Expanding Your Home Safely and Thoughtfully
The bedrooms are too small. There’s not enough space downstairs either. And you’ve done the maths on moving — it doesn’t add up.
A double storey extension is the project you consider when the house has run out of room on both floors and moving feels like the wrong answer — stamp duty, agent fees, uprooting the family from a school and street you’ve invested years in.
Done well, it solves both problems at once. One build programme, one set of foundations, one period of disruption instead of two separate projects.
But it is also one of the most scrutinised projects a Surrey homeowner can take on: planning officers look harder at height, massing, and neighbour impact.
What a Double Storey Extension Actually Does
A double storey extension adds space across two floors simultaneously — typically extending the ground floor living areas while adding bedrooms, bathrooms, or a home office above. The efficiency is real. You pay for foundations, scaffold, and structural work once. The layout of both floors can be rethought together, rather than patched independently over time.
More importantly, it allows the house to be properly rebalanced. Not just bigger, but better organised — bedrooms where they should be, bathrooms where the family actually needs them, living space that finally matches how you live.
The planning and structural complexity is higher than a single storey project, and understanding that early is what determines whether the project proceeds smoothly or expensively.
Is a Double Storey Extension Right for You?
It makes sense when the space problem is real on both floors — and when the scale of that problem justifies the investment.
The families who get the most from a double storey extension typically need two or more additional bedrooms, at least one more bathroom, and meaningful additional living space downstairs — and want to solve all of that in one project rather than two.
It also makes sense when the alternative — moving — feels like the wrong answer. Most Surrey families we work with have built their lives around a particular school, street, and community. A double storey extension is often what makes staying viable for the next fifteen years.
Whether it makes sense financially, structurally, and from a planning perspective for your specific property is what we establish at the beginning, not the end.
The Questions We Hear Every Time
1. How much does a double storey extension cost in Surrey
Build costs run £2,500–£3,500 per square metre. Because the extension adds space on two floors, total costs are substantially higher than most single storey projects. For most Surrey properties, total build costs sit between £150,000 and £250,000 depending on scope, specification, and site conditions.
For context, moving house on a typical Surrey property involves stamp duty, agent fees, and legal costs that can easily reach £50,000–£60,000 — before a single box is unpacked.
2. Will I need planning permission?
Yes, in almost all cases. A double storey rear extension falls outside permitted development for most Surrey properties. Height, overlooking, and overall massing are all assessed by the local authority. The Party Wall Act also applies if extending to or near the boundary — neighbours must be formally notified and an agreement may be required before work starts. Standard householder applications typically take 8 weeks to be determined. We review the full planning position specifically for your property at feasibility stage.
3. Is it more cost-efficient than two separate projects?
Generally yes. One set of foundations, one scaffold, one structural package rather than running the same costs twice years apart. The upfront investment is larger, but the overall cost of achieving the same result is typically lower.
4. How long does the whole process take?
From feasibility to completion, expect twelve to eighteen months. Planning typically takes eight to twelve weeks once submitted. The build usually runs four to eight months depending on scope.
5. Can we stay in the house during the build?
Usually yes, though there will be phases where parts of the house are inaccessible, particularly during structural works and roof alterations. How disruptive those phases are depends on scope and sequencing. We plan for this at the beginning, not as an afterthought.
6. What if planning is refused?
A refusal wastes time and fees. The most common cause is designing without understanding what the local authority will support for that specific property and street. We assess planning risk at feasibility stage, before a penny is spent on drawings.
Where These Projects Go Wrong
Double storey extension problems are predictable. Almost all of them trace back to decisions made too early, without enough information. The planning strategy is assumed rather than verified — and the application is refused or requires significant redesign.
The structural package is coordinated after the layout is set — and the layout has to change when the engineer gets involved. The budget is set against an optimistic reading of the scope — and the gap between expectation and reality becomes apparent when it’s already too late.
The families who avoid these problems are the ones who spent time getting the early picture right. Not the ones who rushed into design because they were keen to get started. Our process is designed to get the sequencing right.
How We Work
Step 1 — Clarity Call (Free)
A 15-minute conversation about your home, your ambitions, and your constraints. You’ll leave knowing whether a double storey extension is the right move and what the sensible next step is.
Step 2 — Feasibility Study
We test realistic layout options across both floors. We assess planning for your home and local authority, including the specific questions around height, overlooking, and massing. We sense-check your budget against Surrey build costs.
Step 3 — Design and Planning
Layouts developed to work structurally, comply with planning, and genuinely support how your family lives across both floors. Application managed in full.
Step 4 — Technical Pack
Fully coordinated drawings and specifications, including structural engineering, that give builders everything they need to price accurately and build correctly.
Step 5 — Build Support (where appointed)
We remain involved throughout construction. On a project of this complexity, having an architect who knows the design on hand when decisions need to be made is a practical safeguard, not an optional extra.
