Structural Calculations for Domestic Extensions

Structural Calculations for Domestic Extensions

The initial planning stage of any building work is vital. To enable the project to be completed to the highest standard, with the best outcomes possible, it’s important to get your plans absolutely accurate. This includes many considerations necessary to comply with building regulations and also the steel beam calculations for extensions.

In most instances, structural supports are required to support load-bearing walls and floors above when alterations are taking place on the ground floor. This is to ensure the safety of your new living space and is also a requirement to meet Part A (Structure) of the current Building Regulations.

Foundation Calculations for Extensions

As the title suggests your domestic extension starts with the foundations. We can design a range of foundation types to suit your individual project requirements/site conditions. Usually, the vast majority of domestic construction is built off strip foundations. Depending on site constraints these are usually at a depth of 1000mm below ground level (BGL) and are 600mm wide. The width matches a JCB standard bucket. This width and depth would meet the minimum standards of Approved Document A guidance document. The main issue affecting foundation depth is the presence of trees within 25m of the proposed extension or deep drainage as foundations are required to be as deep as the drain invert if within close proximity. If trees are present on site and are within a specific zone of influence of 25m, then the foundations must be designed in accordance with NHBC Chapter 4.2 Guidance. This means the foundations would be deeper than the standard 1000mm accepted by Building Control under normal circumstances. If the foundation depth exceeds 1500mm where NHBC Chapter 4.2 applies heave precautions would also be required such as suspended floors and compressible material in the foundation trench internal faces. The other common type of foundation used for domestic extensions is a raft foundation. As the name suggests the raft is designed to spread the building loads across a large area thus reducing the concentrated load on the ground below. Raft foundations are usually used where poor ground is encountered. The third kind of foundation used in domestic construction where strip foundations and raft foundations are not acceptable is piled foundations. This is outside our scope of design expertise, but we can assist you to find a reputable piling engineer.

Steel Beam Calculations for Extensions

If large panels of masonry are being removed, in certain cases, extra steel support is required for the lateral stability of the building. Additionally, steel supports may be required to support new floor joists or roof structures. Building Control often require checks on new or existing masonry walls, piers and foundations which are supporting new steel beams and thus carrying an additional load than they had previously. It’s vital to have the correct beam calculations for extensions when planning and building.

We have vast experience in designing steel beam calculations for extensions of all sizes. Simply email us a PFD copy of your architectural plans or measured survey sketches in a recognised scale. We can also work from AutoCAD drawings. Using this information, we can provide you with a competitive fee quote for your unique scheme. Every project is very different. That’s why our experts work on each project to provide unique beam calculations for extensions and the vital considerations for your new space.

In the example images below, we were engaged to calculate steel supports for the rear of the building. This was to enable our client to achieve an open plan layout, maximizing the internal space.

Floor Joist Calculations for Extensions

Domestic floor joists are horizontal structural members used in residential buildings to support the floor above and distribute loads to walls, beams, or foundations. They’re a key component of floor construction and play a major role in the building’s structural integrity.

Purpose of Floor Joists

• Support the floor load (people, furniture, etc.)

• Distribute weight to load-bearing walls or beams

• Provide a surface for fixing flooring materials

• Often carry ceiling finishes for the room belowTypical Sizes and Spacing

  • Joist Size: 150mm x 47mm up to 250mm x 75mm

  • Spacing: 400mm or 600mm centres (measured from centre of one joist to the next)

  • Span: Depends on size and wood type — e.g., a 200mm x 47mm timber joist can span approx. 3.5 to 4.0 meters