Extensions & Conversions Cardiff
House Extensions & Conversions in Cardiff
More space without moving house. Rear extensions, loft conversions, garage conversions and wraparound extensions built across Cardiff — with planning advice, full project management and a written quote before a single brick is laid.
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Home Extension Builders in Cardiff
House prices across Cardiff have made extending the property you already own far more cost-effective than buying somewhere bigger. The average terraced house in Roath, Canton or Pontprennau gains more in usable space — and more in resale value — from a well-built rear extension than the difference in price to the next rung of the property ladder.
J&Z Property Maintenance builds home extensions and conversions across Cardiff. We handle the full project — planning permission discussions, structural design coordination, groundwork, build, insulation, plastering and first fix — under one contract, with one team and one point of contact throughout. No managing multiple contractors. No invoices you weren't expecting.
Every project starts with a free site visit and a full written quote. We don't start work until you've approved the cost, the scope and the timeline
What Space Problems Do Cardiff Homeowners Face?
Cardiff's housing stock was not built for how we live today. Victorian terraces in Roath, Canton and Pontcanna were designed for households without home offices, without every family member needing their own space, and without the expectation that a spare room might become a permanent bedroom for a relative. The houses are well-built — good bones, solid walls, proportional rooms — but the layouts often fall short of what modern families need.
In Whitchurch, Rhiwbina and Llandaff, larger properties often have loft spaces that are completely unused — head height, boarded, with no particular reason they couldn't become a bedroom or office. Across much of Cardiff, single garages that no longer fit a modern car sit empty or full of boxes, representing a room's worth of usable floor space that isn't being used.
The most common things we hear from Cardiff homeowners: "We've run out of bedrooms." "We don't have a downstairs toilet." "We need a home office but we're working from the kitchen table." "The kitchen-diner is too small for how we actually use it." These are all solvable problems — without moving.
Worth knowing: Many Cardiff extensions fall under Permitted Development - meaning planning permission isn't always required. Loft and garage conversions frequently qualify too. We'll advise you honestly on what your property needs before any work starts.
Our Extensions & Conversions types
Every Cardiff property is different. A rear extension on a Victorian terrace in Roath has different planning, structural and design considerations than a loft conversion on an Edwardian semi in Pontcanna, or a garage conversion on a post-war house in Whitchurch. We assess your specific property before quoting — not a generic price per square metre.
Rear Extensions Cardiff
The most popular way to extend a Cardiff home — knocking through the back of a terraced or semi-detached property to create an open-plan kitchen and dining space. Single-storey or double-storey, we manage the full build from groundwork to plastered finish.
Wraparound Extensions Cardiff
A side-return and rear extension combined — particularly effective on terraced houses with an underused side alley. Dramatically increases ground floor space and natural light. We advise on permitted development eligibility before any design work begins.
Double-Storey Extensions Cardiff
Add space on both floors simultaneously — a rear extension that gives you a larger kitchen below and an extra bedroom above. More complex planning considerations apply; we advise from the outset and manage the application where needed.
Every job comes with a free written estimate before anything starts. No call-out charge. No pressure to commit. We're available evenings and weekends — call 0292 2710665.
Do You Need Planning Permission for a Cardiff Extension?
In Wales, many home extensions fall within Permitted Development rights — meaning you can build without a planning application. The rules differ slightly from England and are governed by the Town and Country Planning (General Permitted Development) Order 1995 (as amended for Wales).
Generally permitted without planning permission in Cardiff:
- Single-storey rear extensions up to 3 metres on semi-detached or terraced properties
- Single-storey rear extensions up to 4 metres on detached properties
- Extensions that don't exceed the height of the existing roof and don't front a highway
Planning permission is usually required for:
- Double-storey extensions
- Extensions on listed buildings or within conservation areas
- Extensions that extend beyond permitted development limits in size or height
We advise on permitted development eligibility as part of every initial consultation — at no charge. If a planning application is required, we manage that process on your behalf.
