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How to Insulate a Loft

What is loft insulation?

Loft insulation is material that’s placed in the roof space of your home to prevent heat loss. This makes the house warmer in winter and cooler in summer. It can be installed in the loft floor or between the beams of the roof. If you plan on boarding up your attic to use as storage space, you should put insulation in the floor. For use as extra living space, it’s better to insulate the roof.

The depth of loft insulation currently recommended by building regulations is 270mm. Loft insulation was first recommended in 1965 at a depth of 25mm. As the benefits of thicker loft insulation became better known, the recommended depth was gradually increased. The current figure of 270mm was first recommended in 2003 and is expected to be increased again in the future.

Loft insulation comes in several forms and many different materials:

  • Blanket or Batt loft insulation – rolls of material, sometimes foil-backed. The most common type of loft insulation, it’s normally made from felt, fibre or wool. Blanket insulation is fairly easy to install. However, it’s bulky so can be tricky to fit around obstacles and might not fit into tight gaps.
  • Loose-fill loft insulation – lightweight granules or loose fibre. Best used together with other types of loft insulation, it’s ideal for topping up existing insulation or filling difficult spaces. You can get loose-fill insulation in all sorts of materials like recycled paper, cork, fibre or wool. It may be unsuitable if your loft is draughty as it probably won’t stay in place.
  • Sheet insulation boards – hard sheets of material, sometimes backed with a moisture-repelling or fire retardant coating. These foam or fibre boards are perfect for insulating between joists and rafters. Commonly made from polystyrene or fibre, you can also find sheet insulation boards in cork, wood or straw.

How to insulate a loft – before you start

Things you’ll need

  • Loft insulation (it’s bulky stuff so don’t feel you need to buy it all in one go if space is limited)
  • A strong board to place across joists to stand and kneel on
  • A tape measure
  • Scissors or a utility knife
  • A staple gun (only needed if there’s no existing vapour barrier)

Prepare the loft

  • Find some battery-powered lanterns and clip-on lamps if there’s no light in your loft.
  • Clear the attic of any rubbish so you’ve got as much room as possible to move around.
  • Measure the loft – it doesn’t have to be spot on.
  • Scissors or a utility knife
  • Calculate roughly how much insulation you’ll need. Remember to take into account the depth of joists or rafters and any additional depth required on top of this.

Look after yourself. Although installing insulation is simple enough, working in the loft can be awkward and uncomfortable. Fortunately, there are things you can do to make it more bearable:

  • The angles of the roof mean there’s limited headroom in some areas, so mind your head.
  • If you’re insulating the floor, you’ll be spending a lot of time on your knees, so use kneepads. They’re really cheap at around £5 upwards, so if you don’t already have some, grab a pair. Kneepads make working at floor-level more comfortable and save you aches and pains.

Some types of insulation can irritate your skin, eyes and respiratory system. If you’re using loft insulation made of irritating material like fibreglass or mineral wool, wear protective gear:

  • Use gloves
  • Wear an overall or dust suit to protect your skin and stop particles getting into your clothes.
  • Wear safety goggles to stop particles irritating your eyes.
  • Wear a dust mask labelled as suitable for working with loft insulation. Disposable insulation dust masks are widely available and cost under £2. Choose one with a valve as it makes it easier to breathe out.

How to insulate a loft – step by step

Step 1: Insulate pipes

Step 1: Insulate pipes - How to insulate a loft | First Utility

The loft will get colder once you’ve insulated it and this increases the risk of burst pipes in winter. Insulate any exposed pipes with pipe lagging. This is inexpensive tubular insulation with a lengthways slit for quick installation.


Step 2: Cap any recessed halogen lights

Step 2: Cap any recessed halogen lights - How to insulate a loft | First Utility

If you have any recessed halogen lights in the rooms below the loft, you’ll need to install protective caps called loft caps or downlight covers. These are very cheap and are essential as they keep loft insulation off the light fittings. Halogen lights become a serious fire risk if they are directly covered with insulation.


Step 3: Make sure there’s a vapour barrier

Step 3: Make sure there’s a vapour barrier - How to insulate a loft | First Utility

For a cold loft, there needs to be a vapour barrier to prevent condensation. Move any existing insulation to check if there is one already. It’ll look like plastic sheeting on the floor between the joists. If there’s no sign of a vapour barrier, you’ll have to install one as otherwise you’ll have problems with damp.

Vapour barrier material comes as rolls of polythene and is labelled specifically as vapour barrier. Cut it to fit between the joists, leaving 10cm gaps around any heat sources like chimneys. Secure the vapour barrier to the plasterboard with a staple gun.


Step 4: Fit the first layer of loft insulation

Step 4: Fit the first layer of loft insulation - How to insulate a loft | First Utility

Remember to only unwrap your insulation in the loft otherwise loose particles and fibres can get spread around the house. If using blanket or Batt insulation in the floor, unroll it into the spaces between the joists.

Keep a lookout for electrical wiring. When you find a cable, make a cut in the insulation and pull the wire through so it rests on top of the insulation.

If using sheet insulation boards between joists or rafters, cut them to fit snugly between the beams. Push them into place but if you’re insulating the roof, don’t push them flush against the roofing felt. An air-gap here is desirable for the best loft insulation.


