Question 1

How much does a double storey extension cost in Cardiff?

Accepted Answer

A double storey extension typically costs between £1,200 and £1,900 per square metre. For a typical 40m² extension (20m² per floor), expect to pay between £48,000 and £76,000. The upper floor is cheaper per m² as foundations and roof are already covered.

Question 2

Do I need planning permission for a double storey extension?

Accepted Answer

Yes, double storey extensions almost always require full planning permission. They must not extend beyond the rear wall of the original house by more than 3 metres and must not be closer than 7 metres to the rear boundary.

Question 3

Is a double storey extension better value than single storey?

Accepted Answer

Yes, a double storey extension typically costs 50-70% more than a single storey but gives you twice the floor space. The shared foundations and roof make the upper floor significantly cheaper per square metre.

Question 4

Will I need a party wall agreement for a double storey extension?

Accepted Answer

If your extension is built on or near a shared boundary with a neighbour, you'll likely need a Party Wall Agreement under the Party Wall Act 1996. This typically costs £700-£1,500 per neighbour for surveyor fees.

Question 5

How long does a double storey extension take?

Accepted Answer

A double storey extension typically takes 12-20 weeks to build. Larger projects with complex designs or difficult access can take longer. Factor in additional time for planning approval, which takes 8-13 weeks.

Category	Low Estimate	High Estimate
Foundations & Groundworks	£5,299	£8,390
Structural Walls	£6,624	£10,488
Roof Structure & Covering	£4,416	£6,992
Windows & Doors	£3,533	£5,594
Plumbing & Drainage	£3,533	£5,594
Electrical Installation	£2,650	£4,195
Plastering & Rendering	£2,650	£4,195
Flooring	£2,208	£3,496
Kitchen/Bathroom Fitting	£4,416	£6,992
Decoration & Finishing	£2,208	£3,496
Professional Fees	£4,416	£6,992
Contingency (10%)	£2,208	£3,496
Total Estimated Cost	£44,160	£69,920

Category	Low Estimate	High Estimate
Foundations & Groundworks	£5,299	£8,390
Structural Walls	£6,624	£10,488
Roof Structure & Covering	£4,416	£6,992
Windows & Doors	£3,533	£5,594
Plumbing & Drainage	£3,533	£5,594
Electrical Installation	£2,650	£4,195
Plastering & Rendering	£2,650	£4,195
Flooring	£2,208	£3,496
Kitchen/Bathroom Fitting	£4,416	£6,992
Decoration & Finishing	£2,208	£3,496
Professional Fees	£4,416	£6,992
Contingency (10%)	£2,208	£3,496
Total Estimated Cost	£44,160	£69,920

Double Storey Extension in Cardiff

Cost Breakdown for Double Storey Extension

Frequently Asked Questions

Get an Accurate Quote for Your Double Storey in Cardiff

Double Storey Extension Costs in Nearby Cities

Double Storey Extension in Cardiff

Cost Breakdown for Double Storey Extension

Frequently Asked Questions

Get an Accurate Quote for Your Double Storey in Cardiff

Double Storey Extension Costs in Nearby Cities