The shape decides both the build rate and whether you need planning permission.
This sets your permitted development allowance and whether party wall notices are needed.
Measured from the existing rear wall. This is the number that decides your planning route.
Not sure yet? Leave it at 3m, the standard permitted development limit.
Roughly when was the house built?
Older ground and shallower foundations carry more unknowns.
Roughly how much floor area it adds, and the level of finish you are picturing.
Tick what you would like in the figure. You can change all of this at survey stage.
Your estimate appears on screen straight away. We confirm it in writing after a free survey, with no deposit and no obligation.
A guide based on London build rates for 2026, including VAT. The figure we put in writing after surveying the property is the one that counts.
We will call within one working day to arrange your free survey.
H&M Construction 1 Ltd did a fantastic job on our loft conversion in West London. The team was professional, tidy and easy to deal with. The new space looks excellent and the whole project was managed very smoothly. We would gladly recommend this team in West London.
We are very pleased with our loft conversion by H&M Construction 1 Ltd. Communication was clear, the workmanship was strong and the team kept everything organised. Our new room feels bright, practical and beautifully finished. We would definitely recommend this team.
H&M Construction 1 Ltd transformed our unused loft into a lovely new living space. The builders were polite, reliable and worked carefully throughout. We were impressed with the finish and how smoothly the project progressed. The workmanship was excellent throughout.
Our loft conversion was completed by H&M Construction 1 Ltd and we are really happy with the result. The team arrived on time, kept the site tidy and explained each stage clearly. The finished space is exactly what we wanted. We are very happy with the finished loft.
We had a great experience with H&M Construction 1 Ltd for our West London loft conversion. The team was friendly, professional and very organised. The work was completed to a high standard and the new space looks brilliant. The finished loft looks very well finished.
H&M Construction 1 Ltd handled our loft conversion with great care from start to finish. The team communicated well, worked neatly and paid attention to the details. We are very happy with the quality of the completed space. We would definitely recommend the company.
Really happy with the loft conversion completed by H&M Construction 1 Ltd. The team was respectful, punctual and kept us updated throughout the work. Everything was finished neatly and the extra space has made a huge difference. We would happily recommend their team.
H&M Construction 1 Ltd did an excellent job converting our loft in West London. The team was helpful, skilled and easy to communicate with. The work was well organised, the finish was neat and the new room looks fantastic. The completed loft looks very well finished.
We chose H&M Construction 1 Ltd for our loft conversion and were impressed by the service. The team worked efficiently, kept the area clean and answered our questions clearly. The final result is smart, practical and well finished. The new loft space looks brilliant.
Our experience with H&M Construction 1 Ltd was very positive. They completed our loft conversion with good communication, careful workmanship and a tidy approach. The new space has been finished beautifully and feels very well built. The final result looks fantastic.
H&M Construction 1 Ltd completed our loft conversion to a very high standard. The builders were courteous, organised and kept us informed during the project. We are delighted with the finished room and would happily recommend them. The completed loft looks excellent.
We are delighted with the loft conversion carried out by H&M Construction 1 Ltd. The team was reliable, tidy and professional throughout. The quality of the work is excellent and the finished space has exceeded our expectations. We would gladly recommend the company.
H&M Construction 1 Ltd made our loft conversion simple and stress free. The team was professional, responsive and careful with the property. The project was well managed and the finished loft looks stylish, spacious and very practical. The finished loft is beautiful.
A single storey rear extension in London runs roughly £2,500 to £4,500 per square metre of new floor area. For a typical 20 to 30 square metre rear extension that puts most projects between £75,000 and £120,000 including professional fees and VAT.
The calculator on this page gives you a range for your specific size, type and specification in about two minutes.
Often not. A single storey rear extension up to 3m on a terraced or semi-detached house, or 4m on a detached house, normally falls under permitted development. Between 3m and 6m you can use the Larger Home Extension Scheme, which means a neighbour consultation rather than a full application.
Flats, listed buildings, conservation areas and most wraparound or double storey extensions need full planning permission.
A straightforward single storey rear extension is usually 10 to 16 weeks on site. Before that, allow four to ten weeks for drawings, structural calculations and approvals.
Party wall notices need two months, so on a terraced house that often sets the start date rather than the build programme.
Yes, and most people do. The kitchen is the difficult part rather than the noise, so we help you plan a temporary kitchen before we start.
The disruptive stages are the foundations and the day the rear wall comes out. We tell you in advance which days those will be.
If you live in a terraced or semi-detached house and the work touches the shared wall, or you excavate within three metres of it, you must serve notice two months before starting.
Most neighbours simply consent in writing at no cost. If they dissent, surveyors agree a schedule of condition first. We handle the notices as part of the approvals stage.
In West London, usually. An extension that creates a proper open plan kitchen and dining space is what buyers in this area look for, and building outwards compares well with moving once stamp duty, agents’ fees and legal costs are counted.
It is not guaranteed and depends on your street and its ceiling price. If we think the numbers do not work on your house, we will tell you.
A side return fills the narrow alley beside the house, usually widening a galley kitchen. A wraparound does the side return and a rear extension as one, wrapping round the back corner.
The wraparound gives more space but almost always needs full planning permission, where a modest side return often does not.
Yes. Architectural drawings, structural engineer’s calculations, the lawful development certificate or planning application, building control and the party wall notices are all handled by us.
You get one point of contact throughout rather than coordinating an architect, an engineer and a builder yourself.
