Date: September 2024
We were brought on board to handle the complete residential groundworks package for a home extension project in Hersham, Surrey. The homeowner was adding a large single-storey rear extension to their detached property, and MJM Groundworks was responsible for everything below ground level — from initial excavation and site preparation through to building foundations in Hersham and a finished concrete slab ready for the bricklayers. As a trusted groundworks contractor covering Surrey, we carry out this type of residential groundworks project regularly, and the work at Hersham is a good example of what is involved.
What the Homeowner Needed
The client wanted a 6m x 4m single-storey rear extension to create a larger open-plan kitchen and dining area, with a utility room to the side. The architectural drawings had been approved and planning permission granted, so our job was to deliver the groundworks in Hersham on time and to specification, allowing the main contractor to follow on without delay. The scope included excavation, extension foundations, drainage modifications, substructure blockwork and a finished concrete floor slab — a typical but comprehensive residential groundworks package.
Excavation and Site Preparation
The project began with protecting the existing garden and setting out the extension footprint using the architectural drawings as a guide. We used a compact 3-tonne excavator to strip the topsoil and excavate the foundation trenches, loading spoil into a grab lorry parked on the driveway for removal. Working in a residential area like Hersham means being conscious of the neighbours — we kept machinery noise to sociable hours, swept the road daily and ensured our vehicles did not block access to neighbouring driveways. Parking was managed carefully too, with all plant and materials stored within the property boundary wherever possible.
Extension Foundations in Surrey
The ground conditions in this part of Hersham were fairly straightforward, with stable London clay encountered at around 800mm depth. The structural engineer specified traditional strip foundations at 1m deep to account for seasonal clay movement and the proximity of a mature tree in the neighbouring garden. We excavated the trenches cleanly to the required depth, and building control inspected and approved them before we poured the concrete. The building foundations in Hersham were completed in two days using ready-mix concrete delivered by a pump truck, which allowed us to reach the rear of the property without damaging the side passage. We were able to begin the substructure blockwork immediately after the concrete had cured.
Drainage Connections to the Existing System
The existing drainage layout needed significant modification to accommodate the new extension. An existing 100mm foul drain ran directly beneath where the new floor slab would sit, so we diverted it around the perimeter of the extension using new 110mm PVC pipework and two new inspection chambers for future access. We also installed new waste connections for the kitchen sink, dishwasher and washing machine in the utility room, tying them into the diverted foul drain. A new rainwater connection was made from the extension roof downpipes into the existing surface water system. All drainage work was tested with a pressure gauge and CCTV surveyed before we moved on to the slab — this is standard practice on our residential groundworks projects to avoid any issues down the line.
Concrete Bases and Floor Slab
With the substructure blockwork complete and the drainage in place, we prepared the oversite by compacting the fill material in layers, then laid a sand blinding coat, damp-proof membrane, 75mm rigid insulation boards and A193 steel mesh reinforcement. The concrete floor slab was poured at 100mm thick and power-floated to give a smooth, level finish — important for the porcelain tiled floor the client had planned. We also formed a step down of 150mm from the existing house floor level to the new extension, as specified on the architectural drawings, and left starter bars for the threshold detail.
Timeline and Handover
The groundworks phase for this Hersham project was completed within ten working days, from first dig to finished slab. We handed the site over clean and ready for the bricklayers, with all spoil removed, the garden reinstated where possible and a full set of drainage records provided to the main contractor. The client and their builder were pleased with the speed and quality of the work, and commented that the site was kept tidy throughout — something we take pride in on every job.
Why Choose MJM for Residential Groundworks
Extension foundations in Surrey need to be done right. Poor ground preparation, incorrect foundation depths or badly connected drainage can cause expensive problems that only show up months or years later. By using an experienced groundworks contractor like MJM, you get the job done properly first time — with building control sign-off, tested drainage and a level slab that the follow-on trades can work to with confidence.
Planning an extension or residential build in Hersham or anywhere across Surrey? MJM Groundworks can handle the complete groundworks package — footings, drainage, concrete bases and excavation. We work across Surrey, Berkshire, Hertfordshire and London. Get in touch for a free quote or call us on 01784 697317.