An extension is a promise that lives in stages: for weeks the money disappears into the ground, then walls arrive in days, then the roof makes it a building, and then the slow indoor work makes it a room. Households that know the rhythm enjoy the build; those that do not spend it anxious.
Mitchell & Andrew Building Services builds extensions across Truro, and this is the honest stage map with the decisions each stage locks in.
Groundworks: the invisible fortnight
The build starts downward: topsoil off, footings dug to the depth the ground and building control require, services located and protected, and concrete poured and cured. Nothing photogenic happens and everything structural does; footings sized and poured right are why the walls above never crack.
Drainage happens here too: new runs, connections and any moved gullies go in while the ground is open. The stage locks in the footprint exactly, so boundary questions and the final position against fences get settled before the dig, not after.
- Footings to approved depth, inspected before pour.
- Drainage and services routed while ground is open.
- Footprint and boundary positions locked here.
Walls up, steel in, roof on
From damp course upward the build accelerates: blockwork and any facing skin rise in courses, openings form, and where the extension opens into the existing house, steelwork goes in to carry the old wall above. Watching the steels land on their padstones is the single most structural moment of the project.
The roof follows fast, joists or trusses, membrane, battens and covering, and the milestone everyone waits for arrives: weathertight. From here rain stops mattering, and the indoor trades can start regardless of the sky. Mitchell & Andrew Building Services sequences hard for this milestone because everything after it is calmer.
- Blockwork rises fast once footings cure.
- Steels carry the house where new meets old.
- Weathertight is the calendar's hinge point.
First fix: the room gets its nervous system
Inside the shell, the unglamorous essentials thread through: electrics cabled to the socket and lighting plan, plumbing runs for radiators or underfloor heating, and any waste routes for a new kitchen or bathroom. Insulation fills the fabric to the specification the drawings promised, then boarding closes the walls.
This is the last cheap moment for changes: a socket moved now is pennies, the same socket after plastering is patching and paint. The layout walk-through with the builder before boarding is the most valuable half hour of the whole build.
The finishing stretch and the knock-through
Plastering, floors, second fix electrics and plumbing, decoration: the extension becomes a room in the final weeks. The knock-through into the existing house is usually held late deliberately, keeping the family sealed from dust until the new space is nearly ready to live in.
The finish line is paperwork as well as paint: building control sign-off, electrical certificates, and the drawings and warranties filed. An extension that ends with its documents in order is worth more on the day it is finished and every day it is ever sold.
Related pages
Questions customers ask
How long does a typical extension take?
The honest span runs from groundworks to decorated room with weathertight as the midpoint milestone. Ground conditions and the indoor specification move the ends; the stage order never changes.
When is the wall into the house knocked through?
Usually late, once the new space is weathertight and largely finished, so dust and weather stay out of the lived-in house. The steel that makes the opening safe goes in much earlier.
What decisions do I need to make early?
Footprint and boundary position before the dig, structural openings before steel is ordered, and the socket, lighting and radiator plan before boarding. Everything cosmetic can wait; those three cannot.
Down, up, dry, wired, finished: five stages, each locking its own decisions. Know the rhythm and the build feels like progress instead of mystery.
Mitchell & Andrew Building Services runs Truro extensions on exactly that rhythm. The contact page starts with your sketch.
