Carrying out construction or renovation work on a building located close to another building is a common challenge here in the UK, particularly on urban builds. In these applications, space can be highly limited for installing external cladding systems. This can prove challenging in applications where the insulation also needs to achieve a Euroclass rating of A2-s1,d0 or better, as conventional insulation solutions with this reaction to fire rating tend to have relatively poor thermal performance. This means a significant thickness of insulation may be needed to achieve required project U-values.
AlphaCore Pad can provide a thinner solution in these applications, combining a thermal conductivity of just 0.020 W/mK and a Euroclass rating of A2-s1,d0.
In this article, we look at the requirements where a building is located close to another including:
- what fire regulations apply for insulation on buildings with close boundary walls
- what insulation options are available for external walls with a close boundary.
What reaction to fire rating should façade insulation achieve when there is a close boundary wall?
The Building Regulations in England, Scotland and Wales set specific reaction to fire requirements that insulation materials fitted as part of the façade system must achieve. These requirements differ depending on the building type, height and which country it is located within. The requirements are typically based on a product’s rating under the Euroclass system.
The Building Regulations are accompanied with guidance documents to give practical guidance on how achieve compliance.
NB There are additional requirements for the fire performance of external and internal finishes. This article provides information on the requirements for the insulation elements of buildings only. The information contained within this article should be used in combination with the full Building Regulations necessary.
For further information on the Regulations and guidance in England, Wales & Scotland, take a look at our pages dedicated to each region.
Scotland
In Scotland, the guidance in the Technical Handbooks states that insulation used within the external wall cladding systems of buildings not more than 1 metre from the boundary with another building typically should achieve a Euroclass rating A1 or A2. Alternative approaches (for example a large scale BS 8414 test, an assessment in lieu of test to BS 9414 or a fully fire engineered solution), could be adopted to use worse performing products.
Note that all insulation used within the external wall constructions of relevant buildings must be Euroclass A1 or A2 rated. In Scotland, this means a building with a storey at least 11 metres above the ground (excluding plant rooms) which contains a:
- dwelling
- building used as a place of assembly, or as a place of entertainment or recreation
- hospital
- residential care building or sheltered housing complex
- shared multi-occupancy residential building.
Learn more about relevant buildings.
The above does not apply where the insulation is fitted within a cavity between two leaves of masonry or concrete (min. 75 mm thick), with cavity barriers around all openings and at the top of the wall-head.
England & Wales
Note that in England & Wales, regardless of proximity to other buildings, insulation used within the external wall cladding system on relevant buildings must be Euroclass A1 or A2 rated. This is a regulation that must be complied with.
In England and Wales, a relevant building is one with a storey (not including roof-top plant areas or any storey consisting exclusively of plant rooms) at least 18 metres above ground level (measured from the lowest ground level adjoining the outside of a building) which contains:
- one or more dwellings
- an institution
- a room for residential purposes.
Why are stricter fire performance set for the external walls of some buildings with a close boundary?
The standards of fire resistance necessary for a particular building are based on assumptions about the severity of fires and the consequences should an element fail. Fire severity is estimated in very broad terms from the use of the building (its purpose group), on the assumption that the building contents (which constitute the fire load) are similar for buildings with the same use. However, the building height is also relevant; with increasing height, more complex provisions are needed. The position of the building in relation to adjacent buildings and therefore the site boundary is also important, in that the risk of undue fire spread to, or from adjacent buildings needs to be controlled.
What are the insulation options when an A2-s1,d0 or better fire performance is needed?
Where a product with a Euroclass rating of at least A2-s1,d0 is required under the Building Regulations or as part of the building specification, the following Kingspan Insulation products can be used within external cladding systems:
| Euroclass rating | Thermal conductivity |
A1 | 0.034 W/mK | |
A2-s1,d0 | 0.020 W/mK |
K-Roc Rainscreen Slab is a rock mineral fibre slab and provides a thermal conductivity typical of standard façade insulation solutions with a Euroclass rating of A1. Whilst it can provide an effective solution for standard applications, its thermal performance can mean a notable thickness of insulation is needed to achieve typical project U-values. This may be impractical to install on building faces with a close boundary meaning the only option is to install a thinner thickness of insulation compromising on the thermal performance of the construction.
In contrast, AlphaCore Pad has a water-repellent microporous silica-based core which delivers a much-improved thermal conductivity of just 0.020 W/mK. This allows it to provide a problem-solving solution in applications where space is limited, such as where a close boundary wall is present, as a lesser thickness of insulation can typically be used to achieve the desired U-value. The boards can be simply lifted and mechanically installed with appropriate fixings, allowing the project U-value to be achieved without adding complexity to the build process.
