Wrap up your home


Loft insulation with Thermafleece is environmentally friendly and can be laid without wearing protective clothing

Insulating your home will save energy and money. This simple guide will show you where to start and what material to use

When Penney Poyzer and her ‘green' architect husband Gil moved into their Victorian semi in Nottingham six years ago, ‘the only form of insulation was mould,' she says.

One of their top priorities was to insulate, internally and externally, from roof space to cellars. Along with other eco renovations, Penney estimates that ‘we now save £1,000 a year on heating bills and our carbon emissions have gone from around 18 tonnes to just a fraction of a tonne.'

‘Insulating the loft is a no-brainer, it's so cheap and easy to do,' says Martin Normanton - who, from top to bottom, and room by room, has dramatically improved the insulation of his 1903 solid wall house in Walsall.  (For details of how he did it, see the Ecovation site)

Nearly 50 per cent of all heat loss in an average home escapes through the walls and roof according to the Energy Saving Trust. In the UK, the amount of heat lost in this way is enough to heat around three million homes a year. Insulating reduces your energy use, carbon emissions and your bill.



If your loft isn't insulated, a third of your heating costs could be going through the roof.

The recommended depth of loft insulation is now 270mm (10 inches), so you may need to top yours up.

Choosing a material involves weighing up the cost, suitability for the space, thermal efficiency (for the lowest heat loss, look for a high ‘R rating' and a low ‘U value') and environmental impact.

The Centre for Alternative Technology (CAT) recommends insulation made of organic materials from renewable resources, and recycled materials. ‘The more natural the material, the better,' says Matthew Slack from CAT. ‘But it's better to insulate with any material than not insulate at all.'

The standard, cheapest materials for loft and roof insulation are mineral fibre and fibreglass. Although these have excellent insulating properties, the energy used in their manufacture - known as ‘embodied energy' - is high. They're also rather nasty to handle - you need to wear gloves and a face mask, as the fibre releases fine particles that can irritate your eyes, skin and throat.

Over time, its performance drops as the fibres flatten. Another commonly used insulation comes in the form of expanded foam sheets made from polystyrene, polyurethane and polyisocyanurate (PIR), often sold as ‘Celotex'. They too have a high embodied energy and some use ozone-depleting HCFC gases in their manufacture.

Thermafleece is a more eco-friendly and natural choice, using wool from British hill sheep to make slabs of insulation. Renewable, reusable and recyclable, Thermafleece only uses 14 per cent of the energy that is required to manufacture fibreglass.

Wool is also an excellent insulator unique temperature- and moisture- regulating properties mean that in summer it can actually reduce indoor temperatures by up to 7°C, and raise them by up to 4°C in winter. The downside is its cost (100mm thick costs £9.50 per square metre), which is about four times that of fibreglass.

Other natural options include Isonat, made from UK-grown hemp and recycled cotton fibres, and Islovas, made from natural flax fibres. Like wool, they are a bit pricy.

Another eco-alternative is Warmcel, a loose-fill cellulose fibre made from recycled newspapers, which costs £9 per square metre. It is biodegradable, has a very low embodied energy, and is an excellent use of waste material.

Highly rated for its thermal efficiency and eco-credentials, Warmcell has been installed in more than a million homes in the UK. It's also simple to do yourself: just fluff it out into the loft space between the joists.

Cost: from £230
Annual saving: up to £220 a year

If you've already got 50-100mm of insulation, topping it up can lead to further savings (around £50-£60 a year).


According to the Energy Saving Trust, more heat is lost through the walls than any other route - approximately 33 per cent in an uninsulated home.

In most houses built after the 1920s, the external walls are made of two layers with a small gap - an air cavity - between them. In the UK, 68 per cent of the housing stock has predominantly cavity walls but only 36 per cent of these are insulated. If all UK cavity-walled houses were insulated, they would collectively save £960 million a year - enough to heat 1.7 million homes a year.

Filling the gap with insulation material decreases heat loss by up to 60 per cent and can reduce heating costs by more than a third. After loft insulation, cavity wall insulation is the most cost effective measure, especially as grants and special discounts are available.

Installation takes only a few hours and involves a professional installer drilling small holes into the outside layer of the wall, then pumping an insulating material into the cavity. The most common method is to inject a chemical foam (urea formaldehyde) but this should be avoided because of the possible health risks of formaldehydes.

Alternatives include blown mineral wool and polystyrene beads.

Cost: around £260
Annual saving £130-£160

EASY AND CHEAP Eliminate draughts

Probably the easiest, cheapest way to cut heat loss is to draught-proof your windows and outer doors. Wherever cold air enters, warm air escapes, and draughts can waste up to 20 per cent of your heating. The Draught Proofing Advisory Association (tel: 01428 654011, www.dpaa-association.org. uk ) has a directory of members; or you can buy draught-proofing materials at a hardware shop, and do a basic job yourself. Lined curtains, blinds and shutters can also help to keep in heat.

Cost: around £75
Annual saving: £20

Tanks and pipes

Insulating your hot water cylinder with a jacket is an easy way to save energy and money. The jacket should be at least 80mm thick.

Cost £10
Annual saving £20

Heat is lost along the whole length of your hot water pipes. The most important ones to insulate are the hottest ones (e.g. between your boiler and hot water tank) and those in the coldest places (e.g. the loft).

Cost £5-£10
Annual saving £20


Solid walls Solid walls lose even more heat than cavity walls. They can be insulated both inside and out. The most cost-effective and least disruptive time to do it would be if you're renovating.


Cost: £40 per square metre
Annual saving: £270-£340


Cost: From £1,800
Annual saving: £290-£350


Double glazing halves heat loss through windows. Anglian Windows (www.anglianhome.co.uk) quoted an average cost for a three-bedroom semi (below).

Cost: £8,500
Annual saving: £80-£100


Where a floor is being replaced, there is the opportunity to include insulation underneath or within the new floor. For solid floors you can insulate on top, using a rigid insulant that will slightly raise the floor height.

Cost: DIY, from £100
Annual saving: £40-£50

Useful links

Energy Saving Trust

Energy Efficiency Advice Centre Tel: 0800 512 012

Centre for Alternative Technology (CAT)


Energy assumptions

All figures shown are approximate and mostly sourced from the Energy Saving Trust, based on a gas-heated semi-detached three-bedroom house, professional installation and subject to a discount from an energy supplier. Savings  assume a gas price of 2.57p/kWh

This article first appeared in the Ecologist in September 2007

More from this author