Building Safety Act impacts envelope design

The introduction of the Building Safety Act requires detail design of the building’s envelope to take place much earlier in the design process. This makes working with an envelope specialist all the more beneficial explains Clayton Kingman, UK Head of Building Envelope at distributor SIG.

The introduction of the Building Safety Act in 2023 is putting pressure on architects to develop the detail design of a building’s envelope much earlier in the project programme than has historically been the case.

Detail design is particularly important where the envelope encloses a Higher Risk Building because the Act introduced a series of three Gateways. A design can only pass through a Gateway once it has been approved by the Building Safety Regulator (BSR) who requires proof that all risks to occupant safety have been considered at each of these key milestones in the design and construction process.

Gateway Two is the point at which the BSR needs to be satisfied that a building’s envelope design will not compromise safety and that it meets the functional requirements of the Building Regulations. Only after the BSR has approved its design can construction commence on site. 

Crucially, once a scheme is granted Gateway Two approval, the BSR will need to be notified of, and will have to approve, any subsequent changes to the envelope design. This is a process that can take up to six weeks. Should the BSR decide a change is unacceptable, construction may then have to be halted. 

Getting it right first time. 

A particular challenge for the development of a building’s envelope design is on projects where pressure to commence construction means Gateway Two approval is being sought before an envelope package contractor has been appointed. Often where this is the case, the additional responsibility for envelope detail design will fall to the architect who will then have to provide the BSR with detailed design and performance information explicit to the envelope system specified. 

To avoid the need to invoke a notifiable change, the envelope design presented by the architect to the BSR at Gateway Two will need to be virtually complete and will have to include thermal performance calculations, condensation checks along with all explicit detail design, fixing and interface details. 

Developing the design to this point is far from straightforward, particularly when an envelope solution involves combining products and systems to provide the best possible aesthetic, structural, thermal and fire performance at the most cost-effective price.

A notable challenge is that often the products selected for a specific envelope solution may not have been combined in the manner dictated by the design, particularly if the envelope must deliver a specific level of thermal or fire performance. 

Staying in the know.

The amalgamation of products requires a comprehensive level of knowledge of the compatibility of individual products and systems and how these will then function when combined with other solutions. In the past, such knowledge would have been assumed to have been the responsibility of the envelope subcontractor but increasingly, following the introduction of the Building Safety Act, it can fall under the remit of the architect.

Thankfully, architects can rely on comprehensive information to be available from competent product manufacturers. However, for specific envelope solutions, it would be wise to assume that manufacturers will not have the same level of knowledge or understanding on the compatibility of their products with other manufacturer’s products. This is where talking to a product-agnostic envelope supplier will be beneficial.

For example, the Building Envelope Team at SIG has in-house knowledge which allows it to put forward a variety of compliant envelope options from multiple suppliers. This can include a variety of options based on performance, cost, value, programme and aesthetics, each of which can be backed up with test evidence to demonstrate compliance to the BSR.

For customers seeking peace of mind, the SIG team can provide an additional level of compliance checks to ensure the suitability of products in specific applications. It also has the capability to provide the documentation to satisfy the BSR, including evidence of the proposed envelope’s fire resistance and to undertake thermal calculations and condensation risk analysis.

Another benefit of working with a product agnostic envelope supplier is they will also have detailed insight into the market, including knowledge relating to a product’s availability. With the change notification aspect of the Act making the notion of value engineering less attractive, it further cements the need for a robust supply chain. Last-minute product substitution due to availability is no longer an option.

The Building Safety Act may result in architects having to take on more responsibility for envelope design. However, by working with a knowledgeable envelope supplier with the resources to provide both technical support and commercial insight, it doesn’t necessarily mean a lot more work.