In this new series, Chartered Surveyor Ian Rock FRICS – Author of the Haynes Home insulation Manual –  explains how to cut your energy bills by boosting your home’s thermal efficiency.


PART ONE: What’s worth doing and what isn’t?


When most of our homes were built, no one paid much attention to thermal efficiency. As a result many households today are paying for warmth that’s lost through cold, draughty walls, roofs, floors, windows and doors. So it obviously makes sense to stem this waste of valuable heat and reduce energy consumption, thereby saving money and making your home more comfortable.

Some improvement works can be done any time the fancy take you – such as laying loft quilt or having cavity walls injected. Other more disruptive jobs, like insulating timber floors, are better suited to being done on a room by room basis or as part of a major refurbishment. So if you’re planning to redecorate or re-fit the kitchen, bathroom or cloakroom any time soon, it could be a good opportunity to line the walls internally with insulation.

As with all home improvements, it’s always a good idea to take a few minutes at the outset to plan how life can go on around the works with the minimum of disturbance. As a rule, the more you can do to reduce dust, mess and power cuts the more harmonious your home life will be!


A few facts about insulating your home

The bottom line when deciding which improvements are worth carrying out is how much money they’re likely to save in relation to their cost. But you also need to consider factors such as the complexity of the work and whether any consents will be needed. And of course you also need to pick the right sort of insulation for your type of property.


Which works are most cost-effective?

It’s a well known fact that nearly half of our body heat escapes via the tops of our heads – hence the importance of wearing a hat in cold weather. The same logic applies with buildings because heat rises. So applying generous layers of insulation at roof level can pay big dividends. The greatest benefit can generally be gained by tackling those parts of the building that leak the most heat; the biggest culprits when it comes to heat loss are actually the walls of your home:-

  • Walls    35%
  • Roof    25%
  • Floor    15%
  • Doors and Draughts    15%
  • Windows   10%


How much money will I save?

A typical semi-detached house of around 90m2  floor area with an average amount of insulation and gas-fired central heating uses approximately 26,000 kWh of energy per year for heating, hot water, cooking, lighting and appliances. This equates to around £2,000 a year (and rising). So even if you can cut this by 10 – 20% it will result in substantial savings.

There are a number of ‘quick & easy’ upgrades, such as draught-proofing, loft insulation and lagging tanks and pipes. These are relatively inexpensive and hence pay back quickly – within a year or two. The ‘payback period’ is the amount of time it will take for an energy saving measure to repay its full cost as a result of savings directly generated in fuel bills. So for example if you spent £2000 on internal wall insulation to achieve savings of  £100 per year, the payback period would be 20 years, equivalent to 5% net return (far better than most savings accounts). Incidentally, double glazing has one of the longest payback periods of all improvements.

The actual figures for costs and likely savings very much depend on the size, type and condition of the property. But as energy prices continue to rise in future the annual savings should snowball. It’s also worth bearing in mind that the cheapest improvement of all is ‘lifestyle’ – ie getting into the habit of switching off lights, lowering thermostats, not leaving doors & windows open.


What will it cost?

The cost of insulating can be substantially lower where DIY installation is a realistic option. But even where you’re employing a builder to do the work, there may still be scope for savings. For example individual trades may not need to charge VAT if their annual turnover is below the threshold (currently £85,000).

Better still, home insulation grants periodically become available, although the money tends to be targeted at qualifying households and may only apply to specific age or income groups. It might be worth checking where you stand with the ‘Energy Company Obligation’ (ECO) – where energy companies are required to seek out and insulate a number of ‘hard to treat’ homes.


Who can do it?

There are a number of surprisingly effective energy efficiency improvements that anyone with basic DIY skills can carry out. But there’s a right way and a wrong way to go about even these simpler tasks, something we will be explaining in future posts. The Haynes Home Insulation Manual is an excellent DIY guide.

The most DIY-friendly projects are things like loft Insulation, draught-proofing, and lagging pipes, tanks and hot water cylinders. More advanced DIY skills are needed for projects such as floor insulation and lining internal walls. Cladding walls on the outside tends to be a specialist job, not least because of the need for access equipment and scaffolding. And whilst it’s possible to hire cavity wall injection equipment, it’s not generally cost-effective as a DIY project.

Remember also that the work will only qualify for a guarantee if it’s carried out by a specialist firm. Specialists in external wall insulation are members of INCA (the Insulated Render and Cladding Association). With cavity wall insulation specialist installers should be members of the Cavity Wall Guarantee Agency (CWGA) and provide a 25 year CIGA guarantee (Cavity Insulation Guarantee Agency).  Replacement windows are generally best installed by a company registered with Fenestration Self Assessment (FENSA).


Do I need Planning Permission or Building Regulations consent ?

