An introduction to loft insulation

Why should I install loft insulation?

Insulating your loft is one of the best ways to improve the EPC rating of your home. If you have a virgin loft (i.e. 25mm or less of insulation) then insulating it will produce massive savings on your energy bill and the great thing is that for many of us, the energy companies offer this insulation free.

Without proper loft insulation, a lot of the warmth produced by your heating system escapes through the roof of your property; in fact, as much as 25% of the heat in an uninsulated house is lost in this way. Loft insulation acts as a barrier, slowing the movement of heat out of the property during the winter and into the property during the summer.

Even if you can’t get it for free, it is an incredibly easy DIY job and below we are going to discuss exactly how you can do that.

The first decision to make is whether you are looking to create a warm loft or cold loft. The majority of us just use the loft space for storage so normally a cold loft will more than suffice, but for some we use the loft space for a games room or a study. To be honest, insulating your loft as a cold loft is far easier than trying to produce a warm loft – mainly because you don’t need to fight gravity.

How to insulate your loft

The method of insulating your loft varies considerably whether you have decide to push forward for a warm loft or a cold loft, but since the vast majority go for a cold loft lets start there.

Insulating your loft at the joists

The purpose of insulation is to produce a barrier that slows the movement of heat either in or out of the property. When you produce a cold loft, you need to lay insulation directly above the ceiling to produce this barrier to slow the movement of heat out of the home during the winter and visa versa in the summer to prevent the home overheating.

The latest building regulations stipulate you need to reach a U-value of 0.16 to conform – now for most of us who don’t talk ‘U-values’, this simply means you need a 300mm blanket of wool insulation (if you decide to use rigid insulation board like celotex or Kingspan then you can achieve this u-value with less thickness).

If you use wool insulation (which is what 95% of homes use), then the best way is first to insulate between the joists. Most joists are about 100mm high, so first you need to roll 100mm thick insulation between the joists (if you go into a DIY store or even to our online store you will be able to buy different thicknesses of insulation – so be sure to get the right thickness!)

Once the 100mm insulation is sitting snugly between the joists you can simply roll out 200mm thick insulation on top of this at 90 degrees to the joists. This produces a carpet of insulation that will significantly reduce heat loss out of your home. The reason why we are such advocates of loft insulation and consider it the no.1 method of saving energy in the home is basically because the insulation is incredibly cheap to buy and the process of producing a cold loft is so easy.

Now a couple of important things to mention; while this is certainly the cheapest way to go, the loft space itself will be very cold in the winter. This means that anything you really value should be kept in the home itself, not in the loft. In addition you need to insulate any pipework and cold water tanks up in the loft as these may now be liable to freezing and the cost of repairing bursting pipes will far outweigh the energy savings produced!

For detailed instructions on how to insulate your loft to produce a cold loft please click below

>>> Insulating your loft at the joists – producing a cold loft <<< 

We include things like capping light fittings, insulating cold-water tanks and the different materials that you might want to consider.

Insulating your loft at the rafters

Gravity is a pain – it makes producing a warm loft that much harder. Unfortunately if one tries to insulate between the rafters by squishing in lots of wool insulation then 9 times out of 10 it will just fall out.

However if your heart is set on creating a warm loft space then it is definitely possible. There are four main ways to insulate your rafters; the first is to use netting and wool insulation. Using solid insulation board is again a really good way to minimise heat loss out of your home. The third way is simply to use reflective foil stapled to the rafters – this doesn’t produce significant energy savings but is by far the simplest way to go, requiring just reflective foil and a staple gun. You might want to use reflective foil anyway even if you do opt for a cold loft.

The final method of creating a warm loft is using spray foam although this will always need to be installed by a professional.

So, looking at each of the methods in turn:

The difficulty in creating a warm loft with wool insulation is basically due to the thickness of wool insulation needed to hit the necessary U-value as specified by building regulations (300mm) although to be honest, if you are doing this yourself, you are not required by law to conform. The way to keep the insulation in place is to use a net that you can then staple to the rafters which acts as a hammock for the insulation.

When you use solid insulation board to create a warm loft the key thing to remember is ventilation – you must keep a 50mm gap between the roof and the rigid insulation board. We would always recommend having a breathable membrane in place between the tiles and the rafters too to allow the roof to breathe. If there is no vapour layer it might result in damp issues, since the warm air may condense in the loft space on cold surfaces. Water and timber don’t work too well together and it could result in the timbers rotting. The best way to achieve the gap is to attach some dowel batons on the inside of the rafters so you can then butt the insulation board up to them ensuring the 50mm gap is still in place. If you measure the thickness of the rafter, then less the 50mm gap – this is the thickness of the rigid board you want to put between the rafters. By doing this the insulation board will then not protrude out past the outside edge of the rafters, which means that you can then very simply attach more insulation boards, fixing them directly to the rafters to achieve the required depth of insulation.

As mentioned, the foil is by far the easiest way to insulate your loft; you simply staple it to the rafters. It is worth starting at the apex of the ceiling and then working down the rafters, overlapping the foil to achieve a continuous reflect surface. You can then tape over the joins.

When professionals come in and install spray foams, they can achieve high thermal efficiency with very little depth. The two downsides of this firstly that it is very expensive compared to the other methods and also it doesn’t allow the roof to breath, locking in the water next to the timber – which as we have mentioned previously can lead to problems.

While having a warm loft space is great because you can then use the space – you are now heating an extra ‘room’ that you wouldn’t normally heat if you insulated just above the ceiling (i.e. a cold loft) – which means your heating bill will be higher.

For detailed instructions on how to insulate your loft to produce a warm loft please click below

>>> Insulating your loft in the rafters – producing a warm loft <<< 

We include detailed instructions of how to create a warm loft including the different methods and the different materials you can use.


    • Potential savings of £40 – £145 pa off your energy bills, paying back in as little as 2 years.
    • CO2 saving of 210kg to 730kg pa.
    • Grants and offers to you if you are a homeowner or a landlord.


    • No limitations


    • Install costs roughly £250.
    • DIY cost of £50 – £350.