Loft insulation and your roof: getting both right
Insulation and ventilation pull in opposite directions if you get them wrong, and the roof pays for it.
The eaves gap
Insulation must stop short of the eaves, or be held clear with ventilation trays, so air can still enter at the bottom of the slope. Pushing it into the corners is the fastest way to create a damp roof.
Cold loft, warm roof
In a standard cold loft the insulation goes at ceiling level and the loft is cold and ventilated. In a converted loft the insulation follows the slope and the build-up must be designed with vapour control, not just stuffed with wool.
Storage boards
Boarding straight onto joists compresses the insulation. Raised boarding systems keep the depth and avoid creating a cold bridge across the whole loft floor.
Downlights and services
Recessed lights, pipework and cabling all breach the ceiling line and let warm moist air up. Sealing them matters as much as the insulation depth.
When we get involved
Insulation isn't our trade, but a roof problem is often an insulation problem. We'll tell you what we see and what needs correcting before the roof gets blamed for it.
FAQs
Badly placed insulation can, by blocking ventilation. Depth itself isn't the problem — placement is.
The loft floor for an unused loft; the slope only where the loft is a habitable room, and then with a proper designed build-up.
Yes, where the eaves are blocked and airflow needs restoring.
Related reading
More on materials & systems and the jobs that usually come with it.
- Insulating a flat roof properlyMaterials & systems
- Flat roof cost: GRP versus EPDM versus feltCosts & budgeting
- Lead flashing: when it fails and what it costs to fix
Looking for something specific? See our roofing services, cost guides, common roof problems or the areas we cover.
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