Openings in external walls

Beta Structural Engineers can offer Clients advice when creating an opening in an external wall.

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Why make an opening in an external wall?

Creating openings in an external wall or completely removing them may be required when an extension is built and the client wants to join the old space with the new space giving the effect of a large open space. These openings can be small ones such as a new window in an external wall to let in more light or to create a new door for access to the outside, or to a garage, or to a lean-to structure. Another example is when a homeowner wants to enlarge an existing door or window.. These openings can also have large spans in cases where the homeowner wants to knock down as much of the wall as possible to create a large open plan space when building side extensions or rear extensions.

The key question when creating an opening in an external wall is: “how large does the opening need to be and how much of the original wall to keep?” We encourage our clients to carefully consider the impact of this decision on their project time and budget. We also hope to address some of the issues that arise when making such alteration to aid the Clients in making this decision. The information given here is for guidance and is therefore generic. Care must be taken when applying this information to a specific project and professional help must be sought. The aim of the information here is to answer some of the frequently asked questions when making such structural alterations.

What are the structural considerations when making an opening in external walls?

External walls are always load bearing structural walls. This applies to gable walls, front and rear walls. Vertical loads supported on external walls may include floor loads, roof loads and weight of walls at higher levels. External loads also play an important part in resisting wind loads and transferring them down to the building foundations. External walls of masonry buildings act together to provide restraint and “buttressing” to each other.

Making an opening in an external wall requires the installation of beam or a frame to ensure the loads being previously carried out by the wall are safely re-distributed. The engineer may specify a concrete lintel or a steel beam and its size must be chosen to suit the loads being previously carried out by the wall. External walls often act as “buttressing” walls for party walls. This means that the rigidity offered by an external wall is required to prop the party walls and preventing them from moving sideways. Creating an opening in an external wall would therefore impact on the rigidity that an external wall has. If the opening in the external wall is not properly designed or not properly executed, the stability of the building may be affected. Building Regulations Document A Clause 2C28 states that “the number, size and position of openings and recesses should not impair the stability of a wall of the lateral restraint afforded by a buttressing wall to a supported wall. Construction over openings and recesses should be adequately supported”. To comply with this requirement the minimum length for external wall corner return dimension back to an opening should be 665mm. For a typical period property party wall of 9”, this means that the minimum length of return required to ensure lateral stability is 550mm if measured from the internal edge of the wall to the edge of the opening (excluding any finishes). If this condition is not met, and the client wants to the opening to be larger, the only way to meet the requirement would be to provide a steel frame that is tied to the party wall. The steel frame would be designed to replicate the rigidity of the removed wall. This has been a very popular way of creating large through kitchen-diner extension keeping as little of the original external wall as possible. Please refer to our page “steel for a modern lifestyle” for more information.

What are the steps required from a client before removing or making an opening an external wall?

Before any building works start, please make sure you have the following in place:

The client needs to obtain the design from a structural engineer specifying clearly the size of the structural element(s) required (e.g. steel beam/RSJ or concrete lintel) as well as clear definition of the supports for this beam. The beam may be directly supported on existing walls or sitting on a new padstone, a metal plate or a steel post that could even require a concrete base.

If the dwelling is in a flat or a leasehold property, a copy of the design report may be needed by the Management Company or the Landlord.

The design will comprise a drawing and a structural calculation report. These need to be submitted to a building control body that is either your local authority Building Control or an Independent Inspector. 48 Hours noticed prior to the start of building works must be given if the Building Notice route is followed. 6 weeks notice is required if the Full Plans route is followed (recommended if the client has planned well in advance). The advantage of this route is to allow the building control body enough time to review the proposed changes and advise if they have any concerns in advance. We are happy to discuss such issues with our clients as they vary from a case to another.

A party wall surveyor shall be engaged if applicable and a notice served in due time.

The design shall be shared with the builder and a written quote shall be obtained based on the drawings. The quote shall be based on the engineer drawings and shall be formal.

What are the structural engineer fees for making an opening in an external wall and providing building control structural calculations/design?

Usually, we would need to visit the site to inspect the layout of the building, establish the loads on the wall. The cost of such a site visit is £250 EXC VAT.

Additional design fees would apply depending on what needs to be designed. As mentioned earlier, sometimes only an RSJ/steel beam/padtstones is required and in other cases a goal post or a box frame is required. The fees would therefore range from £150 for the basic cases and could reach to more than £750 in cases where a goal post or a box frame is required. In these cases, our fee would include the drawings, a design report showing the calculations for submission to building control and the fabrication drawings and connection design when more than one steel member is being supplied and the fabricator would need to know how they tie up together.

In some cases, we work with builders, fabricators and clients in remote locations, where a site survey is prepared by third parties (or by the client) and we can provide them with a design remotely based on their survey. This service is possible due to our partnering scheme with LABC so we submit our design to LABC and a local inspector carries out the inspection.

