First-floor extensions in Caernarfon

Quick reference for homeowners in Caernarfon.

Postcode districts: LL54, LL55 and LL61
County / area: Gwynedd and Anglesey, Wales
Price region: Wales
Guide price: £23,000–£33,500 (£1,660–£2,390 per m²)
Approval route: It may be permitted development if the ground floor goes no more than 4 m and the first floor no more than 3 m beyond the original rear wall, with the first floor 10.5 m from the rear boundary.
Nearest towns: Menai Bridge (7.3 miles), Llangefni (8.1 miles), Bangor (Gwynedd and Anglesey) (8.3 miles)
Distance to Bangor (Gwynedd and Anglesey): about 8.3 miles
First visit: Free, no obligation

About a first-floor extension

A first-floor extension suits you if your house already has a single-storey extension and you need more space upstairs. You get a structural check of the existing walls and foundations, a design that ties the new floor into the house, the approvals your nation needs, building regulations approval and the build, managed by us and carried out by vetted teams working under S&K.

Around Caernarfon we also work in Menai Bridge, Llangefni and Bangor (Gwynedd and Anglesey), and across the rest of Gwynedd and Anglesey. Postcode districts in and near Caernarfon: LL54, LL55 and LL61.

What it costs in Caernarfon

Guide prices for first-floor extensions in Wales are around £1,660–£2,390 per m² of new floor space, including VAT. For a typical project with 4 m × 3.5 m of new first-floor space (14 m²), that's roughly £23,000–£33,500. Steelwork for wide openings is the item most likely to move the figure; we'll know once the engineer has designed it.

Spec	Per m²	4 m × 3.5 m of new first-floor space (14 m²)
Essential	£1,520–£2,200 per m²	£21,500–£31,000
Standard	£1,660–£2,390 per m²	£23,000–£33,500
Premium	£1,990–£2,870 per m²	£28,000–£40,000

Planning and building regulations in Caernarfon

In Wales, a first floor over a rear extension can be permitted development if it goes no more than 3 m beyond the original rear wall and stays at least 10.5 m from the rear boundary, with the ground floor within 4 m. Over a side extension, the 10.5 m, 1 m set-back and 50% width tests apply. Otherwise a householder application costs £585.

Approval in Wales: Householder planning application: £585. Councils normally decide householder applications within 8 weeks.

Building regulations: Building regulations approval under the Welsh Approved Documents, which differ from England's in places (notably energy efficiency).

Design points for Caernarfon homes

Replacing the flat roof

The existing roof usually comes off and is replaced by a new first-floor structure. The room below is exposed for a short time, so we plan temporary weatherproofing and sequence the work to keep the kitchen or living room usable for as long as possible.

Tying into the house

The new floor and walls must line up with the existing first floor, often through a new opening in the rear wall above the old one. Floor levels, the position of upstairs windows and the existing roof all affect where the opening can go, so we survey both floors carefully.

How we'd run your project

Understand the brief
At your home in Caernarfon we agree what you need: bedroom count, bathroom, kitchen space, and how much garden you want to keep.
Choose the approval route
Some designs fit permitted development, most need a householder application. We decide which applies in Wales before drawing in detail.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

Questions about first-floor extensions in Caernarfon

Do I need planning permission for a first-floor extension in Caernarfon?

Caernarfon is in Wales, so Wales planning rules apply. It may be permitted development if the ground floor goes no more than 4 m and the first floor no more than 3 m beyond the original rear wall, with the first floor 10.5 m from the rear boundary. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

Which postcodes do you cover around Caernarfon?

We cover Caernarfon (LL54, LL55 and LL61) and nearby places including Menai Bridge, Llangefni and Bangor (Gwynedd and Anglesey), plus the rest of Gwynedd and Anglesey. The first site visit is free.

How much does a first-floor extension cost in Caernarfon?

Our guide for Wales, which covers Caernarfon, is £1,660–£2,390 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £23,000–£33,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

Can I build on top of my existing single-storey extension?

Often yes, but only after the structure has been checked. Foundations, walls and lintels built for one storey may not carry two. We dig trial holes, look for the original building control approval and ask the structural engineer to confirm what can stay, what needs strengthening and what must be rebuilt.

What happens to the room below while the first floor is built?

The old roof is removed, so the room below is exposed for a short period. We fit temporary weather protection, plan the work so the roof comes off only when the new structure is ready, and agree with you which rooms will be out of use and for roughly how long.

Nearby

Nearby towns we cover for first-floor extensions:

Other extensions in Caernarfon

All two-storey extension services in Caernarfon · First-floor extensions across Gwynedd and Anglesey

Tell us about your house in Caernarfon and we'll call you back to arrange a free, no-obligation visit.