Tembok Carpenter & Building Services
House extensions across Kent
Single-storey, two-storey and wrap-around extensions — designed, approved and built by one accountable team.
What decides the cost and the timescale
Two things set the shape of an extension project before design begins: your planning route, and the ground. Many single storey rear extensions still fall within permitted development, but conservation areas, listed buildings, Article 4 directions, flats and estate planning conditions all remove that option, and Kent has plenty of each. Establishing the route first avoids designing something that cannot be built.
The ground matters just as much. Much of the county sits on Weald clay, which shrinks and swells with moisture, so foundations are frequently deeper than people expect, especially near mature trees. Ground works and drainage are the two lines in a quote most likely to move, which is why they should be surveyed rather than assumed.
- Design and survey, with a brief that states what the room is actually for
- Planning route confirmed: lawful development certificate or a householder application
- Structural calculations, then the building regulations application
- Party wall notices where a shared wall or a neighbour's foundation zone is affected
- Build sequence: foundations and drainage, shell and roof to weathertight, then first fix, plaster and second fix
- Completion certificate from building control, which is the document a buyer will ask for
What's Included
House Extensions — The Tembok Way
The right extension starts with how the new space joins the existing house, then the type and materials follow.
- Architectural drawings
- Planning & building control
- Steel beam installation
- Glazing & roofing
Choosing the shape of the extension
Single storey, two storey, side return, wraparound, orangery and timber or oak frame all solve different problems. A narrow side passage suits a side return; a corner plot might suit a wraparound.
Each type has its own page with more detail, linked below.
What is under the ground near the house
Foundations depend on the soil, nearby trees and existing drains. A drain running where the new wall goes may need diverting or bridging, which building control usually needs to approve.
- Trial holes to check ground conditions
- Drain surveys before foundations are set out
- Tree positions that affect foundation depth
Matching the house or making a contrast
Some extensions use matching brick and tile so they look original; others use cladding or glass for a clear contrast. Local planning policy and the house's character often guide this choice.
Neighbours, and breaking through to the new room
Work on or near a shared boundary can need party wall notices. The last structural step is opening the existing back wall into the extension, usually with a steel beam, once the new room is weathertight.
Light, heat and how the new room is used
Rooflights, bifold or sliding doors and high-level windows decide how bright the new room feels, but glazing also affects heat loss and building regulations calculations. Underfloor heating suits large open spaces; radiators may work better in a smaller addition. Thinking about the furniture layout early helps place doors, sockets and lighting so the room works on day one.
Where the extension joins an existing kitchen or living room, the older room can become darker, so a rooflight near the old back wall is often worth considering.
The main levers on an extension price
Ground, structure and specification decide the cost.
- Extension type, footprint and number of storeys
- Foundation depth and ground conditions
- Drain diversions or build-overs
- Steel beams to open the existing house
- Roof type, rooflights and glazing
- External materials and internal finish level
Guides
Useful House Extensions guides
- Kitchen extensions: layouts, structure and planning
- Ground floor extensions: options, planning and what to decide first
- Two storey and multi-storey extensions: planning and build
- Side return extensions explained
- Householder planning applications explained
- L-shaped extensions: is one right for your house?
- Wrap around extensions: what they are and when they make sense
- Flat roof extensions: build-ups, lanterns and avoiding leaks
- Can you lay EPDM over felt? Overlay versus strip and replace
- Property extensions: types, planning and what to expect
Across Kent
House extensions in Kent
House extensions are the bulk of our larger Kent projects — single-storey rear extensions, two-storey side returns, wrap-arounds and orangery-style glazed additions. We run design-and-build end-to-end: architectural drawings, planning application, structural calcs, building regs and the full build under one written contract.
Most Kent rear extensions sit within permitted development at up to 4m deep for a detached home and 3m for a semi/terrace. Larger schemes go through the neighbour-consultation route or full planning — both routes we submit and follow up on your behalf.
Typical Kent extension build is 14–18 weeks for a 25–35m² rear single-storey, including weather-tight shell at week 6–7 and break-through to the existing kitchen at week 10–11.
Areas covered
House Extensions across Kent & East Sussex
Local area page: builders in Sevenoaks, Tunbridge Wells and Tonbridge.
FAQs
House Extensions — frequently asked
How long does a single-storey extension take to build?
From breaking ground to handover is typically 14–18 weeks for a 25–35m² rear extension, including weather-tight shell at week 6–7 and fit-out from week 10.
Will I need to move out during the extension build?
On most rear extensions you can stay in the house. Phasing the kitchen break-through is where it gets disruptive — we usually move that to week 8–10 once the new envelope is dry.
Can you take on the architect role and the build?
Yes — we run a design-and-build service end-to-end, which avoids the gap where most projects lose money: drawings that aren't buildable, or builders quoting against incomplete specs.
Do I need building regulations approval as well as planning?
Almost always. Planning approves the principle; building regs approve the construction detail. We submit the building regs application in parallel with planning to save 6–8 weeks.
What's the largest extension you can build under permitted development?
Up to 4m deep for a detached house and 3m for a semi/terrace (8m and 6m under the larger neighbour-consultation route until 2025). We confirm yours at survey.
Can you match existing brick, tile or render?
We source matching brick from Imperial Bricks, Kingscourt and reclamation yards; clay peg tiles from Aldershaw or Tudor; and tint render to match weathered originals.
What is the difference between permitted development and planning permission?
Permitted development is a set of national rights that let you build within fixed size and position limits without a full application. Planning permission is a case by case decision by the council. Conservation areas, listed buildings, flats and some newer estates have reduced or removed permitted development rights.
Can I extend a listed building or a house in a conservation area?
Yes, with consent. Listed buildings need listed building consent as well as planning permission, and conservation areas expect extensions to be subordinate in scale and sympathetic in materials. The design argument matters as much as the drawings.
Do I need party wall notices for an extension?
If you are building on or near a shared boundary, or digging foundations close to a neighbour's, notices may be needed. We check this early.
Can an extension be built over a drain?
Often, with building control approval and sometimes the water company's agreement. Drains can also be diverted. We check this early.
Should an extension match the house?
It can match or contrast. Planning policy and the house's character usually guide the decision.
When is the wall to the existing house opened?
Usually near the end of the structural work, once the extension is weathertight, so the house stays protected.
Let's Talk
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