Insulated sectional garage doors: U-values explained
A U-value measures how much heat passes through a material: the lower the number, the better it insulates. Published figures for one leading range show a fitted 42 mm sectional door at about 1.4 W/m²K and a 67 mm thermally broken door at about 1.0 W/m²K, compared with roughly 6.5 W/m²K for a single-skin steel door.
Panel, door leaf or fitted door?
Manufacturers often quote three U-values. The panel or section figure is for the foam-filled steel panel alone. The door leaf figure includes joints. The fitted or installed door figure includes the frame, seals and edges and is the honest one to compare. Always compare like with like, and for the same door size.
How do common panels compare?
| Door type (example figures, 5000 × 2125 mm) | Fitted door U-value |
|---|---|
| Single-skin steel | about 6.5 W/m²K |
| 42 mm double-skin insulated | about 1.4 W/m²K |
| 67 mm thermally broken | about 1.0 W/m²K |
These are published figures for one major manufacturer and a large door; smaller doors and other ranges differ.
When is insulation worth it?
- Integral garages and garages with a room above.
- Garages used as a gym, workshop or utility room.
- Storing anything that dislikes cold and damp, such as bikes, tools or a freezer.
- Garages you heat, even occasionally.
For a detached garage used only for a car, a standard double-skin door is usually enough.
Do Building Regulations set a U-value for garage doors?
An unheated garage is normally outside the heated part of the home, so energy rules for doors are not usually applied to the garage door itself. If you convert the garage into a room, the new wall or door that closes the opening must meet the energy standards for a habitable room, which is building control work.
Seals matter as much as panels
A well-insulated panel with poor seals still leaks heat. Look for a bottom seal that follows the floor, side and head seals, and gaskets between sections, and make sure the door is set up so the seals actually touch.
Sources
- Manufacturer technical data for insulated sectional doors (U-values)
This guide gives general information, not legal or professional advice. Rules change; check with your council or a qualified adviser for your situation.