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MVV

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Frequently asked questions

Straight answers on costs, planning, party walls, extensions, lofts and refurbishments, and on how we work. If your question is not here, ask us directly.

Working with MVV

What does a design and build contractor do?
A design and build contractor takes responsibility for both the design and the construction of your project under a single contract. MVV takes a project from the first brief and concept design, through planning, detailed design and costing, to construction and handover, so you have one team and one point of responsibility throughout.
Where is MVV based and which parts of London do you cover?
Our office is at Gable House, 18-24 Turnham Green Terrace, Chiswick, London W4 1QP. We work across London, including central, West, South West, North West and South East London. Our areas page lists the neighbourhoods we cover in detail.
Do you work with my own architect?
Yes. We work alongside architects and contract administrators on both design and build and traditional contracts. If you already have drawings, we can pick the project up at whatever design stage it has reached.
Is MVV insured?
Yes. MVV carries £10M public and employers' liability cover.
How big is the MVV team?
MVV is a team of 35 designers, builders and project managers. Keeping design and site management within one team means decisions are made quickly and nothing falls between separate firms.
Do you take on commercial and hospitality projects?
Yes. Alongside homes, we deliver commercial and hospitality work, including restaurant fit-outs such as Enoteca Rosso on Kensington High Street and Kiez on Golborne Road in Notting Hill.

Costs and pricing

How much does a house extension cost in London?
Our minimum for a complete house extension is around £85,000, because even a small extension carries almost the same baseline of work as a larger one. The instant estimate gives a range for your specific size and specification. Figures exclude VAT, professional fees and planning.
How much does a loft conversion or a full refurbishment cost?
It depends on the type of work, the size of the property and the specification you choose. Rather than quote a single figure that may not fit your home, we suggest starting with the instant estimate for an indicative range, then booking a consultation for a fully costed proposal.
Do your prices include VAT?
Indicative figures are shown excluding VAT. VAT is charged at the standard UK rate of 20%.
What affects the cost of a project the most?
The biggest drivers are the size and structural complexity of the work, the specification of kitchens, bathrooms, glazing and joinery, and the condition of the existing building. In central London, access, parking and logistics also play a part, as do consents for listed buildings and conservation areas and professional fees such as structural engineering and party wall surveys.
Should I budget a contingency?
Yes. Even with thorough surveys, older buildings can reveal hidden issues once work starts, such as tired wiring, decayed timbers or unexpected structure. Setting money aside for the unforeseen, often in the region of 10 to 15 per cent on period properties, protects both the programme and your peace of mind.
How do I get an accurate price for my project?
Start with the instant estimate for an indicative range in a few minutes. Then book a free consultation: we visit the property, talk through your brief and prepare a fully costed proposal.

Planning and regulations

Do I need planning permission for a rear extension?
Not always. Many houses can add a single-storey rear extension under permitted development rights, typically up to 3 metres deep for a terraced or semi-detached house and 4 metres for a detached house, with larger extensions possible through the prior approval process. Flats and maisonettes do not have these rights, and listed buildings, conservation areas and homes where rights have been removed face tighter limits. We check what applies to your property before design begins.
Do I need planning permission for a loft conversion?
Many loft conversions on houses fall under permitted development, within volume limits of 40 cubic metres for terraced houses and 50 cubic metres for semi-detached and detached houses, as long as nothing projects beyond the roof slope facing the street. Mansard roofs, front dormers, lofts in conservation areas and any loft in a flat usually need planning permission.
What is different about building in a conservation area?
A conservation area protects the character of a whole neighbourhood rather than a single building. Permitted development rights are reduced, so extensions, roof alterations, cladding and some window changes that would be allowed elsewhere may need planning permission, and substantial demolition needs consent. Some boroughs also control smaller details through Article 4 directions. Designs that respect the street in scale and materials tend to fare best.
Do I need listed building consent?
If your home is listed, you need listed building consent for any work that affects its character, inside or out. That can include removing walls, altering joinery or fireplaces, and replacing windows. Carrying out such work without consent is a criminal offence, so it is important to establish what needs approval before anything is touched.
What is a party wall agreement and do I need one?
Under the Party Wall etc. Act 1996, you must notify neighbours before certain works to a shared wall, before building on the boundary, or before excavating near their foundations. Notice is normally due two months ahead for work to a party wall and one month ahead for excavation. If a neighbour does not consent, surveyors agree a party wall award. Most extensions, loft conversions and basements on London terraces involve the Act.
Is building regulations approval the same as planning permission?
No. Planning permission deals with what you build and how it sits in its setting. Building regulations cover how it is built, including structure, fire safety, insulation, ventilation and drainage. Almost all extensions, loft conversions and structural alterations need building regulations approval even when planning permission is not required, and you should receive a completion certificate at the end.
How long does a planning application take?
Councils aim to decide householder applications within eight weeks of validation, and listed building consent follows a similar timetable. Complex or contentious schemes can take longer. Pre-application advice adds time at the start but can make the formal application smoother, and we build realistic approval time into the overall programme.
What is a lawful development certificate?
It is formal confirmation from the council that a proposed extension or loft conversion falls within permitted development and does not need planning permission. It is not compulsory, but it gives certainty before work starts and is useful evidence when you come to sell.

