Insulation material selection - why it matters

Given their purpose, the thermal performance, or lambda value, is a key metric upon which many specifications are based where in theory the lower the lambda the better the thermal performance. Generally, the lowest lambda values are achieved by high density foams such as phenolic and PIR (polyisocyanurate) boards. These have been typically specified where space is limited within a construction and where a thinner insulation solution is preferred to help minimise the size of the element and reduce both material quantities and associated costs.

Other insulants such as mineral wool and wood fibre rigid boards, or flexible batts, commonly have higher lambda values than the high-density foam boards. They require greater thickness to achieve the same results. However, they may be a better specification choice and a more economical selection for projects where space restraints are not a concern or other factors such as moisture permeability or additional thermal mass need to be considered.

As insulation can be used in walls , floors and roofs, the physical form of the insulation is important. Where floor insulation is required to carry a structural load, rigid foam boards such as XPS (extruded polystyrene), EPS (expanded polystyrene) or PIR with high compressive strength could be better suited.

For insulating between rafters or joists more flexible insulation batts may be preferred for ease of installation. Flexible insulation also has the ability to fit tightly between timber structures to minimise gaps that can diminish the performance of installed insulation. Insulation batts and rolls are commonly used to insulate lofts at ceiling level as they are lightweight and easy to install. However, these insulants can lose some of their insulation efficiency if compressed.

Insulation that is comprised of a closed cell foam structure like Phenolic, PIR or XPS are moisture resistant. This makes them suited for use in applications that are likely to be exposed to water such as when insulating under the slab of a ground floor.

These insulation materials are diffusion closed, meaning they do not allow water vapour to pass through. In contrast, mineral wool and wood fibre insulation products are diffusion open. Both types can be used across a range of applications when paired with appropriate moisture controlling membranes.

However, in situations where the building fabric is designed to breathe, such as solid wall or heritage buildings, diffusion open insulation is often considered a more suitable choice by specifiers, as it works in harmony with the building’s natural moisture movement. It is also be used in new-build applications to help minimise the risk of trapped moisture within the construction, known as interstitial condensation, which can lead to damage to the building fabric.

EPDs of insulation materials provide third-party verified and standardised data on the environmental impacts of the insulation across its product lifecycle. This includes the extraction of raw materials, manufacturing, transport to site and installation, as well as end of life disposal, incineration or possible reuse or recycling. EPDs therefore give specifiers a way to evaluate the embodied carbon of different products and this can be an important metric for projects with a focus on sustainability.

Naturally derived materials such as wood fibre insulation may have lower embodied carbon than other insulating materials as they store biogenic carbon as well as act as insulation to help reduce carbon emissions from the buildings in which they are installed.

Insulation materials derived from chemicals such as Phenolic, PIR, XPS and EPS may have higher global warming potential (GWP) depending on formulation and manufacturing processes.

The EPD process takes all these factors into account and enables a fair comparison to be made when factoring embodied carbon into the specification of insulation construction materials for a project.

The need to provide good thermal comfort all-year-round by mitigating the risk of overheating is part of an increasing awareness to put the homeowner at the heart of the design and specification of new build housing. This idea has gained some traction in parliament through the APPG (All Party Parliamentary Group) on Healthy Buildings^[1].

Although the buildings themselves are not healthy, the group proposes that buildings should provide a ‘healthy’ internal environment for the occupants. As well as the ability to stay warm in the winter and cool in the summer, indoor air quality is important. This can be affected if the materials specified in the house allow a build-up of condensation that can in turn lead to mould growth. This leads housebuilders to look for materials that can reduce this risk. Diffusion open wood fibre insulation allows the fabric to breathe and can help reduce the risk of moisture build-up when considered as part of a wider moisture management strategy.

Wood fibre insulation from STEICO is formed from at least 80% wood fibre and the naturally derived raw material comes from PEFC* certified forests. Our range has wood fibre insulation construction materials suitable for use throughout the fabric of a building.

Many of STEICO’s products have EPDs that reflect the bound carbon dioxide equivalent content of the wood. For example, STEICOuniversal dry binds 353kg CO_2eqduring Lifecycle Stage A1 as defined in EN 15804+A2 and can thus contribute to climate protection making it a viable option for developers who are looking to reduce the embodied carbon within their projects.

To enquire about using our wood fibre boards on your next project, contact our expert team here who will be happy to help.