A Complete Guide to Loft Insulation

Storage Space

If you plan on using the loft for storage space, you will want to lay boards across the joists before you fit loft insulation. Unfortunately, if you only insulate between the joists before laying down the boards, the insulation won’t be enough.

To ensure you get enough insulation (270mm), you can raise the level of the floor to fit enough mineral wool beneath. In order to do this, you can lay timber battens across the joists, or you can fit purpose-built plastic feet on the joists to support the new floor.

Leaving a ventilated air gap between the loft insulation and the boards is important because it prevents condensation on the underside of the boards. Avoid squashing the mineral wool when fitting the boards on top, as this will decrease the insulation’s effectiveness.

Damp

By insulating your roof, you will prevent heat from escaping from your living space and make your loft considerably colder. This could potentially increase any existing damp or condensation issues, so if you are installing loft insulation yourself, please bear in mind that you may need to increase ventilation to avoid this.

Before doing anything, it is worth seeking professional advice first to see if you can fix any existing issues concerning damp or condensation.

Warmth

There is an alternative way to insulate your loft, you can use rigid insulation boards, scaled to size and placed between and over the rafters. Alternatively, you can use spray foam loft insulation sprayed between the rafters.

Whichever method you use, this is not a DIY job and would require a specialist to insulate your roof. Here are some pros and cons:

Pros

• The loft will be warmer than if you used standard joist insulation, so you wouldn’t need to worry about pipes freezing

• You can lay boards down on the floor to create storage without having to raise for ventilation

Cons

• Insulating rafters is considerably more expensive than placing loft insulation between joists

• As well as insulating the roof, you would have to insulate any surrounding areas, such as gable walls, party walls and any chimneys in the loft space. Leaving these uninsulated will allow the heat to bypass your new insulation, making it ineffective

Rooms

If you want to convert your loft into a room, or it’s already being used as a living space, then you need to ensure that all the walls and ceilings between heated and unheated rooms are insulated.

Sloping ceilings can be insulated in the same way as using insulation boards on the rafters but with an added layer of plasterboard on the inside of the insulation. Vertical walls can be insulated the same way.

Flat ceilings can be insulated like a standard loft by laying boards across the joists. Make sure to insulate the wall and ceiling around any dormer windows and use high performance or double glazing for any windows or skylights.

Similar to loft insulation in the rafters, this isn’t a DIY job and would require a specialist to ensure the insulation is professionally done and that proper ventilation is provided where needed.

Ventilation

A house needs a steady amount of air flow so it stays fresh, dry and looking healthy. A professional installer will make sure not to block or seal any intentional ventilation. If you are doing DIY, make sure that you don’t cover any vents, grilles or airbricks.

Accessibility

If it’s difficult to access your loft, you can have what’s called blown loft insulation installed by a professional. They will use specialist equipment to blow insulation materials such as mineral wool fibre or polyurethane foam into any difficult spaces.

Flat Roofs

Flat roofs should preferably be insulated from above. A rigid insulation board can be added on top of the roof’s weatherproof layer or placed directly on top of the roof surface, with a new weatherproof layer added on top of the insulation.

The best time to install is when the roof covering needs replacing, as it’s now a requirement for flat roofs to be insulated to comply with building regulations.

Although it is possible to insulate a flat roof from underneath, it can lead to condensation issues if handled incorrectly.

Installing flat roof insulation could save you a similar amount on your heating bills as loft insulation but will vary depending on how much of the house has a flat roof.