Architect Paula Murphy answers your questions.
Q. I have an en-suite off my bedroom, I have a problem with mould on the ceiling, I have washed it to try to clean it, but it keeps reappearing, I cannot put a window in the roof because of the situation of the attic. A colleague tells me they had the same problem and put boards - I think it was floorboards - on the ceiling and it solved the problem. Can you please advise?
A. Mould needs three conditions to thrive: humidity; slight heat; and little or no light. An internal bathroom such as yours can provide near perfect conditions for mould growth and it most frequently occurs on the ceiling or on the grout. It takes hold surprisingly quickly and not only is it unsightly, but it can pose health concerns.
It is likely that the mould has taken hold of your plasterboard and will continue to reappear unless you tackle the source of the problem.
I would recommend removing the plasterboard and replacing it with a material that is more resistant to mould growth, such as vinyl, fibreglass, etc. In the case of your colleague, timber, most likely treated with mould retardant, can appear to tackle the issue, but it more frequently results in the problem reappearing on adjacent surfaces or, more worryingly, behind the product.
The most likely cause of the mould is lack of ventilation. The humble extractor is one of the most important items in a bathroom and upping the performance of yours can be achieved at very little cost. A basic (though surprisingly often overlooked) requirement is it must ventilate to the outside. I recommend using a humidity-activated model which will start up when required and continue for a surprisingly long time after you have showered. If using a standard variety it must be linked to the light and have a time delay. Set it at the longest delay possible and, more importantly, use it.
Once you replace the ceiling (and I am not convinced timber is the answer), treatment with an eco-friendly anti-mould treatment can be undertaken at a minimal cost. Treat any plasterboard walls as well. (Follow the manufacturer's instructions.)
Also ensure that the entire ceiling area is insulated, particularly at the edges (and walls, if relevant) and provide a good source of heat to the bathroom prior to showering to raise the surface temperature of the walls and ceilings. I favour heated towel rails on timers.
Tackle damp floors quickly, and promptly remove wet clothes and towels. Don't dry your clothes in the bathroom.
Ensure the adjacent bedroom is properly ventilated as moisture-laden air (from breathing) can gravitate towards the bathroom.
A final tip is to purchase an inexpensive moisture meter which will measure the relative humidity (moisture in the air ), which needs to be less than 40-50pc to prevent mould. This will quickly tell you when conditions are above this limit and you can adjust your ventilation or length of shower accordingly. You are likely to be surprised by the results. Best of luck.
For more site specific advice consider hiring an registered architect in your area. Check RIAI.ie for a complete list of registered members.
Paula Murphy (MRIAI) is an architect working in Tipperary and South Dublin; paulamurphy.ie
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