Loft Insulation

Insulate your home and stop the ‘great escape’

A well-insulated house keeps warmth exactly where you need it – indoors. Loft insulation is a simple and effective way to reduce your heating bills, and you can even do some types yourself.

You could get this work funded by a grant – click here for information.

Heating your home isn’t cheap, and with the price of gas, electricity and oil going up all the time, it seems to cost more every winter to stay warm.

To save money you need to stop the heat escaping, and the best way to do this is to insulate your home. The better the insulation, the warmer you’ll feel and the more money you’ll save.

Professional installation costAround £250
Annual saving per yearAround £15
Payback time16 years
DIY installation cost£120-£200 *
DIY payback time5 to 8 years

These figures (correct April 2015) assume you have 100mm of insulation and top it up to the recommended 270mm. If you have no insulation at all, then savings can be up to £182 a year.
* This price depends on materials, and assumes there was no grant available for DIY.

Standard loft insulation

Standard loft insulation is appropriate for most homes, when rolls of insulation are laid over the floor joists.

Generally speaking, if your home has an accessible loft with no damp or condensation problems, it will be a good candidate for loft insulation.

Even if you already have some insulation your loft may need a top-up. The recommended depth for mineral wool insulation – the most common material – is 270mm (about 1ft), but there are other materials (usually more expensive) which require different depths.

Loft insulation is effective for at least 40 years, and it will pay for itself over and over again in that time. Some people may be eligible for funding towards the cost of professional insulation, depending on your circumstances and how much insulation you currently have.

Call for advice, if you live in our area, otherwise visit the government website for local schemes. 

Laying insulation is usually a straightforward job for a competent DIY-er. Mineral wool insulation can be bought in big rolls (also known as ‘blankets’ or ‘quilts’) from builders’ merchants or DIY stores. See our separate DIY loft insulation factsheet for more information on aspects that need to be considered, such as ventilation and safety.

It is important not to compress insulation with items that you are storing in your loft. If you need to use your loft for storage an installer should be able to leave a small section partially insulated with boarding on top. Most areas have local companies who can help with loft clearance.

If your loft is boarded these will need to be removed before the insulation is laid or topped-up. It is important not to compress the new insulation with items that you are storing in your loft, but you can re-board part or all of the loft afterwards, using specialist products that raise the floor level above the insulation. 

For lofts with difficult access – e.g. small hatches and very little space – standard loft insulation rolls aren’t suitable. Instead a loose, fire-retardant insulation material is blown into the loft using specialist equipment. This is a job for a professional installer and can take a few hours depending on the size of the loft.

Room-in roof insulation for pitched roofs

If your loft has been converted into a habitable space then standard loft insulation is not suitable. Some lofts may have been insulated when they were converted, but if not the unheated space still needs to be insulated to prevent heat from escaping. Equally if you’re thinking about loft conversion, make sure to consider insulation before you start work.

Room-in-roof insulation involves fitting insulating material between and over the rafters (the sloping timbers that make up the roof itself).

This can be done with rigid insulation boards, cut to size, or alternatively you can have foam insulation sprayed between the rafters. Plasterboard is then applied on top of the insulating material to create the walls and ceiling of the room.

If you want to install room-in roof insulation after your loft has been converted you will need to factor in redecoration costs as the plasterboard will need to be removed. Room-in roof insulation is also generally more expensive than standard loft insulation as it usually requires the work of a trained insulation specialist, rather than being a DIY job.

If you were to do the work yourself be aware that as well as insulating the roof, you will have to insulate all areas, including any gable walls, stud walls, party walls and chimneys in the loft space.

If you leave these uninsulated, then the heat will bypass your new insulation making it largely ineffective, and potentially causing cold spots and damp issues.

Flat roof insulation

Flat roof insulation is most likely to be relevant on extensions, such as a kitchen or bathroom. These roofs can lose a lot of heat and are expensive to insulate, so it is usually best doing it at the same time as regular maintenance or repairs.

With warm deck insulation a layer of rigid insulation board is laid on top of the existing roof deck, with a vapour barrier in-between to prevent condensation build up. A new roof deck is then fitted on top of the insulation boards.

With cold deck insulation the internal ceiling is removed and either mineral fibre or rigid insulation boards are added between the roof deck and the ceiling, with at least a 50mm gap between the insulation and the deck. A vapour barrier is created between the internal ceiling and the insulation.

This work should always be done by a professional. Even so, cold deck insulation is usually not the most effective way of insulating a flat roof due to potential condensation build up if not done properly.

Warm deck insulation tends to be the cheaper of the two options, especially if done at the same time as repairing or replacing the roof’s finish. 

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