Everything You Should Ask a House Extension Specialist Before Signing
Ed Miller
You’re not hiring someone to “add a room.” You’re hiring someone to open up your house, mess with its structure, disrupt your life for months, and then (hopefully) stitch everything back together so it feels like it was always meant to be there.
That’s a big ask.
So before you sign anything, you need more than a friendly quote and a few glossy photos. You need answers that hold up when the weather turns, the inspector has a bad day, and the budget starts squeaking.
Hot take: if they won’t be painfully specific, don’t hire them.
Vague contractors are expensive contractors. I’ve seen “we’ll figure it out as we go” turn into blown schedules, rushed finishes, and that constant low-grade stress where every email feels like it might cost you £800. That’s why experienced, quality house extension specialists will usually be crystal clear about scope, timelines, and finishes from the start.
Specificity is a kind of insurance.
Ask questions until the scope feels almost boring.
Start with you: goals, constraints, and the stuff you’ll regret later
A good extension brief isn’t poetic. It’s measurable.
You want to get clear on:
– What the space must do (home office that closes off? open kitchen-diner for hosting? bedroom + shower for aging parents?)
– What you can’t change (budget ceiling, boundary limits, planning constraints, structural realities)
– What you’ll trade (size vs. finish quality, speed vs. disruption, bespoke vs. standard)
Now, here’s the thing: people obsess over square footage and forget how they’ll live through the day. Light switches. Storage. Where shoes land. The sightline from the sink. I’d rather see you spend an hour on lighting layers than another week arguing over tile color.
One-line reality check:
Your extension won’t feel “expensive” if the lighting is an afterthought.
Ask your specialist how they handle lighting design: circuits, dimming, task vs. ambient, and whether the plan includes switching positions that match real habits (not theoretical ones).
Costs: the quote is not the cost
Some specialists will hand you a number that sounds confident and smooth. That’s not a budget. That’s a sales tactic.
You want itemisation, assumptions, and a contingency that’s actually realistic.
A typical contingency allowance sits around 10, 15% for residential renovation/extension work (and yes, extensions are renovation work because you’re tying into an existing building with unknowns). If someone tells you “we won’t need contingency,” they’re either inexperienced or performing.
One specific reference: the UK Office for National Statistics reported material-price inflation spikes in construction during recent years, which is exactly why pricing assumptions and timelines matter. Source: ONS, Construction Output Price Indices / construction inflation reporting (UK).
(If you’re outside the UK, the principle still holds: supply chains change fast and “allowances” are where budgets go to die.)
Ask for this, in writing
Not a long list, just the right one:
– What’s fixed price vs. provisional sum vs. prime cost allowance?
– What exactly is included in “electrics,” “plumbing,” “kitchen,” “finishes”?
– What’s excluded that people assume is included? (Skip hire? decorating? flooring? external making good?)
– How do they price changes: margin, labour rate, lead time impact?
And don’t ignore ongoing cost. Better insulation, glazing, and airtightness can reduce energy bills, but only if the detailing is competent. Bad detailing costs you twice: once in install, then again every winter.
Site conditions & design fit (the unglamorous part that saves your skin)
Extensions fail quietly at the joins. The connection between old and new is where cracks appear, water creeps in, and floors end up annoyingly uneven.
So get practical early:
– Drainage and ground levels: where does water go now, and where will it go after?
– Soil and foundations: is a soil report needed, or do they rely on assumptions?
– Existing structure: are they opening load-bearing walls, and how are loads redirected?
– Movement: how are they detailing the junction between old and new so seasonal movement doesn’t wreck finishes?
Material compatibility matters more than people admit. Matching brick is one thing; matching weathering and thermal behaviour is another. A modern tight extension bolted onto a drafty old house can create condensation problems in weird places. It’s solvable, but only if someone is thinking.
Now, this won’t apply to everyone, but if your site has large trees, clay soil, or historic drainage quirks, demand they talk through risk like an adult. No hand-waving.
