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Roof and Rafter Insulation

Heating a property is becoming more and more expensive as the cost of gas and electricity continue to rise. With the government also committed to reducing carbon emissions, there is a real drive towards making homes more energy efficient. As well as installing an efficient heating system, good insulation of your house will help to push down the cost of heating.

Heat produced to warm the house will rise, and a significant amount of heat can be lost through the roof; an un-insulated property could lose around 25% of its heat through the roof.

Cut home heating costs by installing good roof and rafter insulation.

The cost of heating your house can be reduced by installing efficient roof and loft insulation.

Properly insulating lofts and flat roofs is a very simple way of cutting out that heat loss and keeping the house warmer at a lower cost.

Good insulation can last up to 40 years, and will have paid for itself within the first few years.


What is Roof Insulation?

Roof or loft insulation works by the same principle as a duvet or blanket, as it covers the house and retains the heat. Loft insulation is typically bought in rolls and can be laid out between the beams that make up the floor of the loft. It is often put down in two layers and it is recommended that the insulation be at least 270mm thick.

There are a variety of different materials which can be used for roof and loft insulation, including:

· Loose-fill

This is loose material made up of cork granules, mineral wool or cellulose fibre, and vermiculite. It can be bought by the bag and poured into the spaces between joists and beams. It is particularly useful for lofts, which have poor access, or irregular shaped buildings which may have small awkward spaces in the loft

· Matting

Otherwise referred to as quilt insulation, can be bought in rolls of varying thickness. By far the most common is mineral wool, which is made from rock fibre or glass fibre. There are other materials, such as sheep’s wool, that are available to use as matting, but mineral wool is currently the most popular choice of loft insulation.

· Rigid insulation boards

These insulating boards can be used for walls and floors as well as ceilings, and can be easily cut to size; making it useful for jobs where space in the loft is limited. It is most commonly made from polyurethane (PUR), or from polyisocyanurate (PIR), and can be cut to size to suit any space.

· Blown insulation

This type of insulation is made of cellulose fibre, which is fire resistant, usually derived from recycled newspapers or mineral wool. Installers can blow the loose material into sectioned off areas to the required depth, using specialist equipment.


Selecting the Right Insulation

The type of insulation you choose will depend on the type of property you have and the type of roof to be insulated.

If the loft has easy access and a regular beam pattern, you can use matting insulation and it is relatively easy to do it yourself. Rolls of mineral wool can be bought from most DIY shops and laid between the beams, to a recommended depth of 270mm.

If the loft is to be used for living space or storage and you are laying down wooden boards for the flooring, you can lay mineral wool insulation between joists before laying the floor.

This will not give the required depth of insulation, however, so you will need to use rigid insulation boards below the wooden boarding to achieve the desired depth. You can buy wooden boarding with insulating boards pre-bonded, which will make the job easier.

When using the loft for living space, you could install pitched roof insulation, by fitting insulating rigid boards to the rafters. Boards should be cut to the required size to fit between rafters, and covered by plasterboard. Depending on how deep the rafters are, you may need to use insulated plasterboard to get the right thickness of insulation.

The best loft insulation for a loft, which is difficult to access may be loose insulation which is blown into the space by a professional installer. It is a job that will only take a professional a few hours with the right equipment.

Loose-fill insulation can be used if you have a loft with irregular beams or is difficult to access.

Professional insulation installer blowing loose fill between loft joists.

Loose-fill insulation can be used if you have a loft with irregular beams, which make it difficult to lay mineral wool or matting.

It can be poured into the space between joists to the recommended depth of 270mm.

Insulating materials are measured in terms of their thermal conductivity, for loft insulation the value can vary from 0.044 W/mK to 0.37 W/mK. Building regulation specify that roof and loft insulation should have a U value of no more than 0.16 W/m2K. To achieve this U value, insulation materials require a certain thickness depending on their thermal conductivity:

· 0.044 W/mK – 270mm
· 0.040 W/mK – 250mm
· 0.039 W/mK – 240mm
· 0.037 W/mK – 230mm


Flat Roof Insulation

Flat roof insulation is a different matter, as flat roofs are usually insulated from above. Rigid boards can be fitted on top of the weatherproof layer, or on top of the timber roof surface then a new weatherproof layer can be installed over the insulation. If insulation is fitted as part of a replacement flat roof, it must comply with building regulations.


Loft Insulation Prices

The cost of insulating a roof or a loft space can range from £100 – £350; and the Energy Saving Trust suggest that you could save up to £175 per year, by installing insulation which is 270mm thick into a previously un-insulated property. The insulation could easily pay for itself within a few years, and could also save around 720kg of CO2 per year.



Relatively cheap to install, and with a quick payback, roof insulation is a very simple way to improve the energy efficiency of your home and reduce you heating bills.

There are a variety of different types of insulation and which you use will depend on the property. It may be that you can fit the insulation yourself if you have a loft with easy access; but if it is difficult to get to, or you are insulating a flat roof it is best to call in the professionals.

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