How to buy loft insulation

Roof insulation

  • Find out if insulating your roof or your loft could help you save on your energy bills
  • How to insulate a flat roof and a pitched roof, and what options are available for both
  • Warm loft insulation and cold loft insulation explained - and which one to choose

Without insulation your energy bills could be going through the roof. In this guide, we'll help you work out what type of insulation to go for, how much it will cost, if you can get it for free, and how much you could save by insulating your roof.

Do you have a flat or pitched roof? 

The type of insulation you should choose will depend on the type of roof you have.

If you have a pitched roof, there are two options: warm or cold loft insulation.

For flat roofs, there are three options available: warm deck, cold deck or inverted roof.

Cold loft insulation for pitched roofs

The simplest and cheapest roof insulation is the classic cold loft option. This is often called just loft insulation

This type places insulation over and between the wooden joists, above the ceiling of your home's top floor. 

It will stop the heat escaping from the living area of your home, but leave the loft space uninsulated. This means it will remain cold in winter and warm up in summer. 

This is the only type of roof insulation you can apply to have the costs covered by an insulation grant. It's also fairly easy to do as a DIY project, and you can buy loft insulation from most high street DIY stores.

Roof insulation

If you use your loft for living or storage, insulation can be placed under the roof

Warm loft insulation for pitched roofs

If you can't install cold loft insulation because, for example, you're using your loft as a living space, you will need to consider warm loft insulation.

For a warm loft, you install insulation directly under the roof in the plane of the roof's pitch (slope). Insulation will reduce heat loss and your loft space won't become excessively hot in summer or cold in winter. 

It's not as easy as laying rolls of insulation, but it can still be done as a DIY job if you'd rather not pay an installer. 

One important point to remember with a warm loft solution is the need for ventilation immediately below the roof tiles. This prevents condensation build up or water getting in through or around the tiles, which could cause the roof structure to rot.

Types of warm loft insulation 

The materials used to insulate under the roof include batts of mineral- or glass-wool insulation, held in place by battens of wood attached to and across the rafters. Alternatively, polystyrene slabs (that are sometimes foil-covered) can be fitted. These usually have to be cut to size.

Spray foam roof insulation

Spray foam insulation can help strengthen your roof

Another option is EPS (expanded polystyrene) squeeze products; these are manufactured in a concertina shape that springs open when they are pushed into place.

Spray foams are mainly professionally installed, but also available as a DIY measure. Spray foam may also provide additional physical strength where a roof is not in the best condition - as it helps hold the structure together. Missing or slipped tiles must be fixed before applying the foam insulation. 

Flat roof insulation

There are three types of insulation for flat roofs and a professional should help you to decide which one is best for you.

  • Warm deck or warm roof has insulation above the roof deck (the panel underneath the roofing material that's usually made of wood), and is recommended in damp and cold areas such as Britain.
  • Cold deck or cold roof has insulation below the roof deck and the associated joists. Typically, you leave a gap for ventilation, as condensation may form that can lead to rot. In both warm deck and cold deck options, the weather membrane, typically formed of roofing felt and bitumen, will be the topmost layer, protecting against rain.
  • Inverted roof has insulation that goes above the weather membrane, effectively protecting it from heat and cold that can shorten its life and that of the roof deck. It can even protect against wear and tear if there is access to the roof. With an inverted roof, the top-most layer is generally gravel or a similar material.

You'll almost always need to use a professional installer to fit your flat roof insulation, and there are no energy grants available to help with the cost. A good time to insulate a roof is when it's being replaced, although in many cases a roof that is in good condition can be retro-fitted with insulation.

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