Roof and loft insulation

If you want to store things in your loft and keep your home well insulated, you’ll need to put boards down on the loft floor.

Adding insulation between the wooden beams (called joists) will reduce heat loss and improve energy efficiency. However, this may not meet modern recommended insulation levels on its own. To increase performance, you can raise the floor slightly and add a second layer of insulation across the top of the joists. Then you can fit the boards.

Remember to leave a small gap for ventilation between insulation and boards to prevent condensation. If you’re using mineral wool, make sure you don’t squash it: this will reduce its effectiveness as an insulator.

Insulation slows heat escaping from living spaces, making your loft space cooler. This makes condensation more likely or can worsen existing damp problems.

 If you do have damp in your loft, get professional advice before installing insulation. It is important to fix what is causing the damp problems before adding any insulation.

 If your loft is damp-free and you’re adding insulation to your loft yourself, it’s important to think about ventilation to prevent damp.

Some companies offer to fix a damaged or leaking roof by spraying foam insulation onto the underside of the roof without fixing the problem first. We don’t recommend doing this. As with any insulation, you need to make sure that the roof is dry and in good condition before adding any insulation.

Get the facts about spray foam insulation.

Another option for loft insulation is to fit rigid insulation boards between and over the sloping timbers that make up the roof itself, called rafters.

This isn’t a DIY job, so you’ll need a professional to insulate your roof.

Advantages

• The roof space will be warmer than with standard loft insulation, so your installer won’t need to worry so much about freezing tanks and pipes.
• If the installer is insulating the actual rafters, they won’t need to install insulation in the ‘floor’ of the loft. If they insulate the loft floor, they might not be able to board it due to thickness of the insulation material. Installing insulation boards between the rafters means an installer can still board the loft floor, letting you use the loft space for storage.

Disadvantages

• Insulating at rafter level is much more expensive than most standard loft insulation.
• In addition to insulating the roof, an installer will have to insulate any gable walls, party walls, and chimneys in the loft space. If they leave these uninsulated, then the heat will bypass the new insulation, reducing its effectiveness.
• Insulating at rafter-level is much less energy-efficient than insulating the loft floor. This is because you’ll be heating the air in the loft before it gets to the insulation above, as well as the air in the rest of the house.

Want to turn your loft into a heated, useable room? You’ll need a loft conversion to create a room in the roof.

As with warm loft insulation, insulating a loft conversion is not a DIY job. You’ll need a professional installer to ensure that the insulation is appropriate and that adequate ventilation is in place.

Make sure that all the walls and ceilings between a heated room and an unheated space are insulated.

Sloping ceilings can be insulated in the same way as a warm roof, but with a layer of plasterboard on the inside of the insulation. Vertical walls can be insulated in the same way. Flat ceilings can be insulated like a standard loft.

Make sure the installer insulates all the areas of the wall and ceiling around any dormer window, too. And if they’re putting a window or skylights, use high-performance glazing.

Insulation helps keep heat in your home, but it also changes how air and moisture move through the space. Without enough airflow, warm air from your home can get trapped in the loft. This can lead to condensation, which over time can cause damp, mould, or even rot in the roof’s timber. Air needs to flow in and out of your house so that it stays fresh, dry and healthy.

A good installer will be sure not to block or seal any intentional ventilation and may need to add additional ventilation. If you’re doing any DIY insulation, make sure that you don’t cover any vents, grilles or airbricks.

If your current ventilation isn’t enough, you might need to add vents or use ventilation trays to keep air circulating properly. It’s a good idea to get professional advice if you’re unsure about how insulation will change the ventilation in your loft.

In Northern Ireland, building regulations require you to have adequate ventilation when installing loft insulation. This usually means installing more vents if there aren’t enough in place already. Check with your local building control officer to find out what you need to do for your home.

If your loft is hard to access, then a professional can install blown insulation. They’ll use specialist equipment to blow appropriate insulation material into any awkward space that is hard to get to. This material could be mineral wool fibre, treated cellulose or polyurethane foam.

Ideally, a flat roof should be insulated from above.

An installer can do this. First, they’ll add a layer of rigid insulation board on the roof’s weatherproof layer or on top of the timber roof surface. They can then add a new weatherproof layer on top of the insulation.

Building regulations generally require a flat roof to be insulated. So, if you’re replacing the roof covering anyway, you can install insulation at the same time.

While it’s possible to insulate a flat roof from underneath, this can lead to condensation problems if not completed correctly.

Installing flat roof insulation can save similar amounts on energy heating bills as loft insulation. But how much you can save will depend on how much of the property’s roof is flat.

Insulating between and over the joists will help keep your home warmer, but it also makes the loft space above much colder. That’s not a problem, but it does mean that any pipes or water tanks in the loft are more at risk of freezing in winter. Therefore, they’ll need to be insulated too.

• Water tanks can be insulated using a British Standard insulating jacket, which is designed to fit over the tank and help prevent heat loss.
• Pipes should be wrapped with foam pipe insulation, which can be cut to size and easily fitted.
• If your water tank is far from the loft hatch, make sure you have secure boards to walk on. This lets you reach the tank safely for maintenance.

Find out more about insulating pipes and water tanks.

Also, since the air in the loft is colder, you might notice draughts coming through the loft hatch into the rooms below. To prevent this:

• Fit an insulated loft hatch.
• Add draught-excluder strips around the edges to reduce heat loss and stop cold air getting into the rooms below.

Find out more about draughtproofing.