Lee, SE12 · 1930s semi-detached
Both homeowners worked from home, but their shared workspace was too cramped. We replaced their underused garage with a dedicated office, utility room and downstairs WC, giving them more room to work without taking over the family’s living spaces.
The transformation
The attached garage of this 1930s semi-detached house was no longer being used for parking. It had become somewhere to store general belongings, and Alice and Paul already had sheds and other storage in their garden.
Both homeowners worked from home. Their old shared workspace had been too cramped, and although Paul had another working area elsewhere in the house, Alice still needed an office of her own.
Rather than give up a bedroom, they decided to replace the garage.
An attached garage used mainly for storage.
A new side extension containing a home office, utility room and ground-floor WC.
We demolished the garage completely and constructed a new, insulated side extension from the foundations up.
The original garage stopped short of the back of the house. We extended the replacement building farther towards the garden so that it aligned with the rear of the property.
At the front, we kept the extension within the existing building line. Bringing it farther forward wouldn’t have served a useful purpose and would have reduced the available driveway space.
The new 22 sqm is divided into three rooms: the utility and boot room at the front, the WC in the middle and Alice’s office at the rear.
Added area: 22 sqm
Design approach
Alice wanted an office she could spend the working day in, not simply somewhere to put a laptop.
The finished room has a purpose-built desk and substantial shelving for books and documents. There’s also a separate seating area where she can read or review papers away from her desk.
Natural light was another priority.
The pitched roof includes two Velux rooflights, with one above the office and another above the utility room. In the office, the window and glazed timber garden door provide additional daylight and views outside.
Together, these features give Alice somewhere she can work, read and meet colleagues without needing to use the family’s living rooms.
The entrance to the new extension is immediately to the right as you enter the house.
This means someone visiting Alice can reach her office and the nearby WC without walking through the family’s main living rooms.
The WC is also available to the rest of the household outside working hours.
The utility and boot room sits at the front of the extension, beside the main entrance.
It gives the homeowners somewhere for coats, shoes and umbrellas rather than carrying them through the rest of the house.
We also relocated the washing machine and dryer from the kitchen into this new room.
Removing those appliances freed up space in the existing kitchen cabinetry for storage.
The homeowners wanted the new building to complement their existing 1930s home.
We used brickwork and red brick detailing selected to match the character of the property.
The pitched roof was finished in grey concrete interlocking tiles, chosen to relate to the existing roof coverings.
The homeowners also preferred timber windows and a glazed timber garden door.
The build
The most sensitive part of the construction was the new foundation running alongside the neighbouring garage.
The supporting concrete visible beside that garage was only around 150 mm thick. Digging the whole length of our new foundation at once could have disturbed the ground beneath the neighbouring building and caused movement.
The structural engineer therefore specified a method called hit-and-miss excavation.
Instead of opening one continuous trench, we excavated and concreted short sections in stages. Each section was allowed to gain strength before the adjoining section was opened.
This allowed us to construct the new foundations while maintaining support to the neighbouring garage.
The original garage had a lower roof than the new extension.
The neighbour had ducting that projected over the boundary above the old garage roof. When the new roof was raised, the ducting became an obstruction.
We discussed the issue with the neighbour and arranged for the ducting to be diverted.
The change was completed without a dispute or delay to the project.
We also needed to manage rainwater where the new roof met the neighbouring garage.
Leaving an open gap between the buildings could have allowed water to collect or enter the structures.
Our roofing specialist formed a concealed gutter along the boundary, carrying rainwater towards a downpipe at the garden end.
This created a properly drained junction between the two roofs.
Alice and Paul stayed in their home throughout construction.
Most of the work took place along the side of the property, so the main living rooms remained usable. There was construction noise, but they didn’t need to move out.
The project took 12 weeks from demolition to practical completion and was delivered to programme.
Handover was straightforward, with no significant snagging issues reported.
Planning & approvals
Permitted development + LDC
The homeowners obtained a Lawful Development Certificate for the replacement side extension.
Formal Party Wall Award obtained
A formal Party Wall Award was obtained before work involving the neighbouring property and boundary.