Beta Structural Engineers have the expertise to provide you with a design that meets the Building Regulations and ensure that your builder has a practical and safe design to work with. We provide the following:

• Sizes of beam and pad-stones or steel frame and bottom ground beam – depending on the size of opening and loads in question.
• Drawings and specifications for the builder to execute the works safely.
• A structural calculation report to be submitted to the Building Control department of the local authority to satisfy them that works are compliant with the Building Regulations. If the dwelling is in a flat or a leasehold property, a copy of the report may be needed by the Management Company.

What is the building cost for removing an external wall?

In the same way that the design fees vary depending on the location and type of wall and the size of the opening, also the cost of removing it would vary. The prices given here are only indicative and would vary depending from a builder to another and from a project to another.

To understand the building cost, it is important to go through the stages of removing a wall. This is not a construction method statement and is simply a list of activities to give client some appreciation of the logical sequence of activities.

• Removing or re-locating services such as water pipes, radiators, electrical wiring and switches, and any other services (e.g. ducting/ventilation if any). Any built-in furniture or kitchen cabinets attached to the wall would also need to be removed.
• Providing temporary supports to carry any loads that are currently resting on the intended opening. For example, if the floor above is supported on the wall, then its joists must be propped before making the opening. The wall at higher levels must also be supported. It is usually the responsibility of the contractor to safely provide adequate temporary that would ensure stability at all times. In some cases, we are asked by the client or the contractor to provide guidance on the construction method statement and the temporary works design.
• After securing all loads above the wall, the opening will be made by removing the wall starting from top to bottom. Where demolition activities are carried out, we always advise builders that no impact tools shall be used and that caution shall be exercised to control dust, vibration and noise and execute works during operation hours. This is the stage that is most disruptive and causes most inconvenience. It is highly recommended that all measures are put in place to control dust and exposure to risks of noise of vibration are well managed. An experienced builder in refurbishment works is required to manage these risks.
• After making the opening, the new structural elements shall be installed. Usually, a padstone or a metal plate is inserted when only an RSJ is replacing the wall. If a steel post is required, a concrete base would need to be added (causing damage to flooring). This is usually the case when the span is large and there is not enough masonry support. The steel beam or RSJ or concrete beam is installed and any gap between the beam and the supported elements need to be filled (using dry packing cementitious grout or hard gap fillers such as metal shims). In some cases a box frame is required which also includes a bottom beam that sits on the old wall foundation and is encased in concrete.
• The temporary supports can now be removed.
• Making good (plaster, skimming, decorating). The making good shall include the wrapping of any steel elements with double plasterboard to provide the required fire protection.

The costs of these activities range from £1500-2500 for simple cases where only an RSJ and padstones/metal plates are used and a minimum of 550mm return is kept either side of the opening, up to £6000-8000 in cases where a large opening is made to give a through open-space kitchen with a span of 5m-6m or more. The prices vary from a project to another and are given here for planning and budgeting purposes only. A written quote based on design drawings must be given in writing to establish the actual cost for a specific project.

How can the client reduce the design fees?

We can sometimes offer clients an online service without a site visit. This is based on our extensive experience working with builders and clients on the removal of external walls in residential and commercial properties. Our work has included projects in most London boroughs and has included areas outside London such as Surrey, Leeds, Bath and St Leonards on Sea! For areas that we can’t visit due to distance, we would need a measured survey. We can advice clients on what information they need to send us so we can support them with our online service. This would eliminate the need for us to visit and charge for the inspection time. We would only do so in cases where we have all the information that can lead to making a clear and conclusive decision on what is required based on the measured survey (a floor plan with the opening size indicated as well as answering questions on joists direction and wall materials/thickens).

Which London boroughs can you visit to inspect?

We cover all of London. Please contact us to enquire about our case studies in the preparation of Building control and Structural Calculations for making openings in external walls in the following London boroughs: 

Building Control and Structural Calculations (Building Regulations) in Kingston upon Thames: opening in external walls.
Building Control and Structural Calculations (Building Regulations) in Richmond upon Thames: opening in external walls.
Building Control and Structural Calculations (Building Regulations) in Hounslow: opening in external walls.
Building Control and Structural Calculations (Building Regulations) in Ealing: opening in external walls.
Building Control and Structural Calculations (Building Regulations) in Hammersmith and Fulham: opening in external walls.
Building Control and Structural Calculations (Building Regulations) in Brent: opening in external walls.
Building Control and Structural Calculations (Building Regulations) in Hillingdon: opening in external walls.
Building Control and Structural Calculations (Building Regulations) in Merton: opening in external walls.
Building Control and Structural Calculations (Building Regulations) in Barnet: opening in external walls.
Building Control and Structural Calculations (Building Regulations) in Harrow: opening in external walls.