Guide to choosing steel frame wall insulation
Steel frame constructions offer a practical solution both for mid and high-rise buildings, and as part of modular home systems. As with all external wall constructions, the choice and position of the insulation can have a notable impact on the thickness of the construction and the finished floorspace within the building, so it is important to carefully consider the different options.
This article looks at a number of key points to consider including:
- Should steel wall insulation be fitted between or outside the studs?
- What insulation is best for steel frame wall constructions?
- What U-values should steel frame walls achieve?
Where should insulation be fitted?
We recommend warm constructions for steel frame walls. This is where the insulation is fitted externally, sheathing the studs. This sheathing insulation can either be fitted by itself or in combination with a suitable between stud or internal insulation. This warm construction helps to minimise thermal bridging via the studs and also limits condensation risk as the external face of the stud is not left exposed to the cold.
Which insulation is best for steel frame constructions?
This will depend on a range of factors including the building use, its height, and the target U-value.
In many buildings under 11 metres in height, Kooltherm K112 Framing Board can provide a thin insulation option due to its low thermal conductivity of just 0.019 W/mK. This is lower than many other commonly used insulation materials, meaning the desired U-value may be achievable with a lesser thickness of insulation. Kooltherm K112 is designed for use externally as a sheathing board on buildings with a masonry finish.
If you’re also looking to install insulation internally in a warm construction on many buildings under 11 metres, Kooltherm K118 Insulated Plasterboard can provide a simple option, combining insulation, drylining and vapour control in a single board.
For projects where there is a requirement for the external wall insulation to achieve a Euroclass rating of A1 or A2-s1,d0, either within the Building Regulations/Standards or as part of the building specification, K-Roc Framing Slab can provide a between stud solution as part of a warm construction.
The rock mineral fibre slab has a thermal conductivity of 0.036 W/mK and is manufactured in 610 mm widths, allowing them to be neatly located between studs at standard 600 mm widths. Where a rainscreen approach is chosen for the external façade, it can be combined with K-Roc Rainscreen Slab which has a thermal conductivity of 0.034 W/mK. Both products achieve an A1 Euroclass rating.
If you require a slimmer warm construction in these rainscreen applications, you can combine K-Roc Framing Slab with AlphaCore Pad. This insulation features a water-repellent, microporous silica-based insulation core. The boards are suitable for use in rainscreen systems and achieve a Euroclass rating of A2-s1,d0. At the same time, they achieve a thermal conductivity of just 0.020 W/mK – this can support slimmer constructions when compared with common alternatives such as mineral fibre slabs.
What U-value should steel frame walls achieve?
Under the Building Regulations and Standards, the U-value requirements for steel frame walls will depend on the building type, the country it is located in and whether the installation is on a new or existing building.
For new build projects, the Building Regulations/Standards in England, Scotland and Wales all set an area-weighted limiting U-values, which the external walls must meet on average. In all cases, no area should achieve a worse U-value than the threshold value shown below.
An area-weighted Notional Dwelling/Building specification U-value is also provided. This specification is used by energy assessors and is applied to a notional building of the same dimensions as the actual building. From this, they can generate the performance targets for the actual building. Whilst not compulsory, they often form the starting point for building specification.
Learn more about the energy targets in the Building Regulations and Standards
Our technical services team can provide U-value calculations and condensation risk analyses for SFS applications.
