ventilated loft we were able to install a positive input ventilation system to bring fresh air into the house. We also installed a better extract fan with humidistat control and trickle function to effectively deal with the mould growth in the en-suite shower.

We trimmed the bottom off some doors to encourage air flow around the house and insulated the back of the loft hatch which makes it much less prone to attracting condensation and mould.

Finally we changed an existing external vent cover for one that didn't flap in the night and keep the occupants awake.

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See our page on solutions for condensation problems for further information.

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cold walls, no ventilation cause damp, condensation and mould