- Flat roof
- Cavity wall
THE ROOF IS ONE OF THE MAIN AREAS OF HEAT LOSS IN AN UNTREATED HOME AT AROUND 25%
There are three main ways that roofs are insulated depending on loft usage and type of roof.
1. Standard loft insulation on the floor of the loft.
The recommended depth for standard loft insulation (i.e. laying insulation on the floor of an unused loft) is 270mm or 10-12 inches. The first layer (typically 100mm deep) is placed between the joists (below left). If there is any existing loft insulation and this is in good condition the new material can simply be placed on top. Additional layers of insulation can then be placed on top, laid across the joists in the opposite direction. Key things to remember with this method are:
a. Condensation – once the loft is insulated the space becomes a lot colder. In order to reduce the risk of moist air from below entering the space, loft hatches should be draught proofed. To avoid problems with water, pipes should be lagged and any water storage tanks insulated (do not place insulation beneath the tank otherwise this will freeze).
You may need additional ventilation if you insulate your loft and if you use a professional installer this is something they should always check for.
b. Storage – if you require a small area for storage, you should locate this as close to the loft hatch as possible to avoid disturbing the insulation. You may want to use a higher performance material (e.g. rigid insulation board) as the material will be thinner here.
c. Wiring – Insulation should not be placed over any existing cables as they need to dissipate heat. Failure to do this results in a fire risk. If cables have enough slack, they can be raised above the insulation.
2. Insulation at rafter level
Some loft spaces are inherently easier to make energy efficient than others. Where you cannot easily apply rolled loft insulation between the joists there are other, more ‘complex’ options. Rafter level insulation should only be done where there is an existing room in the loft space, or when you are planning to convert, otherwise you are heating an empty space for no reason.
If you are re-roofing then you could consider placing the insulation above and between rafters (below). This may involve getting planning approval in as it will slightly raise the roof level. As with standard loft insulation, you should always consider ventilation with a 50mm space between the insulation and roof structure. If there is a room in the loft space you should also consider insulating the walls.
3. Flat roof
Flat roofs can also be insulated with the best method being to put rigid insulation above the roof deck. It can go above or below the weather proof membrane. The insulation chosen should be a type unaffected by moisture. When replacing weatherproof membranes there may be opportunities to improve the thermal performance of the roof. Flat roofed bays will loose a lot of heat if untreated and refurbishing this could be an opportunity for a small green roof.
Contact Bristol Energy Efficiency Scheme for grants and subsidies on roof and cavity wall insulation - 0800 082 2234
CAVITY WALL INSULATION
The majority of housing built from 1930 onwards is of cavity wall construction with approximately 20% of UK housing of solid wall construction. Both types of wall can be insulated to reduce heat loss and make the building more efficient but in very different ways.
If a property is suitable for cavity wall insulation it is easy and quick (4-8 hrs) to insulate. Holes are typically drilled through the mortar joints and insulation (typically polystyrne beads) is injected (A) then filled with colour matched mortar / render. Alternatively old weatherboarding can be removed and mineral wool or similar be inserted (B). A thorough survey should take place beforehand to check suitability and highlight any defects or dampness that must be rectified before it can be insulated. Cavity wall insulation should always be done by a registered contractor that can offer a 25 year guarantee from an independent body, the Cavity Insulation Guarantee Agency (CIGA).
Most households can access grants for this type of insulation.
Energy Saving Trust