Permits, zoning, approvals: who owns the pain?
This part is boring right up until it delays your build by eight weeks.
You need a clear map of:
– what approvals are required,
– who submits what,
– what documents are needed (and when),
– what happens if the authority asks for revisions.
A quick way to expose weak planning
Ask: “Show me the approval path for a project like mine.”
If they can’t outline the stages, submission, review cycles, conditions, inspections, then you’re the one who’s about to learn the hard way.
Also: permit timing isn’t just admin. It shapes scheduling, subcontractor availability, and sometimes even cost (expiring quotes, seasonal constraints, remobilisation).
One small but telling question: Who attends inspections, your firm, the builder, or me?
You want the answer to be “we do” or at least “we handle it with you,” not “good luck.”
Timelines, trade-offs, and the myth of the “quick build”
Look, everyone wants it done fast. But fast builds are often just compressed decision-making. That’s when mistakes sneak in.
Ask for a schedule that includes:
– design freeze date(s)
– long-lead items (windows, steel, bespoke joinery, kitchen)
– inspection points
– buffer time for weather and approvals
If the timeline has no buffer, it’s fiction.
Here’s my opinionated rule: if they promise a finish date without explaining the assumptions, they’re guessing. And guessing is fine… as long as it’s labelled as guessing.
A good specialist will talk about sequencing, what can overlap, what must wait, and where the critical path lives.
One-line paragraph for emphasis:
A “nice” schedule isn’t a schedule. A buildable schedule is.
Contractor vetting: don’t just ask for references, ask for the right references
References are curated. You’re getting their happiest customers.
So ask for:
– one client from 12+ months ago (post-warranty reality)
– one project that had a problem (and what they did)
– one job similar to yours in age, structure, and complexity
Also request a portfolio, sure, but press for constraints: tight access, awkward neighbours, tricky rooflines, occupied homes. Pretty photos don’t prove competence. Context does.
And yes, confirm insurance. Public liability. Employer’s liability. Contract works. If they don’t know what you mean, pause the conversation.
Contract talk (a little dry, very necessary)
If it’s not in the contract, it’s not real.
You want clarity on:
Scope of work
Detailed enough that you can point to it when someone says “that wasn’t included.”
Change orders
Written approval only. Cost + time impact stated up front. No “we’ll sort it later.”
Payment schedule
Tie payments to completed milestones, not calendar dates. Dates get missed. Milestones get measured.
Warranties and defects
Define defect periods, response times, and what “making good” includes (repainting? redecorating? re-sealing?).
Dispute resolution
Spell out what happens before things get ugly: escalation steps, mediation, adjudication/arbitration (depending on your jurisdiction).
I’m going to be blunt: handshake deals are charming until your ceiling cracks and nobody remembers who agreed to what.
Communication: the quiet factor that makes projects livable
Ask how often you’ll get updates and in what format. Daily texts can be chaos. Monthly emails are too slow. Weekly written updates plus an on-site walk-through? That’s usually the sweet spot.
A few pointed questions I like:
– Who is my day-to-day contact?
– How fast do you respond to urgent issues?
– Where do decisions get documented, email, project app, shared folder?
– How do you handle variations so I’m not ambushed at the end?
If they don’t have a system, you become the system. That’s not what you’re paying for.
The pre-sign checklist (short, sharp, useful)
Before you commit, you should be able to answer “yes” to these:
– I have a written scope with inclusions/exclusions I understand.
– I’ve seen a realistic schedule with buffers and long-lead items flagged.
– Permits/approvals responsibilities are assigned, not assumed.
– The quote is itemised and identifies provisional sums/allowances.
– Change orders require written approval with cost and time impact.
– Payment is tied to milestones.
– Insurance is confirmed and current.
– References include at least one older project and one “problem” project.
– Communication cadence and documentation method are agreed.
If you can’t get there, slow down. A delay now is cheap. A delay mid-build is brutal.
And if the specialist is solid, they won’t pressure you to rush the decision, they’ll help you make a clean one.