Mansard roof extensions
London architect guide
Inspiration and ideas
Mansard roof extensions are the most cost effective way to maximise the floor area of your house or flat when compared to adding the same floor area with a rear or side extension.
Mansard roofs are a widespread and traditional method of adding an extra storey to the top of a Georgian, Victorian or Edwardian building.
Named after a French architect, Francois Mansart, the mansard roof comprises a sloping roof clad in slate or tiles, set back behind a parapet, with dormer or attic windows, which either project from or are recessed into the slope.
It emerged in the eighteenth century in Britain, when it was also referred to as a kirb roof. It allows extra accommodation at roof level, partially hidden behind a parapet wall, without having a great impact on the appearance of the façade below.
As part of this mansard roof extensions London architect guide we have selected some projects to lend architectural inspiration and design ideas for your mansard roof extension.
For more advice and information see the following:
Royal Institute of British Architects (RIBA)
- Do I need an architect for my extension or home project?
- Why work with an architect?
- How do architects calculate their fees?
Planning Portal
You can read here our latest Loft conversion cost planning permission architect guide for everything you need to know about your loft conversion project.
How much value does a loft conversion add? Please read our advice to Samm Webb as published for Homebuilding & Renovating on March 2023, and click below to read our full advice and guide to homeowners as prepared by George for the purposes of this article: Architect guide – How much value does a loft conversion add.
GOAStudio London residential architecture
George Omalianakis, BA (Hons) B.Arch Pg Dip Environmental Design.
Chartered RIBA architect and ARB registered.
RIBA Conservation Registrant specialism in conservation areas, period and Listed buildings.
Residential expert contributor for magazines including Which? magazine and Ideal Home.
Last reviewed by George Omalianakis for GOAStudio: August 2026
Mansard roof extensions London architect guide – Design aspirations and key considerations
Designing the staircase is the single most important thing we will need to consider for any type of roof extension or loft conversion.
There are building regulation restrictions in regards to the risers, goings, and head heights in regards to the staircase. There are fire regulations to consider, and plumbing/drainage issues when an en-suite is to be created.
The design challenge is about how to exercise intelligent spatial planning around all the relevant restrictions so that both the new loft layout, and the layout of the floor below do not get compromised when the staircase is added to the existing floor plan.
Start considering how you would like to use your new space, and how it will interact with the rest of your home. It’s important that the new extension blends with the rest of the building and is easily accessible, so when considering the staircase think about its long-term use as much as its style.
Mansard roof extensions London architect guide – Types and options for your home project
This type of roof extension is appropriate for properties with what is commonly known as “butterfly” or “V” roofs.
Such roof extensions practically add a full new level to your property, and they can be the perfect solution to houses or flats in conservation areas. The planners will take a view on whether a mansard roof can be added and where.
And here is the rule of thumb when it comes to planning: if the majority of the properties in your terrace have mansard roofs then it is likely the planners will approve an application for a mansard roof to your property.
There are two main types of mansard roofs:
Traditional
Traditionally most mansard roofs have two separate slopes or pitches, however they are more expensive to construct and less common these days.
Modern
Modern roof extensions often have a flat roof profile at the top, with a gentle slope to the rear.
There are several crucial elements to the correct appearance of a mansard roof, namely materials, slope of the roof, proportion of the dormer windows and extension of the party walls and chimneys. Such roof extensions always require planning permission from your local authority.
Design development stage
During the design development stage we will get to explore lots of ideas but you can start the process now by considering answers to questions as such:
- “How can we best use this new room? Will it be our new master-bedroom, a study space, a nanny’s room? What other bedrooms are available in the house, and what would work best for our changing needs and family?”
- “Space permitting, how about adding an en-suite, a walk-in wardrobe, or even a coffee area in front of a Juliet balcony?”
- “What do we think about rooflights in the bedroom? They bring more light into the room but how about the rain ticking on the glass; is it charming or just plain annoying?”
- “Planning permitting, how about we sacrifice some of the internal floor area to create a small balcony with doors opening up to it directly from our new (master-) bedroom?”
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Not sure where to start with your renovation or extension?
Read this before you meet an architect, speak to a builder or spend money on drawings.
This free, architect-prepared guide walks you through the 15 essential questions every homeowner should ask before starting a project.
"Should we renovate, extend… or walk away?
15 Questions every London homeowner must ask before starting a project to include homes in Conservation Areas and Listed Buildings."
Whether you're planning a modest rear extension or major alterations to a listed home, it will help you avoid expensive mistakes and give you clarity on what’s possible for your property. Includes guidance on:
Planning approvals. Conservation areas.
Timelines and costs. Appointments you need to make.
Design and sustainability options.
When to press ahead and when to walk away
We provide architectural services for residential projects in the following London Boroughs:
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We specialise in
- Greener homes
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- Listed Buildings
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GOAStudio London residential architecture limited.
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