What Should I Know Before Starting a House Extension? Your Pre-Consultation Checklist
Nobody expects you to have every detail sorted before you pick up the phone. Most people who get in touch with Kirkwood have a general sense of what they want, a loose budget, and a fair few questions still unanswered, and that’s a perfectly good place to be.
Even so, there are a handful of things worth knowing beforehand, and a few worth having ready before that first chat. The checklist below covers both. Go through it whenever suits you; there’s no rush. By the end, you’ll be in good shape for a genuinely useful first conversation.
Feel ready now?
What You Need to Know (Not What You Need to Do Yet)
Before diving into the checklist, three bits of context are worth understanding first; they’ll help everything else make sense.
Getting the order right matters more than getting the budget exactly right. Almost every problem on an extension project traces back to doing things in the wrong sequence. The order that works is: design and build service first, planning second, structural engineering and building regulations third, builder last. This holds true whether you’re extending a semi in Billericay or a terrace in Chelmsford. Go to a builder first, and you’ll get an estimate that shifts. Start with drawings instead, and you’ll get a number you can actually rely on.
Three separate professionals need to be involved, not just one. Design drawings, structural engineering, and building regulations paperwork all have to be in place before a builder can pick up a tool. Plenty of homeowners only know about the design stage going in. Knowing all three exist from the outset means no nasty surprises on cost later.
You don’t need a fully worked-out idea before the first call. A general direction is plenty. Something like ‘we want to open up the back of the house and get a bigger kitchen’ is a perfectly usable starting brief. The design team helps shape it from there.
With that in mind, here’s the checklist.
Your Pre-Consultation Checklist — Before You Start a House Extension in Essex
Everything below is worth a moment’s thought before your first conversation with an extension company in Essex, whether you’re in Brentwood, Wickford, or anywhere in between. The right-hand column shows just how little most of these actually ask of you before that call.
What to do/know | Why it matters | What you actually need | |
☐ | Understand your planning route. | Know if your project needs planning permission, qualifies as Permitted Development, or needs a Lawful Development Certificate. | You do not need to work this out yourself — a good design company will assess this for you as part of the first call. |
☐ | Know your rough budget — including professional fees | Professional fees (design, structural engineering, building regulations) add 10–15% on top of the build cost. Budget for this from the start | Many homeowners budget only for the build and are surprised by professional fees later |
☐ | Know your extension type in general terms. | Rear, side, loft, double storey, garage conversion — you do not need a firm decision, just a direction. | You do not need detailed plans. A rough idea of the space you want is enough for the first conversation. |
☐ | Check your property’s planning history. | Previous extensions, planning conditions, and conservation area status all affect what you can build. | Search your address on your local council’s planning portal. Kirkwood checks this before any first call. |
☐ | Speak to a design company before a builder. | Design should come before builder engagement. A builder cannot give you a fixed price without drawings. | Getting a builder quote first is the most common mistake on extension projects. |
☐ | Understand the three professional stages. | Architectural design → structural engineering → building regulations. All three are needed before building starts. | Many homeowners only know about stage 1. Stages 2 and 3 are equally important and have separate fees |
☐ | Know your neighbours’ situation. | If you share a wall (terrace or semi), you will need a Party Wall Agreement before work starts. | Party Wall Agreements are required — they are not optional and cannot be served after work begins. |
☐ | Have an idea of your timeline | Extensions in Essex typically take 6 to 12 months from first call to completion. Is your timeline realistic? | Rushing the design and planning stage is the most common cause of delays later on. |
☐ | Book a free Discovery Call. | A 30–45 minute call with Kirkwood will tell you your planning position, realistic costs, and next steps. | The call is free and commits you to nothing — it is the most efficient first step for any Essex homeowner. |
Getting through this list, or even just giving most of it a bit of thought, puts you in a good position for a genuinely useful first conversation. You’re not expected to have all the answers yet. That’s exactly what the first call is for.
