Is it possible to insulate solid walls?

17 September 2020 Kingspan Insulation UK
How to insulate solid walls

Over 8 million homes here in the UK feature solid walls. This means there is either no cavity within the wall, or only a very slim one which is unsuitable for cavity wall insulation. These constructions are a source of heat loss, making it expensive to heat a home. Fortunately, in many cases it is possible to improve their performance by installing solid wall insulation. Insulation can either be fitted on the outer face of the existing wall (external wall insulation - EWI) or on the inner face (internal wall insulation - IWI). 

In this blog, we look at the advantages of these different approaches, and how to decide which might be right for your home.

How can I tell if my property has solid walls?
Solid walls are most common on homes built before the 1920s. In most cases, brick-built solid walls will be roughly the length of a brick plus a few extra centimetres for plaster (usually around 230 mm in total). An easy way to measure this is by standing in an external doorway. 

Another common sign of a brick built solid wall is if alternate bricks have been fitted with their short edge facing outwards. These bricks will typically run across the full width of the wall meaning no cavity is present.

If you are unsure about what type of construction your home uses, contact a suitable TrustMark certified installer, who should be able to quickly identify your home’s construction.

If you live in a house that has a non-traditional construction such as a concrete, steel or timber-framed building, you will need a specialist retrofit professional to advise you on your options.

Why is it a good idea to insulate solid walls?
Having a well-insulated and less draughty home can make a real difference both to annual bills and your health. The most recent English Housing Survey showed that most properties built before 1920 (typically solid walled) fell in the worst bands for Energy Efficiency (F or G). This meant that their average energy bills were more than double the cost of homes built after 2002 (£1259 compared with £603). This can be a serious issue, preventing some owners from being able to afford to heat their home. Properties in these bands were also shown to be more likely to suffer from issues such as damp which can allow mould to grow, putting your health at risk.

In many cases, owners of solid walled homes may have already fitted certain improvements to reduce heat loss, such as loft insulation and double glazing. However, with the external walls making up a good deal of the outer surface area of a home, it is important to consider how insulation may also benefit the property.

How much could I save by fitting solid wall insulation?
The Energy Savings Trust estimates that annual savings from fitting solid wall insulation range from around £105 for a flat to £375 for a detached home, but it also depends on the efficiency and fuel cost of your heating system and savings can be more. 

In addition, a recent Government study has suggested that fitting solid wall insulation in your home may also help to increase its value.

Why choose external wall insulation?
External wall insulation applications are generally much simpler, faster and less disruptive than internal wall insulation installations. The insulation is typically fitted as part of a system including external render or cladding such as timber boards or brick slips (thin bricks which mimic the appearance of a full sized brick). In addition to improving the insulation performance of your home, external wall insulation systems can also help to give your property a face lift and cut down on outside noise.

External wall insulation systems are often a good option for homes located in areas which are exposed to lots of wind driven rain as they help to prevent moisture from penetrating into your walls and potentially causing damp. Additionally, you typically get less heat loss from junctions when insulating externally.

In some cases, it may not be possible to fit external wall insulation. Common examples include semi-detached or terraced properties where only one household is looking to make improvements. Additionally, if the property is listed or located within a conservation zone then planning restrictions will often prevent the external alterations necessary for this work. 
Why choose internal wall insulation?
As mentioned, internal wall insulation applications may be the only option if your property has planning restrictions or if you simply would prefer to retain the original external aesthetic. As the insulation is fitted on the inner face of walls, these systems will allow your home to warm up more quickly when heating is turned on.

For a standard solid brick wall this can be achieved by fixing timber studs to the walls with a strip of damp-proof membrane to separate the two layers. A layer of insulated plasterboard can then be fixed to the battens with suitable fixings and the surface skimmed. In some cases, it may also be necessary to fit insulation on the ground floor and around any joists.

Internal wall insulation applications require a good deal of work. Before any insulation is installed, it will be necessary to clear the room and to strip away features such as skirting boards, plaster and coving and radiators which are attached to external, walls and to reposition sockets and pipework. Floorboards will also need to be removed so that installers can check the condition of the floor joists and ventilation. 

All of this means that ideally this work should be carried whilst the property is unoccupied. For example, if you have recently purchased a house, you may choose to have the work carried out before you move in. If this isn’t possible, then another way to limit disruption is by having the work carried out room by room rather than all at once.

Does insulation choice matter when fitting solid wall insulation?

It’s important that a coherent approach to retrofit is adopted when looking to make changes to any property and proper assessment and development of a design and plan for improvements is part of that approach; what is right for one property, may not be right for another, but as all solid wall insulation options will increase the thickness of your walls, it is important to use wherever possible a material with a low thermal conductivity (also known as a lambda value). These are more effective at preventing the main forms of heat loss, meaning a slimmer layer of insulation can be fitted. This is particularly important for internal wall applications as the thickness of the insulation will impact the overall space in the room. 

What are lambda values, R-values and U-values?

Find out more about the importance of lambda values when selecting insulation.
Kingspan is committed to providing insulation materials with the lowest possible thermal conductivities, helping you to stay warm without having to compromise on space. Our Kooltherm range boards include options which are suitable for both internal and external wall applications and achieve the lowest thermal conductivities of any commonly used insulation materials.

Why is extra ventilation needed when installing solid wall insulation?
In addition to reducing heat loss, all solid wall insulation installations should also make your home more airtight – cutting down unwanted draughts. For this reason, it is important that controlled ventilation is introduced to keep fresh air circulating, preventing condensation issues and maintaining healthy internal environments. Depending on the requirements for your home, which should be determined by the installer, this can include everything from trickle vents on windows to a full mechanical ventilation system. 

Can solid wall insulation cause damp?
When designed and installed correctly, solid wall insulation should not lead to damp problems.  

Before carrying out any work, installers should carry out a careful pre-assessment of the condition of your property to ensure that it is in good condition and the walls, floor and roof are dry. This should include addressing any existing damp problems, along with issues such as missing pointing, broken bricks or damaged guttering which may cause issues in the future.

The installers should also carefully plan and design the installation with close attention paid to junctions around features, such as windows and doors. In internal wall insulation applications, they will also need to look carefully at junctions around the floor and ceilings and any penetrations such as joists or pipework to ensure a continuous layer of insulation and vapour protection.

As internal wall insulation applications will mean that external walls remain cold at all times, there may be cases where installers advise that solid wall insulation cannot be fitted. This may be the case where the materials used to construct the wall are particularly porous and planning restrictions prevent effective external weather proofing. You can learn more about how installers can prevent damp issues here.

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