Building safety and the BSR

What is a higher-risk building?
In England, a building at least 18 metres or seven storeys tall containing two or more residential units. Building work on these buildings is overseen by the Building Safety Regulator rather than the local authority or a private route.
What is a BSR or Gateway 2 application?
Building control approval from the Building Safety Regulator for work on a higher-risk building. For new buildings this is Gateway 2, and it is a hard stop: work cannot lawfully start until the application is approved.
Does a refurbishment in a high-rise block need BSR approval?
Usually, yes. Work on an existing higher-risk building needs the regulator's approval before it starts, unless it is limited to minor exempt work, competent person scheme work or genuine emergency repairs, which are notified and regularised instead.
How long do BSR applications take?
The statutory target is 12 weeks, and through 2025 new-build decisions commonly took 25 to 40 weeks. The regulator has committed to deciding non-complex new-build applications within 18 weeks, and remediation applications within 12, by March 2027, so complete, well-evidenced applications are the fastest route through.
What is the Building Safety Levy?
A charge from 1 October 2026 on building control applications in England that provide new dwellings or purpose-built student bedspaces, paid by the developer and collected by local authorities. Schemes under 10 dwellings are exempt, and refurbishments that create no new dwelling are not what it targets.
Can MVV handle work on higher-risk buildings?
Yes. MVV is a design and build contractor working alongside specialist fire engineers and consulting structural engineers, preparing application-ready compliance documentation and delivering the works with one accountable team. The people writing the compliance case are the people who build it.

Extensions, lofts and basements

How long does a house extension take to build?
As a guide, a single-storey rear extension typically takes several months on site, after design and approvals. Larger or more complex projects take longer. Your proposal sets out a programme for your specific scope.
Which type of loft conversion is right for my home?
It depends on the roof, the property type and planning. A rear dormer is the most common option on London terraces and adds useful head height. A hip-to-gable conversion suits semi-detached and end-of-terrace houses with a sloping side roof. A mansard creates the most space but usually needs planning permission, and a roof light conversion is the simplest where the roof is already tall enough.
Can I live at home while the work is done?
Often, yes, particularly for rear extensions and loft conversions, where much of the work happens before the new space is opened up to the house. For full refurbishments, or projects that take out the kitchen, bathrooms or services throughout, moving out for part or all of the programme is usually quicker and less stressful. We talk this through when planning the sequence of works.
Can you build a basement under my London home?
In many cases, yes, but basements are among the most tightly regulated projects in London. Boroughs such as Westminster and Kensington and Chelsea have specific basement policies that limit depth and extent, and basements involve structural engineering, party wall agreements, construction management plans and careful logistics. We assess feasibility, including what your borough allows, before design begins.
Do I need a structural engineer?
For most extensions, loft conversions, basements and any removal of load-bearing walls, yes. A structural engineer designs the steelwork, foundations and supports and provides the calculations building control needs. As a design and build contractor, we coordinate the engineer as part of the design team.

Refurbishment and period homes

What does a full home refurbishment include?
A full refurbishment usually covers layout changes, new electrics, plumbing and heating, kitchens and bathrooms, flooring, joinery and decoration, often alongside repairs to the building fabric. We define the scope with you at the design stage, so the proposal reflects exactly what will be done.
Can you keep the original features of a period home?
Yes. Cornicing, fireplaces, panelling, sash windows and original floors are often what gives a period home its value. We repair and restore them where we can and plan new services around them, as on our Park Lane project in Mayfair, where the original wood and marble flooring was restored rather than replaced.
Do you make bespoke joinery?
Yes. Bespoke joinery is one of our services, from wardrobes and storage to libraries, media units and window seating, designed to suit the proportions of each room.
I own a flat. What do I need before starting work?
Most London flats are leasehold, so you will usually need a licence to alter from the freeholder, and the managing agent may set rules on working hours, deliveries and protecting the common parts. Flats also have no permitted development rights, so external changes need planning permission. We help prepare the drawings and information freeholders ask for.

On site

Who manages the project day to day?
Your project is run by our own project management team, who coordinate design, trades, deliveries and inspections and keep you updated throughout. Because design and construction sit with one team, questions on site are answered without passing between separate firms.
How do you keep disruption to neighbours to a minimum?
We plan access, deliveries and working hours around the street and the council's rules, protect shared areas, and keep the site tidy and secure. Talking to neighbours early, and keeping them informed as the work progresses, avoids most problems before they start.
Who is responsible for health and safety on site?
Under the Construction (Design and Management) Regulations 2015, a homeowner's duties as a domestic client normally pass to the contractor, or to the principal contractor where more than one is involved. On an MVV project, we take on that responsibility and run the site to the required standard.
What happens at the end of the project?
Before handover we walk through the finished work with you and resolve any snagging items, confirm building control sign-off and pass on the certificates and manuals for the systems installed.

The instant estimate

How does the instant estimate work?
You describe your project and answer a short set of questions. Our AI Estimator measures the work, and a pricing engine built on real London build costs produces an indicative range, shown on screen and emailed to you. Any cost for the estimate is shown before you start.
How accurate is the instant estimate?
It gives an indicative range based on your project type, size and specification. It is not a quotation. Every project is priced individually after a site visit.