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Insulation & Energy Improvements
How better insulation can make your home warmer, cooler, quieter and cheaper to run
Insulation is one of the most important home improvement subjects, but it is often one of the least exciting to homeowners at the start of a project. People tend to focus on kitchens, extensions, bathrooms, glazing, patios and finishes. Yet the comfort of the finished home often depends on what is hidden behind the plasterboard, below the floorboards, inside the roof space and within the walls.
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If you are carrying out a major refurbishment, extension, remodelling project or older house upgrade, insulation should be considered seriously from the beginning. This is especially true in period homes, 1930s houses, Victorian terraces, Edwardian properties and older family homes where the original construction was never designed for modern comfort or modern energy costs.
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A poorly insulated home can lose heat through the roof, walls, floors, windows, doors and gaps around the building. The Energy Saving Trust states that a typical uninsulated home can lose around 25% of heat through the roof, around 33% through the walls, and 10–20% through the floor. That makes walls, lofts and floors some of the most important areas to consider when improving energy performance.
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Insulation is not only about keeping warm in winter. It can also help keep a home cooler in summer. With hotter UK summers and more frequent heatwaves, this is becoming increasingly important. A better insulated home can reduce heat loss in cold weather and slow heat gain during hot weather, helping the house feel more comfortable throughout the year.
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Good insulation can also improve sound comfort, reduce draughts, make rooms feel less cold, support better heating performance and improve the overall feel of the home. In many cases, insulation is not the glamorous part of the project, but it is one of the parts that determines whether the finished home feels solid, warm and high quality.
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Walls, floors and hidden insulation opportunities
If you are carrying out a major refurbishment, the walls should be one of the first places to look. Most homes have more wall area than almost anything else, and walls can be a major source of heat loss. That is why wall insulation can have such a big impact, particularly in older homes.
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Where external walls are being stripped, replastered or remodelled, it may be worth considering insulated plasterboard or rigid insulation, such as Celotex or similar products, fixed internally to external walls. Even a relatively modest thickness, such as 50mm insulation board, can make a noticeable difference to comfort when used correctly. This can be particularly useful in cold rooms, exposed elevations, older solid-wall houses, rear additions, converted spaces and rooms that always feel difficult to heat.
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However, internal wall insulation needs proper thought. It can slightly reduce room sizes, affect skirtings, sockets, radiators, window boards and reveals, and may require careful detailing around corners, floors, ceilings and openings. Moisture and condensation risk also need to be considered, especially in older solid-wall properties. The aim is not just to add insulation, but to create a proper insulated layer that works with the existing building.
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Party walls are a slightly different issue. If the wall divides two heated homes, thermal improvement may be less important. But walls to unheated spaces, garages, side passages, stores, basements, cold extensions or poorly heated neighbouring areas can be worth considering. In some cases, insulation may also improve acoustic comfort, although sound insulation and thermal insulation are not always the same thing.
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Floor insulation is another area that many homeowners overlook. In older houses with suspended timber floors, there may be very little between the room and the cold air below. In simple terms, the floorboards may be only around an inch of timber separating the living space from a ventilated void. That is why ground floor insulation can make such a noticeable difference.
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The Energy Saving Trust says floor insulation can reduce heat loss and could save around £70 a year for a typical property in Great Britain, with higher savings possible in larger detached homes.
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If floorboards are already being lifted during refurbishment, this is an ideal time to consider insulation between the joists. Rigid insulation boards, mineral wool systems or other suitable insulation methods may be used depending on the property and the specification. Draught sealing around gaps, skirtings and floorboards can also help.
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Basements can make this job easier in some homes. If there is access from below, floor insulation may be installed without lifting every floorboard above, although the exact method depends on the structure, access, services, fire safety and ventilation requirements.
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The key point is simple: if you are already opening up walls, floors or ceilings, consider insulation at the same time. Retrofitting it later can be more disruptive and more expensive.
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TOP TIP: During a major refurbishment, look for “open-up” opportunities. If walls are being stripped, floors are being lifted or ceilings are being opened, that may be the best time to add insulation, improve draught sealing and future-proof the home.
Windows, glazing gas and loft insulation
Windows are another major part of home comfort. Many homeowners already have double glazing, but not all double glazing performs the same way. Two windows can look similar but have very different levels of insulation depending on the frame, glass, spacer bars, seals, cavity width, coating and the gas inside the sealed glazing unit.
Modern double glazing often uses gas-filled cavities to improve thermal performance. The most common gas is argon because it offers a good balance of performance and cost. Krypton can perform better in some high-performance or narrower glazing cavities, but it is more expensive. Xenon is generally the highest-performing and most expensive option, but it is rarely used in normal domestic glazing because the cost is usually hard to justify.
A simple order from best performing to cheapest is usually:
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Xenon — highest performance, highest cost, rarely used in ordinary homes
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Krypton — very good performance, more expensive, often used in specialist or high-performance glazing
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Argon — good performance, widely used, usually the best-value upgrade
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Air-filled units — cheapest, but generally lower thermal performance than gas-filled units
For most homeowners, argon-filled double glazing is the normal practical choice. Krypton may be worth considering where performance matters and budget allows, particularly with premium windows or specific problem areas. Xenon is usually too expensive for mainstream residential use.
