The key is designing the upstairs as carefully as the downstairs, and making the new roof sit naturally with the old one.
Why build up as well as out
Extra bedrooms, a bigger main bedroom with an en suite, or a family bathroom are the usual goals upstairs, with a kitchen or living space below. It uses less garden than two separate projects and leaves the house with one coherent shape.
Planning permission
Permitted development allows some two storey rear extensions, but the limits on depth, distance from boundaries and window positions are tight. Many two storey side and rear extensions need a householder planning application.
Planners look closely at overlooking, loss of light to neighbours and whether the extension looks subordinate to the house. A lower ridge line and a set back from the front are common ways to satisfy that.
- Distance from the side boundary
- Overlooking from new upstairs windows
- Ridge height relative to the house
- Materials matching the existing building
Foundations and structure
Two storeys put more load on the ground, so foundations are designed for it. Ground conditions, nearby trees and drains all influence the design, and building control will inspect the trenches before concrete goes in.
Upstairs, floor joists, lintels over openings and any steels to open up the existing house are specified by an engineer.
Roof junctions and matching the house
Where the new roof meets the old is where leaks start if it is done poorly. Valleys, lead flashings and matching tile or slate courses need careful carpentry and roofing. As a carpentry led builder, roof structures are something we handle ourselves.
Planning the upstairs layout
Joining a new upstairs room to the existing landing can mean losing part of a bedroom to make a corridor. Look at the layout as a whole: sometimes rearranging existing rooms works better than simply bolting a room on.
Think about where bathrooms go relative to soil pipes, and about stair position if the extension changes how the house is entered.
Materials and appearance
Most planners expect a two storey extension to match the house in brick, render, tile or slate, with windows of a similar style and proportion. Where an exact brick match is hard to find, a contrasting material such as timber cladding on the upper floor can look deliberate rather than mismatched. Agree samples early, as a planning condition may require their approval before work starts.
Neighbours and party walls
A two storey extension close to a boundary may need party wall notices, particularly where foundations are dug near a neighbour's wall or where you build on the line of a shared wall. Serving notice early, and talking to neighbours before the planning application goes in, usually makes both processes smoother.
Planners will also consider neighbours' comments, so explaining the design and how it limits overlooking can make a real difference.
Heating, insulation and the upstairs rooms
New upstairs rooms must meet current insulation standards, which usually makes them warmer than the older rooms around them. Check that the existing boiler can cope with the extra radiators or an en suite, and plan ventilation for any new bathroom. Getting this settled at design stage avoids having to upgrade the system halfway through the build.
Build order and living through it
The shell goes up first: foundations, walls, floor, roof. Only then is the existing wall opened on each floor, which keeps disruption short. First fix, plastering and finishing follow, just as in a single storey job.
With over 40 years of building experience, we start with a free site visit and provide a fixed-price written quote before work begins.
Common questions
Does a two storey extension need planning permission?
Often yes, though some rear extensions qualify under permitted development. Planners pay close attention to neighbours' light and privacy.
Is a two storey extension much more work than a single storey one?
It is more work, but foundations and roof are shared, so it is usually better value per square metre than building twice.
Can I stay in the house during the build?
Usually. The existing walls are opened late in the build to keep disruption short.
Do you do the roofing yourselves?
Yes, roof carpentry and roofing are part of our published services.