How Much Does a Home Extension Cost in Cardiff?
| Extension / conversion type | Typical Cardiff price range | Key variables |
|---|---|---|
| Single-storey rear extension | £20,000 – £45,000 | Size, glazing spec, kitchen fit-out if included |
| Wraparound extension | £35,000 – £65,000 | Complexity of combining side return and rear |
| Double-storey extension | £40,000 – £80,000 | Structural complexity, bedroom count, bathroom spec |
| Loft conversion (Velux) | £18,000 – £28,000 | Number of Velux windows, staircase design |
| Loft conversion (dormer) | £28,000 – £45,000 | Dormer size, en-suite inclusion, head height |
| Garage conversion | £8,000 – £18,000 | Insulation spec, plumbing if bathroom included |
| Side return extension | £20,000 – £40,000 | Length of return, glazed roof option |
All figures are indicative ranges based on typical Cardiff residential projects completed in 2024–2025. Every project is quoted individually following a free site visit. Your written quote will include all labour, materials and project management — no hidden costs.
Why Choose J & Z for Extensions & Conversions in Cardiff?
We're a Cardiff-based team with real tradespeople — not a call centre. When you ring us, you speak to someone who knows the job.
- One team, one contract. Most extension builders subcontract groundwork, brickwork, roofing and electrics to separate trades. We manage all of it — one contract covers the full project, one team is on site throughout, one number to call if anything changes.
- Planning advice before the quote. We assess permitted development eligibility on your first site visit. If you need a planning application, we tell you upfront and can manage it. No surprises after you've committed.
- Built for Welsh weather. Cardiff's climate means insulation specification, damp-proofing and drainage details matter more than in dryer parts of the UK. We specify and build accordingly — not to the minimum standard, but to what the site actually needs.
- Written quote, fixed scope. Every project is quoted in full before work starts. The scope is agreed in writing. If something changes on site, we discuss it before it affects your cost.
We're a trusted property maintenance and building company covering Cardiff and Newport with a track record of extension and conversion projects across the city built job by job over five years.
Planning a full interior renovation alongside your extension? See our home renovations page and for structural and groundwork projects, see our builders page.
FREQUENTLY ASKED QUESTIONS - EXTENSIONS & CONVERSIONS CARDIFF
Do I need planning permission for a rear extension in Cardiff?
Not always. In Wales, single-storey rear extensions up to 3 metres on terraced or semi-detached properties — and up to 4 metres on detached houses — typically fall within permitted development, meaning no planning application is required. However, properties in conservation areas, listed buildings, or those proposing larger extensions will need Cardiff Council approval. We assess your permitted development eligibility during the free initial site visit.
How long does a home extension in Cardiff typically take?
A single-storey rear extension takes 10–16 weeks from groundwork to completion in most cases. A loft conversion typically takes 8–12 weeks. A double-storey extension is usually 16–24 weeks depending on structural complexity. These timelines assume planning permission is already in place where required — allow 8–12 weeks for a planning application through Cardiff Council if needed.
Can you manage the full project including planning?
Yes. We handle the full project from initial design coordination through to final finish. Where a planning application is required, we manage that process on your behalf including drawings, application submission and correspondence with Cardiff Council. You don't need to coordinate separate architects, structural engineers and builders — we bring it all together.
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What is the difference between a dormer and a Velux loft conversion?
A Velux loft conversion installs roof windows into the existing roofline without changing the roof structure — it's the less disruptive and less expensive option but only works where there is sufficient existing head height. A dormer loft conversion builds out from the roof to create a vertical-walled space, adding significantly more usable floor area and head height. Most Cardiff terraces benefit more from a dormer, but we assess both options on site and advise accordingly.
Does a garage conversion add value to a Cardiff home?
Generally yes — converting an integral or attached garage into a habitable room typically adds more value than the build cost in Cardiff's current market, particularly when it creates a bedroom or home office. The key is that the conversion meets building regulations requirements for insulation, ventilation and damp-proofing, which is what distinguishes a professional conversion from a DIY one that buyers and surveyors will flag..
Do you work across all Cardiff postcodes?
Yes — we cover all Cardiff postcodes including CF1 through CF24, and surrounding areas including Pontypridd, Caerphilly, Penarth and the Vale of Glamorgan. Most of our extension work is concentrated in inner Cardiff — Canton, Pontcanna, Roath, Cathays and Llandaff — where the Victorian and Edwardian terraced stock is most suited to rear and wraparound extensions.
How do I get a quote for a home extension in Cardiff?
Call us on 0292 2710665 or fill in the estimate form on our contact page. We'll arrange a free site visit at a time that suits you — evenings and weekends available. After the visit we'll provide a full written quote covering all labour, materials and project management. No obligation, no charge for the visit.
Find Out What Your Cardiff Home
Can Become
One free site visit and we'll tell you exactly what your property can achieve, what it will cost and what planning it needs. Call 029 2271 0665 — no call-out charge, no obligation.