How Much Does Loft Insulation Cost in the UK? DIY vs Professional Installation

Prices checked: 13 October 2026. This guide concerns accessible, dry, cold lofts insulated at ceiling level with mineral-wool rolls. It does not price a loft conversion, rafter-level insulation, spray foam, structural repairs or loft boarding.

The merchant figures are Wickes' displayed consumer retail prices, excluding delivery. Both rolls were on promotion at £27 each when checked. Availability, offers and checkout prices can change; use the coverage of the exact product, not a generic 'price per roll'. Confirm the final VAT-inclusive amount and delivery charge before buying.

If the existing layer is dry, reasonably even and suitable to keep, you are buying the missing depth. In our top-up example, 100mm already exists and a 170mm layer brings the nominal total to 270mm. An empty loft needs both layers, so the roll budget is higher.

Do not count wet, heavily compressed or contaminated insulation as a sound existing layer. Removal, disposal, correcting a leak or dealing with pests can change the scope completely. Ask the installer to specify whether the quote retains, redistributes or replaces the old insulation.

270mm is a commonly used mineral-wool planning depth and the basis of the Energy Saving Trust comparison. It is not a universal legal thickness for every insulation material or roof build-up. Thermal conductivity, the design and the applicable building requirements matter.

Illustrative assumptions: 40m² of loft floor, a sound existing 100mm layer, one additional 170mm layer, straightforward access and a chosen 5% cutting allowance. The 5% is an example allowance, not a manufacturer rule or a change to the calculator's defaults.

Allow for 40 × 1.05 = 42m². Divide by the selected 170mm roll's 6.47m² coverage: 42 ÷ 6.47 = 6.49 rolls, rounded up to 7 rolls. Seven rolls cover 45.29m² before cutting.

At the checked £27 promotional price, the roll budget is 7 × £27 = £189. At the displayed crossed-out reference price of £38, the same purchase would be £266. This shows why a dated promotional price should not become a permanent cost promise.

Neither total includes delivery, your time, protective equipment, access improvements, pipe or tank insulation, hatch work, ventilation changes or boarding. Add separately priced items to get the actual project budget.

Keep the 40m² area and 5% allowance, but start with an empty loft. This illustration uses 100mm between the joists and 170mm across them. Check that the actual joist arrangement, product instructions and ventilation details suit that build-up.

For the 100mm layer: 42 ÷ 11.08 = 3.79, so buy 4 rolls. For the 170mm layer: 42 ÷ 6.47 = 6.49, so buy 7 rolls. Each layer needs its own coverage calculation; do not divide 42m² by the combined coverage of two different rolls.

At £27 per roll, the materials total is (4 × £27) + (7 × £27) = £297. Using the displayed reference prices instead gives (4 × £37) + (7 × £38) = £414. Again, these totals exclude delivery, labour and extras.

The 100mm-to-270mm example is not identical to Energy Saving Trust's 120mm-to-270mm top-up benchmark. Nor is the benchmark a quote for a 40m² loft. Compare your own like-for-like written supply-and-fit quote with your own complete DIY budget.

Area and the additional depth are only the start. Restricted access, awkward joists, stored belongings, damaged insulation, travel and minimum job charges can affect the price. A loft that needs clearing or remedial work is not equivalent to a clear, dry loft.

The current Instaloft installation service describes a survey of existing depth and condition before finalising a quote, and lists 100mm, 170mm and 270mm options. It does not provide a fixed public price on that page, so we have not invented an installer rate or treated its service as a quoted £/m² offer.

Ask for a written scope: material and conductivity, retained existing layer, added and total depths, measured area, waste allowance, removal, ventilation provision, hatch and tank/pipe work, waste disposal, delivery and the final VAT-inclusive payable amount. Separate optional raised boarding or a ladder from the insulation price.

Energy Saving Trust's benchmark is useful for an initial sense-check, not a guarantee that a particular firm will charge £600 or £750. Obtain comparable quotes with the same depth and exclusions before deciding whether DIY is worth the time and access risks.

For a suitable cold loft, mineral-wool rolls are a different product from rigid PIR boards used in other roof arrangements. Match the roll thickness, coverage and conductivity to your plan. A merchant category is a browse destination, not approval of every product in it.

Measure the loft and existing depth before ordering. A wool-cutting saw is an optional tool for glass or stone insulation wool, not a saw for PIR boards. Follow the insulation manufacturer's handling and protective-equipment instructions; tools are not included in either materials example.

Energy Saving Trust identifies damp, difficult access, flat roofs and lived-in lofts as reasons to seek professional advice. Fix the cause of damp first. Do not block intentional eaves ventilation or squash mineral wool beneath storage boards.

Ceiling-level insulation leaves the loft colder, so pipes and tanks need consideration. Electrical cables, recessed lights, flues and other heat sources also need the appropriate clearances and installation details. Do not assume it is safe to bury every fitting; get electrical advice where necessary.

Potential grants depend on eligibility and location. Check the Energy Saving Trust funding guidance rather than assuming free installation is available to everyone. This is a budgeting guide, not a roof design or a guarantee of energy-bill savings.