This is why selective window upgrades can make sense. Replacing every window in a property can be expensive. If the existing double glazing looks acceptable and is functioning reasonably well, homeowners may choose to focus first on the most important areas: large glazed doors, cold living rooms, bedrooms exposed to weather, north-facing windows, rooms with excessive glazing, or areas where comfort really matters.
This is especially important in open-plan extensions and living spaces with large areas of glass. A kitchen diner with sliding doors, bifolds, rooflights and side windows can look fantastic, but it also needs good thermal performance. Poor glazing can make the room cold in winter and hot in summer. Good specification glass, shading, ventilation and insulation all need to work together.
Loft insulation is the other obvious improvement, and most homeowners already know that the attic should be insulated. But knowing it and checking it properly are not the same thing. Many lofts have some insulation, but not enough by modern standards.
The Energy Saving Trust says topping up loft insulation from around 120mm to 270mm can still save money, while insulating a totally uninsulated loft to 270mm can save around £230 a year in Great Britain.
Loft insulation is often one of the best value insulation improvements because it is usually relatively simple, long-lasting and effective. But it still needs to be done properly. Insulation should not be crushed under storage boards. Ventilation should not be blocked. Damp, roof leaks or condensation issues should be dealt with before insulation is added. Downlights, cables, tanks and pipes may also need proper attention.
Insulation also helps with summer comfort. A well-insulated roof space can slow down heat transfer into the rooms below. This can be particularly useful in loft rooms, top-floor bedrooms and houses that overheat during hot weather.
IMPORTANT POINT: Do not judge windows only by whether they are “double glazed”. The frame, seals, glass coating, cavity, spacer bars and gas inside the unit all affect performance. In many homes, selective upgrades to the most important windows may be more sensible than replacing everything at once.
External insulation, payback periods and long-term value
External wall insulation can be one of the most powerful upgrades for older solid-wall properties. Instead of insulating from the inside, insulation panels are fixed to the outside of the property and finished with render, cladding or another suitable external finish.
This can make the home feel much warmer and more protected. In simple terms, it wraps the outside of the building in an insulated layer.
Done properly, it can improve comfort, reduce heat loss, refresh the appearance of the property and create a much more modern external finish. “Snug as a bug” is a fair way to describe the aim.
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External insulation can be particularly attractive where the outside of the house already needs work. If the render is poor, the brickwork is unattractive, or the homeowner wants a modern rendered finish, external wall insulation may achieve both an energy improvement and an appearance upgrade at the same time.
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However, it is not a small job. It can affect window sills, reveals, rainwater pipes, soil pipes, vents, flues, meter boxes, roof edges, eaves, boundaries and external detailing. In some areas, planning permission may be needed, especially where the appearance of the property changes, the home is in a conservation area, or the building has special character. It also needs competent installation. Poor detailing can cause damp, cold bridging or long-term maintenance problems.
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The Energy Saving Trust gives typical solid wall insulation costs of around £12,000 to £18,000, depending on the property and the work involved, with potential annual savings for a typical semi-detached home shown at around £330 for internal or external solid wall insulation.
This is where payback periods need to be understood properly. Not every insulation upgrade pays back at the same speed.
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Some improvements are relatively low cost and can produce quick benefits. Draught proofing, loft top-ups, hot water cylinder jackets, pipe insulation and floor draught sealing can often be quick wins. The Energy Saving Trust says draught proofing around windows, floors and doors could save around £85 a year in Great Britain, while a hot water cylinder jacket can save around £40 a year.
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Other improvements cost more but can transform comfort. Internal wall insulation, suspended floor insulation, better glazing and external wall insulation may take longer to repay purely through energy savings. But that does not mean they are poor investments. They can improve comfort, reduce cold spots, make rooms more usable, improve the feel of the property and support future upgrades such as heat pumps or lower-temperature heating systems.
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A useful way to think about insulation payback is:
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Fast payback / low cost: draught proofing, pipe insulation, hot water tank jackets, loft top-ups where access is easy
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Medium payback / strong comfort gain: suspended timber floor insulation, selective wall insulation, improving cold rooms, upgrading poor windows
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Longer payback / major upgrade: external wall insulation, full internal wall insulation, whole-house glazing replacement, deep retrofit work
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The best time to do the more expensive insulation works is often when the house is already being refurbished. If walls are already being replastered, floors are already lifted, scaffolding is already up, or the exterior is already being rendered, the additional cost and disruption may be easier to justify.
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Rising energy costs, carbon reduction, summer overheating and future property expectations all point in the same direction: better insulated homes are likely to become more important. A home that is cheaper to run, more comfortable in winter, more stable in summer and better prepared for future heating systems will usually be more attractive than one that simply looks good on the surface.
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Insulation is not always visible when the project is finished, but you feel it every day. You feel it when the living room is comfortable. You feel it when the bedroom is not freezing. You feel it when the floor is not cold underfoot. You feel it when the heating does not have to work as hard. You feel it when the house stays cooler during a heatwave.
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For homeowners planning a serious refurbishment, insulation should not be treated as an optional extra. It should be part of the core design conversation.
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Thinking about insulation or energy improvements?
If you are planning a refurbishment, extension, loft conversion, garage conversion, new glazing, render upgrade or whole-house improvement project, it is worth thinking about insulation early.
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APN Home helps homeowners look at the bigger picture, including walls, floors, roofs, windows, external insulation, heating performance, ventilation and long-term comfort.
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Good insulation is not just about saving money. It is about creating a home that feels better, performs better and is ready for the future.