Not if the lantern is well specified. A modern double or triple glazed lantern with a thermally broken frame still loses more heat per square metre than an insulated solid roof, but it covers only part of the roof, and Building Regulations cap rooflight performance at 2.2 W/m²K.
How does a lantern compare with a solid roof?
An insulated roof is expected to reach around 0.16 W/m²K when renovated, while a rooflight may be up to 2.2 W/m²K. Glass therefore loses many times more heat per square metre. The effect on the room depends on how much of the roof the lantern replaces.
What keeps a lantern warm?
- Low-emissivity coatings and argon-filled units
- Warm-edge spacers and thermally broken frames
- An insulated upstand, continuous with the roof insulation (site-built upstands should reach about 0.35 W/m²K)
- Careful airtight sealing at the kerb
Why can a lantern still feel cold?
Cold glass can make a room feel draughty on winter nights, and gaps at the upstand let warm air escape. Oversized glazing in a small room makes this worse. A survey of the roof build-up and the room size shows what is realistic.
Wednesfield Trade Windows is a family-run, Certass registered installer, and the survey confirms what needs sign-off on your property. See our roof lanterns for more detail.
Thinking about a roof lantern? We supply and fit lantern roofs across Wolverhampton and the surrounding area, and you deal directly with us, the owners. Call 01902 633355, message us on WhatsApp, or request a quote.