A surveyor’s guide to home insulation – how to insulate your home

Insulation in the roofspace of a houseThe heating bills resulting from another cold winter are a vivid reminder of just how much it costs to keep your home warm. Check our list of home insulation tips to ensure you don’t waste money heating the great outdoors instead of your home.

Loft Insulation

The biggest source of heat loss in the home – up to 25% – is through the roof, so begin by making sure the loft is properly insulated.  This is a cost-effective DIY job that can be completed in a couple of hours.

Check the depth of your existing loft insulation.  Government research shows the recommended depth of blanket insulation is 270mm. If your home was insulated some time ago, it is worth checking the depth as recommendations have changed over the years.

If additional insulation is required, make sure you clear the roof space of stored items and clutter first. Always wear protective clothing when using insulating materials, including gloves and a face mask.

Measuring up for loft insulation

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 the joists and the length of the 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 to fit either 400mm or 600mm widths.

Laying the insulation

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

Start at the farthest corner, unrolling the first length so that is fits between the ceiling joists.

Ensure you 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 achieved the recommended minimum depth of at least 270mm.

Insulation works by trapping air in the insulation material.  Squashing insulation down will reduce its effectiveness, 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.

Leave a space around electrics

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, if they are not protected by other means.

Insulating the loft hatch

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

Lagging Pipes and Tanks

Once the floor of your loft is well insulated it will trap cold air in the loft space. 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 beneath it free of insulation to stop the water freezing. Wrap insulation around and over the cold water tank, fixing it with string or tape.

Draught-Proof your Home

External doors

Make sure your front door has only 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 are available in a variety of finishes to match the door.  The seal or bristles must overlap the door frame.

If air comes in 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 of over 5mm, pin strips of quadrant-shaped moulding over the gap instead.


Suspended wooden floors in older homes need a flow of air beneath them to stop problems of condensation and rot. However, you can make the ground floor rooms warmer and more energy efficient by filling (caulking) any gaps between the boards with a clear flexible sealant or by inserting thin strips of wood or natural fibre rope into larger gaps. A number of proprietary caulking strips are also available, such as Draughtex or StopGap, which leaves a ‘shadow’ effect between the boards.

Insulation Beneath a New Floor

If you are planning to lay a new floor covering, first take the opportunity to lift the floorboards and fit glass mineral wool insulation between the floor joists. The cost of this will be recouped through lower energy bills in just a couple of years.

Lifting floorboards

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

To stop the insulation dropping through the joists, staple plastic garden netting between the joists at the bottom of each side. Alternatively, nail lengths of batten along the sides of each joist. You will then be able to lay the rolls of loft insulation or rigid pieces of wall insulation on top of the netting or batten between the joists.

Once the entire floor is insulated, re-lay the floorboards, replacing any damaged sections and nailing or screwing down firmly to avoid any squeaking or movement.

Avoid leaving any wide gaps between the boards.

Finally, use a nail punch to push the nails below the surface of your floorboards.

Insulating Windows

Double glazing is a big investment but 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.

Helpful Hints

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

Check around your kitchen and bathroom waste pipes and fill any gaps. If you use an aerosol or expanding foam always follow the instructions on the can.

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

Switch to energy saving light bulbs.  Manufacturers claim these last around ten times longer than ordinary light bulbs, and each bulb you fit could potentially save around £40 over its lifetime.

Back to February 2020 Newsletter

© www.PropertySurveying.co.uk