Short answers to the questions people ask most about buying, renovating and extending a home in England and Wales, from viewings and planning permission to builders, payments and snagging. Each answer links to the chapter of Your House, Your Project that covers it in full.
General information, not advice on your project. The answers explain how each rule works as at October 2026. Rates, fees and thresholds change, so check the current figure at the source on the
references page, and take professional advice where your project needs it.
Getting started
Where do I start with a house renovation or extension?
Start with four questions, in this order: what will it really cost, am I allowed to do it, who is responsible for what, and what happens if it goes wrong. The size of the project changes the answers, not the questions.
Then decide what you are actually trying to fix. Most home projects sit at one of three scales: refitting a room where it is, knocking two rooms together, or extending. Each step up brings in more people, more permissions and more time, and jumping up a scale halfway through costs more than choosing the right one at the start. Before anything is designed, find out what the site allows: the planning history, the sewer map, the distance to the boundaries and any wildlife.
In the book Chapter 1: Three Projects, Three Scales →
Do I need an architect for an extension?
Not always. Design runs on a scale. A like-for-like kitchen needs no drawings. A builder’s own drawings can work for a small extension or a change of layout, with an engineer doing any structural calculations. An architectural technologist (chartered members use the letters MCIAT) is often the right choice for extensions and loft conversions. A registered architect earns the fee when the design itself is the hard part: a complex layout, a listed building, a conservation area or a contested planning application.
Two checks apply whoever you choose. “Architect” is a protected title, so check the Architects Register; similar titles such as “architectural designer” are not protected. And ask who pays if the design is wrong, which usually means professional indemnity insurance. Where the builder also designs the work, an independent design review is worth its modest fee.
In the book Chapter 2: Building Your Professional Team →
Before you offer
What should I look for when viewing a house I want to renovate?
The things that decide the cost are usually in plain sight. Look at the age of the services: the consumer unit, the boiler’s plate and service sticker, and labels on the windows. Note the things that are expensive to change: where the drains run, which walls line up from floor to floor, the depth from the back wall to the rear boundary, and where a skip and scaffolding would go.
Watch for signs worth asking about: fresh paint on one wall, a patch of new plaster, a dehumidifier, diagonal cracks from the corners of windows and doors, and textured ceilings in a house built before 2000. Ask the agent how long it has been on the market, why the owners are selling, and what work has been done with paperwork. View twice if you are serious, once in the rain if you can.
In the book Chapter 3: What to Look for at a Viewing →
How can I tell if I can extend a house before I buy it?
Test the change you have in mind before you offer. Will it need planning permission, or is it permitted development, and has a condition on an old permission removed those rights? Is the house listed or in a conservation area? Is it leasehold? Are any trees protected? Is there a public sewer under the footprint? Can the drainage cope with more bedrooms? Could bats, newts or nesting birds set the timetable? Is the plot deep enough, and can machinery get in?
Most of these can be checked in an afternoon from the council’s planning register, the listing records, the sewer map and a tape measure. Then ask whether the street will support the finished value. If you cannot answer half the questions yet, that tells you what to find out first.
In the book Chapter 3: What to Look for at a Viewing →
Will an extension add value to my house?
It depends on the street more than the extension. Every street has a ceiling price, the most anything there will sell for however much is spent on it. Find it from sold prices, not asking prices, and ask what the best-selling houses had. If your estimate of the finished value is above the best price the street has achieved, the estimate is far more likely to be wrong than the street is to set a new record.
Buyers usually pay more for an extra bedroom (especially two to three, or three to four), usable space, light, off-street parking, a kitchen that photographs well, storage and an easy garden. They usually pay less than it costs for a high-specification bathroom in a modest house, expensive fittings and home automation. Spend on those for your own enjoyment, knowing it is not for value.
In the book Chapter 4: Value and Cost: Working Out the Numbers →
How do I estimate renovation costs before I buy?
There are three ways, and they are not equally reliable. A rate per square metre is quick but the least reliable: use it to compare houses, never as the basis of an offer. Your own priced list of the work is slower but far better. A builder’s walk-round estimate catches things you will not.
At offer stage, combine the last two. Ask two builders to walk round with you, making clear it is not a request for a quote, and ask what they would be worried about as well as what it would cost. Use the higher figure, not the average. Then add the costs a builder’s figure leaves out: fees, permissions, surveys, site problems, finance and a contingency.
In the book Chapter 4: Value and Cost: Working Out the Numbers →
What renovation costs do people forget?
A first estimate is usually right about the building work and silent about everything around it. The usual gaps are: purchase tax at the higher rates if you will own more than one home; specialist surveys such as asbestos, drainage, structural and utility surveys; planning fees and the reports a council can ask for; party wall surveyors; a build over agreement with the water company; highway licences for a skip or scaffolding; and building control fees.
