With about 25% of the heat in your home lost through the roof [1]knowing how to insulate your loft could save up to £55 a year on your energy bills.[2]It can help reduce waste, keep your home consistently warm, and help the environment.
Follow our guide to learn how to insulate your loft cost-effectively, with tips on installing it yourself and the benefits you can look forward to.
EASY AS HACK
You can save about £35 a year by topping up existing loft insulation from 5cm to 27cm.[1]
At a glance
Insulating your loft benefits you and the environment:
- No energy wastage
- Lower energy bills
- Consistent temperatures
- Reduced emissions
what is roof insulation?
Roof insulation is a layer of material installed within your roof structure to reduce heat loss. It usually sits between the top-floor ceiling and the loft but can also be installed under the roof, sloping or flat.[2]
Loft insulation can be made from various materials and comes in blankets and rolls, loose fill, sheets and boards, and blown fibre.[3]These are the different types of insulation that can be used:
Insulation rolls/blankets:
- Mineral wool
- Glass fibre
- Sheep’s wool
- Foil-backed felt
Loose material/blown fibre:
- Mineral fibre
- Cellulose
- Cork granules
- Recycled newspaper
Sheets and rigid board:
- Foam boards (PIR or polystyrene)
- Cork
- Straw
- Wood
Blown fibre:
- Recycled paper
- Wool
preparing to insulate your loft
The following advice is for insulating a pitched roof. Before laying loft insulation, you must ensure the attic is safe to access:
- Remove any fixed boards and clear as much space as possible
- Remove as many items as you can, giving you room to move[4]
- Check for any dampness or leaks (you can cause mould if you insulate a damp loft or one with condensation issues)[1]
- Assess any electrical and lighting cables)[3]
- Install covers on ceiling downlights to prevent them from overheating
- Check for any existing insulation under the cold water tank and around the pipework
- Ensure you have the necessary tools, safety equipment and insulation before you begin.[4]
how to lay loft insulation
How you lay loft insulation will depend on whether you intend to store things in the loft and whether you have opted for cold or warm insulation.
cold loft insulation
Which? recommends warm loft insulation under a pitched roof as it’s the simplest and cheapest type to install by DIYers. You add insulation on the loft’s ‘floor’ between the joists.
The area above the insulation remains cold or hot depending on the season, so don’t store anything differing temperatures would affect. You will not need insulation between the rafters if you are laying it on the floor.
Materials: Pre-cut batts (resembling small quilts) made of glass fibre, mineral wool or natural sheep’s wool.[5]
warm loft insulation
Warm loft insulation could be the better option if you’re storing many items in your loft or your belongings are affected by rising and falling temperatures.
This form of insulation involves placing material in the cavities between the rafters on the roof’s inner slope. However, it’s not as simple to install as cold loft insulation and can be more expensive because the heat rises into a more substantial space. You may also need a professional installer. [3]
Materials: Foam or polystyrene insulation boards or sheets.[3]
measure the insulation
Blanket insulation
If you are laying insulation on the loft floor (cold insulation), measure your loft’s width and length to determine how much blanket or quilt insulation you’ll need in square metres, and cut it to size.
Check the height of the joists (usually 100mm) to know the depth and width of insulation required.[3]The thickness may depend on whether you have installed insulation and are topping up. Natural materials like wool and wooden floors are eco-friendly choices.[6]
Loose-fill insulation
Read the manufacturer’s specifications to calculate how many litres or bags you need using loose-fill loft insulation.[3]
Rigid loft boards
You cannot step on the blanket or loose-fill insulation. So, measure the space for rigid loft boards, including joist extenders or spacers, to stop them from touching the insulation. This step is essential if you want to use the loft for storage.[2]
Insulation boards or sheets
Calculate how much insulation you need. Install the insulation between and across the rafters.[3] When adding insulation to the roof’s underside, staple a multifoil layer to the sloping rafters.[7]
lay the insulation
The best method for laying insulation on the loft floor is to start in one corner and work backwards towards the loft hatch.
