A double storey extension adds new rooms on the ground floor and the first floor in one build. Most people use it for a bigger kitchen or living space downstairs and an extra bedroom, bathroom or study upstairs, without the cost and upheaval of moving.
This page helps you choose between the main two-storey options and explains what drives the planning route, structure, cost and timescale. We survey the house, prepare the design, coordinate planning and Building Regulations, then build and manage the project through to handover.
A double storey extension is a new structure that rises to two full floors and joins the existing house at both levels. Downstairs it usually opens into the kitchen or living room. Upstairs it connects to the landing, so the new rooms work as part of the first floor rather than an add-on.
It makes most sense when you are short of space on both floors at once. If you only need a larger kitchen, a single storey rear extension is simpler. If you only need a bedroom and the roof has enough height, a loft conversion may cost less and leave the garden alone. When you need both, building up uses the same foundations and roof for twice the floor area, and takes less garden than spreading everything across one level.
The design also has to suit the plot. The distance to your back boundary, the gap to the side boundary, your neighbours’ windows and the shape of the existing roof all affect what is realistic. We look at these at the survey before any drawings are started.
The position of the extension changes the planning route, the structural work and how the new rooms connect to the house. These are the main options we assess.
The most common layout: a kitchen or family room opening to the garden, with bedrooms or a bathroom above. It is the only two-storey type that can fall under permitted development. See our guide to the double storey rear extension for boundary distances, neighbours’ light and landing layouts.
Uses the strip beside a semi-detached or detached house. It always needs a planning application, and councils often look closely at the gap left to the side boundary and how the extension sits next to the main roof. Our side extensions page covers the single storey alternatives.
Building on top of an attached garage or single storey extension saves new groundwork only if the existing foundations and walls can take the extra load. That has to be checked by an engineer, and strengthening is common. Building over a side garage usually needs planning permission.
Some homes suit a larger ground floor that wraps around the corner, with a two-storey section on one part only. See wrap around extensions for how the ground floor side of that works.
If the bedroom is the real goal, compare room sizes, fire escape rules and en-suite drainage across each route on our bedroom extension page before deciding.
A loft conversion adds space upstairs without using garden, but it depends on head height and a workable stair position. Types include a dormer loft conversion and a hip to gable loft conversion.
Two floors put far more load on the ground than one, so the foundations are designed for the full height from the start. The depth depends on the soil, nearby trees and any drains running under the footprint. Trial holes and a drainage check early on reduce the chance of surprises once digging starts.
If a public sewer runs under or close to the new walls, the water company normally needs to agree a build over arrangement before work goes ahead. Existing manholes may have to be moved.
Where the extension opens into the existing house, steel beams carry the upper wall and floor across the new opening. A structural engineer calculates these, and the calculations form part of the Building Regulations submission.
The roof is where a two-storey extension succeeds or looks bolted on. The usual options are a pitched or hipped roof set below the main ridge, or a roof that runs into the existing slope with a valley. On rear extensions, the roof pitch should match the house as far as practicable to stay within permitted development. The new roof often sits over an existing first floor window, so that room may need a new window position.
It depends on where the extension goes. A two-storey rear extension may fall under permitted development, depending on the property and any restrictions that apply. A two-storey side extension always needs a planning application. Planning permission and Building Regulations approval are separate, and you need to deal with both.
Under Class A of the Town and Country Planning (General Permitted Development) (England) Order 2015, an extension of more than one storey has to meet all of these, among other conditions:
Two-storey extensions are not permitted development on Article 2(3) land, which includes conservation areas. The larger home extension prior approval route only covers single storey extensions. Your property needs to be checked against the full rules, and a Lawful Development Certificate gives written confirmation before you build.
Applications go to the local council: Nottingham City, Rushcliffe, Broxtowe, Gedling or Ashfield, or Erewash for Long Eaton, which is across the county border in Derbyshire. Councils aim to decide most householder applications within 8 weeks of validation.
Every double storey extension needs Building Regulations approval, whether or not it needs planning permission. Building control checks the foundations, structure, insulation, drainage, ventilation, electrics and fire safety, with inspections at set stages during the build.
On two floors, fire safety matters more than on a single storey build. New first-floor bedrooms need a safe escape route, which usually means escape windows and linked smoke alarms. We prepare the technical drawings and structural calculations and arrange the inspections.
If you share a wall with a neighbour, or plan to dig foundations close to their property, the Party Wall etc. Act 1996 may apply. It sets out when notice must be served before work starts and how disagreements are settled.
