Insulating Your Loft or Attic - How to Fit Loft Insulation

Summary: How to insulate a loft by installing loft insulation to stop the heat escaping through your roof. Understand the equipment you will need and what the effects of adding insulation to your loft or attic.

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There are a few types of loft insulation available for the DIY enthusiast to place in the loft or attic. This is a very worthwhile job as you can see from the table below. The main type of insulation used by the house owner is mineral fibre or glass fibre matting. This is dealt with in detail below. There are also sections on loose fill materials like mineral wool, vermiculite and mineral or cellulose fibres. All are effective insulators, as is reflective foil insulation, also dealt with later.

Rolling out insulation in the loft

Rolling out insulation in the loft

Using less than the recommended amount of insulation will cost you money. As much of 15% of your heating can be lost through the roof with no insulation in place. This represents about £155.00 per year wasted not to mention the tonne of CO2. The table below shows the savings that can be made with proper loft insulation. The data in the table was provided by The Energy Saving Trust

Loft insulation (0 - 270mm) Loft insulation (50 - 270mm)
Annual saving per year (£) Around £155 Around £45
Installed cost (£) Around £500 Around £500
Installed payback Around 3 years Around 11 years
DIY cost From £250 Around £180
DIY payback From 2 years Around 4 years
CO2 saving per year Around 1 tonne Around 300kg

The easiest form of insulation to install is a mineral fibre insulation or fibreglass matting. Both types come in rolls. It works by trapping warm air between the fibres of the mat and stopping it rising further to escape.

The rolls are usually 600mm (24in) or 400mm (16in) wide. Thicknesses range from 100mm (4 in) to 200mm (8 in). This is because this distance is the distance specified between ceiling joists in most modern homes. The full thickness of insulation in the United Kingdom (Aug 2013) should be a minimum of 270mm. Loft roll, given time, will settle and become thinner. This will have the effect of collapsing the tiny gaps between the fibres which trap the heat and it soon becomes useless as the heat can pass straight through it.

Use the following instructions to make insulating your loft as easy as possible.

Access to your loft is usually through a loft hatch in the landing ceiling, If this hatch is not big enough take a look at our project on enlarging a loft hatch. Make absolutely sure you have a solid ladder, or better still a loft ladder, to give you safe access in and out of the loft.

Before you start, take note of the below points:

  • Clear all rubbish and clutter out of the loft
  • To stand in the loft use a length of board about 25mm thick and at least 1.3m long, to lay across at least 3 joists. The ceiling joists themselves are not meant to be stood on as they are not load bearing and the gaps in between the joists are 12mm plasterboard which will not support the li8ghtest of humans!
  • Use a proprietary lead lamp to provide adequate lighting in your loft. If you have a large loft you intend to use often why not fit a roof window. If you are thinking of installing a roof window at the same time, these are available from many of the DIY sheds or from specialist suppliers
  • It is very important that your loft is ventilated. Poor ventilation leads to condensation forming in the loft and this condensation can soon rot roof timbers and cause structural damage. If there are no roof windows (the quickest and easiest way of providing ventilation in a loft) Then follow the loft floor along to the point where the roof comes down to meet it. At this point (called the eaves) there should be a gap between the underside of the roof and the outside wall. This gap should be about 25mm wide and will usually have a meshed grill within it stopping insects and birds getting into the loft. Any cracks or holes in the ceiling should be filled before laying your covering
  • All wiring in the loft must be lifted and laid on top of the insulation otherwise the cables will overheat and become a fire hazard

Tools and Equipment You Will Need


Sturdy hardwearing gloves


Safety goggles

Tape measure

Tape measure


Craft knife

Dust Mask

Dust mask

Make sure that you are wearing all the protective clothing. Fibre insulation contains many small fibres which, when worked loose, will get into eyes, mouths and noses very easily. Mineral insulations can cause irritation to the skin so wearing gloves is also important. A disposable coverall is a good idea to prevent spread of fibres from your clothes.

How Much Insulation?

Measure the area of your loft floor. Rolls of mineral insulation will state on the roll what area they cover. A roll of mineral insulation is cut into smaller sections which are designed to roll out between the ceiling joists so measure between your joists to make sure you buy the right insulation.

Fitting loft insulation

Make sure all cracks, gaps and holes in the ceiling are filled with either a standard filler or decorators caulk.

  • It’s a good idea to clean between the gaps in the joists thoroughly, even to the point of hovering all the dust up. This stops the fibre gaps being filled by dust
  • Start from the eaves (see above) remembering to leave the ventilation gap. Work towards the centre of the loft. Lift all electric cables above the insulation and cut away around visible light fittings
  • Cut the roll in the centre of the floor when rolling out from the eaves on both sides. You will need the craft knife for this. There should be no gaps between the edges of the insulation and the joists. Insulation can be cut to fill any gaps
  • Build up the insulation to the required thickness, and do not insulate under the water tank
  • Make sure your loft is completely insulated
  • More insulation can be laid at 90 degrees to the first layer to improve heat savings

Loose fill insulation comes in two forms, blown and placed. The blown insulation is usually done by specialist loft insulators and is comprised of mineral or cellulose fibres such as rock wool. Rockwool is a man made fibre with excellent soundproofing qualities as well as good insulative qualities. Rockwool is usually placed mechanically into the roof space by specialists and the ceiling joist height very often needs to be raised to accommodate the correct thickness of loose fill.

Vermiculite is another often used loose fill insulation. Vermiculite is a natural mineral which expands (not hugely!) with heat. This expansion is called exfoliation. Vermiculite is fireproof and is often used to insulate new flue liners placed in chimney stacks as well as laid loose in lofts. It is also used as a very lightweight aggregate for floor screeds when mixed with sand and cement. Vermiculite and rockwool have an advantage over mineral or glass fibre insulation in that they do dot have fibres which can irritate the skin. Reflective foil insulation is made from layers of aluminum foil surrounding a wadding or layer of wool material. Usually reflective foil insulation is about 25mm thick and gives a very good U value for its relative thickness. It is easily cut and placed and reflects heat rather than absorbing it.

Go to our video section on insulation to watch a film on how to insulate your home in improve your carbon footprint as well as save you money.

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