Then the site and the time: private drainage, wildlife surveys, asbestos removal, the cost of running the site (scaffolding, welfare and waste, known as preliminaries), the final clean, finance, insurance, council tax on an empty home, and rent if you move out. Put a figure against every line that applies, and mark each as evidenced or assumed.
In the book Chapter 5: The Costs People Forget →
How much contingency should I allow for a renovation?
As a working allowance, set it against the cost of the building work: about 10% for straightforward work on a house in known condition, about 15% for a typical renovation where some of the work is still behind surfaces, and 20% or more for older or neglected houses, structural work, drainage or anything you could not inspect properly. Very few renovations are fully known, so 15% is a sensible default.
Keep it as a separate line and record every time money comes out of it. Then test the whole budget: add 15% to the building work, take 10% off the finished value, and let the programme run half as long again. If the plan still works with all three together, it can absorb the overruns most projects meet.
In the book Chapter 5: The Costs People Forget →
Tax and money
Is Land Transaction Tax in Wales the same as Stamp Duty?
No. In England the tax on buying a home is Stamp Duty Land Tax; in Wales it is Land Transaction Tax, collected by the Welsh Revenue Authority. They are separate taxes with their own rates, bands and rules, so a Welsh purchase follows Welsh rules only.
Both are charged in bands, like income tax, so people often overestimate the bill by applying the top rate to the whole price. Both charge higher rates if you will own more than one home at the end of the day you buy, and those can add a great deal. Use the official calculator before you offer. If you pay the higher rates because you bought before selling your old home, you can usually claim them back once it sells within the time limit.
In the book Chapter 6: Tax, Time and Money Back →
Can I get reduced VAT on building work?
Most work on an existing home, including extensions and general renovation, is charged at the standard rate. A reduced rate applies in specific cases: renovating a home that has been empty for the two years before work starts, changing the number of homes in a building, or converting a building that was not a home into one. The conditions are in HMRC’s VAT Notice 708.
Two points decide whether you benefit. The builder charges the reduced rate on the invoice; you do not pay the full rate and claim the difference back. And materials you buy yourself carry the full rate, so on a qualifying job it usually pays for a VAT-registered builder to supply them. Gather evidence that the house was empty before work starts.
In the book Chapter 6: Tax, Time and Money Back →
Are there grants for home improvements in England and Wales?
Some, and few people ask. The Boiler Upgrade Scheme helps towards a heat pump in England and Wales and is not means-tested. In Wales, the Nest scheme funds energy improvements for households that meet income, benefit or health criteria. Some councils offer grants or loans to bring long-term empty homes back into use, repairs to historic buildings can attract heritage funding, and Disabled Facilities Grants help adapt a home.
Scheme names and amounts change often, so check GOV.UK or GOV.WALES before choosing a heating system, and never put grant money in your main budget. Be wary of firms that say you qualify before they have assessed your home: some sell leads rather than advice.
In the book Chapter 6: Tax, Time and Money Back →
Permission
Do I need planning permission for an extension?
There are three routes. Permitted development grants permission nationally for some work, as long as it stays within set limits and conditions. Prior approval is a lighter process for some permitted work, including larger single-storey rear extensions in England, where neighbours can comment. Full planning permission is a formal application judged against local policy.
England and Wales have separate rules, with different classes and limits, so guidance for one does not apply to the other. Check the published limits against your actual drawings, not a summary: a project can break them by a few hundred millimetres. Flats and maisonettes have no householder permitted development rights at all. If you rely on permitted development, a lawful development certificate proves it when you sell.
In the book Chapter 7: Planning and Permitted Development →
What can remove permitted development rights?
Four things: the house being listed; the house being in a conservation area, National Park or other protected area; an Article 4 direction, where the council has removed certain rights across an area; and a condition on the original planning permission for the house. New-build estates often have their rights removed by condition, which surprises people who assume a modern house is the easy case.
The council’s planning register is public. Reading the planning history of a house takes about twenty minutes and is one of the most valuable checks a buyer can make, because a condition from twenty years ago can turn a permitted extension into a full application.
In the book Chapter 7: Planning and Permitted Development →
What if a previous owner built an extension without planning permission?
The council can take enforcement action for a set period, after which the work becomes immune. The periods now differ. In England, building work substantially finished on or after 25 April 2024 can face enforcement for ten years; work finished before that date keeps the old four-year limit. In Wales, building work still has a four-year limit.
The limit is not automatic: the owner has to prove the period has passed, usually with a certificate of lawfulness backed by continuous evidence. Before exchange, find out what was built and when. If the period has passed, ask for the certificate as a condition of the sale; if not, reflect the risk in your offer or reconsider. Take advice from a planning consultant and your solicitor.
In the book Chapter 7: Planning and Permitted Development →
Do I need listed building consent?