Book a free discovery call
Kirkwood’s Discovery Call covers everything on this checklist — your planning position, realistic costs, the right order to do things, and exactly what the process looks like for your specific home in Essex. 30 to 45 minutes. Free. No obligation.
What to Bring to the First Call
A few things genuinely help going into that first conversation, and quite a lot of things don’t matter yet at all.
- A rough sense of what you’re hoping to achieve; a sentence or two does the job
- A ballpark budget, even a wide one (something like ‘somewhere between £50,000 and £80,000’ is plenty useful)
- A few photos of the property if you happen to have them, particularly of the rear and side where the extension might go
- Anything you already know about past planning applications on the property
What you don’t need yet:
- Detailed drawings or measurements; Kirkwood carries out a full measured survey if you decide to proceed
- A finished brief; the design takes shape as the process goes on
- Any planning expertise of your own, that’s Kirkwood’s job
- A builder already lined up, that conversation happens once the design is settled, not before
What Happens After You Make Contact
Once you reach out, here’s roughly how things unfold, without any pressure attached.
- Kirkwood looks into your property before the call itself, planning history, what’s nearby, and local planning rules, so the conversation is useful from the start rather than starting from zero.
- The Discovery Call covers what you’re hoping to achieve, your planning position, realistic costs from design through to build, and what the process looks like specifically for your project.
- If you decide to go ahead, a measured survey happens next, and the design work begins. If you’re not quite ready, that’s fine too; plenty of people come back to Kirkwood months down the line with no issue.
The call itself is free and asks nothing of you in return. But by the time it’s over, you’ll know where you stand on planning, roughly what to budget, and exactly what your project actually involves.
Which is, in the end, exactly what the checklist above has been getting you ready for.
Frequently Asked Questions
What should I know before starting a house extension?
Before starting, it helps to understand your planning route, whether that’s permitted development or full planning permission, and to have a rough budget in mind that accounts for professional fees, not just the build. Know that professionals should be engaged before a builder, and that a Party Wall Agreement will be needed if you share a wall with a neighbour. You don’t need everything finalised; a general direction and a budget range are enough to get started.
What do I need to prepare before contacting an extension company?
A rough idea of what you want to achieve, an approximate budget range, and photos of your property if you have them. Drawings, measurements, planning knowledge, and a builder lined up aren’t needed at this stage; a good extension company will work through all of that with you on the first call.
Should I speak to a designer or a builder first?
A designer, or a design and build company, first. Without a complete set of drawings and a technical package, builders can only give you an estimate rather than a fixed price. Speaking to a builder too early means dealing in guesswork. The design should always come first.
Do I need planning permission before I can start an extension?
Not always. A lot of house extensions in Essex qualify as Permitted Development, meaning no full planning application is required. A Lawful Development Certificate is still worth getting even so, since it confirms the work is lawful. Kirkwood assesses your planning position during the free Discovery Call, before any drawings are drawn up.
How much should I budget for a house extension in Essex?
A single-storey rear extension in Essex typically costs from around £35,000 to £65,000 in 2026, covering design, planning, structural engineering, and the build. Professional fees usually add another 10 to 15 per cent on top of the build cost, so it’s worth budgeting for these from the outset rather than being caught out later.
How long does a house extension take from start to finish?
From first contact to completion, a standard single-storey extension in Essex takes around 6 to 9 months. That covers design (4 to 6 weeks), planning or permitted development approval (5 to 10 weeks), structural engineering and building regulations running alongside each other (5 to 8 weeks), and the build itself (10 to 14 weeks).
What is the right order to start a house extension project?
Design company first, planning second, structural engineering and building regulations third, and a builder last. Working in this order means that by the time a builder prices the job, they’re working from a complete and accurate brief, which is what makes the cost fixed rather than a rough estimate.
What is a Lawful Development Certificate and do I need one?
It’s a formal document from your local council confirming an extension is lawful under Permitted Development. Even where planning permission isn’t required, it’s worth having; solicitors and buyers often ask for it when a property is sold. Kirkwood applies for this on behalf of clients as part of its service.
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