Loft insulation

Around 25% of heat in an uninsulated home is lost through the roof. Loft insulation is one of the most effective and affordable ways to improve your home’s energy efficiency. It is relatively simple to install and typically pays for itself in less than two years through energy bill savings.

The current recommended depth for loft insulation (mineral wool) is 270mm.

If your home was built or insulated more than 15 years ago, you likely have around 100mm or less. “Topping up” your insulation to the modern standard can save an average detached home up to £350 per year on energy bills.

Materials

  • Mineral wool (rolls): The most common and cheapest option. It is easy to lay between and across joists.
  • Sheep’s wool: A natural, breathable alternative that is easier to handle but more expensive.
  • Blown-in cellulose: Recycled paper or wood fibres blown into the loft space by a professional. Good for lofts with limited access.
  • Rigid foam boards: Used for insulating the “rafters” (the sloping part of the roof) if you want to create a warm attic room.

Key considerations

1. Storage and floorboards

If you want to use your loft for storage, do not squash the insulation down with floorboards. Squashing insulation reduces its effectiveness by about 50%. Instead, use loft legs to raise the floorboards above the required 270mm of insulation.

2. Ventilation

Good airflow is essential to prevent damp and condensation in your roof space. Ensure that your insulation does not block the eaves (the edges of the roof) where air enters. You may need to install “eave vents” or “lap vents” to maintain airflow.

3. Pipes and tanks

Once your loft is insulated, the space above the insulation will be much colder in winter. You must insulate any water pipes and the cold water tank to prevent them from freezing.

Safety note: If you have any electrical cables in your loft, do not cover them with insulation. They should ideally be clipped above the insulation to prevent overheating, or left uncovered if they are high-current cables (like those for electric showers).

DIY vs Professional

Most people can install loft insulation themselves if the loft is easy to access and has no damp issues. However, you should hire a professional if:

  • You have an unconventional roof (like a flat roof).
  • The loft is difficult to access or has very low clearance.
  • There is existing damp, rot, or infestation.