The short answer
Rolled mineral wool is usually the lower-cost option, at roughly £5–£12 per square metre installed, and it is the only method you can sensibly fit yourself. Blown loose-fill insulation — cellulose or mineral fibre injected with a machine — typically costs £10–£20 per square metre because it must be done professionally. Blown insulation earns its premium in awkward lofts: irregular joists, restricted access or spaces where laying rolls is impractical. Both methods aim for the same 270mm effective depth and the same Part L roof performance.
Rolled and blown insulation both work, but they suit different lofts and different budgets. Here is how the costs and the practicalities compare.
Rolled vs blown at a glance
- Rolled mineral wool£5–£12/m²
- Blown loose-fill£10–£20/m²
- DIY possible?Rolled yes, blown no
- Best for awkward loftsBlown
- Target depth270mm equivalent
How the two methods differ
Rolled insulation comes in batts or rolls of mineral wool (glass or rock fibre). You lay a first layer between the joists and a second layer across them at right angles to reach the recommended 270mm. It is widely sold at builders' merchants, easy to handle and the natural choice for a clear, regularly spaced loft.
Blown insulation is loose material — typically recycled cellulose or loose mineral fibre — blown in through a hose to an even depth. Because the loft has to be sealed at the eaves and the depth controlled with a machine, it is a professional-only job. Its advantage is that the loose fill flows into gaps, around pipes and into irregular bays that rolls struggle to cover neatly.
Comparing the cost and the trade-offs
On a straight materials-and-labour basis, rolled wool is cheaper, especially if you fit it yourself. Blown carries a higher per-square-metre rate because of the equipment and the skilled operator, but it can be faster on a difficult loft and avoids the compression and gaps that come from forcing rolls into tight bays.
| Factor | Rolled mineral wool | Blown loose-fill |
|---|---|---|
| Typical installed cost | £5–£12/m² | £10–£20/m² |
| DIY option | Yes | No — professional only |
| Best loft type | Clear, regular joists | Irregular, restricted, awkward |
| Coverage of gaps | Manual, gaps possible | Flows into gaps well |
| Disturbance | Can be re-lifted later | Harder to part later |
Indicative UK figures for guidance, 2026. Actual cost depends on loft area, access and condition.
Which should you choose?
For a standard, accessible loft with regular joist spacing and nothing in the way, rolled mineral wool usually wins on cost and is straightforward to top up or lift later if you need to access cables or pipes. If your loft has uneven joists, very restricted headroom, lots of obstructions or difficult access, blown insulation can give a more complete, even result for the extra outlay.
One practical point: if you ever plan to board part of the loft for storage, rolled insulation under a raised batten system is the more common arrangement, because you can see and manage the layers. Whichever method you pick, the goal is the same — an even 270mm-equivalent layer, ventilation kept clear at the eaves, and no insulation packed under the cold-water tank so it does not freeze. Because insulation currently attracts 0% VAT on supply-and-fit until 31 March 2027, the professional blown route is a little more affordable than it would otherwise be.
Performance, not just price
Cost is only half the comparison; what each method delivers thermally matters too. Both rolled and blown insulation are rated by their thermal conductivity (lambda value) and, once installed to depth, by the roof's overall U-value. The headline target — around 270mm of mineral wool — exists because that depth brings a standard loft to the U-value expected under Part L of the Building Regulations. A well-laid blown layer and a well-laid rolled layer to the same effective depth perform very similarly; the difference in practice comes from how completely the loft is covered.
This is where blown can edge ahead in an awkward space: gaps, compressed sections and missed bays around obstructions all create thermal bridges that quietly leak heat, and loose-fill flows into those gaps better than a rigid roll forced into an irregular bay. In a clean, regular loft, careful rolled installation closes those gaps just as well for less money. So the decision is less 'which material is better' and more 'which method will achieve a complete, gap-free 270mm in this particular loft' — and that is best judged by looking at the space itself, its joist layout and its access.
Frequently asked questions
Is blown insulation worth the extra cost?
In an awkward loft, often yes — loose-fill reaches gaps and irregular bays that rolls cannot cover well, giving a more even result. In a clear, regular loft, rolled wool usually does the same job for less.
Can I lay rolled insulation over existing blown insulation?
Usually yes, provided the existing material is dry and in good condition. Laying rolls across the top to reach 270mm total is a common way to top up an under-insulated loft.
Does blown insulation settle over time?
It can settle slightly over many years, reducing depth a little. A good installer blows to a depth that allows for settlement so the long-term figure still meets the recommended standard.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific loft. They are guidance, not a quotation.