- Plug any air leaks and gaps in the loft ‘floor’ with sealant and tape and rubber grommets around lighting cables
- Leave a 25mm gap for ventilation at the bottom of the rafters to help prevent condensation[7]
- Don’t overlap or compress the insulation, or it loses its insulation properties
- Do not insulate the space under the water tank if you have one
- Cover a water tank with an insulation jacket
- Cover any pipes with pipe insulation[4]
ensure the insulation is fitted
Blanket insulation
Lay blankets of insulation flatly and snugly between the joists. The insulation should be a minimum depth of 27cm.
You may need to cut it using a sharp knife to avoid stretching or tearing.[3]
Loose-fill insulation
If you use loose-fill insulation (helpful in period and listed homes), pour it from the bag between the joints. Make sure any wires go on top of it and cap any downlights. It’s best to use a professional for blown insulation.[7]
layering
Once you’ve laid your insulation blanket between all the joists in the area, you can lay a second or top layer across them at right angles. Experts recommend this if you’re not using the loft for storage.[7]
Don’t forget to add a layer of foam insulation to the loft door.[7]
flat roof insulation
Although you can fit insulation on flat roofs, such as those on extensions, it’s more challenging and costly to install. However, you’ll also make similar savings.[8]
The types of insulation for flat roofs are:
- Warm deck insulation – rigid board is laid over the existing roof deck with a vapour barrier in between and a new roof deck on top.
- Cold deck insulation – adding mineral fibre or ridged insulation between the roof deck and the internal ceiling, creating a vapour barrier.[2]
You will need a professional to install insulation correctly on flat roofs.
benefits of loft insulation
The benefits of insulating your loft include the following:
- You can save on your energy bills
- Other insulation options are easy for professionals
- Greener options are available for some insulation materials
- Allows you to keep the heat in your home
- Cold-loft insulation is easy to install
things to consider before insulating your loft
You should think about the following things before insulating your loft:
- Storage space – you must lay rigid boards over the joists; otherwise, the insulation won’t be thick enough
- Damp lofts – if your loft is prone to dampness or condensation, you will need to address the problem first[9]
- Ventilation – be careful not to cover any vents
safety tips when insulating your loft
Follow our safety tips when insulating your loft:
- Lay crawl boards across joints to support your weight while working[4]
- Wear gloves, a ‘bump’ cap, safety goggles, protective gloves and a dust mask when handling insulation [9]
- Never touch old cables in a loft without checking whether they are live.[10] Get expert advice from an electrician to ensure electrical wires and cables are safe before insulating your attic
- Isolate any heat-producing fixtures and install light covers on downlights.[4]
- Keep anything you need, including the packaged insulation, within reach – the tools you’ll need include a hand brush, tape, sealant, a tape measure, scissors or a knife, and a saw [9]
- Only use insulation that is specified for lofts
- Get help – when moving insulation rolls into the loft
Loft insulation can prevent problems like damp, mould, and frozen pipes — all of which can lead to home insurance claims.
Find out more about Ageas Home Insurance.
FAQs
how much does it cost to insulate your loft?
How much it costs to insulate your loft will depend on its size and accessibility.[6]
how much can loft insulation save you on your energy bills?
How much loft insulation can save you on energy bills will depend on your property type. On a detached house, you could save up to £380 a year.[6]
can i insulate my loft myself?
You can insulate your loft when it’s easily accessible, with no damp issues, and it isn’t a flat roof. It’s also easier to get a professional to install warm loft insulation.
should i insulate between the joists?
Yes, insulating between the joists of your loft will keep your house warmer.
Sources
[1] Department of energy and climate change
[2] Centre for Sustainable Energy
[3] www.which.co.uk
[4] How to install your loft insulation guide
[6] https://www.evergreenenergy.co.uk/insulation/loft-insulation-guide
[7] How much energy does loft insulation save
[8] Issues with insulation being damp
