Looking to add loft insulation? Our guide outlines how much you can expect to pay

The recommended depth of standard loft quilt applied above top floor ceilings is 270mm (about 10in). How much loft insulation will cost will depend on the type you want to use and how much of it you need. Here are the main options…

Mineral wool or glass fibre wool insulation
DIY stores typically sell rolls of mineral wool or glass fibre wool insulation in thicknesses of 100mm or 200mm (4in or 8in). These are usually the cheapest type of insulation and are designed to simply be unfurled over the loft floor. A standard 100mm (4in) thick roll of mineral wool that’s 9.72m x 1.140m (31.7ft x 3.7ft) costs about £2.25 per sq m.

Assuming you need to top up your existing insulation by 200mm (8in), you’d be looking at £5 per sq m, so in total roughly £200 for an average loft of about 40 sq m.

Polyester loft roll insulation
Another popular type of loft roll is polyester made from recycled plastic bottles, which is softer and claims to be non-itchy.

Natural insulation
Natural materials such as sheep’s wool are much nicer to work with but are more expensive, costing around £17 per sq m for 100mm (4in) depth, and need to be applied to a greater thickness to get the same level of insulation, say about 300mm (12in) depth.  

Unless your loft has a lot of awkward spaces, it’s normally advisable to stick to one of these quilt products sold in rolls, particularly as they readily lend themselves to DIY installation.

Cellulose fibre insulation
Cellulose fibre insulation is an interesting alternative material (made from treated recycled newspapers) that’s professionally installed using blowers to achieve consistent depth of coverage. Thermofloc Loose Fill Cellulose Insulation costs around £29 for 12kg (26.5lb). The manufacturer recommends 4kg (8.8lb) per sq m per 100mm (4in) depth. 

Reflective insulated foil
Sheets of reflective insulated foil, such as SuperFOIL SF19+ Multifoil Insulation – around £120 for a 1.2m x 10m (3.9ft x 32.8ft) roll – are another option but are generally better suited to new builds or for insulating at rafter level, which is a more complex operation.  

If the idea of boldly shimming up loft ladders on a DIY mission isn’t your cup of tea, then employing tradespeople to do it for you will likely set you back around £250 per day in labour rates. This is a consistent figure regardless of the type of insulation used. Add this onto how much your chosen loft insulation costs.

Unfurling rolls of loft quilt is a straightforward job and can be done relatively quickly. For a typical rectangular roof space with decent headroom, it may only take a couple of hours. But you’ll need to factor in at least the same amount of time for preparing access. Most lofts are home to piles of belongings that need to be cleared out of the way. Then there’s the pipework and lengths of electric cable that need to be negotiated with care to avoid damaging them.  

So you will normally need to allow a full day to insulate a typical loft (or half a day for two installers working in tandem). If you opt for more sophisticated materials or there are problems with restricted access, the job could take twice as long.  

Before laying insulation, it’s important to check for pipes and cables. Once obscured under fresh quilt there will be few clues to their location, or to the whereabouts of joists that you can safely tread on. To help prevent injury and damage, special raised boarded walkways can be fitted (some of which have integral insulation).   

It’s advisable not to ‘bury’ any electric cables within insulation. But paying an electrician to re-route all the cabling could add several hundred pounds to the cost. In most homes, electric cables in lofts only supply the lights in the rooms below, and if these are all modern LEDs it’s unlikely an electrician would regard there was any significant risk of cables overheating. If it’s not possible to rerun cables above the new insulation, a good alternative is to fit lengths of split-sided conduit sheathing around them to form an air space.    

Although mineral-based insulation materials like Rockwool are inert and fireproof, where you’ve got recessed ceiling lights in bathrooms, etc, it’s advisable to fit downlight protection hoods over them (these look like upturned flower pots and cost about £7 each). 

To finish the job, any water tanks in the loft should be insulated with a lagging jacket, and any exposed pipework lagged with lengths of foamed tubing.