How to Add an Extension Without Ruining Your Period Home

Bridging old and new - and what I learned from doing it myself

If you own a Victorian or Edwardian home and you're thinking about extending it, the anxiety is real. I know, because I've been there. Eight years ago, my husband and I extended our Edwardian semi in South West London - and the process taught me more about period homes, planning departments, and the importance of blinds than I could have anticipated.

This blog post is partly practical advice, partly the honest account of what we actually went through. I hope it's useful.

The rear of the house before work started. The lean-to kitchen and pantry occupied the back of the ground floor.

Start by Understanding the Problem You're Solving

The first thing I'd say to anyone considering an extension is this: be really clear about what isn't working before you start designing anything. We moved into our house in November 2017 knowing we'd extend - but we lived in it for several months before committing to a plan, and that time was extremely valuable.

The problems became very clear, very quickly. The original lean-to kitchen at the back of the house was small, cold, damp, and - bluntly - had mice. It had a step down into it from the dining room, which made it feel disconnected and awkward. It was not a kitchen you wanted to cook in, let alone host from. (My husband and I both cook a lot, and having friends and family round for meals matters to us. That tiny lean-to was simply not fit for purpose.)

Beyond the kitchen, the whole house felt dark. Our house is south west-facing at the back, but none of that light was getting through. You couldn't see the garden from the front door. The rooms felt closed off from each other and from the outside. That was the core problem we needed to solve.

The original lean-to. The garden connection was almost non-existent.

"Living in a house for several months before you start designing is not wasted time. You'll understand it properly - where the light is, how you actually move through it, what drives you mad - and that will make your brief to an architect much better."

What We Decided to Do - and Why

We worked with architect Paul Altham Lewis from early 2018. Our brief was clear: create a proper kitchen-dining-sitting space at the back of the house, maximise the light coming through from the south west, and connect the house to the garden.

We never intended the extension to replicate the Edwardian style of the original house. That was a deliberate choice. We weren't trying to pretend the extension had always been there - we wanted it to have its own identity while sitting appropriately alongside the rest of the building. The design that emerged was a flat-roof extension with a large rooflight, floor-to-ceiling aluminium bifold and sliding doors wrapping around two sides, and a dark rendered exterior. It is clearly a modern addition. That's the point.

Before: cramped lean-to kitchen, separate dining room, family room. After: one continuous kitchen-dining-sitting space flowing to the garden

The floor plans show the transformation clearly. The original layout had a tiny kitchen tucked behind a separate dining room. Nothing flowed. The new layout opens the entire rear of the ground floor into one space: kitchen, dining, sitting room - all connected and all facing the garden.

Three Approaches to Old and New

Before I go into the detail of our project, it's worth pausing on the broader question of how to relate a new extension to a period house - because there isn't one right answer.

Replicating period details for a seamless feel

You may want the extension to feel as though it was always part of the house. This means matching materials (brick, tiles, sash windows), replicating profile details like skirting and cornicing, and choosing period-appropriate fixtures. Done well, it's beautiful. Done badly, it looks like a pastiche.

Deliberate contrast

This is the approach we took. A clearly modern extension, sitting alongside the original building rather than pretending to be part of it. The structural shapes, materials, and proportions are what matter here - get those right and the contrast can be genuinely striking. I'd argue it can also be more honest about the building's history: this part was added in 2018, and it looks like it.

Hybrid

A mix of both - perhaps a modern kitchen with Edwardian-profile skirting boards and column radiators in the rest of the space. This can work very well and is often the right answer for interiors even when the exterior is more emphatically modern. In our case, the engineered oak floor throughout the whole of the downstairs is a version of this: it's a modern material and finish, but it references the original wood floors and makes the house feel coherent from front to back.

The Build: What Actually Happened

Planning permission was submitted around March 2018 and we were breaking ground by July 2018. The build completed in December 2018 - so roughly six months from start to finish.

It wasn't entirely smooth. We hit a planning issue that's worth knowing about: the council challenged whether the original lean-to kitchen was part of the house's original footprint, or a later addition. Their position was that it was an addition - which would have restricted how far back we could extend. We believed (and still believe) it was original, and our neighbouring semi had an identical configuration. But we couldn't find period maps or plans that conclusively proved it, so on the architect's advice we amended the plans rather than fight it. We ended up losing perhaps half a metre to a metre of length as a result.

