The Importance of Opening Up Works: House Extensions

As an architect practice with over 40 years of combined experience, we have come to realise the importance of opening up works when it comes to drawing up structural designs for a house extension. These works not only minimise guesswork but also provide a solid baseline for understanding the existing structure of the building, allowing us to plan and execute the new space safely and efficiently.

When it comes to structural investigations, it is not uncommon for the Structural Engineer to make assumptions about the building before crunching the numbers of the structural design. However, relying solely on assumptions carries significant risks. Therefore, whenever possible, it is preferable to carry out opening up works as a means of gathering concrete information about the structure, ensuring that the design process is based on accurate data rather than guesswork.

Opening up works are typically requested by the Structural Engineer, and sometimes the Architect, when there is a need for further investigation of the building’s structure. These works involve carefully stripping away precise surface areas to reveal specific sections of the underlying structure that the Structural Engineer needs to physically inspect before producing a suitable structural design for the extension.

There are four common types of opening up works that are often carried out for extensions:

1. Trial pits: These are holes, usually measuring around 1 square meter, that are excavated by hand and positioned adjacent to the outside wall of the building. The purpose of trial pits is to check the depth and type of foundations that the building sits upon, providing essential information for the design process.
2. Lifting floorboards: This type of opening up work is performed to investigate various aspects, such as the continuity of suspected load-bearing walls, the condition of dwarf walls, joist integrity, and water table saturation. It is crucial to minimise the disturbance to the flooring and only remove the necessary sections for inspection.
3. Boarded attics: Attic spaces are sometimes boarded over, and these boards may need to be removed to assess the presence of voids behind or beneath them, as well as to check the direction and sizing of joists. Fortunately, the advent of keyhole cameras has allowed us to minimise disruption during this process.
4. Exposing walls and ceilings: In some cases, sections of plastered walls and/or ceilings need to be removed to inspect the presence of supporting members, such as reinforced steel girders. Additionally, exposing walls and ceilings allows us to check for the existence of spreader plates supporting the girders, the integrity of the supporting wall, and the nature and quality of any connections.

When carrying out opening up works for an extension, it is best practice to have the instructing Structural Engineer present along with the tradesmen. This ensures that the tradesmen can work under the direct instruction of the Structural Engineer and allows for real-time inspections. By being present on-site, the Structural Engineer can inspect the exposed areas firsthand, avoiding the need to rely solely on photographs. Moreover, this approach holds the Structural Engineer accountable for the work they produce and ensures that their expertise is fully utilised.

To minimise disruption, it is important to keep the size of the openings as lean as practicable. Additionally, any necessary making-good should ideally be completed on the same day, immediately after the inspection. This helps to maintain the project’s momentum and ensures that the opening up works do not cause unnecessary delays.

Undoubtedly, carrying out opening up works for an extension can be a logistical challenge and may cause temporary inconveniences. However, the benefits of doing so far outweigh the temporary disruptions. These works allow the Structural Engineer to accurately baseline the makeup of the building, providing vital information for designing an optimally structured extension. By avoiding assumptions and relying on concrete data, we can create designs that are not only safe but also efficient and sustainable, aligning with our studio’s focus on low energy and low embodied carbon designs.

In conclusion, when embarking on a house extension project, it is essential to prioritise opening up works. These works serve as a critical step in the design process, allowing us to understand the existing structure, identify potential issues, and develop an extension that seamlessly integrates with the building. By investing in opening up works, we can ensure that our designs are not only beautiful but also structurally sound, energy-efficient, and environmentally conscious. So, embrace the process, trust in the expertise of your Structural Engineer, and unlock the true potential of your home with a well-planned and thoughtfully executed house extension.