Warm air rises. In a newly formed loft room, that can mean condensation, cold corners and mould unless you plan for airtightness and ventilation together.
Start with the build-up:
Aim for continuous insulation around the room “box.” Avoid thermal bridges at eaves, dormer cheeks, and steel penetrations. A continuous vapour control/air-tight layer (taped boards or membranes) should wrap the warm side—don’t leave gaps at service penetrations.
Cold roof vs warm roof:
– Warm roof (insulation above rafters) improves continuity and reduces risk at eaves; often chosen with new coverings or dormers.
– Cold roof (insulation between/under rafters) can work but needs careful ventilation strategy for the voids and meticulous air-tight detailing inside.
Ventilation options:
– Dedicated extract from bathroom loft suites; avoid “borrowing” leaky routes.
– Whole-house MVHR branch where a system exists or is planned—great comfort and moisture control if detailed well.
– Background ventilation: plan trickle vents and controlled paths; random gaps are not ventilation.
On site discipline:
Brief the contractor: tape every joint, seal every service hole, and photograph layers before they’re covered. Simple blower-door testing (optional) catches issues early and pays back in comfort and bills.
Read more on loft-conversions.