It wasn't a disaster. The final space is still excellent. But it's a good example of the kind of thing that can happen, and why having an architect who knows how to navigate planning conversations is worth so much. Paul managed the back-and-forth with the council directly; we were copied in but didn't have to fight those battles ourselves.

On planning and period homes

If your home is listed or in a conservation area, you will need to work with a conservation officer. Even if it isn't, period properties often come with planning complications around what's "original" and what isn't - particularly for rear extensions.

An architect who knows your local authority is invaluable. They can manage the process, anticipate objections, and advise you honestly on what's worth fighting. They will also help you make better design decisions than you'd make alone.

Be prepared for the plan to change. It almost always does. Build in time and some financial contingency for this.

The Key Design Decisions

The rooflight

Paul was keen on a large rooflight from the outset, and he was right to be. Ours is 1.5m x 1.5m - he'd have gone bigger if lead times hadn't made it impractical. In a rear extension with a flat roof, a rooflight is one of the most effective ways to bring light deep into the space. On a bright day, the quality of light in that room is remarkable - you're very aware of the sky above you, the time of day, the weather. It's one of the things I love most about the space.

The 1.5m x 1.5m rooflight with the bifold doors open. On a clear day, the light in here is extraordinary

Glazing on two sides

The bifold and sliding doors wrap around two sides of the extension - the rear and one side. This was to maximise light and garden connection, not just to open the space up in summer. Even with the doors closed, the amount of glazing means the room feels connected to the outside. The planners didn't object to this at all.

The bifolds open fully onto the deck.

In summer, the boundary between inside and outside more or less disappears.

The flooring

We had UV-oiled engineered oak fitted throughout the whole of the ground floor in one go. This was deliberate. Running the same floor from the front of the house through to the back of the extension makes the whole ground floor feel coherent - it reads as one space even though the original house and the extension are clearly different architecturally. It's a small decision with a large effect. If I were advising a client doing something similar, I'd push hard for this kind of continuity in the flooring.

The kitchen window

The old dining room window - now in what's become the kitchen area - was a four-pane sash. We kept the same opening size but replaced it with a single-pane aluminium window that opens outwards, matching the bifold frames. The builder was sceptical; we were insistent. I'm glad we were. Putting an old sash window in a room with modern aluminium bifold doors would have looked odd. The whole rear of the house is now the modern part, and it reads consistently.

What It Looks Like Now

The finished space: kitchen in the foreground (where the old dining room was), dining table, sitting area, and the garden beyond.

Morning light through the glazing. The southwest orientation means the afternoons and evenings are even better.

The dining and sitting area with the bifolds fully open. The deck continues the level of the floor, which helps the inside and outside feel connected.

The extension from the garden. The dark render, flat roof, and aluminium frames are deliberately contemporary - a new part of an old house, not a replica of it.

What I'd Do Differently

Honestly, not much. The space works extremely well for how we live. But there are two things worth passing on.

First, the blinds. With this much glazing on a southwest-facing elevation, the space gets very warm in summer. We have click-fit bifold blinds on all the windows (from Blinds2Go, in a silvery grey-white tone that diffuses light without killing it entirely) and they're essential. We didn't have them fitted immediately - we waited about a year, which was a mistake. If you're doing an extension like this, cost the blinds into the build from the start and have them ready to install the day you move in. They're not a luxury.

Second, if I were designing it again, I'd think harder about external shade - a natural wood slatted canopy attached to the exterior of the extension, contrasting the dark render. With summers getting progressively warmer, having some architectural shading above the bifolds would be a real asset.

Three Things to Remember

Bigger is not always better. The most common mistake I see is extensions that overwhelm the original footprint of the house. Our planning challenge meant we ended up slightly smaller than planned - and the space is still more than we need. Getting the scale and proportion right matters far more than maximising square footage.

Work with an architect early. Not a design-and-build firm who will design around what they build. A proper architect, ideally one who knows your local authority. The investment is worth it for the design quality alone, before you even get to planning.

Think about flow from the start. The single question that should drive an extension brief is: how do you want to move through this house, and how does that change? For us, the answer was: we want to open the front door and see the garden. Everything else followed from that.

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I'm Hannah Ashe, an interior designer specialising in Victorian and Edwardian homes across London, Surrey, and beyond. If you're planning an extension or a renovation and you'd like some professional guidance on making the old and new work together, I'd love to hear from you.

Our home is currently listed with The Modern House - you can view the full listing here.