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Loft insulation materials

We’ve already looked at the basics of loft insulation. With temperatures in the UK reaching well below zero in several places this winter already, it’s a good time to look at the next step – choosing the right material for your loft.

One thing to bear in mind before making your choice is that if you’re going to apply for a grant from your local council, you’ll need to check that the material you’re planning to use qualifies under their scheme. Information on many of the grants and subsidies available through councils and energy companies is available from the Energy Saving Trust.

Blanket insulation

These rolls of glass fibre, mineral wool or rock fibre are the most commonly used form of insulation – many homes have had blanket insulation since the 1970s or even earlier. It comes in rolls prepared to a standard width of 400mm (1′ 4″) to fit between joists, in a variety of thicknesses, commonly 100mm or 150mm.

If your home happens to already have blanket insulation laid down in the roof, check the thickness. In previous decades when energy efficiency wasn’t the major concern it is now, a mere 25mm (1″) thickness was thought to be enough! You can improve the insulation markedly by adding extra layers to bring it up to the current recommended minimum of 150mm (6″).

It’s possible to buy blanket insulation either unbacked or backed. Backed rolls have the advantage of being more tear-resistant; depending on the type of backing, they may also act as a vapour barrier to stop warm, moist air from rising into the roof void and condensing, causing mould and mildew to spoil anything stored up there or – worse still – dry rot to attack the roof timbers.

Loose-fill insulation

This consists of granules or pellets which are poured onto the floor of the loft between the joists, again to the recommended minimum depth of 150mm (6″). Vermiculite (a type of mica) is the most common material, but there are others such as mineral wool, cellulose (made from recycled paper and flameproofed) and cork granules).

It’s not ideal for use in a draughty loft, as the pellets can get blown about in stiff winds. Then again, if your joists are spaced unevenly, it’s much better than blanket insulation for filling all the nooks and crannies.

The other thing to remember is that your joists are likely to get covered, at least in some places, so you’ll need to create some kind of walkways to enable you to get about without putting your foot through the ceiling of the rooms below.

Sheet insulation

This is made out of glass fibre or mineral fibre, and can be rigid or semi-rigid. Rather than fixing it to the floor of the loft, it tends to be fixed against the rafters, which means that the whole roof space is warmed by the heat rising from below. This is the stuff you need if you’re contemplating a loft conversion, or if you’re keeping things in the loft which would suffer if they’re exposed to freezing temperatures in winter.

It’s more efficient than blanket insulation, so the sheets are much thinner. Putting plasterboard over them (as you’ll want to do if you’re converting the loft) makes them even more effective in keeping the heat in. On the other hand, you still need to make sure that there’s space between the sheets and the roof tiles for the air to circulate and any moisture to escape without condensing and causing mould and rot to develop.

Blown-fibre insulation

This is loose-fill insulation with knobs on – a professional company comes and blows mineral fibre through a large hose into the spaces between the roof joists, to a depth of at least 150mm (6″). Like loose-fill insulation, though, it’s apt to blow about in draughty lofts, so be sure to check carefully with the contractor if you’re in any doubt.

Remember: even if you don’t qualify for a grant, and you have to pay the typical £250-£300 to insulate your loft to the recommended minimum depth of 150mm or six inches, you’ll save enough on heating bills to get your money back within a year – not to mention the warm glow you’ll get from having done something to help combat climate change!

2 Responses to “Loft insulation materials”

  1. anna berent

    I live in Islington, London, where I have a very large Victorian house with a boarded loft. I am anxious to discover whether this would lend itself to blown fibre or loose fill insulation under the boards. Also whether, as a landlord, I would be able to get any sort of a grant towards the cost.

  2. HouseWiz

    Thanks for your questions, Anna.

    You don’t mention whether the boarded loft is being used for storage or living. If it isn’t, then the easiest solution would be to simply lay blanket insulation over the top of the boards – remembering, of course, to leave a space near the eaves for air to circulate. However, assuming that the loft space is being used for storage, then blanket insulation is obviously not a viable answer.

    There’s no reason why boards in your loft should prevent you having either loose-fill or blown-fibre insulation – indeed, both of those types of insulation would lend themselves to boards as a means of keeping the insulation from blowing about. But if the boards in your loft are proper floorboards rather than, say, MDF sheets – and I’d expect that, it being a Victorian house, they’re the real McCoy – then you’re probably looking at blown-fibre insulation and a contractor rather than trying to lift the boards and put in loose-fill insulation yourself.

    As for whether you can obtain a grant, you’ll need to check with your local authority – but I’d be very surprised if you’re not eligible for some kind of assistance.

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