A Guide to Extending Your House
Our aim is to make the process of extending your house as straightforward as possible. This guide walks through the main stages of a typical domestic project — from first ideas to finished build — and points you to the official guidance wherever that helps.
As part of our service we offer a free initial consultation (depending on proximity) to review the feasibility of your scheme and provide an accurate fee proposal.
From first ideas to finished build
Every project is different, but most follow the same path. Tap a stage to see what happens and our typical timescales.
Brief, design & budget
Most of our clients do not have a firm brief at the outset, but do have an idea of budget. We are experienced in teasing out what matters most and adapting the design to suit our clients’ needs and budget.
We prepare proposal options for you to view on a 3D computer model, so you can picture the ideas before any commitment. We usually finalise a scheme shortly after this first proposal meeting, then prepare the drawings needed to seek planning permission.
What you’ll need to get the go-ahead
Planning permission, Building Regulations, party walls and listed buildings — here’s how each one applies, and the official guidance for each.
This is one of the first questions on any extension or loft conversion. Many smaller projects can be carried out under Permitted Development rights and do not need a formal planning application. Larger or more prominent work — and almost anything in a conservation area or to a listed building — will need a householder planning application, which your local (district or city) council must normally decide within 8 weeks.
The Planning Portal’s interactive house guide is the clearest way to see what applies to your project: Planning Portal interactive guide. We advise on all of this during the initial consultation and, where an application is needed, prepare and submit it on your behalf.
Where your project falls under Permitted Development, we always recommend obtaining a Lawful Development Certificate. This is a formal confirmation from the council that the work was lawful without planning permission — useful to keep with your house records and often asked for when you come to sell. We can obtain this for you.
Will I need planning permission?
Almost all extensions and alterations need Building Regulations approval, whether or not planning permission is required. (There are a few exceptions, such as certain porches, conservatories and outbuildings.) We prepare the detailed drawings and construction notes and submit the application for you.
We always recommend the “Full Plans” route rather than a Building Notice, so your builder works from approved drawings rather than relying on getting it right on site. More on the difference here: Full Plans or Building Notice?
If your project affects a shared wall, or involves foundations close to a neighbour’s property, the Party Wall etc. Act 1996 may apply and notice may need to be served. We flag this as part of our service and point you to the right next step. See the government’s Party Wall booklet.
If your property is listed, almost any work to alter, extend or demolish it will need Listed Building Consent, usually alongside planning permission. Please get in touch early so we can guide you through it.
Tendering & construction
We work with a number of local builders and can put you in touch with ones suited to your project.
We always recommend a formal contract, such as the RIBA Domestic Building Contract or the JCT Homeowner Contract. Most clients gather builders’ prices using our package of drawings and notes; we can also run the tender for you as an optional extra.
A typical extension takes around 3–6 months to build, depending on the scheme. Most clients work directly with their builder during construction, with us available to answer questions and visit site by agreement.
What will it cost?
Our own fees and project timescales are set out stage by stage on our Services page — please refer there for our current fees. Beyond our fee, the largest cost is the build itself; the guide below gives a ball-park. (Correct as at June 2026.)
Build cost varies considerably, but as a ball-park £3,000–£4,000 per m² (excluding VAT) is typical. We suggest allowing around £3,500 per m² +VAT, counting the floor area of all storeys. This excludes large fitted items such as kitchens and bathrooms.
Builders can give a rough idea from the planning drawings, but will usually only firm up a quotation once the Building Regulations drawings are available. This is a general guide only — every project is different, and we’ll talk costs through with you at the free consultation.
Ready to talk it through?
Get in touch for a free initial consultation — we’ll review the feasibility of your scheme and give you an accurate fee proposal.
Get in touch