Two-storey foundations are often deeper than single storey ones, so the Act is more likely to come into play. Notices need to go out one to two months before the relevant work, so it is worth starting early.
A two-storey project has more approvals than most single storey work, so the order matters.
We measure up, check boundaries, access and drains, and talk through the rooms you want on each floor.
Layouts are drawn for both floors, including how the first floor joins the landing and how the roof meets the house.
We confirm whether a Lawful Development Certificate or a householder planning application is the right route.
An engineer designs the foundations, beams and floor, ready for the Building Regulations submission.
Building Regulations approval, Party Wall notices and any build over agreement are dealt with before work starts.
You get a written, itemised quotation and an agreed programme once the design is settled.
Groundworks, shell and roof first, then the break-through, services, plastering and finishing.
Final building control inspection, snagging and handover of the completion paperwork.
As a broad 2026 guide, the ranges below run from around £60,000 for a compact two-storey rear extension to £175,000 or more for a large or complex project. Your own figure depends on the size, the ground, the structure and the finish you choose.
| Approx. total new floor area | Typical project | Indicative budget |
|---|---|---|
| 30 to 40m² | Compact two-storey rear extension | £60,000 to £100,000+ |
| 40 to 50m² | Kitchen-diner downstairs, bedroom upstairs | £80,000 to £120,000+ |
| 50 to 60m² | Larger family extension with an extra bedroom or bathroom | £100,000 to £150,000+ |
| 60m²+ | Large or complex two-storey or wrap around project | £120,000 to £175,000+ |
It helps to treat the project as separate stages rather than one number. Design and structural work come first. Then the planning stage, if an application or a Lawful Development Certificate is needed. Building Regulations approval and any Party Wall notices usually run alongside. Construction of a two-storey extension then typically takes several months, followed by finishing and sign-off. None of these stages runs to a fixed date, because council decisions, neighbours and the weather all play a part.
Most households stay at home during the work. The new shell is built first while the house stays closed off. The disruptive part comes when the existing rear or side wall is opened up, which can mean a period without a kitchen downstairs and dust and noise upstairs when the landing is broken through. Scaffolding goes up for the first floor and roof, and access to the garden is limited.
We manage the trades, book the building control inspections and keep you informed about which rooms are affected each week, so you can plan around the noisy stages.
A two-storey extension can match the existing brickwork closely or contrast with it through glazing and cladding. For photos of our own completed work, browse the project gallery or see how we handle feedback on the reviews page.
We work across Nottingham and nearby towns. Each area page explains which council handles planning there.
Short answers to the questions we are asked most before a two-storey project. The details for your house are confirmed at the survey.
As a broad 2026 guide, our indicative ranges run from around £60,000 for a compact two-storey rear extension to £120,000 to £175,000 or more for large or complex projects. Foundations, steelwork, the roof tie-in, drainage, glazing and the kitchen and bathroom specification make the biggest difference. You get a written, itemised quotation after a free survey.
It depends on the position. A two-storey rear extension may fall under permitted development if it meets every condition and your property has no restrictions, such as a conservation area, an Article 4 direction or removed permitted development rights. A two-storey side or front extension always needs a planning application. Building Regulations approval is needed in every case.
In England, an extension of more than one storey can go no more than 3m beyond the rear wall of the original house, and no part of it can be within 7m of the boundary opposite the rear wall. Other conditions cover height, eaves, roof pitch, materials and side windows. A Lawful Development Certificate confirms the position before you build.
Often, but the existing foundations and walls were probably not designed for another floor. A structural engineer needs to check them, and strengthening or new foundations are common. Building over a side garage usually needs a planning application, and Building Regulations approval is always required.
They solve different problems. A loft conversion adds rooms at the top of the house without using garden, if the roof has enough head height and a stair can fit. A double storey extension adds space on both floors, so it suits households that need a bigger kitchen or living area as well as another bedroom.
Construction typically takes several months once work starts. Before that, allow time for design, structural calculations, any planning application or Lawful Development Certificate, Building Regulations approval and Party Wall notices. These stages do not run to fixed dates, so we set out a programme once approvals are in place.
Yes, in practice. The foundations, the beams over openings into the existing house, the first floor and the roof all need calculations, and building control will ask for them as part of the Building Regulations application. We arrange this as part of the design stage.
Most households do. The shell is built while the house stays closed off. The harder weeks come when the existing wall is opened up, which can leave you without a kitchen downstairs for a while, and when the first floor is broken through to the landing. We explain which rooms are affected before each stage.
A free site survey tells you where an extension can realistically go, which planning route applies and what the main cost drivers are for your plot. You then get a written, itemised quotation.