Question submitted to The Daily Telegraph September 2016
I have a mid-terrace property I own and rent out which has condensation in the loft area. Some seven years ago I took advantage of my local council's scheme for installing loft insulation. They put in 250mm-thick insulation on the floor area and insulation in the rafters. A builder has suggested removing the insulation in the rafters and keeping the floor insulation plus fitting four roof vents, quoting £380. Is this the way to go? If he removes the insulation in the rafters, could this damage the existing roofing felt?
Billy Heyman, Managing Director of BTL Property answers your question;
Condensation is caused when water vapour comes into contact with colder areas. In your case, this is happening through warm air rising from the floors below and coming into contact with cold spots on the roof.
There is really only one long-term cure for this, and it is pretty extreme as it involves stripping off the roof tiles and fitting a breathable vapour barrier beneath them. This allows the water-laden air to escape. Presuming this is not the route you want to take, the proposal from your builder will help to reduce the amount of condensation, but it won't totally remove it. You need to ensure that the insulation from the rafters is removed carefully and the vents are cut in correctly, but do not expect to see a huge difference.
There is really only one long-term cure and it is pretty extreme
Ask your builder to look at the floor of your loft space. Are there any gaps into the rooms below? This is usually caused by cable or pipe runs. Get them to pack insulation over these holes to prevent the hot air rising.
There are also a number of small measures you can take around the house to help reduce the loft condensation. If you are drying clothes, use a washing line. If you use a tumble dryer, ensure it is vented correctly and not expelling water-laden air into your property. Make sure extractor fans in your bathrooms are turned on and working. If you have trickle vents on your windows, keep them open. If you need to go into the loft, don't leave the hatch open any longer than necessary. Finally, try not to fill the loft full of clutter - they were never designed as storage spaces and need space for the air to flow.
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