Facts about Loft Insulation

Updated: Jul 7, 2019

Every day the heat we lose from our home has an impact on the environment and on our pocket books. Through insulation we can save money and the planet.


Heat travels from hot to cold, so when we heat our homes, heat will escape from any uninsulated

area to the cooler temperature outside.

You will lose 25% of the heat in your home through the roof if it is uninsulated. A brick house with poor insulation will lose over a third of its heat through the walls, one-quarter through the roof and the rest through the doors, windows and floors.


Different materials have different properties. So metal is a good conductor – this is why it is great for saucepans and why teaspoons get hot. There are products such as Kingspan or Celotex that are polystyrene rigid boards with a foil backing. These are the best insulators however expensive.

Then there is spray foam that can be used. The most common insulator is Mineral Wool.


The key to mineral wool is it needs to be fluffy to work. What I mean by that is, if for example you have 200 mm of mineral wool fitted in your loft, however you board your loft out and compress it down between the joist, you will have pushed it down to 100 mm. The loft insulation works by trapping the heat in the air pockets of the mineral wool. So you want to keep it big and fluffy. The rule of thumb when boarding a loft is to only board 20% . You can build the joists up so as not to compress the insulation down..


Insulation saves over 600 times more energy each year than all of the compact fluorescent lights (CFLs), Energy Star Appliances, and Energy Saving windows combined.


For every Btu (British Thermal Unit-the measure by which energy is calculated) consumed in the production of insulation, 12 Btus are saved each year by the use of insulation.


People sometimes ask me if they should insulate in the rafter gaps as opposed to the joist. The problem with this is the heat will travel into the loft space and not stop until it reaches the rafters. So essentially you are heating the loft space (like another floor in your house). So this will cost you more in your heating. Ideally you want to insulated at the joist position and stop the heat from your home getting past the ceiling.


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. 25 mm 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.


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 300 mm 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).


it is a fact that with inadequate loft insulation, you could lose a quarter of the heat in your home. We all know that heat rises and the only place for it to go is out through your roof. You can always tell those homes which have poor insulation because in the winter their roofs have no snow or ice on them – the escaping heat has melted it!



A flat roof should preferably be insulated from above. A layer of rigid insulation board can be added either on top of the roof's weatherproof layer or directly on top of the timber roof surface with a new weatherproof layer on top of the insulation. This is best done when the roof covering needs replacing anyway. If your flat roof needs to be replaced anyway, you must now insulate it to comply with building regulations.

It is possible to insulate a flat roof from underneath, but this can lead to condensation problems if not completed correctly.

Installing flat roof insulation could save you similar amounts on your heating bills to loft insulation. The savings will vary depending on how much of the property has a flat roof.


Now you know the basics of loft insulation there is no reason not to have it done. You will get a better rating on your EPC Certificate with an insulated loft. If there is an existing amount of loft insulation of 100 mm or less or none. If you contact your utility provide they can provide you with guidance on how to have this done.


Insulating between the joists of your loft will keep your house warmer, but make the roof space above colder.

This means pipes and water tanks in the loft space could be more likely to freeze, so you will need to insulate them. If your water tank is some distance from the loft hatch, you will also need something to walk on for safe access.

The cooler air in your insulated loft could mean that cold draughts come through the loft hatch. To prevent this, fit an insulated loft hatch and put strips of draught-excluding material around the hatch edges.





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