The majority of heat that escapes your property is lost through the roof. Inadequate insulation is therefore costly, making your energy bills quickly pile up.

Loft insulation can help to retain heat in your home and reduce your energy bills by as much as 25%, saving you money in the long term as roof insulation can last for up to 40 years.

In this article, we will explain step by step the best DIY method for insulating your loft. We will also point out snags to look out for and recommend when professional help is best sought after.

How to insulate a loft roof

When insulating a loft, you must first decide what you would like to use the attic space for. How you insulate a loft roof for storage purposes, for example, will be different to how you insulate a loft conversion. Installing insulation to the floor of a loft is relatively simple and can be a DIY job. In comparison, room in roof insulation is more complicated and almost always needs professional input.

Next, you will need to decide which insulation to use. There are many different types of home insulation, however, the most common way to insulate a loft is with either loft rolls or rigid insulation boards. These are usually the cheapest but most effective methods, particularly if your loft is already in a good state.

It is also important to consider factors such as:

  • Damp
  • Ventilation
  • Inaccessible loft spaces
  • Flat roofs

If you experience any issues with these factors, it is generally best practice to consult with a loft and roof insulation expert first. They can assess the extent of any damage caused by damp and adequately allow for ventilation. Further, they will be able to use specialist equipment to blow insulation materials such as polyurethane foam into hard to reach places.

How to insulate and board a loft

Where the attic space is mainly to be used for storage, you can simply insulate the flooring and install boards. It is essential, however, to ensure that the installation process is performed correctly in order to maximise the heat retained.

Below is the cheapest and most simple method for installing insulation, known as cold roof insulation. This is done by laying loft insulation rolls between roof joists.


  1. Put on safety equipment such as goggles and gloves. Turn of electricity to the unit.
  2. Remove any existing boards in the loft area. Clear as much space as possible to give yourself a large, safe working area.
  3. Check for lighting or electrical cables. If there is enough slack for the wire to be lifted on top of the insulation without overstretching, you may continue. If not, consult with a qualified electrician before continuing.
  4. If required, cut any larger width rolls (1140mm) to size depending on the spacing between your joists.
  5. Starting at the eaves, lay the loft roll down leaving a 25mm gap from the eaves. Gently fluff the insulation up as you go to help it reach its maximum depth. If you run out of roll, gently push the new roll of insulation up against the previous roll for a snug fit.
  6. When you hit a cross beam, cut the insulation using a long, sharp knife with a serrated edge so that it fits against the beam. Do not bend or squash insulation to fit. Start again from the other side of the cross beam.
  7. Continue rolling the insulation out between the joists across the loft floor, until the base layer is complete.
  8. Lay the second, top layer at right angles to the base layer. The top layer will run across the top of the joists, so you shouldn’t need to cut any rolls to size. Continue until the top layer is complete, ensuring all joints are butted together.

Don’t forget to properly insulate pipes and water tanks to prevent water freezing in the winter!

To lay boards over the insulation and jists, you need to raise the floor level to accommodate the depth of the new insulation. Install timer battens across the hoists or use plastics legs fitted to the joists to support the new floor.

Make sure you do not squash the insulation roll when you fit the boards as this will impact the insulation value. Further, ensure that there is enough gap for adequate ventilation to prevent a build-up of condensation.

How thick should loft insulation be?

How thick your insulation should be will depend on which type of insulation you use. The types of insulation most commonly used in loft and attic spaces are blown mineral wool (glass or rock wool), blown cellulose, or quilted mineral wool (glass or rock wool).

Current government recommendations for loft insulation is that a depth of between 250mm and 270mm is required but some new build properties are increasing their level of loft insulation to 300mm.

According to the National Insulation Association, the recommended depth for loft insulation is as follows:

  • 270 millimetres for glass wool
  • 250 millimetres for rock wool
  • 220 millimetres for cellulose

How much does it cost to insulate a loft?

The price of installing insulation in your loft will depend on the materials you use, the spaces between joists, and whether you have any existing insulation or not.

Loft rolls are usually the cheapest option for cold roof insulation. To calculate how many packs of loft floor insulation you will need, you must first measure the relevant loft space.

  1. Measure the length and width of the space that will be insulated. Make sure that you measure in the same unit, typically metres.
  2. Calculate the overall square metres of the space by multiplying the length by the width.
    Length (m) x Width (m) = Area of the loft in square meters (m2)
  3. For the base layer, subtract 10% as the rolls are laid between the joists rather than on top of them.
    Area of loft / 100 x 90 = Area of loft m2
  4. Assess the coverage per pack of loft roll. The packaging or product description should tell you the number needed. Round up to the nearest whole if needs be.
    m2 / Pack coverage = Number of packs needed
  5. For your top layer, repeat steps 2 and 4. You do not need step 3 as the joists will be covered by the top layer, so you do not need to accommodate them.

Final thoughts

Cold roof insulation is a relatively straightforward method, that you may be able to install yourself at home. This cheap option helps to retain heat and saves money on energy bills in the long run.

Here at Heat Insulation, however, we have faced many instances where the expertise of our professional heat insulation technicians has proved invaluable. Better yet, by using a reputable installer, you can take advantage of grants and schemes such as the Home Upgrade Grant. These Government aided schemes can save you significant money installation costs!

If you are interested in loft and roof installation, please get in touch to discuss the best option for you.