Insulating your home can seem like a daunting task, but B&Q are here to help. With our easy to follow guide you will find everything you need to know about loft insulation all under one roof.
Types of insulation
Insulation designed for lofts comes in the form of blanket rolls, boards, panels and foil. It may be made from glass mineral wool, rock mineral wool, polystyrene, recycled plastic bottles or natural fibre products such as sheep's wool.
Blanket insulation is traditionally made from glass mineral wool. It is sold in rolls usually 100mm, 150mm, 170mm, 200mm or 270mm thick, and is available perforated to cut and fit between widths of 400mm, which matches the joist spacing in older houses, and 600mm for more modern houses. It is compression packed for easier handling and will expand to the required thickness when unwrapped. Glass mineral wool is irritating to the skin, so gloves and protective clothing are essential. Alternatively you could choose encapsulated or non-irritant blanket insulation.Shop loft insulation
This consists of glass mineral wool encapsulated between thin plastic on the bottom and part metalized polythene film on the top. It is a light, quilt like insulation packaged in a roll. Because the glass mineral wool is encapsulated, it is much more comfortable to work with, though gloves and protective clothing still need to be worm when cutting and handling. It is available in dimensions suitable for laying between and on top of joists.Shop loft insulation
Semi rigid rock mineral wool slab insulation is designed to be friction fitted between rafters, which means it is quick and easy to install without the need for additional fixing. It also has acoustic insulation properties, and can be used to insulate and soundproof a stud partition wall by fitting it between timber or metal studs.Shop constructional insulation
Polystyrene loft board
If you need to install storage boards in your loft you should combine blanket insulation laid between the joists with extruded polystyrene loft boards laid on top. These are quick and easy to cut and fit, have a high compressive strength, and can also be installed over existing timber loft boards. Chipboard loft boards are finally laid on top and secured to the joists.Shop constructional insulation
Reflective insulating foil can be rolled across the rafters and secured with a staple gun. Each row is butted up against the next and the join taped together. This is only a top up product: you also need adequate insulation at the joists.Shop constructional insulation
These expanded polystyrene panels are simply squeezed in place between the rafters. Like reflective foil they are suitable as a top up insulation but you will also need adequate insulation at the joists.Shop constructional insulation
How to insulate your home
Without proper insulation as much as 50% of your heating could be disappearing straight through the walls and roof. Leaking heat means leaking money! Loft insulation is surprisingly quick and easy to install, and is one of the most effective steps you can take to make your home more energy efficient and bring down your bills.
How much insulation?
Most homes have some insulation, but it may not be as effective as if could be. A minimum of 270mm insulation is recommended for loft floors, but it is also common to find as little as 25mm, particularly in older houses. Sometimes existing insulation has been compressed by storage boards laid over the top: this makes it much less effective. Insulation can easily be topped up using blanket insulation (also known as loft roll). This is available in different thicknesses and width's designed to be laid between and on top of joists. However, if you want to be able to walk in the loft or store boxes, then you will need to lay solid polystyrene board insulation on top of the insulated joists and secure chipboard loft boards on top.Shop constructional insulation
Shop loft insulation
Fitting insulation at the joists (on the loft floor) reduces the amount of heating rising into the loft space, so in winter it will get colder up there than it used to. If you use the space for storing perishable items such as photos or books, you can insulate the sloping roof to keep more heat in the loft. The insulation can either be expanded polystyrene panels fitted between the rafters or reflective foil stapled to the rafters.
Alternatively you could install multi-foil insulating quilt at the rafters. Although more expensive than conventional products, its far more efficient and gives and much higher level of insulation than equivalent thicknesses of conventional insulating material.
However, rafter insulation should be used as a top up only; you will need 270mm of insulation at the joists otherwise you will be wasting energy and money to heat an uninhabited loft space. If you convert a loft into a room, the insulation requirement is different and you will need professional advice as well as building control approval.Shop constructional insulation
The 'R' value
The insulating properties of a material are described by the thermal resistance or 'R' value. This is how much the material stops heat passing through it. The higher the 'R' value the better the insulation. A minimum 'R' value of 6.1 is recommended in a loft, and preferably up to 7.0. Simply add the 'R' values of different products together to get there combined 'R' value. To work out the approximate 'R' values of your existing insulation see the 'R' values table.Shop loft insulation
Laying blanket insulation
Rolls of blanket insulation are easy to lay and fit. To calculate how many rolls you need, measure the length and width of your loft. This may be difficult to do in the loft area. If the ground floor is the same size as the loft, you can measure that instead, or even measure around the exterior walls of the house. Multiply the length by the width to determine the area, and then dived that figure by the coverage per pack of insulation to work out how many packs you need.
The rolls can be heavy, so if you are using the larger ones either have someone pass them up to you or cut them to size before taking them into the loft area. Once the second layer of insulation is down, you can no longer see the joists, so this method is only suitable for a loft or part loft that does not need to walked on or used for storage. If laying mineral wool insulation, as here, you will need protective clothing and gloves.Shop constructional insulation
Shop loft insulation
Clear the loft as much as possible to give yourself a large safe work area. Remove any old storage boards. Use planks to create a flat storage area for a few rolls close to where you are working. Make yourself one or more walk boards, long enough to span three or four joists and wide enough to kneel on.
Start in the corner and work back towards the hatch. Position your walk board along the adjacent joists. Begin laying the first roll at the eaves, leaving a 25mm gap for ventilation. Use 100mm insulation between the rafters.
Continue unrolling between the joists across the loft floor area. If one roll isn't long enough to reach to the other side, start a new roll and butt the joints closely together.
Once you have unrolled your first length, lightly push the insulation down against the joists so there are no gaps, taking care not to compress it. Carry on across the loft area.
For narrower areas, cut the insulation to the required width and lay it between the joists in the same way. Do not pack or compress insulation into awkward corners.
When you reach the cross beam, cut the insulation flush with the beam (see step six) then start again on the other side, working in from the eaves.
How to insulate your home - first steps
How to insulate your home - measuring up
How to insulate your home - types of loft insulation
How to insulate your home - laying the rolls between the joists
How to insulate your home - down lights
How to insulate your home - laying insulation boards