Inspected and signed off
A private Building Control inspector oversaw the relevant work, and the completed extension received its completion certificate.
Costs today
£74,000+
Estimated starting price today · Includes VAT
This starting price covers a straightforward single-storey extension built into available space beside your house.
It follows our standard side-return construction specification, but includes the additional external wall and foundations needed for a standalone extension.
The core build comes with our workmanship warranty: 10 years on structural work, 5 years on roofing and 2 years on electrical and plumbing work.
Kitchen units, appliances, kitchen fitting, finished flooring and decorating are separate unless included in your quotation.
Specialist glazing, underfloor heating and work to renovate or rebuild existing rooms are additional.
Architectural drawings, structural engineering, planning, Building Control and Party Wall fees aren’t automatically included in the headline construction price.
Things about your house and site that become clear once we’ve surveyed it.
No rear access or a narrow side passage means materials and waste move by hand.
Clay soil, nearby trees or poor ground can need deeper foundations.
Building over or near a public sewer may need diverting or an agreement.
Removing load-bearing walls needs larger steels and more structural work.
Old wiring, damp or problems found once walls are opened.
Surveyor fees and any work needed to protect next door.
This project involved more than building an extension onto an empty part of the garden.
We first needed to remove the existing garage, then construct a larger replacement containing three finished rooms.
We demolished the attached garage completely and built the new extension on fresh foundations, extending farther towards the rear garden.
The foundations required staged excavation beside the neighbouring garage. We also arranged for the neighbour’s ducting to be diverted and constructed a concealed gutter between the roofs.
The finished extension includes Alice’s office with bespoke desk and shelving, a utility and boot room with the relocated laundry appliances, and a ground-floor WC. Timber glazing, two rooflights, vinyl flooring and an EV charger were also part of the completed project.
Key takeaways
Before replacing a garage, consider how you actually use it.
If it’s mainly storage, think about where those belongings would go instead.
If you use it for parking, tools or other equipment, you’ll need to decide whether losing that space is worthwhile.
For Alice and Paul, alternative storage was already available, so replacing the garage made sense for their household.
A home office needs to suit the work you’ll actually be doing.
Someone who mainly makes video calls might need a different layout from someone who regularly meets colleagues, stores large quantities of documents or needs somewhere to read away from their desk.
Think about those requirements before deciding how much room the office needs.
They’re easier to accommodate in the original plans than after the walls have been built.
If you’re building close to another garage, extension or boundary wall, the neighbouring structure can affect how your foundations need to be constructed.
Ask what information is available about the neighbouring building and whether your structural engineer needs to specify a particular excavation method.
Understanding those requirements early can help you plan the work and avoid surprises once digging begins.
Where a new roof meets a neighbouring structure, rainwater needs somewhere to drain.
Ask how the junction will be waterproofed, where the water will go and whether any concealed gutters will be accessible for maintenance.
These details aren’t always visible once the work is finished, but they matter to the long-term condition of both buildings.
Two extensions of the same size can involve very different amounts of work.
A straightforward extension containing one unfinished room is different from a project with three fitted rooms, bespoke joinery, additional plumbing and electrical work.
Ask which items are included in the quotation, which are allowances and which will be priced separately.
That makes it easier to compare builders and understand what you’re paying for.
Alice and Paul had previously used another contractor for their loft conversion and found the experience stressful.
That made them cautious about starting another substantial building project.
After their side extension was completed, they left this Trustpilot review.
A superb service! We are delighted with our side extension which Ben and his team completed without any problems, to schedule and a high standard. Always responsive and with attention to detail in the project management. We would highly recommend ConstructX Group and have employed for further work.
They asked us back for further work
Following the extension, Alice and Paul asked Construct X Group to complete additional improvements to their home.
We returned to apply silicone rendering to the front of the house, redecorate the external timber elements and install a new kitchen supplied by the homeowners, together with the associated plumbing and electrical work.
These were separate from the side-extension contract.
Get a realistic picture of what’s possible for your home, likely costs, timings, planning requirements and what the project would involve.
You’ll speak with Eddie
Managing Director
Delivered this project
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