You can always tell who hasn’t insulated their loft space because of the pigeons and seagulls sitting on their roof, enjoying all the warmth coming up from the house below. Heat rises, and those wily birds are quick to take advantage.
In uninsulated homes, a quarter of the heat lost wafts out through the roof. So fitting insulation in your loft, attic or roof space is a great way to improve your home’s cosiness factor. And there’s even more good news: it lasts for more than 40 years and should pay for itself many times over in energy bill savings, as the cost of loft insulation is comparatively low.
Loft insulation is a barrier of material within your roof space. It can either be laid between the joists (the horizontal beams along the floor of your attic) or the rafters (the angled beams that support the roof).
Either way, it slows down the transfer of heat between your living space and the outside world, creating a warmer home in winter and a cooler one in summer. Insulation between the joists keeps warmth in your living space below and creates a cold loft, while insulation in the rafters allows you to keep warmth in the roof space as well.
Other benefits of roof insulation include:
Loft insulation for an average 3-bedroom, semi-detached house with gas central heating can start at about £50 for DIY installation, and could take less than a year to pay for itself thanks to lower energy bills.
These figures are from the Energy Saving Trust website, and show the benefits of installing roof insulation of up to 270mm.
|Type of residence||Detached||Semi detached||Mid terrace||Bungalow|
|Fuel bill savings per year||£240||£140||£135||£200|
|Typical cost of loft insulation installation||£395||£300||£285||£375|
|Carbon dioxide savings per year||990 kg||580 kg||550 kg||820 kg|
This table shows the benefits of increasing your loft insulation thickness from 120mm up to 270mm.
|Type of residence||Detached||Semi detached||Mid terrace||Bungalow|
|Fuel bill savings per year||£25||£15||£15||£20|
|Typical cost of loft insulation installation||£310||£250||£240||£295|
|Carbon dioxide savings per year||95 kg||55 kg||50 kg||80 kg|
Both tables are based on insulating a gas-heated home. The installation costs are unsubsidised averages and will vary.
It’s possible (in fact quite simple) to lay roof insulation yourself, as long as:
For anything more complicated than this, you’ll need to be an experienced DIY-er or bring in a professional installer who knows how to insulate a loft in the most appropriate and effective way.
Flat roofs should always be insulated by a professional, and if the space is damp you’ll need to sort that out before starting any loft insulation work.
If you live in a period home, or one that was built using local traditional stone or other materials,make sure you use appropriate loft insulation materials and methods. Otherwise your home may not be able to retain heat, or stay dry, in the way it was meant to. In fact, it may be best to consult or employ local craftspeople who are trained in the relevant techniques.
If you do have a dry attic with easy access and evenly-spaced joists, the cheapest and simplest way to insulate it is between the joists, with rolls of blanket roof insulation. This can be made of mineral wool, glass fibre or recycled materials.
This will bring your roof insulation up to a depth of 300mm, which should be plenty to stop the heat escaping from the rooms below.
If you want to store bits and pieces safely in your attic you’ll need to fit boards over the joists. However, if you simply fill the spaces between the joists with insulation and then board over the top, you won’t achieve an adequate depth of loft insulation.
To increase the thickness of your roof insulation layer, you can:
Whichever you decide to do, don’t put in 270mm of mineral wool and then just squash it down, as this will reduce its efficiency, so you might as well have used a smaller amount.
Remember, insulating between the joists will create a cold roof space, so if you’re keeping anything up there that needs to stay warm, it’s better to insulate between the rafters rather than the joists.
Make sure the hatch fits snugly. If it doesn’t, you may need to replace it. If it seems to fit more snugly in the winter than in summer, you may have damp in your loft, and you’ll need to tackle this before thinking about roof insulation.
Once you’ve got a close-fitting hatch, apply draught-stripping between the hatch and the frame.
Check there aren’t any other holes going up into the roof – above the airing cupboard, for instance, or around pipes. If there are, you should seal these before you insulate your attic.
If you’re using the loft as a bedroom, games room or study, you’ll want to keep it as warm as the rest of the house – so there’s no point in insulating the attic floor. Instead, you need to insulate the roof. The usual way to do this is by inserting rigid insulation boards between the rafters. They should be cut to exactly the right size so they fit snugly and don’t allow any draughts through. To get the required 270mm thickness of insulation, you may have to insulate over the rafters as well, using insulated plasterboard.
Unless you love the look of insulation boards (unlikely) you can then cover them with plasterboard and paint or wallpaper it.
You can also use this method if you want to keep the loft warm for other reasons.
You’ll have to use a professional installer, who can blow granules of insulation into your loft with specialist equipment. The roof insulation material will be cellulose fibre or mineral wool, treated to make sure it’s fire retardant. This should take just a few hours, depending on the size of your loft.
If you’ve got a flat roof you can still insulate it, but it’s better to insulate it on the outside rather than the inside. Insulating it from below can cause condensation problems.
When your roof is next due for replacement, you’ll have to insulate it anyway, to comply with government regulations. So if that date’s coming up soon, it makes sense to do both jobs together. You can add a layer of insulation between the timer roof surface and the outer weatherproof layer.
However, if your flat roof isn’t due for replacement for a few years, you can add the insulation board directly on top of the weatherproofing.
Insulation between the joists will make your attic much colder, so this could worse your damp problem. Even rafter insulation can encourage damp, as it stops draughts and reduces natural ventilation. So if you decide to insulate your loft you may also need to increase the amount of ventilation, and in that case you’ll need Building Control Approval.
We recommend getting professional advice from a builder or damp expert before you start on this project. Talk to them about sorting out the damp before you think about insulating the loft.
Yes. If you’re laying insulation between the joists, the roof space will become extremely cold in winter. So you need to insulate (lag) your tank and pipes individually to make sure they don’t freeze and burst. If they do, the repairs will cost far more than the savings you make from loft insulation.
However, if you insulate between the rafters rather than the joists of your attic, the space will be warm and your pipes should be fine.
Visit the National Insulation Association (NIA) website for contact details of NIA members in your area. Installers listed on the site have agreed to follow a code of professional practice.
*Source and notes for graphs and table
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