Structural Considerations for Internal Walls

Understanding Load-Bearing Walls

Before you make any changes to your internal walls, it's crucial to understand what a load-bearing wall is. Simply put, a load-bearing wall carries the weight of other parts of your property. For example, you'll find them supporting:

• Your Roof: Some internal walls help to hold up sections of your roof structure, including the ceiling joists in your loft space.

• Walls Above: An internal wall on a lower floor can support another wall directly above it.

• Floor Joists: You might find floor joists built into or resting on top of these walls.

Other situations can also arise. For instance, if someone removed a ground floor chimney stack, they might have installed a beam to support the remaining stack above. This beam would then transfer its weight downwards onto an internal wall, which in turn passes that load to the foundations.

How to Identify a Load-Bearing Wall

You absolutely must determine if a wall is load-bearing before you consider making any alterations. To ensure safety and accuracy, we strongly advise you to hire a qualified structural engineer or surveyor. They can expertly assess the wall's function and, if you plan to remove or modify it, they will design the correct beam to safely take over its load.

Providing Support for New Internal Walls

When you build a new internal wall, regardless of whether it carries a structural load or not, it requires robust support from the structure beneath it. This underlying structure must be strong enough to bear the wall's own weight, plus any additional loads it might accumulate.

For Walls Not Carrying Structural Loads:

• Timber or Metal Frame Walls: You can generally support these types of walls on existing floor joists (not the floorboards). If your new wall runs parallel to the joists, you might need to install a double floor joist underneath for extra strength. However, if the wall runs perpendicular (at a 90-degree angle) to the joists, you can usually place it directly across them. In either scenario, additional support could still be necessary. Therefore, it is highly advisable to have a structural engineer or surveyor check if your floor joists are adequate.

• Masonry Walls: Because masonry walls are considerably heavier, you should not support them on timber joists or beams. Instead, you might need to install a new steel or concrete beam. Alternatively, you can position them directly onto existing foundations or a concrete floor. If you plan to support a masonry wall on an existing concrete floor, keep in mind that determining the floor's thickness and strength can be difficult. Unless you are absolutely certain of its suitability, we recommend using the lightest possible construction method.

For Walls Carrying Structural Loads:

A new load-bearing wall will demand more extensive support, which will vary based on the specific load it needs to carry. These walls must have a dedicated foundation or a robust structure that can effectively transfer the load down to the existing foundations.

• On an Upper Storey: If you are constructing a new load-bearing wall on an upper floor, supporting it directly from existing floor joists will almost certainly be insufficient. The combined weight of the wall and the load it supports will likely exceed the joists' capacity. This situation usually requires installing a new beam, which itself must have adequate support.

• On the Ground Storey: If your existing ground floor is timber, similar considerations apply as for an upper-storey wall. You could also provide a new foundation beneath the floor, although this can be challenging due to limited space. If your ground floor is concrete, you will probably still need a new foundation unless you can definitively prove that the existing floor is strong enough to handle the new loads.

Damp Proofing for Your New Walls

• New Ground Bearing Foundation or Slab: If you build a new wall off a ground-bearing foundation or slab, you must incorporate a damp proof course (DPC) at least 150mm above the external ground level.

• Existing Concrete Floor: When a new wall passes through an existing concrete floor, you must ensure continuous damp proofing. This means linking the new wall's DPC with any damp proof membrane already present in the existing floor. This is a complex procedure, as you must take great care not to damage the membrane or the floor itself.

• Existing Timber Floor: If your new wall passes through an existing timber floor, make sure any new timber in contact with or supported by the wall is positioned above the DPC line. Additionally, if there's ventilation in the void beneath a suspended timber floor, you will likely need to install air bricks in your new wall to maintain adequate airflow through that void.

Beams for Removing Load-Bearing Walls

Structural Support for Beams

When you remove a load-bearing wall, you must install a beam to take over the loads that the wall previously supported. This new beam requires support at both ends, usually from existing walls. These supporting walls must be capable of transferring the loads safely down to the foundations. Each end of your new beam should have a minimum bearing (overlap) of 150mm onto the existing supporting wall. The existing wall directly beneath these bearing points may need strengthening to prevent it from crushing. This could involve installing a dense concrete padstone (which can be either cast on site or pre-cast) to help distribute the load more widely. The precise size of these padstones depends on your specific circumstances, so we recommend you consult a structural engineer or surveyor before you begin any work.

Fire Safety for Beams

• Steel Beams: You typically need to protect steel beams against fire to achieve 30 minutes of fire resistance, as measured in a standard test. You commonly achieve this by properly fixing two or more layers of plasterboard around the beam. The required thickness of the plasterboard depends on the manufacturer's specific instructions.

• Exposed Timber Beams: If you prefer to have an exposed timber beam, you will generally need a calculation to demonstrate its inherent fire resistance. This resistance depends on the beam's size and the type of timber used.

• Concrete Beams: Concrete beams, which typically contain internal steel reinforcement, generally offer adequate fire resistance properties. This is true provided the concrete sufficiently covers the steel reinforcement inside.