Understanding the changing nature of insulation

Article written by Simon Ayres, Managing Director, Lime Green Products Ltd for the AT Journal issue 141.

1 How are UK Government guidelines for insulation changing?
2 Changing how we think about insulation
3 Presence of moisture
4 Moving beyond U-values
5 Installing insulation
6 Related articles on Designing Buildings

[edit] How are UK Government guidelines for insulation changing?

Building standards are and have changed, which is impacting insulation choice, shifting the way we think about insulation in different kinds of buildings and walls. This article discusses the new guidelines, what they mean for designers and explains the importance of design choice in avoiding common insulation pitfalls

[edit] Changing how we think about insulation

Insulation has a crucial role to play in ensuring a building and its occupants remain healthy. Although, often, properties are not built with this in mind, and as a result, many buildings with solid masonry walls in the UK don’t have effective insulation installed.

Until recently, it was thought that, for retrofit projects with solid masonry walls, impenetrable, vapour-tight barriers were the most suitable solution for controlling internal condensation.

However, recent research published by the Brick Development Association records that a large volume of the moisture present in solid masonry walls is caused by driving rain and leaks, which can lead to further problems for the building. It also found that when moisture builds up in this way, in warmer weather, it is likely to be driven inwards against the impenetrable, vapour-tight barriers. Over time, this can cause the moisture to accumulate in the building, with no means of escape, leading to eventual rot in lintels and joist ends.

Recognising the risk of this insulation solution, British Standards BS 5250:2021 for the management of moisture in buildings now prohibits the use of dew point calculations for solid-walled properties. Instead, it advocates for breathable insulation on both sides of the wall, ensuring any moisture has a means of escape once the wall dries out.

[edit] Presence of moisture

The recent changes to building standards promotes an alternative perspective on moisture and insulation in solid-walled properties.

Previously, moisture was often thought of as something that needs to be eliminated from a building in its design phase. However, in reality, moisture will always be present. That is why BS 5250:2021 now suggests it should be seen as an interactive matter, and focus should instead be placed on moisture management, ensuring any moisture present has a way to escape through the building’s fibres.

[edit] Moving beyond U-values

When insulating a building, it is important to think beyond the U-values of individual materials in isolation.

Although considering heat transfer is important in reducing overall heat loss, the lowest U-value alone will not necessarily equal optimal thermal performance in reality. Instead, it is important to think about how the insulation materials will work together as a whole system.

[edit] Installing insulation

When selecting the most suitable methods and materials for retrofitting internal insulation to solid masonry walls, there are four main steps to consider: assess, design, install and maintain.

[edit] 1. Assess

When installing insulation as part of a retrofit project, regardless of size, it is first important to understand the building itself. Think about the amount of energy the building is losing through its walls, floors and ceilings, for example, and consider how much insulation can help you to save.

Ultimately, your insulation will change the physics of your solid wall, and there is no one-size-fits-all answer about the ‘correct’ way to do this. Your decision should be informed by a number of different factors, such as:

[edit] Wall type and build-up

What materials is your wall made from?
Is it a solid wall or cavity wall?
How thick is it?
What condition is the wall in?

[edit] Mortar type

Is the wall’s mortar lime or cement-based?
This will affect how the wall absorbs and deals with moisture.

[edit] Existing internal lining

Is there any existing internal lining?
If there is, is it plasterboard, lime, gypsum or something else?
This is important as you need to ensure your insulation can bond successfully to the existing wall. In some cases, you may need to remove internal lining before installing internal insulation.

[edit] Existing internal finish

Is the wall finished with paint, wallpaper or another material?
You will need to remove wallpaper or impermeable paint before installing insulation to retain breathability and ensure the insulation performs effectively.

[edit] Existing external finish

Is your external finish cement render, lime render or paint finished?
Understanding how moisture can escape from the wall externally is key to ensure it does not become saturated following periods of heavy rainfall.

[edit] External condition

Consider the overall condition of your building – for example, is there any maintenance needed?
Look at any water pipework, window frames, wall penetrations and ground conditions, for example.

[edit] Internal condition

Are there any damp patches, mould or stains that could indicate internal condensation?

[edit] 2. Design

Once you understand the building in more detail, you can start to think about the most suitable materials for your insulation.

It is important to keep three things in mind when designing your insulation solution:

It is also important to minimise thermal bridging to reduce risk of mould growth, as well as considering insulation for joists and floors, as well as walls, to minimise risk of condensation.

[edit] 3. Install

How you install your internal wall insulation will vary depending on the materials you are using. However, generally, when installing insulation it is essential to fit it without gaps or cavities, as these can encourage cold air travel and the growth of damp or mould.

It is also important to consider the different properties of different insulation products. For example, some materials, such as lime, have high-alkaline properties, making them antibacterial, which reduces the risk of damp in the wall.

[edit] 4. Maintain

When you take the time to assess, design and install insulation based on the needs of your individual building, there is often very little maintenance required on an ongoing basis.

When your insulation does not match your wall, it can result in serious maintenance issues further down the line, with BS 5250:2021 noting how non-breathable insulation can cause extreme issues in solid-walled properties, such as rot.

For more information, or to understand the most suitable insulation solution for your retrofit project, explore Lime Green’s insulation guides.

This article originally appeared in the AT Journal issue 141 entitled "How are UK Government guidelines for insulation changing?"

--CIAT