Woodlands Road, Manchester: Rear Extension & Specialist Foundation WorksProject Overview
Project Overview
What began as a relatively straightforward rear extension on Woodlands Road in Manchester developed into a significantly more complex structural project once works commenced on site.
The client’s brief was to create a larger kitchen and improve the rear garden area, while also addressing an existing retaining wall that had deteriorated and required attention.
313 Developments was appointed to coordinate the project from the design and statutory approval stages through to construction, managing the architectural, structural and specialist elements required to deliver the extension.
The proposed plans create a substantially larger kitchen and dining space, with the architectural drawings showing a proposed kitchen/dining area of approximately 35m².
The Brief
The project had three principal objectives: to increase the size of the existing kitchen, resolve the deteriorating retaining wall at the rear of the property, and improve the use and layout of the external space.
Prior to construction, the required design, planning and Building Regulations work was undertaken. The architectural package established the proposed ground-floor arrangement, demolition requirements, drainage strategy and structural elements associated with the extension.
Excavation then commenced for what was initially anticipated to be a conventional strip foundation.
The conditions encountered on site required the foundation strategy to be reconsidered.
Ground Conditions and Structural Redesign
Once excavation works began, it became clear that the ground conditions were unsuitable for the conventional foundation solution originally anticipated.
Rather than proceeding with a system that was not appropriate for the site conditions, the foundation design was reassessed by the structural engineer.
A revised engineered solution was subsequently developed using a piled foundation system with reinforced ground beams. The structural calculations specifically provide for piled foundations to support the proposed single-storey extension.
The change required close coordination between the construction team, structural engineer and specialist piling contractor to ensure that the revised solution could be incorporated into the project while accommodating the existing property and site constraints.
Specialist Piled Foundations
The revised structural design incorporates 12 piles, each 150mm in diameter, supporting a reinforced ground beam system. The engineering calculations specify a safe working load of 150kN per pile with a factor of safety of three.
The piles are being installed to approximately 6 metres below ground level and will be concrete filled.
The structural specification identifies permanently steel-cased, cast-in-situ concrete-filled mini piles together with reinforced concrete pile caps and ground beams.
The reinforced ground beams have been designed at approximately 500mm wide by 450mm deep, with reinforcement specified to transfer structural loads between the individual pile locations and support the new construction above.
Although this element of the project will ultimately sit beneath the completed extension, it represents a substantial and technically important part of the overall construction.
Existing Drainage Constraints
A further complication was the presence of a substantial existing drain within the proposed construction area.
Its position conflicted with the new foundation and wall layout, requiring the drainage arrangement to be altered as part of the works.
The structural drawings identify existing drainage and services within the piling zone and require their position and depth to be established to avoid damage during installation of the piles.
The architectural drawings also identify a proposed drainage route connecting into the existing main sewer.
On site, elements around the existing inspection chamber have therefore been repositioned to provide the necessary clearance for the proposed external wall and foundation arrangement.
This work has required the drainage and structural packages to be considered together rather than as separate elements of the build.
Internal Design Coordination
While the structural works have been progressing, development of the internal kitchen design has continued in parallel.
The kitchen layout is being refined with the client to ensure that the enlarged space delivers the required functionality as well as the intended finish.
The architectural proposals show the extension forming part of a considerably larger kitchen and dining area, creating a more substantial reconfiguration of the rear of the property rather than simply adding additional floor area.
Coordinating the internal design alongside the structural works allows key construction decisions to be considered in the context of how the completed space will ultimately function.
Current Construction Stage
The project is currently progressing through the specialist foundation stage.
Piling works and reinforcement to the ground beams are underway ahead of inspection and the concrete pour.
Once the reinforcement and foundation arrangement have received the required approval, the beams will be prepared and concrete pumped into the system using a long-reach boom.
Additional piles are also incorporated within the structural scheme to accommodate steel columns required during later stages of the project. Once the new structure has progressed sufficiently, sections of the existing rear wall will be opened and structural steelwork installed to form the connection between the existing property and the extension.
The structural design also incorporates a 150mm reinforced concrete ground-floor slab using C35 concrete and A393 reinforcement mesh.
Technical Resolution
The Woodlands Road project demonstrates the importance of responding appropriately to conditions identified during construction.
The original brief remains focused on delivering a larger kitchen and an improved rear environment for the client, but achieving that outcome has required a substantially more involved structural solution than initially anticipated.
Following the discovery of unsuitable ground conditions, the project team moved from a conventional foundation approach to a fully engineered piled foundation and reinforced ground beam system. This has been coordinated alongside alterations to the existing drainage, future structural steelwork and the developing internal layout.
By addressing these constraints at foundation level, the project can proceed on a properly engineered basis, providing the structural platform required for the subsequent extension and internal works.
Project Summary
Project: Residential rear extension
Location: Woodlands Road, Manchester
Scope: Design coordination, planning and Building Regulations, groundworks, specialist piling, reinforced ground beams, drainage alterations, structural works and kitchen design coordination
Status: In progress