Insulation guidelines are changing, and it’s shifting how we think about insulation in buildings and walls. Simon Ayres, co-founder and managing director, Lime Green Products Ltd, explains what the changes mean for architects and designers and unpicks the importance of design choice.
Changing how we think about insulation
Insulation is an integral part of any building, and it has a critical role to play in ensuring a building and its occupants remain healthy. However, many buildings still aren’t constructed with insulation top of mind. This is particularly true for solid-wall properties, with many of these across the UK not having suitable insulation.
Until relatively recently, impenetrable vapour-tight barriers were believed to effectively control condensation, and as such, these were commonly used as internal insulation for retrofit projects with solid masonry walls.
However, the Brick Development Association’s research recently discovered that a high portion of moisture in these walls originates from driving rain and leaks, which can lead to further building issues. Any moisture built up this way is expected to drive inwards against the vapour barriers during sunny weather, which can cause water to accumulate, as well as the eventual rotting in a building’s joist ends and lintels.
The above findings have now been backed up by changes to building standards. The British Standard BS 5250:2021 for the Management of Moisture in Buildings now says the Glaser method of dew point calculation is no longer compliant, suggesting more sophisticated Hygrothermal models. In addition to advocating for the use of breathable insulation on both sides of the wall to prevent trapped water accumulating.
Moisture presence
The changes are encouraging an alternative view of moisture and insulation within solid wall buildings. Previously, moisture has been deemed as something to be removed during the design stage, as its presence can be believed to indicate something wrong. However, BS 5250:2021 now deems all moisture as an interactive matter, suggesting how the design process should consider moisture management, rather than prevention. Moisture will always be present within a building, but it has to be able to escape.
Moving beyond U-values
When insulating a building, it’s all in the details. Although heat transfer through a wall is significant when designing, as it reduces the overall heat loss and enhances the internal comfort of dwelling, it’s also important to consider other aspects, rather than just U-values in isolation.
Those designing and building properties often aim for the lowest U-value to create optimal thermal performance. However, even when constructed with materials with low U-values, a building won’t necessarily be effectively insulated. It’s important that designers and buildings are also considering the values of windows and joists, for example. Like moisture, the idea of insulation in isolation is usually ineffective. Instead, thinking of insulation as a continuous system will result in improved thermal performance for your building.
Installing insulation
When retrofitting internal insulation to solid masonry walls, there are four main steps that should be considered to ensure you’re using the correct method and materials: assess, design, install and maintain.
- Assess
If planning or designing any retrofit project, it’s essential to understand the space you’re working with first. By considering how much energy the building is presently losing through its walls, you can begin to understand what you can save with continuous insulation.
There’s no standard answer to the correct materials and methods for internal insulation, but you can use checklists to keep track of your analysis. These should cover:
- Wall type and build-up – what is the main material? Is it solid or cavity? What condition is it in?
- Mortar type – for example, is it lime or cement-based?
- Existing internal lining – if there is any, is it plasterboard, gypsum, lime or another? You may need to remove any existing lining before installing internal insulation.
- Existing internal finish – is this paint, wallpaper or something else? Wallpaper and watertight paint may need to be removed prior to insulation to ensure moisture can pass through effectively.
- Existing external finish – because of the effects of driven rain, it’s important to establish whether this is lime or cement render or paint finished. If the moisture gets trapped in your building, this may saturate the wall.
- External condition – it’s important to assess the overall condition of your building to understand any maintenance they may be needed prior to installing insulation. For example, look over all the water pipework, wall penetrations, ground conditions and window frames.
- Internal condition – are there any signs of condensation, such as brown damp patches, stains or black mould?
- Design
Once you’ve assessed your building, you can decide which insulation is best.
When specifying an internal wall insulation solution, consider the following:
- Your building should have a target thermal performance
- You should know the potential risks that might occur when installing it
- You should understand the physical and aesthetic spatial impact on a property.
All these attributes influence one another and understanding them will support your decisions.
During the design process, make sure thermal bridging is minimised to prevent mould growth. Also, consider the insulation of floors, joists and walls to lower the risk of condensation.
- Install
The actual installation of your internal wall insulation will vary depending on your chosen products.
It’s crucial to ensure that insulation is fitted without gaps or cavities. Although gaps can be used inside dry lining systems, they often support cold air travel and the growth of damp or rot.
You should also consider the various properties different materials might have. For example, lime products have certain high-alkaline properties, meaning the material is antibacterial and will reduce the likelihood of damp or rot.
- Maintain
When wall insulation is specifically designed and fitted for your individual building, there’ll be little chance of maintenance once completed. You’ll need to continue with general maintenance, however, committing time into the assessment and design stages will reduce a significant amount of upkeep in the long run.
If your insulation doesn’t match your wall, maintenance complications may occur further down the line, with BS5250:2021 stating how non-breathable insulation in solid wall buildings can cause severe issues, such as floor rotting.