Cold loft ceiling, 300 mm Loft Roll 44
Glass mineral wool laid at ceiling level to 300 mm, with the roof space above left cold and ventilated.
Layers, outside to inside
| Layer | Thickness | W/(m·K) | R |
|---|---|---|---|
| Knauf Loft Roll 44 | 200 mm | λD 0.044 | 4.55 |
| Knauf Loft Roll 44 | 100 mm | λD 0.044 | 2.27 |
| Plasterboard (generic) | 13 mm | λ 0.21 | 0.06 |
Where this fits
The cheapest worthwhile insulation in a UK house, and the one most often done badly: the depth is easy, the edges are not. Heat leaves through the hatch, the gaps around downlights and the wedge above the wall plate where the roof pitch pinches the insulation to nothing. Laying the second layer across the joists rather than between them is what makes the difference between the number below and the wall you actually built. Do not compress it into a floored storage area — a squashed roll insulates roughly in proportion to what is left of it.
What the calculation assumes
Series calculation through the full 300 mm. Ceiling joists bridge the lower 100 mm and are not modelled, so a real ceiling performs somewhat worse than this; the cross-laid upper layer is what keeps the gap small. Surface resistances are the EN ISO 6946 defaults for this element. This is an indicative figure for comparing constructions, not a compliance calculation.
Sources
- Knauf Loft Roll 44 — declared data · checked 2026-08-25
Change it, or use it
Open it in the calculator to swap a layer, change a thickness or solve for a target U-value — the result keeps its own URL, so a build-up you have altered is still something you can send to someone. Or take this one straight into the editor, where it arrives as a named wall type you can assign to the walls you have drawn: the thickness follows and the U-value comes with it. Nothing is assigned until you say so.