The good news is that planning permission isn’t normally required. Even if you want to smother the outside of your home with thick slabs of insulation, this is now classed as ‘permitted development’ so you shouldn’t have to worry about making a planning application. Inevitably there are some exceptions, notably with Listed buildings – where even minor internal alterations need consent. Also where properties are located in a Conservation Area, any changes to the ‘principle’ elevation (normally the front) are likely to need consent.

However it’s a different story when it comes to complying with the Building Regulations because they take a keen interest in the subject of energy efficiency – although more for new construction than ‘retro-fitting’. Nonetheless, minimum heat loss targets are stipulated – known as  ‘U-values’ – for renovation work to any ‘thermal element’. A thermal ‘element’ simply means any part of the ‘envelope’ of the building.

So where the walls, roof or floors are due to be replaced or renovated, minimum U-value standards may apply. U-values tell you the rate at which heat is transmitted through the wall, roof or floor, measured in Watts per sq metre (Wm2/K). The lower the figure the smaller the heat loss.


Thermal element  

      Target U-value W/m2K
FLOOR 0.25
PITCHED ROOF(loft insulation) 0.18


A thermal element counts as being renovated if any layer of its construction is replaced or added to (excluding decoration). This applies where the work covers 50% or more of the total area of the element, for example where you’re replacing an old felt covering to a flat roof the Building Regs stipulate that you must also upgrade the insulation.

Windows and external doors are similarly defined as ‘controlled fittings’ which means that an application needs to be made to Building Control  – although in practice FENSA registered installers normally ‘self-certify’ the compliance of the works (consent is not required where only the glass is being replaced).


Energy Performance Certificates

By law all residential properties being sold or rented must have an Energy Performance Certificate (EPC) which measures the building’s energy efficiency, from a cosy A down to a cold and draughty G. The first point to bear in mind is that EPCs aren’t always terribly accurate, especially for older properties or those of non-standard construction. The recommended improvements listed in EPCs are computer generated and shouldn’t be taken as gospel.

The second point is that, like them or not, EPCs are becoming increasingly important. For example, unless a property can achieve a rating of ‘D’ or higher it won’t qualify for Feed-in Tariff payments for solar generated electricity. And it’s now illegal to let  accommodation unless it meets a basic level of energy efficiency. So improving your home’s EPC rating is another good reason to invest in beefed up insulation.


What type of property have you got?

There’s a wide variety of insulation products on the market, something we’ll be looking at in the next post. The right choice of materials depends on the age and type of property. If you’ve got a copy of the survey from when you bought your home this should identify the basics.

The first task is to identify the type of wall construction. Most homes built since the 1930s have cavity walls. These comprise 2 parallel walls or ‘leaves’ with a gap in the middle – perfect for filling with insulation (with a few important exceptions). Cavity walls are typically 250mm – 300mm thick with the bricks laid end-to-end so only their sides are visible. In contrast, older solid brick walls are typically only about 230mm thick with one brick laid sideways and the next brick laid across the wall with only its head visible.

Things can get considerably trickier when it comes to identifying modern timber frame buildings. These are not suitable for having their cavities injected with insulation – in fact it can cause serious damage. The trouble is, the external walls of timber frame buildings generally look identical to those made from conventional masonry – the main difference is the (hidden) inner leaf which is built of timber panels supporting most of the loadings. The easiest way to verify the type of construction is to look up in the loft and see if the gable or party walls are made of timber rather than conventional brick or blockwork.

There are various other unothodox types of construction – such as concrete or steel frame buildings. These were widely built in the postwar period by local authorities, and are generally best suited to having the walls insulated externally.

Of course it’s not just the type of walls you need to identify. Depending on the age of property, there are many different sorts of roofs, floors and windows. But whatever type of construction you’re dealing with there’s one key thing to check before insulating – the building must be well maintained and watertight. It’s sometimes said that ‘a wet building is a cold building’. This is because insulation materials have a nasty habit of losing their thermal powers if they get damp. So be sure to fix any leaks and sources of damp before insulating.


What about older buildings?

Britain has a wide variety of traditional house types with solid walls built with materials as diverse as mud, oak frame, solid stone and handmade brick.

Before carrying out insulation work on old houses it’s important to understand that they work in a totally different way from modern buildings. Whereas modern cavity-walls rely on impervious outer layers that form a rigid barrier to block out wet weather, older solid walls work very differently, temporarily absorbing rain into the external surface until it can later evaporate out, helped by the drying effects of the wind and sun. This natural cycle is known as ‘breathing’. So if you cover walls with thick sheets of polyurethane insulation it can interfere with this process, potentially trapping moisture and causing damp problems. Fortunately, as we shall see in the next post, there are a number of natural insulation materials that keep old walls happy by allowing them to ‘breathe’.




NEXT MONTH:  Picking the optimum type of insulation for your property – and how improved ventilation can cure clammy, dank, mouldy walls and ceilings.

  Ian Rock’s home insulation tips are taken from the Haynes Home Insulation Manual. For further information see