How much loft insulation do you need?

How much loft insulation do you need?

Over the years, insulation has become an increasingly worthwhile investment for homes and businesses. Energy bills have soared over the last 10 years and loft insulation is a relatively cheap energy efficiency measure to install, so it makes sense that people are looking to install it where possible and benefit from lower energy bills.

Back in the eighties, just 25-50 millimetres was considered sufficient, whilst building regulations now dictate that a new build needs to have 270mm of insulation in the loft to achieve the required u-value of less than 0.16w /m2k  (based on standard rock wool or sheep wool insulation).

Diminishing returns of installing additional insulation

With loft insulation, there is a law of depreciating returns, which means the first few centimetres of insulation will save you many times the cost of the installation, but each extra centimetre adds less value, to the point where it is no longer worthwhile to add any more. With cheaper energy prices 30 years ago, that extra few centimetres of insulation was just not worth it, but with the recent astronomical rises in fuel costs, that extra £10 a year saving has suddenly become £30, and that starts to become a lot more attractive.

Is it worth topping up your loft insulation?

In the following table you can see the energy savings from adding additional insulation in to your loft. The energy savings often cited by publications are based on going from no insulation to a depth of 270mm, however in our experience, most homes will have some level of insulation; it is actually quite rare to find a property with no insulation at all.

The numbers in the table are based on a typical turn of the century mid terrace property. It has solid walls but a modern boiler and has an area of 86m2

Current Insulation level Savings/year by Increasing to 270mm ROI based on cost of £300
 None £173  2 years
 12mm  £111  3 years
 25mm  £71  4.5 years
 50mm  £44  7 years
 75mm  £29  10 years
 100mm  £13  23 years
 150mm  £7  43 years


The actual savings will of course depend on how warm you like your home and how long you have your heating on for. A well insulated property will keep the heat in longer and therefore make your boiler work less hard. The insulation lasts a long time as well, so even if it takes 20 years to pay back, it will still pay for itself in its lifetime.

Because the savings can vary so much depending on the fabric of your home, and how much heat you need, the savings can vary considerably, so it may be worth getting an energy assessment to see if your home could benefit from adding extra insulation in the loft.

How much loft insulation is enough?

If you already have 270mm of loft insulation, whatever the material, you will not benefit from a top up. The cost of materials and installation will be too high for the few pounds a year you will save.

If you have less than 75mm, you are looking at making significant savings with an excellent return on investment of around 10 years or less. The cost/benefit of insulating up to 350mm is very marginal, but may be of benefit if you spend a lot on heating. The installation cost is of course much reduced if you are insulating up to 270mm anyway – so you should check with your assessor to see how much insulation will be right for your property.

If you are able to install the insulation yourself, the costs will be much lower, and you will likely at least halve the periods for return on investment.

It is also worth noting that we have not considered any future energy price increases in our figures. Obviously, one would expect energy prices to continue to rising, and that being said the savings could be far larger and the payback far quicker than stated above.

Free loft insulation is currently available in some areas

Any home within a CSCO postcode area or in receipt of certain benefits can get free loft insulation, as long as you currently have 50mm or less in your loft, and it is possible to insulate more than 50% of the space. You can get in touch with us if you think you may qualify for a free assessment.

Installing loft insulation

Interested in installing loft installation? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

If you would like us to find you a local installer, just fill in the form below and we will be in touch shortly!

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