Loft Insulation: Everything You Need To Know

By Ian on Thursday 14th December 2023

300mm of loft insulation with a storage area on loft legs.

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Homes lose a significant amount of heat through their roof. Having enough insulation to stop this happening can reduce energy bills and keep your home warmer. How much loft insulation do you need? Can you install it yourself? We answer these questions and more in our guide to loft insulation below.


What Is Loft Insulation

The dictionary definition of ‘Loft Insulation’ is probably something like the following.

Loft insulation, also known as roof insulation, is a material used in construction that stops heat escaping through roofs of properties.

Everyone already knows this, but, there are a couple of different types of loft insulation and ways of installing it. The most common is mineral wool. It’s rolled out between the ceiling joists where it creates a barrier between the heated and unheated parts of your home. You can also use a rigid board insulation, like Kingspan in a similar way. Don’t put it between your joists and stand on it though!

Insulation at the ceiling joists is the most efficient way to use loft insulation. Some insulation, like foam, is installed at the rafters (against the external roof material). Insulating this way allows heat to get in to your loft space. Do you really need to heat your loft space? Looking at the construction of roofs, they are designed with a high air change rate. This helps with ventilation and reduces condensation. Roofs that are insulated at the rafters leak all the warm air through these ventilation channels, but if you insulate at the ceiling joists, you are preventing most of the warmth from reaching them.

Why Do We Need It?

Having a warm home and spending less money on energy bills are two separate, but closely related issues for home owners and tenants. Some homes are really difficult to heat and are never truly ‘warm’. To give yourself the best shot at being able to bring the temperature to the 20s, wasted energy needs to be cut. Loft insulation plays a key role in this. Studies have shown that 25% of wasted energy is lost through the roof. Walls, floors, doors and windows also play a role in heat loss too. By making sure you have the recommended amount of loft insulation (270mm), you are giving yourself the best chance of getting your home warm.

If you are refurbishing your home, its the perfect time to add insulation and improve its energy efficiency.

For mineral wool insulation, it is recommended that each loft space has a 270mm blanket covering the joists above the ceiling. If you go the rigid insulation board route, this is about twice as efficient as mineral wool, which means you’ll need around 120mm. This will get you a U-Value of 0.16 W/m2K, which is the current building regs standard. What benefits will you get with this minimum recommended amount (in order of obviousness)

  • Your home will be warmer
  • You’ll save money on your energy bills
  • Your home will warm up faster
  • Your home will stay warmer for longer
  • Your boiler wont need to work as hard which will increase its life span.
  • Improve your EPC score

Can I Insulate My Loft Myself?

Yes! Its a straightforward job but there are a couple of important notes.

You need to make sure your roof is leak free and there is no condensation or damp problems. If you have any of these issues your new insulation will get wet which will cause damage to your home, make the insulation useless and make any repairs harder work.

Work safely. If you are not sure how to do the job or confident to do it in a safe manner, get a professional in. Although the job is straightforward, its not easy work. In essence, all you need to do is remove any insulation there already and roll out the new stuff. But, you’ll be crouched over most of the time with a face mask on and it becomes easier to step off your crawl board and fall through the ceiling as the day goes on.

Loft Storage

The number one rule when you’ve got good insulation is not to squash it! The insulation will work much better if its not compressed with your stuff. If you’re going to put 270mm of insulation in your loft and compress it down to 100mm, you should have just put 100mm of insulation down. Heat will find the path of least resistance so don’t think you can get away with ‘I’ll just put my Christmas decorations on this bit, the rest of it will be okay’.

Seriously though, if you want to use your loft for storage, you can install a section on loft legs that will give you a platform raised above your insulation without squashing it down.

Loft Insulation & Your EPC

To get top marks on your EPC you’ll need a minimum of 270mm of insulation at your joists in your loft. It has to fully cover the loft space without any reduction in thickness. If you have less than 100mm of insulation, you will get a recommendation to improve it. To find out more about how loft insulation impacts your EPC or to book an Energy Performance Certificate, give us a call on 01925 699 321.


Improving your loft insulation can have a host of benefits beyond a warmer home and saving money. Having 270mm of loft insulation is an inexpensive job which you can do yourself. Make sure to use loft legs if you want storage too! A home loses 25% of its wasted energy through the loft so its a job worth doing.

About the Author

About Ian Kay

Ian is a seasoned energy assessor helping his customers, reduce energy usage and save money on their bills. He holds qualifications from both City & Guilds and ABBE for Domestic EPCs and Commercial EPCs (Level 3 NDEA and Level 4 NDEA). With a background in the building trade he can provide his customers with a unique perspective and advice. Ian combines his deep industry knowledge with practical advice to create blog posts that help visitors understand the complexities of energy performance certificates and reducing operating costs. When not immersed in the world of energy assessments, Ian enjoys exploring the great outdoors and spending quality time with his family.

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