Step 5: Fit the second layer of loft insulation

Step 5: Fit the second layer of loft insulation - How to insulate a loft | First Utility

For floor insulation, top up the whole area until the overall depth is 270mm. Insulate the sides and tops of any tanks. Only insulate underneath when the tank is raised at least 10cm above the top of the floor insulation, otherwise water within could freeze.


Step 6: Board or plasterboard over the insulation

Step 6: Board or plasterboard over the insulation - How to insulate a loft | First Utility

Get a cold loft ready for use by boarding over the insulation. Leave an air-gap above the insulation to prevent condensation. Create the air-gap by raising the floor level with plastic loft legs or wooden battens. Fit chipboard loft panels over the top.

Finish off a warm loft with plasterboard. Attach it to the rafters so that the insulation and beams are covered. If you think the insulation between the rafters is a bit thin, use insulated plasterboard to bump it up.


Step 7: Insulate the loft hatch

Step 7: Insulate the loft hatch - How to insulate a loft | First Utility

A cold loft won’t be efficient if the loft hatch is left uninsulated. Insulate it by attaching sheet insulation board to the upper side. Then seal gaps around the edge using draught exclusion strips. There’s no need to insulate the loft hatch with a warm loft as in this case you want heat to rise into the roof space.


Why should you insulate a loft?

There are four significant benefits to insulating a loft:

Lower energy bills

Heat rises, so if your loft isn’t insulated, up to 25 per cent of your home’s heat is escaping through the roof. This heat loss costs you money. If there is existing insulation in your loft and you top it up you’ll save about £20 on your annual energy bill. If there is no insulation at all, insulating the loft will save you up to £225 a year. Insulating a loft pays for itself in under a year for DIY and under two if you hire someone to do it. These figures were calculated by the Energy Saving Trust and are based on 2017 fuel prices.

Reduced carbon footprint

Insulating a loft produces carbon dioxide savings of up to 90kg a year if you’re topping up insulation. Carbon dioxide savings can reach 990kg a year if there’s no existing insulation.

Improved EPC rating

By insulating your loft you’ll be improving the rating of your EPC, or Energy Performance Certificate. This is great news if you’re thinking of letting or selling. An EPC is required when marketing a property for rent or sale and summarises information about the building’s energy efficiency. Potential tenants and buyers are shown the EPC and will feel the extra warmth in your home when viewing it.

Increased property value

By increasing the EPC rating of your home you’ll also be increasing the value of your property.

Are there any stats about heat loss?

There are various stats about heat loss in the home. In summary, the stats for heat loss through uninsulated parts of the house are:

  • Up to 25 per cent of heat loss through the loft and roof
  • Up to 25 per cent of heat loss through windows and doors
  • Up to 35 per cent of heat loss through walls
  • Up to 15 per cent of heat loss through the floor
  • Up to 15 per cent of heat loss through draughts

When is the best time to insulate a loft?

You can insulate a loft at any time of year. However, if you do it in the summer, be aware that it’ll be very hot in your loft. Heat rises and collects in the attic so expect it to be several degrees warmer than outdoors. You’ll find it more comfortable to work up there in the early morning, if that’s possible. Alternatively, keep plenty of water close at hand and remember to drink frequently.

Can I insulate a loft myself?

You can insulate a loft yourself unless your home has damp problems or a flat or dormer roof. You might also need to call somebody in if your loft doesn’t have proper access. If you’ve got damp, you’ll need a professional to assess your attic before it is insulated. For a flat or dormer roof, you’ll need a professional installation. When there’s poor access, you may have to get a professional to use blown insulation, installed with specialist equipment. In all other cases, insulating a loft is a straightforward DIY job.

Cold loft or warm loft?

An insulated loft is known as a ‘cold loft’ or a ‘warm loft’ depending on whether the insulation is installed in the floor or the roof. By insulating the floor, heat is trapped underneath within the main part of the house, creating a ‘cold loft’. A cold loft is suitable for storage. By insulating the roof, heat is able to rise through the floor, creating a ‘warm loft’. This is ideal when you want to use your attic as living space.

Cold loft

If you want to make a cold loft you’ll need to place insulation both between and above the joists to reach the recommended depth of 270mm. As such, you’ll need two different thicknesses of insulation. When boarding up the floor, you’ll need to leave a gap above the insulation otherwise condensation will form on the underside of the floor. To do this, use purpose-built ‘loft legs’ or fit wooden battens across the beams.

Warm loft

To make a warm loft you’ll need to fit sheet insulation boards between the rafters. Once installed, the whole inner roof can be finished with plasterboard. To increase the depth of insulation, finish with insulated plasterboard instead.

If my loft is damp, can I still insulate it?

You may be able to insulate your loft if it’s damp, but you’ll have to get a professional assessment first. Loft insulation can worsen damp issues, so it’s important to call in an expert. They may be able to fix the damp problem. If that’s not possible, additional ventilation might be recommended to control condensation.

How much would it cost me to get somebody else to insulate the loft for me?

For an average terraced or semi-detached house, it’ll cost you around £230 to top up insulation or a maximum of £300 for full installation. A detached property will cost about £280 for topping up and just under £400 for all-new loft insulation.

It’s easy to get someone else to insulate your loft for you. Want something that takes all the hassle out of getting a quote, making a booking and actually insulating the loft? Check out First Utility Home Services to find top-rated local tradespeople in a jiffy.


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