Mouldy loft space. How to solve the problem

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Steven Dickinson.

👉You may like this video.

This video addresses a common issue faced by homeowners: mould and black fungus growing on the back of underfelt in a loft (or attic, as it's called in the U.S.). A customer sent me photos showing the problem in their loft and asked if I could offer a solution.

In this video, I explain:

How to properly ventilate a loft space to reduce condensation.
The importance of sealing the ceiling to make it airtight and stop moisture-laden air from rising into the loft.
How the thermal properties of the roof and loft space play a role in preventing excessive moisture buildup.
If you're dealing with mold, condensation, or moisture issues in your loft, this video may help you understand the problem and explore potential solutions.


Recommendations:

Sealing the Ceiling
Ensure that the ceiling below the loft is sealed properly to prevent humidity from rising into the loft space. Any gaps or leaks will allow warm, moist air to escape, increasing condensation risks.

Improving Ventilation
Install additional vent tiles higher up the roof.
Consider using corrugated trays at the eaves to ensure airflow from the soffit.
Be cautious about external humidity levels; bringing in high-humidity air during cold weather can worsen condensation.

Heating the Loft Space
A heater with a thermostat or humidity sensor can be installed in the loft to maintain a slightly warmer temperature during exceptionally cold periods. This prevents the temperature from dropping below the dew point, reducing condensation. The energy cost for such a system is minimal compared to the potential damage from mold.

Monitoring Conditions
Use relative humidity monitors placed in various parts of the loft (high and low levels) to track temperature and humidity fluctuations. This data can help identify patterns and determine the effectiveness of any interventions.

Tweaking Insulation Placement
While reducing insulation isn’t ideal due to energy loss, ensuring it doesn’t block ventilation paths and making small adjustments may improve the situation.
00:00 Mould in loft space or attic
00:18 Truss timbers or traditional construction
01:35 Plastic Sarking felt or underfelt
02:26 Thermal bringing though sarking felt
03:45 Loft vents installation
04:21 Roof tile
04:49 Discussion about insulating a loft
08:00 Things you could do to vent your loft
09:56 What I would do first to vent the loft