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Structural Design and Calculations: House Alteration and Extension

The owners of this impressive bungalow had planned some exciting and ambitious building works that would completely transform their home. Our structural engineers provided a complete set of designs and calculations to enable them to get building regulation approval, move forward with the works and ensure that their dream home would be structurally sound.


The property

The house was a substantial bungalow which had been extended and altered over the years. During our site visit, our Oxford structural engineers noted several features of the property that would need to be carefully considered when planning works. First, there was an indoor swimming pool in one corner of the site. There were also various changes in level throughout, with a difference of up to 80cm between the height of the roofs at the front and rear of the property. In addition, much of the garden to the rear of the property was raised, with brick retaining walls.


The works

Demolition and rebuilding

The plans included demolishing the existing pool building filling in the pool. This space would then be used for a new single-storey extension, which would include a master bedroom, ensuite and covered outdoor hot tub. The new roof was going to be made of exposed timber joists and glulam beams, with projecting cantilevers.

Our first task was giving structural advice on the demolition and infilling of the existing pool structure. We provided specifications for the ventilated void, drainage holes, backfill material and new concrete trench foundations.

We then put together designs and calculations for the beams, rafters, reinforced slabs and retaining walls.


New extension

Our clients had also planned a new single storey extension in the northern corner of the of the garden, which would become a new kitchen and games room.

The rear walls to this extension needed to provide a retaining function, because the external ground level was approximately 1.5 metres above the new internal finished floor level.

We assessed the retained ground and the associated forces that would be placed on the rear walls to determine whether they would need to use reinforced concrete. We provided specifications for the wall, along with beam calculations and designs throughout the extension.


Remodelling existing spaces

The remodelling works our clients had in mind included removing the existing trussed roof over the rear living room and replacing it with a vaulted ceiling. They also wanted to demolish the rear wall to create a connection to the new extension, and partially demolish the front entrance lobby, so that they could build a new front wall.

Working in tandem with the architects, we drew up plans to show where existing beams would be removed, and where new supports would be put in place. Existing trusses and purlins were retained wherever possible, and steels designed to support the new vaulted roof.


Allcott Associates Structural Designs and Calculations

Throughout the project, we worked closely with the client and architect to make sure that our designs aligned with their vision for the property. Whenever possible, we provided several alternative designs for the architects and client to consider, and we were able to adjust as the project progressed to meet with changing specifications and new decisions the materials to be used.

Our final deliverables will include structural drawings at a RIBA Stage 4 level of design, and a comprehensive package of structural calculations for all elements, that will be suitable for submission to building control. We have worked closely with the architect and other members of the design team throughout the project to discuss options and to provide structural advice to achieve a co-ordinated design.


bungalow remodel structural design

The swimming pool area was being redeveloped into a master bedroom with an outdoor hot tub



Structural engineers house extension

The extension included a new kitchen and games room

structural designs and calculations house extension

We provided structural designs and calculations for all aspects of the works

house extension structural designs

Our structural engineers worked closely with the architects to design the best way of infilling the pool and creating the new master suite

roof designs and calculations structural engineers

We also provided designs and beam calculations for the removal of the existing trussed roof and its replacement with a vaulted ceiling

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