Why Do Extension Quotes Vary So Much for the Same Job?

If you're thinking about adding more space to your home in Solihull—whether a sleek single-storey extension or a substantial two-storey addition—you've probably noticed something baffling: quotes from builders for the seemingly same job can vary wildly. One company might offer £25,000, another £42,000. Why such a gap? And how do you know you’re getting a fair deal?

After 12 years working MyBuilder vs local builder as a residential project manager and estimator, pricing extensions across the UK and especially navigating the Solihull market, I’m here to break down what really drives these fluctuating costs. We’ll also look at local economic data, planning considerations, and what you often forget to budget for. Plus, I’ll explain why “it depends” is the most frustrating answer when getting quotes, and how you can sanity-check prices yourself.

The Solihull Price Gap Is Fueling 'Extend-Not-Move' Decisions

Data from the Office for National Statistics (ONS) May 2026 local house price breakdowns show that the average price per square metre in Solihull has risen significantly over the past two years—pushing homeowners into a tricky dilemma. Moving costs—involving stamp duty, agent fees, legal costs, and the hassle factor—add tens of thousands to the price tag but yield no additional living space.

For example, moving might cost you an extra £30,000-50,000 in fees and taxes with no increase in home size, whereas extending could cost somewhat less per square metre and give you exactly the additional space you want. This is why many Solihull homeowners are choosing to extend rather than relocate, driving up demand—and inevitably, quotes—for local home extensions.

Moving Costs Add No Space — But Can Break the Bank

Stamp Duty Land Tax (SDLT): A tiered tax in England on property transactions that can easily run into thousands for homes over £250,000.
Agent Fees: Typically around 1-1.5% of the sale price, often several thousand pounds.
Legal Fees: Conveyancing and associated costs of moving home.
Stamp Duty Calculator Tools: Use HMRC’s tool to estimate your exact figures.

For Solihull families, extending becomes the smarter financial choice, if the budget and planning rules align—and that’s where getting clear, comparable quotes becomes vital.

Why Extension Quotes Assume Different Specs

Here’s the crux: two quotes that seem to be for the “same job” often aren’t quoting for the same specification at all. If quotes don’t explicitly state what’s included, you’re comparing apples and oranges—commonly the cause of massive price discrepancies.

Common Reasons Quotes Differ on Specs

Verbal Brief vs Drawings: A verbal description might miss critical details that only detailed architectural drawings capture, such as ceiling heights, window sizes, or material quality.
Materials and Finish: Quotes may assume different qualities of bricks, insulation levels, windows, and finishes. A basic quote might exclude plastering or flooring that another includes.
Structural Work vs Cosmetic: Are the quotes considering underpinning foundations (crucial for two-storey extensions) or just single-storey builds?
Internal Fixtures: Kitchens, bathrooms, electrics, and heating can be major cost drivers but are sometimes left out or quoted separately.

Always ask your builder or estimator to confirm exactly what’s included in their quote and specify this down to finishes and fixtures. Only then can you compare like for like.

Extension Costs by Size and Type: Single-Storey vs Two-Storey

Understanding the usual cost per square metre helps you sanity-check quotes before getting too excited about a low figure.

Extension Type Typical Cost per m² (Excluding VAT) Notes Single-Storey Extension (Basic) £1,600 - £2,100 Includes foundations, brickwork, roofing, flooring, and basic fixtures Single-Storey Extension (High Spec) £2,200 - £3,000+ Higher quality materials, architect-designed, premium finishes Two-Storey Extension (Basic) £1,900 - £2,500 More complex foundations, structural reinforcement essential Two-Storey Extension (High Spec) £2,700 - £4,000+ Often architect-designed with high-end finishes

Be mindful these costs exclude VAT, which is typically 20% on residential construction—some companies include VAT in their quotes, some don't. Always ask explicitly.

Planning Considerations: Don’t Forget the Rules

Before you even get close to cost comparison, make sure the extension you want is feasible under planning and permitted development rules. Ignoring these can cause delays, disputes, or unexpected extra costs that blow your budget.

Solihull Council provides very useful pre-application enquiry services. Submitting a pre-app lets you get early feedback on your plans — including if you need a full planning application or if your extension falls within permitted development rights.

Permitted Development usually covers smaller single-storey extensions with limits on height, footprint, and proximity to boundaries.
Planning Application is often required for larger or two-storey extensions or if the property is in a conservation area (which parts of Solihull have).

Check these restrictions upfront to avoid surprises. Permitted development rights can save you thousands in fees and waiting times, but if your extension doesn’t qualify, budget for planning application costs and possibly longer lead times.

Where To Check and Validate Quotes

Besides your builder’s explanation and detailed quote, there are some handy tools and review platforms to cross-check quotes and builder reputation.

Checkatrade: Find reputable contractors and see verified customer reviews—always ask to see previous projects similar to yours.
MyJobQuote: An online platform to get multiple quotes for your extension ensuring you get competitive offers.
Solicit Multiple Quotes: At least 3 written quotes, all based on the same drawings/specs—never accept a verbal-only quote.
ONS Local Cost Indicators: Use local data to confirm your quotes are within a fair market range.

What People Forget to Budget For

When homeowners see a tempting price for an extension, they often overlook these crawling costs which can add 10-20% extra to the total cost or cause significant delays:

Contingency Fund: Building work rarely goes 100% according to plan. A sensible contingency of 10-15% is recommended.
VAT: As mentioned, usually 20% on workmanship and materials unless you qualify for exemptions.
Planning Application Fees: For Solihull, fees vary depending on project size but expect £200-£500+.
Party Wall Agreements: If extending near neighbour boundaries, legal agreements and surveys may be needed.
Utilities Upgrades: New wiring, heating alterations, or water supply adjustments associated with the extension.
Interior Decoration and Furniture: Often a significant final cost after construction.

Final Takeaway: How to Spot a Fair Quote and Make Smart Decisions

In Solihull’s current market, extending is increasingly a sound financial move—but only if you approach the process carefully and armed with knowledge. Here’s my pragmatic checklist:

Get detailed drawings before seeking quotes, so every builder is pricing the exact same job.
Always request fully itemised, written quotes with VAT included/excluded clearly stated.
Check the quote’s scope: materials specs, finishes, testing, fees, and internal fit-out.
Use ONS local data and tools like Checkatrade and MyJobQuote for comparison.
Don’t forget planning checks with Solihull Council’s pre-application enquiry to avoid legal pitfalls.
Budget for unforeseen costs: contingency, planning fees, and VAT.
Remember the alternative cost of moving: stamp duty and fees add no space and could be more costly.

With these tips, your next extension quote won’t feel like a confusing black box. Instead, it’s a step closer to your dream home without breaking the bank—or your patience.

Written by a former project manager with 12 years estimating UK article 4 direction solihull extensions and helping homeowners understand budgets—because your investment deserves transparency and clarity.