Condensation in the Attic - How to Stop it!

You’ll know that you’ve got condensation in the attic if you’ve gone to get stored items from your roof-space only to find them covered in mold.

Or, worse still you can physically see water droplets forming on the underside of your roof cover or water tank.

So why does it happen?

Condensation will form in your attic if warm moisture laden air comes into contact with a cold surface. In the real world this means moist air from your house coming into contact with the underside of your cold roof tiles or the side of your water tank etc.

For a more detailed explanation see my article on condensation in buildings.

Condensation can happen for lots of different reasons, perhaps your roof hatch doesn’t fit well and allows warm air (which is full of water vapor) up into the roof void. Water vapor can also get into your roof void through breaks in the fabric of the building such as gaps around pipes or services or cracks and holes in the plaster or around light fittings etc.

How can you stop condensation in the attic?

The first step is to stop the warm moist air from contacting with the cold surfaces in your attic. There are a few ways to achieve this but in my opinion the best is to

  1. Make sure all cracks are sealed and seal where wires and services go through the ceiling. You should also make sure your roof hatch is well sealed. 
  2. Insulate your roof. There are two different ways of doing this:
Cold Roof Insulation"Cold Roof" Insulation

  • “Cold roof” insulation - This type of insulation is laid on the floor of your attic area between the joists. It stops the heat from the rooms of your house getting up to the roof void. This method is called cold roof insulation as the attic space will be colder than the heated rooms below.

    This would be my preferred option, where possible, as it means you’re not wasting heat trying to keep your attic warm. Although you may want to keep it warm for storage reasons.

    In conjunction with “cold roof” insulation you’ll also need to make sure your attic is adequately ventilated. The reason for this is that when adding insulation (typically 300mm thick) it’s easy to block or limit the eaves ventilation points around your facia and soffit boards with your new insulation.

    So part and parcel of adding “cold roof” insulation is to fit additional roof vents (typically tile and/or ridge vents) to ensure there is adequate ventilation which will dilute any moist air which may be present.
"Warm Roof" Insulation
  • “Warm roof” insulation – this type, as the name suggests leaves the attic space warm as the insulation is laid between the rafters (against the underside of the roof cover).

    It’s a more difficult type of insulation to install correctly as you can’t put the insulation tight against the underside of the roof cover because you need to leave a ventilation gap. But it will mean the loft area is warmer and should reduce condensation in the attic significantly.

    This type of insulation is more common on chalet style properties where there are habitable rooms in the roof area and it is fairly unusual in traditional houses with a full roof-space.

So if you have condensation in the attic I’d suggest contacting an insulation company and arranging to get it insulated and ventilated correctly. You should of course consider upgrading the ventilation in your home

Please note if you’re thinking about insulating your attic be aware that you have a legal obligation to notify building control as they will want to confirm that adequate ventilation etc. has been provided.

You can get more info on Building Control in mainland UK here and in N.Ireland here

› Attic Condensation

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