How to Upgrade your Home Insulation

For most people undertaking a major renovation project, upgrading the house’s energy efficiency will be a key goal. To get this right, you need to address each of the core components of the external envelope (floors, walls, windows and roof) and look at how their performance could be improved.

In this article I’ll explore the main options for upgrading each thermal element, but it’s important to take a holistic, whole-house approach so that everything works together.

You’ll need to account for the risks involved in altering a property’s structural fabric and be careful to avoid cold spots (which can cause condensation), along with making the necessary adjustments to heating systems and ensuring there’s adequate ventilation.

Before you get started Don’t upgrade insulation before you’ve dealt with basic upkeep. A well-maintained building will perform relatively efficiently, whereas a wet wall leaks energy fast – so it’s important to ensure that your property is dry and free from defects.

Without a proper assessment of the property, it’s impossible to predict exactly how much energy saving any particular insulation strategy will deliver. That’s because homes vary widely in terms of shape, construction, location, condition and services.

Even apparently homogenous buildings, such as those on terraced streets, may have been altered or extended in different ways. What’s more, patterns of occupation and energy use will also differ significantly. But the underlying principles remain the same. Here’s how to approach your eco upgrade.

1. The roof

Heat rises, so a great deal of energy can be lost through an untreated attic void. If your home has a pitched roof and a flat ceiling below, leaving you with an unoccupied loft, it should be simple, cheap and cost-effective to add insulation.

Typically, you’ll be aiming to incorporate 270mm of mineral wool tucked between (and possibly over) the joists. There are a few things to bear in mind, however:

• Don’t make the common mistake of forgetting to insulate the loft hatch.
• Never block the eaves – in most cases, these need to be kept clear to allow for adequate ventilation and thus prevent condensation.
• The loft void will move outside of the house’s thermal envelope, so you may need to insulate round cold water tanks to prevent freezing.
•  A little insulation goes a long way, whereas it takes a lot to do a little more work. It might not be worth topping up if, say, you already have 150mm of mineral wool.
• You may want to consider other products, such as sheep’s wool for its natural sustainability or options such as blown cellulose if the space is difficult to access.

If the roof has already been converted to offer living space, any thermal top-up would need to be integrated into the sloping ceilings – which can present more of a challenge. In most retrofits, insulation is added between the rafters, but it will be necessary to leave an air gap above this to allow for sufficient cross-ventilation.

You can complement this with a layer below the rafters, but this will of course reduce head height. To minimise this effect, high-performance rigid foam insulation is normally used here.

2. Ground floors

Solid ground floors are difficult – and sometimes impossible – to insulate. It’s not usually cost-effective to dig them out and add thermal protection beneath them, while adding insulation over the top will raise the floor level and is likely to cause issues at doorways and staircases. Instead, consider investing in a good quality underlay, which will do an effective job in most cases.

Measure	Main risks	Actions	Level
Solid wall insulation	Heritage impact Moisture build-up Indoor air quality Thermal bridging	Assess condition of building Use a whole-house approach Employ qualified contractors	High
Cavity wall insulation	Moisture build-up	Assess location for suitability Repair walls before injection Monitor internal walls	Medium
Loft insulation	Moisture risk	Ensure ventilation at eaves Check roof for condensation	Low
Suspended floor insulation	Moisture risk Indoor air quality	Ventilate below floor Check effect on ventilation within the building	High
Window upgrade	Heritage impact Thermal bridging at window reveals	Seek expert advice for historic windows Use a whole-house approach	High
Improving air tightness	Indoor air quality Moisture risk	Add ventilation if required Monitor moisture levels	High

Table adapted and reproduced by permission of the Sustainable Traditional Buildings Alliance (www.stbauk.org)

If there’s sufficient space and access, suspended timber ground floors can be treated from below. Alternatively, the floorboards can be lifted and insulation retrofitted between the joists from above.

This should be done very carefully if you’re dealing with an historic floor, as it may be an important part of the house’s character and value. It’s also essential to ensure that air bricks at all sides of the property are left clear and unobstructed, as this strategy reduces natural ventilation. If the sub-floor airflow is insufficient, you could end up with rotting joists.

3. Windows

You might be surprised to learn that, often, more energy is lost through gaps around window frames than through the glass itself.

With that in mind, maintaining and upgrading existing units is always a solid plan. In many cases, existing frames can be repaired and retained, deeper casements inserted with double-glazed panels and new seals fitted.

Even adding a thick set of curtains – or opting for well-fitting shutters – will substantially reduce heat losses. If a single-glazed window has a U-value (a measure of heat loss, where lower figures indicate better performance) of 4.3 W/m2K, investing in heavy curtains could drop the figure to as low as 2.5 W/m2K, or even 1.7 W/m2K with well-fitting shutters.

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