Insulation -Loft/Roof

Insulating your loft

Insulating your loft is a highly cost-effective way of reducing your heat losses as about a quarter of all heat losses in an unimproved building are through the roof (though a good deal less in a five storey Georgian or Regency house). It is also a relatively straightforward job in a traditional building if the loft space is accessible.

If you have a loft and there is already some insulation up there, it probably is not enough. The recommended minimum depth is 270mm of mineral wool, fibreglass or sheep’s wool insulation. Topping up your insulation, or replacing it if it is old, poorly installed or damp, will make a noticeable difference to your heat loss. Ideally, lay insulation both between and across the rafters (if rigid board insulation is used for the latter, the space is more easily used for storage once the job is complete).

Many people install loft insulation themselves. Rolling out insulation between the joists of a loft is a relatively straightforward job. However, there are tricky details which you need to get right, and which may justify a professional job. There are two things to pay attention to: maintaining ventilation to the roof space (see “Considerations”, and ensuring that there are no gaps which allow the heat to get past the insulation.

Covering up the entire floor area of the loft is not always easy. If you have a loft hatch, this must be insulated and have an effective draught-seal. You may need to install a new loft hatch to achieve this. If you have a water tank in your loft, the insulation must be taken up and over it (if you go under it, the water will freeze in the winter). Any exposed pipework must also be insulated. Avoid installing ceiling-recessed downlighters in top rooms but, if there are any penetrations in the ceiling below the loft for lights and cables, these must be carefully sealed to prevent warm air escaping into the roof. Cables should run on the cold side of the insulation to prevent overheating.

A frequent reason for not wanting to insulate the loft is the wish to continue using it for storage, however products are available to allow you to insulate your loft properly, whilst still using it for this purpose. It’s possible to buy loft legs which you nail or screw to your loft joists enabling you to create a solid platform above the loft insulation, and solid insulating boards are also available. Whatever you do, don’t install conventional loft insulation and compress it with things stored upon it, as this will vastly reduce its insulating performance.

 Insulating other roofs

Many of the traditional homes of Cheltenham do not have loft spaces.

Mansard roofs – with four sloping sides that become steeper towards the bottom, and which are often found in Georgian buildings, are not so straightforward to insulate. If you have a mansard roof, you can install rigid board insulation in the manner of internal wall insulation.

Roof rooms and dormer windows –  use the opportunity to combine roof renewal with comprehensive insulation both between and below the sloping rafters.

Flat roofs – Many older buildings in Cheltenham have areas of flat roof, typically over extensions or porches, or the roof behind the parapet may be entirely flat. Insulating these areas can in many cases be relatively difficult so care is needed to make sure the work is effective and does not cause problems. If insulation work is being carried out to the main areas of roof it is important that flat roofed areas are not forgotten. See the resources for more details.


Insulating the roof prior to tiling. Insulating the roof space from the inside. Insulating a dormer window.