A double-storey extension adds two floors of new space to your house in one build, typically a larger kitchen or living room downstairs with an extra bedroom, bathroom or en-suite above, sharing one set of foundations and one roof.
Thinking about a double-storey extension in Portishead? We take charge of the whole project, co-ordinating every trade involved, and one person keeps you updated. Guide prices for the South West sit at £61,000–£122,000 including VAT, and a typical job takes 14–22 weeks on site. Your own figure depends on what the survey finds and the specification you settle on.
- Guide price
- £61,000–£122,000 inc VAT
- Time on site
- 14–22 weeks on site
- Postcodes
- BS20
- Planning rules
- England
- Local area
- North Somerset
- Survey
- Free, with a written quote
How much does a double-storey extension cost in Portishead?
These are guide costs, not quotes. For a double-storey extension in Portishead the range is £61,000–£122,000, VAT included, reflecting prices in the South West that are about 2% above the national guide. Once we have visited for a free survey, you get a firm figure for the scope you approve.
| Type of job | What it usually involves | Guide in Portishead |
|---|---|---|
| Small (15–20m² total) | A compact rear or side extension adding a small room on each floor. | £41,000–£66,000 |
| Typical (30–40m² total) | A larger kitchen or living room below with a double bedroom or en-suite above. | £61,000–£122,000 |
| Large (50m² plus total) | Wide or deep extensions, often with a new bathroom, steelwork and high-spec glazing. | £102,000–£184,000 |
Expect these to shape the final quote:
- Combined floor area across both storeys
- Bathrooms, en-suites and plumbing on the upper floor
- Foundation depth, ground conditions and drains to divert
- Scaffolding duration, access and the level of finishes
What’s included?
- Insulated cavity walls with brick or render to match the house
- First-floor joists, stud walls and new openings upstairs
- Scaffolding for the full build, erected and inspected
- Electrics, plumbing and heating by qualified trades, with certificates
- Windows, external doors, plastering and internal doors
- Building control inspections and completion certificate
Local housing and a double-storey extension
Somerset's building stone varies widely: Bath stone in Bath, golden Ham stone around Yeovil, blue lias in villages on the Levels and Mendip stone in the north. Weston-super-Mare has Victorian villas and terraces, Taunton and Bridgwater have brick terraces and post-war estates, and new housing continues to spread around the larger towns.
The Somerset Levels are low and prone to flooding, coastal areas face Bristol Channel winds, and Exmoor is wet and exposed.
That mix of housing shapes how we approach a double-storey extension in Portishead: the age and construction of your home affect the materials, the method and, in the end, the price.
Planning and building rules in Portishead
England, Wales, Scotland and Northern Ireland each handle planning a little differently. Portishead comes under England, covered below, and we raise any questions with the council before your quote is finalised.
In England, a two-storey rear extension can only be permitted development if it is no more than 3 m deep, at least 7 m from the rear boundary and finished to match the house. Most double-storey and all two-storey side extensions need full planning permission.
Building Regulations approval is needed, with structural calculations for beams, foundations and the roof. The Party Wall etc. Act 1996 often applies on semi-detached and terraced houses.
Rules change and every property is different, so we check the planning history and constraints for your address before we quote.
How does the job run?
Free site survey
We begin by looking at the job in person. During the free survey we discuss options, materials and budget for a double-storey extension, and photograph or measure anything the quote needs to reflect.
Price and scope agreed
You get the price in writing, itemised so you can see where the money goes. As long as the specification stays the same, that is the price you pay for a double-storey extension.
Dates and permissions
Once you accept, we agree start dates, order materials and deal with any planning, building control or neighbour notices the job needs. You'll know who is coming and when before work begins.
Finish and handover
Work goes ahead as scheduled and you deal with one contact throughout. When the last trade leaves, we clear and clean the site, talk you through what has been done and pass on any certificates and care instructions.
What you can expect from us
Common questions
Which postcodes in Portishead do you cover?
We cover BS20, along with the rest of Somerset. If your postcode is not listed, get in touch anyway: our coverage is UK-wide, and we can usually arrange a survey wherever you live. Enter your postcode in the guide-price tool or contact form and we will confirm.
How is the new roof joined to the existing house?
The new roof is usually tied into the existing roof so the two read as one. On a rear extension this often means a lower ridge or a hipped end, with valleys where the slopes meet. We strip back some existing tiles, fix new rafters and battens, and lay matching tiles or slates. Lead or proprietary flashings seal the junctions so water runs off properly.
Can the new upstairs room have its own bathroom?
A new upstairs room can usually have an en-suite, provided waste pipes can reach the soil stack or a new one can be installed. Running the waste pipe to the right falls is the main design question, and a pumped system is an option where gravity will not work. We plan bathroom positions at the design stage so pipes, ventilation and insulation are built in rather than added later.
How much does a double-storey extension cost?
A typical double-storey extension of 30–40m² across both floors costs £61,000–£122,000, built to a plastered finish. As a rough guide, allow around £1,400–£2,600 per square metre plus fixed costs for groundworks, scaffolding and fees. The second storey usually costs less per square metre than the first, because foundations and roof are shared. Bathrooms upstairs and a complex roof add most. We confirm a fixed price after the survey.
Who do I deal with during the job?
One point of contact manages your project from survey to handover. They schedule the trades working under our contract, keep you updated on progress, and are the person to call with any question. You don't need to coordinate builders, electricians or decorators separately, because that is part of what we do.
Nearby towns
If your address falls within BS20, we cover it. The same goes for neighbouring Nailsea, Clevedon and Bishopsworth, which we include alongside Portishead when arranging surveys and quotes.