How to fit loft insulation

If you’re looking to install your own loft insulation because you’ve missed the deadline for the available grant schemes for loft insulation, double check that there aren’t any schemes that you’re eligible for - there are a few still going so check our Grants for FREE Wall & Loft Insulation pages to be sure.

If you simply want to do it yourself fitting or toping up loft insulation is a relatively simple and inexpensive job, and you don’t need any specialist skills to do it. Just follow our step by step guide to install your insulation quickly and easily.

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1. Measure how much loft insulation you need:

It’s recommended that your insulation reaches a minimum depth of 270mm, although you can fit as much as you like. So the first thing to do is to measure how much insulation you already have – if it’s less than 270mm then you could save yourself money on your heating bills by fitting more; as much as 15% every year in some cases.

If you do need to top up your insulation or fit your insulation from scratch, you then need to measure the size of your loft and also the gaps between the ceiling joists. Download your free loft insulation calculator to help you use your measurements to work out roughly how many rolls of insulation you’ll need to buy.

Your joist width can dictate which insulation you need to buy. Standard ceiling joists are usually 370mm apart and some insulation rolls are pre-cut to this width, such as glass mineral wool. For wider joists of 400 or 600mm there are insulation rolls that are perforated for either 400mm or 600mm widths, such as the Combi Loft Roll.

Count the spaces between the joists as you will need this to work out the exact number of rolls that you will need.

So that you can work safely and don’t accidently put your foot through your ceiling, get some chipboard panels to lay across the joists to walk on.

2. Lay the insulation:

First thing you need to do is to clear the loft of any clutter that is up there. This is often the hardest part!

Before you start make sure that:

  1. You read and follow the insulation manufacturer’s instructions; there will always be specific guidance for fitting each insulation product and you should follow these closely.
  2. You have the correct protective clothing; you should have suitable clothing, a mask and gloves. Lofts are generally very dusty places and you shouldn’t be breathing in mineral wool fibres!

If you need to lay two layers of insulation to reach the required depth of 270mm, start with the thinnest layer first (if they are different depths). Start at the farthest point from the loft hatch or entrance to your loft, and work back to it. Lay the first roll between the ceiling joists, and then any further rolls on top, until you have a depth of 270mm.

Try not to squash the insulation material down – it works by trapping air in it, rather like a duvet. It will not be as effective if it is squashed down.

Make sure that you leave at least 25mm between the insulation and the roof. This is particularly important at the eaves. This allows ventilation to the roof space.

3. Electrics and your loft insulation:

If you have recessed ceiling lights in your ceiling you will need to ensure that you leave an uninsulated space of at least 75mm around each of them. This will ensure that they do not overheat and do not pose a fire risk.

Electrical wiring should be laid over the top of any insulation that you fit. This is safer and you will find it easier to access it in future if you or an electrician needs to. Do not bury your wiring underneath the insulation.

4. Insulating your loft hatch and pipes in the loft:

Don’t forget to insulate your loft hatch or entrance to the loft space as well as the loft itself, as warm air will escape through here too. Cut a piece of your insulation and either tack it or tape it to the top of the loft hatch.

You loft will now be a cold space, so if you have any pipe work running through it, it is a good idea to insulate these pipes using foam insulation tubes to ensure that the water will not freeze in them. They are ready cut so all that you need to do is cut the tube to the length of the pipe and then slip it over the pipe.

If you have a cold water tank in the loft, do not insulate under the tank, as this will increase the chance that the tank will freeze. Instead wrap insulation around the outside of the tank, holding it in place with either string or tape.

While you are adding insulation to your loft it is worth considering draught proofing and insulating other part of your home. There is lots of great advice about how to do this on the internet. We recommend that have a look at DIY Doctor who have a complete section dedicated to DIY draught proofing and insulation projects.

How much will my loft insulation cost?

Your loft insulation costs will entirely depend on the size of the loft and the depth of insulation needed. This determines the number of rolls that you need, and they cost in the region of:

  • Combi Cut Loft Insulation – around £27 per roll and covers approx 13.8sq m.
  • Space Blanket – around £15 per roll and covers approx 2sq m.

Loft insulation is usually a very good investment – if you spend around £250 to add insulation to your loft where previously you had none, it could save you as much as £180 per year on your heating bills. You can even get your loft insulation free if you meet certain criteria – take a look at our HHCRO scheme page for more information

Download your free loft insulation calculator to see how many rolls you’d need to buy now!

Or see if you qualify for free loft insulation!




My house is semi-detached/terraced and my neighbour(s) doesn't want cavity wall insulation. Can you still insulate my walls?
Yes, your house can still be insulated. The installer will need to make a hole at the top and bottom of the wall to insert a spacer at the junction between the two houses. This prevents insulation being blown into the cavity of your neighbour's house.
How can I tell if my new home's previous owners have already insulated the cavity walls?
If a house was built within the last ten years, it probably has cavity wall insulation installed as slabs when the walls were built. You can tell if previous owners have had it installed after the house was built by looking at the outside of the external walls under your windows. If there are small holes of about an inch diameter filled in with something, this indicates that your walls have been filled with insulation. Another way to tell is by looking at the tops of your external walls, which may be open under your roof. If you can look inside the tops of the walls you may be able to see whether there's any insulation in them.
Are there grants available for cavity wall insulation and are there strict criteria as to who is eligible, like with loft insulation?
There are grants available for cavity wall insulation available through the CERT (Carbon Emissions Reduction Target) scheme, which is available through the energy suppliers. You can apply to any of the larger suppliers regardless of whether you're a customer of theirs. The scheme is now only available through British Gas and Scottish Power, as most of the scheme shave run out - apply now if you could benefit. The ECO (Affordable Warmth) scheme is due to replace CERT, and is currently operating, but has stricter criteria on who's eligible, focusing on less well off customers.
I want to use my loft for storage, how can I do that if it is insulated to the depth recommended?
You or your installer can instead lay down innovative loft boards called Space Board. These are insulation boards made from Polyfoam extruded polystyrene designed to be placed on top of the ceiling joists instead of the 170mm mineral wool insulation. You should still aim to lay down 100mm of standard insulation between the joists.
I already have some loft insulation - do I need to install more?
If your loft insulation is 100mm or less you would certainly benefit by having it topped up with more insulation to make it up to a 270mm thickness. The Energy Saving Trust estimates that top-up loft insulation can save the average householder as much as £60 per year at current energy prices.
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