Builders in Cardiff

If you are comparing builders in Cardiff, the first thing to know is that Wales makes its own rules. The Welsh Government publishes its own guidance on planning permission and building regulations, and some of it differs from the English guides that dominate search results. A Cardiff builder should be working from the Welsh versions, and you should check the same pages yourself.

What is different about building in Cardiff?

Two systems apply to most jobs: planning permission, and building regulations approval. They are separate. Planning decides whether the development is acceptable. Building regulations check how it is built, covering things like structure, fire safety, insulation and drainage. You can need one, the other, or both.

Cardiff's housing mix shapes the work. The 2021 Census shows Cardiff had the lowest home ownership of any Welsh council area, at 58.3%, and the highest share of privately rented households (24.3%). It also had the lowest share of three-bedroom households (38.8%) and the highest share of households living in one or two rooms (12.8%) (Welsh Government, Housing in Wales: Census 2021, read 12 October 2026). The figures do not say what homeowners want to build. But a city with many small homes and a large rental sector is likely to see steady demand for extensions, loft rooms and refurbishment. That is our inference, not a measured figure.

Across Wales, terraced houses were 26.6% of households in 2021. We have not found a verified Cardiff-only terrace figure, so we do not quote one.

Do you need planning permission for an extension in Cardiff?

Often not, for a modest one, but the limits are specific. The Welsh Government says an extension is generally permitted development if it stays within its limits and conditions. A single-storey rear extension cannot go more than 4 metres beyond the rear wall or be more than 4 metres high. Within 2 metres of a boundary, eaves cannot exceed 3 metres and the total height cannot exceed 4 metres. No more than half the land around the original house can be covered by extensions (gov.wales, planning permission: extensions, read 12 October 2026).

Conservation areas are stricter. A rear extension of more than one storey is not permitted there, and a single-storey side extension must not project more than 3 metres and must be set back at least 1 metre from the front of the house. Rights can also be removed by an Article 4 direction, which the Welsh Government says are most common in conservation areas. Only the council can tell you whether your street is affected, so check with Cardiff Council's planning service before you pay for drawings. The Welsh Government's householder permitted development guide sets out the national rules. If you are unsure, ask the council for a formal view before work starts.

These householder rules are written for houses. If you own a flat, ask the council what applies, and check whether your lease or the freeholder's consent controls alterations. In a city with this much private renting, that is worth knowing early.

Does a loft conversion need permission?

It depends on volume and location. The Welsh Government's loft conversion guidance says a roof extension must be under 40 cubic metres for a terraced house and under 50 cubic metres for other houses. It cannot go beyond the plane of the existing roof slope on the front elevation, cannot be higher than the highest part of the existing roof, and, apart from hip-to-gable enlargements, must be at least 20 centimetres from the eaves. Roof extensions are not permitted in conservation areas, national parks, areas of outstanding natural beauty or World Heritage Sites, and a planning application is required if rights were removed by a condition or an Article 4 direction (gov.wales, planning permission: loft conversions, read 12 October 2026).

For loft conversion in Cardiff, the terrace limit is the one to check first. Earlier roof work on the house can count towards the limit. Ask the builder to measure and show you the calculation before you commit.

What do building regulations cover?

Whatever the planning position, most structural work needs building regulations approval. The Welsh Government says most extensions require approval and points out that the Party Wall etc. Act 1996 may also apply (gov.wales, building regulations: extensions, read 12 October 2026). For a loft conversion into living space, its guidance says to contact building control, and the regulations look at the strength of the new floor, the stability of the existing roof, safely designed stairs, safe escape from fire and sound insulation between the conversion and the rooms below (gov.wales, building regulations: loft conversions, read 12 October 2026).

Cardiff Council's building control team handles applications for work in the city. Ask your builder who submits the application and who arranges the inspections.

Building without the right approval carries risk. If a buyer's solicitor later asks for approvals and there are none, a sale can stall. Our guide to building regulations for home improvements covers the general principles, but check the Welsh Government pages above for anything specific to Wales.

What are Cardiff house prices doing?

The UK House Price Index put the average price in Cardiff at £272,252 in July 2026, up 2.7% from £265,146 a year earlier. The Welsh average was £215,037, up 2.6% (UK House Price Index Wales: July 2026, page updated 18 September 2026). The Office for National Statistics reports that Cardiff had the third-highest average price in Wales and that first-time buyers paid about £234,000, a provisional figure (ONS, housing prices in Cardiff, read 12 October 2026). Prices do not tell you what a job will cost or add in value, so ask a local valuer before you spend.

How do you hire a builder in Cardiff?

The core checks are the same everywhere, and our guide on how to hire a builder covers insurance, written quotes, staged payments and cancellation rights. Add some Cardiff-specific questions:

1. Which planning rules are you working to? Ask them to name the Welsh Government guidance, not generic advice.
2. Does the job need building regulations approval, and who applies?
3. Have you built in a conservation area or an Article 4 area here?
4. If it is a terraced house or a flat, who has to be told, such as neighbours under the Party Wall Act or a freeholder?
5. What is your programme, and who does the council inspect with?

You can search for a builder near you or browse by city. Our ranked list is ordered by verified reviews from the last 12 months, then by distance, and nobody pays to move up it. A labelled Featured slot sits above the list. An enquiry goes to one builder only. The directory is still being filled town by town, so confirm insurance and any scheme membership on the scheme's own site, not ours.

Looking for specific work? See our pages on extensions and loft conversions, and the loft conversion cost guide for how to read published prices. We do not quote Cardiff prices on this page, because we have not found a verified local figure.