Range from the cheapest single storey extension £39,000 (Complex Construction based in AL7) to the dearest single storey extension £54,840 (Red Swan Construction based in SG2).
Comparing extension builders estimates for fitting a downstairs toilet gives you an idea of who will be better value but the best way to compare costs is to get actual quotes.
What to do - Get rates and quotes to build a single storey extension in Welwyn by posting a job with HaMuch and we will send it to extension builders in Welwyn.

"Single storey extension"
WELWYN
| Location in UK | Hourly Rate | Daily Rate |
|---|---|---|
| Single Storey Extension near Welwyn Garden City | £36 | £229 |
| Single Storey Extension near Hertford | £39 | £247 |
| Single Storey Extension near Hatfield | £53 | £244 |
| Single Storey Extension near Stevenage | £37 | £239 |
| Single Storey Extension near Harpenden | £70 | £264 |
| Single Storey Extension near Hitchin | £37 | £238 |
| Single Storey Extension near East Hertfordshire | £37 | £241 |
| Single Storey Extension near Ware | £40 | £252 |
| Single Storey Extension near St Albans | £52 | £246 |
| Single Storey Extension near North Hertfordshire | £37 | £239 |