How To Insulate Your Loft

Knowing how to insulate your loft can seem like a daunting task. However, this is a simple job and the good news is you don’t need specialist DIY skills! One person should be able to do it in a few hours.

Before you get started on any of our ‘how to’ guides, please take a moment to read through our DIY safety tips and always follow the manufacturers’ instructions.


What You’ll Need:

1. How much loft insulation will I need?

When it comes to saving cash this is a no-brainer. The thicker your loft insulation, the more energy and money you save. The recommended minimum thickness of 270mm can cut your heating costs by a healthy 15%. Follow the simple steps below to see how much loft insulation you’ll need.


  • Measure the depth of your current loft insulation.
  • Subtract your current depth from the recommended minimum of 270mm to find out how much new insulation to buy. You may need more than one layer of insulation to get the right depth.

Area of your loft

  • Measure the size of your loft: Total area required = length x width

Joist gap

If your existing loft insulation is level with the joists, skip this section and go straight to Section 2: Insulating your cold water tank.
But if your current insulation isn’t level with the joist, carry on with this section:

  • Most joist gaps are between 400mm and 600mm wide. Measure the distance between your joists to work out what type of loft insulation roll you need.

Safety guide

Make sure your loft is safe to work in before you start! Use crawl boards to avoid damaging the ceiling below. Lay electrical wiring over the top of the insulation. Leave a 75mm gap between the insulation to prevent a fire hazard. It’s also a good idea to wear a dust mask, goggles and gloves during this job.

2. Insulating your cold water tank

  • Before you insulate your loft we suggest you insulate the cold water tank first. That’s because loft insulation prevents heat escaping through your loft – so there’s a chance the water in the tank could freeze.
  • You can use ordinary loft insulation. Wrap it round your tank and tie with string to keep it in place.

3. How to fit your loft insulation 

  • Clear your loft to make installation easier.
  • Using crawl boards, start at the furthest corner. Unroll the first length so it fits between the joists or sits on top of the existing insulation.
  • If you have existing insulation between your joists, place the new insulation on top to the height of the joists. Then position your second layer across your joists to the minimum 270mm depth.
  • Press the insulation down lightly as you move across the loft. But don’t compress it – this will make your insulation less effective.
  • When one roll finishes, begin another by butting the two ends together. Make sure there are no gaps. When you reach the opposite end of the loft, cut the material. Leave enough ventilation space from the eaves.
  • It’s also worth insulating your loft hatch as heat can escape from it. Cut a piece of insulation material to the size of your hatch and secure the material to the back of it.

Watch our video on how to lay and fit loft insulation:

  • If you need storage, we suggest you build a small platform near your loft hatch using loft panels. Keep this to a minimum to ensure maximum energy saving.
  • You only need a 100mm insulation depth when you lay loft panels.
  • Simply slot the loft panels together and secure them to the joints. The end of each panel should meet near the joists to strength.

And that’s how to insulate your loft! For more insulation tips, check out our other guides here



Writer and expert