1. Whether you are moving water
Moving a kitchen or a bathroom to a different part of the house is the single most expensive decision most homeowners make without realising it. Waste has to fall, and it has to fall to somewhere that already exists. If the new position means chasing a channel through a slab, or building a step to get the fall, the cost climbs quickly.
Keeping wet rooms roughly where they are, and moving fittings within them, is dramatically cheaper than relocating them. If your budget is tight, this is the first place to look.
2. Whether the wall is carrying anything
Removing a non-structural wall is a day's work. Removing a load-bearing one means propping, a correctly sized beam, padstones to spread the load, and often an engineer's design and certificate. The wall looks the same from your side either way.
This is why a builder who quotes an open-plan conversion without going into the roof space is guessing. Ask what the wall carries, and ask how they know.
3. The condition of what is hidden
Electrical wiring from the 1970s, galvanised plumbing on its last legs, a roof structure that has been modified, or a damp-proof course that failed years ago. None of these are visible on a walk-through, and all of them will need doing once you have opened the house up.
A proper pre-quote survey converts these from surprises into line items. That is uncomfortable at quote stage and far cheaper than discovering them at week nine.
4. Access to the site
A house with a driveway you can back a truck into is cheaper to renovate than a house at the end of a shared lane, and a first-floor job is more expensive than the same work at ground level. Everything has to be carried, and labour to carry it is real money.
Sectional-title and estate work adds a second layer: restricted hours, lift bookings and sign-in procedures can extend a programme by weeks without adding a single hour of building.
5. Your specification, not your square metres
Area matters far less than people expect. A modest bathroom finished in large-format porcelain with frameless glass and imported mixers can cost more than a large one finished sensibly. Specification is the lever you control most easily, and it is the one to pull when the number comes back higher than you hoped.
6. Whether the job needs approved plans
Anything that changes your footprint, your height or your roof line needs council approval, which means professional fees and a submission timeline before a brick is laid. Internal, like-for-like work usually does not.
The cost is not only the fees. It is also the holding time, which matters enormously if you are renting elsewhere or paying interest on an investment property.
7. How the job is run
Badly sequenced trades cost money in ways that never appear as a line item: a tiler standing idle, a second visit from an electrician, a stone template taken before the carcasses were level. Sequencing is invisible on a quote and it is a large part of what separates a good contractor from a cheap one.
And three things that matter less than you think
Paint colour, tile pattern and cupboard door style all feel like big decisions and are almost cost-neutral within a given quality band. Agonise over the layout instead. That is the decision you cannot undo.
- Colour choices: essentially free to change before you order
- Tile layout: a setting-out decision, not a cost decision
- Door and handle style: real differences exist, but they are small next to structure and services
Written by Edward Whelan, Spoednik Construction · Updated August 2026
