How much does it cost to insulate an attic?

So you want to insulate you loft space or attic? It is a wise move – around 30% of the heat in your home is lost through the roof, so insulating that space in between is going to really save you some money on your heating bill, and also help you do your bit for the environment.

The cost of this sort of work is going to depend on both the type of insulation you want to use, and how the insulation is going to be installed. This is sometimes really straightforward, or sometimes very involved and expensive.

Methods of Insulation

Simple joist level loft insulation

The easiest way to insulate your attic is to lay insulation horizontally across the joists, to a depth of 270mm or more. The process takes a couple of hours for a skilled installer, and is a cheap and easy way to insulate the space. The disadvantages are that you will have to board the loft, or use loft lifters, in order to store anything in the loft. The space will also be cold, so if you intend to use the space in any capacity, remember it is going to get very, very cold in winter and very, very warm in summer.

Insulation at rafter level

If you intend to use the space in the loft, for storage or for anything that might require a bit of temperature control, you will want to insulate at rafter level. Insulating at the sloping rafter level is slightly trickier and will require a bit more technical expertise, but you can use a number of different materials and it will not affect the usefulness of the space to any great degree – apart from keeping it insulated of course.

Roof room insulation

If you have a roof room, you will have a trickier time trying to insulate the space. If it has none or poor insulation, then you have a few courses of action:

  • Insulate the residual space behind the stud walls – this is easy to do, just like the joist insulation, so is an easy win.
  • Insulate the stud wall, usually with a rigid board insulation, but can also be a vertical application of wool insulation, like Optimal Sheep Wool
  • Either tear down the sloping ceiling, insulate and refit the ceiling OR insulate the ceiling internally. You could use a thinner insulating material, like thermal liner, if you don’t want to be so drastic.

Types of Insulation Material

Fibreglass insulation

Fibreglass insulation, made from spun glass, is very cheap to install (around £6 per square meter), but is a nightmare to install because of its itchy fibres.

Mineral or rock wool insulation

The most commonly found insulation material in a loft space is mineral wool or rock wool. It is pretty cheap stuff and has a good insulating effect. It isn’t particularly nice to work with, but it will be cheap and easy to install. Typical costs are around £9 per square meter.

Rigid board insulation

If you need an insulation material with a big more rigidity, able to keep upright and provide maximum insulation for the space available, rigid phenol board insulation is probably the best choice. Still relatively cheap, this sort of insulation is commonly used for rafter application, or in roof rooms and loft conversions. The material will cost around £10-12 per meter but obviously the installation method is going to add to this cost.

Spray foam insulation

Spray foam can be a useful alternative insulation material, but it is quite pricey and will need to be installed by an expert. It requires a thinner thickness of insulation compared to other insulation. Closed cell spray foam insulation is generally more expensive than open cell. Modern icynene spray foam costs upwards of £27 per square meter, so it’s not cheap, and it’s very difficult to remove if you later change your mind.

Premium Insulation and sheep wool

Sheep wool is a really nice material to work with. It is not as irritable as mineral wool, and has plenty of additional benefits, like breathability of the material and its absorption of formaldehyde, something found in many new buildings.

Sheep wool is a great product, but it can prove quite a bit more expensive than standard insulation, at around £25 per square meter just for materials, so it isn’t for everyone.

Type of Insulation Estimated Cost
Fibreglass £6 per m2
Mineral wool £9 per m2
Rigid board £10 per m2
Sheep wool £25 per m2
Spray foam £27 per m2

Installing loft insulation

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