How to insulate your home



The biggest source of heat loss (up to 25%) in the home is through the roof, so begin by making sure the loft is properly insulated.  This is a very cost effective DIY job that can be completed in a couple of hours.  Always wear protective clothing when using insulating materials, including gloves and a face mask. 

Check the depth of your existing loft insulation.  Government research shows the recommended depth is 270mm. 

If you need to add more insulation, clear the roof space of clutter first.


Lay down some chipboard loft panels to allow you to work safely without having to balance on ceiling joists.

Measure the gap between the ceiling joists – standard joists are usually about 370mm apart.

Rolls of glass mineral wool insulation are usually sold in 370mm widths to fit standard joist spacing.

Count how many spaces there are between you joists and the length of your loft.  You can then easily calculate how many rolls of insulation you’ll need.

For wider joist widths of 600mm use Combi Loft Roll which is perforated for either 400mm or 600mm widths.


Wearing gloves and a face mask, lay the insulation to a depth of 100mm at first.

Starting at the farthest corner, unroll the first length so that is fits between the ceiling joists.

Leave a minimum of 25mm gap between the insulation and the roof covering at the eaves to provide ventilation to the roof space.

Once you have completed one layer, lay further rolls until you have the recommended minimum depth of at least 270mm/

Insulation works by trapping air in the insulation material.  By squashing insulation down its effectiveness is reduced so try not to squash it.

If you want to board part of the loft, do this above the initial 100mm layer of insulation.  Use an insulation board such as a “Space Board” in these areas.


For safety and access, electrical wiring should be laid over the top of the insulation and not buried beneath it.

Always leave a minimum of 75mm of space around any recessed ceiling lights so they don’t overheat.


Warm air can escape through an uninsulated loft hatch, so cut a piece of insulation material to the size of your hatch and tape or tack it to the back of the loft hatch.


Once the floor of your loft is well insulated it traps cold air in the space above.  Therefore, it is important that exposed water pipes are protected by wrapping them in foam tube insulation – the tubes are ready cut so just need to be slipped over the pipes.

If your cold water tank is in the loft, leave the area under it free of insulation to stop the water freezing.

Wrap insulation around and over the cold water tank, fixing it with string or tape.


External doors

Make sure your front door only has a 2mm or 3mm gap at the top and sides and a 5mm gap at the bottom.

Self-adhesive foam or flexible vinyl strips can be used to seal around the edges and top of the door frame.

Use a draught excluder to seal the bottom of any external doors.  These plastic or metal strips have a rubber seal or rows of nylon bristles to keep the cold out.

Draught excluders can be bought in wood or metal finishes to match the door.  The seal or bristles must overlap the door frame.

If there is air coming through the letterbox when it’s closed, fit a letterbox draught excluder.

Skirting boards

Squeeze clear flexible sealant between the floorboards and the base of the skirting.  Work along the board in a smooth continuous motion.

For larger gaps, over 5mm, pin strips of quadrant-shaped moulding over the gap instead.


Suspended wooden floors in older homes need a flow of air underneath them to stop problems of condensation and rot.  However, you can make the ground floor rooms warmer and more energy efficient by filling gaps between boards with a clear flexible sealant or by inserting thin strips of wood into larger gaps.


If you are planning to lay a new floor covering, take the opportunity to lift your floorboards at the same time and fit glass mineral wool insulation between the floor joists.

The cost for this could be recouped through lower energy bills in just a couple of years.

Lifting your floorboards

To lift floorboards use a thin bladed cold chisel and club hammer.  Lever them up, working along the board to prise away all the nail fixings.

To stop the insulation dropping through the joists, simply staple plastic garden netting between the joists at the bottom of each side.  Alternatively, nail lengths of roofing batten along the sides of each joist.

Lay rolls of loft insulation or rigid pieces of wall insulation between the joists.

Once the entire floor is covered, relay the floorboards replacing any damaged sections and nailing firmly to avoid any squeaking or movement.

Avoid leaving any wide gaps between the boards.

Use a nail punch to push the nails below the surface of your floorboards.


Double glazing is a big investment but has great results, instantly halving heat loss through your windows.

As a shorter-term DIY measure, secondary glazing can be fitted to the inside of the window frame.  These units are sold as kits.

Use a flexible sealant to fill any gaps around the secondary glazing frame and your window frame.


Insulating your hot water tank and pipes will help keep the water hot, cutting heat loss by around 75% and saving money.

Check around your kitchen and bathroom waste pipes and fill any gaps with an aerosol of expanding foam.  Always follow the instructions on the can.

A thick curtain hung at the front and back doors can be very effective in keeping out draughts and retaining heat.

Switch to energy saving light bulbs.  They last around 10 times longer than ordinary light bulbs, and each bulb you fit could save around £40 over its lifetime.  Also, fill gaps and draughts around skirting boards and floors with a tube of sealant.  This could save around £50 a year.

April 2009