Case study: A semi-detached house in Leeds with mould problems

The problem

This 4-bed detached property is currently vacant and due for refurbishment. All the rooms on the first floor show signs of quite severe mould growth. Additionally there is a severe patch of dampness in the corner of the living room.

Our assessment

There were two separate problems in this house. The damp and condensation on the first floor was clearly caused by a lack of ventilation in a house that presumably had a family of at least three, and possibly four or five people.

The damp patch on the living room was almost certainly caused by a defective rainwater down pipe that was discharging water against the wall. Unfortunately because the walls were cavity insulated the insulation itself will have become water logged causing a section of the wall to become particularly cold which then attract condensation.

Our solution

The property is being professionally refurbished and we were able to implement a solution as part of the refurbishment work.

A straightforward repair to the rainwater down pipe was all that was needed to stop it discharging water against the wall.

On the first floor the existing extract fans in the bathroom an shower room were replaced with our preferred units, controlled a humidistat (i.e. they move into boost mode when detecting higher levels of humidity).

The existing fans had been controlled by a light switch and overrun timer. The problem with fans that operate in this way is that firstly the light has to be switched on and secondly the room is almost never sufficiently dry when the fan shuts off. Better quality fans that use a trickle function provide a gentle movement of air which results in far better drying were installed.

We also installed a positive input ventilation system to bring filtered fresh air into the property. Most of the bedrooms had primitive air vents in the walls and whilst we would not install these (because of uncontrolled draughts) they do help control humidity. In the bedroom with no ventilation we installed a passive vapour vent to provide a route for moisture to escape to the outside.

We had initially recommended trimming a number of bedroom doors but as these were being replaced anyway, and adequate gap between door and floor was left in line with government recommendations.


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

mould on bedroom ceilings
mould on bedroom ceilings ...
mold on ceilings
... in several rooms
Fitting a passive vapour control vent
Fitting a passive vapour control vent
vapour control vent
Vapour control vent
external vent cover
External vent cover
severe mould in a bedroom
We also found this drainpipe was the source of dampness and mould in the living room vent cover
Request a survey & report
Covid 19 ventilation guidance

UK government advises:

"Good ventilation can help reduce the risk of spreading coronavirus"
"Where possible consider ways to maintain and increase the supply of fresh air"

Too much humidity and not enough ventilation
= damp, condensation & mould

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