For any work that would affect the building’s character as a building of special interest, inside or out: windows, roofs, render and doors, but also staircases, plasterwork, fireplaces, panelling and partitions. Even painting a wall that has never been painted can need consent. The grade shows how significant the building is, not how much of it is protected. Structures in the grounds can be listed with the house.
Consent is separate from planning permission and building regulations. Work without it is a criminal offence for both owner and builder, not knowing is no defence, and there is no time limit: a new owner can be required to put old unauthorised work right. In Wales the law is now the Historic Environment (Wales) Act 2023. Speak to the council’s conservation officer before any work.
In the book Chapter 8: Listed Buildings and Conservation Areas →
What can I change if my house is in a conservation area?
The rules are less severe than for a listed building but tighter than ordinary planning. Demolishing an unlisted building, or most of a boundary wall, can need permission. Some permitted development rights are restricted, and an Article 4 direction can remove more, often covering windows, doors, roofs and front walls. Every tree is protected: you must notify the council before working on one.
Design is judged against the conservation area appraisal. Changes often refused include front dormers, replacing timber sashes with uPVC, removing chimneys, rendering brick or stone, and taking down front walls for parking. Budget for specialist materials and longer approvals.
In the book Chapter 8: Listed Buildings and Conservation Areas →
Do I need the freeholder’s permission to renovate a flat?
Very likely, for anything structural and possibly for much less. The lease decides what you own (the demise) and what you may alter. Leases control alterations through a covenant that is fully qualified, qualified or absolute, and which one yours contains makes all the difference. Minor work may need only a letter of consent; anything structural usually needs a formal licence to alter, and you normally pay the freeholder’s fees.
Work without consent is a breach of the lease, and it usually surfaces when you sell. Flats also have no householder permitted development rights, and the party wall rules can apply to floors and ceilings. Ask a solicitor to confirm what you own and what needs consent before you commission drawings.
In the book Chapter 9: Leasehold and Flats →
Surveys and the ground
Should I get a Level 2 or Level 3 survey for a house I want to extend?
For a house you plan to renovate or extend, a RICS Level 3 survey is usually the right starting point, and for anything built before the Second World War or visibly neglected, choose it. It describes how the building is put together, the likely causes of defects and the repair options, not just a condition rating. A mortgage valuation is for the lender and says nothing useful about condition.
Tell the surveyor what you plan to do before the inspection. Read the “not inspected” entries first, treat “further investigation” as an instruction, and get prices for every condition rating 3 item before you renegotiate. The main survey also tells you which specialist surveys to commission next.
In the book Chapter 10: Surveys, Reports and Searches →
What is a build over agreement and do I need one?
It is permission from the water company to build over or close to a public sewer, separate from both planning permission and building regulations. What triggers it is where the pipe runs, not the size of the project: as a general rule, building over a public sewer, within three metres of one, or within one metre of a public lateral drain needs agreement. Many drains owners assumed were theirs became the water company’s in October 2011. Check the exact requirements with your own water company.
Manholes cannot be built over, the company will usually want a camera survey first, and the pipe cannot change beneath the new building. Get the sewer map early and let the sewer shape the design, rather than designing first. Building without agreement leaves the company free to remove whatever blocks its access.
In the book Chapter 11: Drainage, Flooding and the Ground →
How do I check flood risk before buying a house?
Check every property, not just those near a river: the most common cause of flooding is rain. In England use the Environment Agency’s long-term flood risk service; in Wales, Natural Resources Wales’s flood map. Look at three separate risks: rivers and the sea, surface water from heavy rain, and groundwater, which matters most for basements and lowered floors.
If any of them shows, get an insurance quote before exchange, because the premium is the quickest guide to how the market sees the risk. Flood Re helps with cover for many homes at risk, but not those built on or after 1 January 2009. Ask the seller directly whether the house has flooded.
In the book Chapter 11: Drainage, Flooding and the Ground →
What should I check if the house has a septic tank?
Find out what the system really is, where it discharges, when it was last emptied and whether there is any history of pollution. In England, the Environment Agency’s general binding rules do not allow a septic tank to discharge directly to a stream, ditch or river. In Wales, septic tanks and small treatment plants must be registered with Natural Resources Wales, and untreated discharge to a watercourse is not acceptable either.
If the tank discharges to a stream or ditch, budget for replacing it as a certainty. Adding bedrooms adds load, so a system that copes now may not cope later. If a new drainage field is needed, a percolation test before exchange shows whether the ground will take it.
In the book Chapter 11: Drainage, Flooding and the Ground →
Can bats or nesting birds delay building work?
Yes, and money cannot speed them up. A preliminary bat roost assessment can be done at any time of year, so commission it early. If it finds potential roosts, emergence surveys can only be done in the active season, broadly May to August, and work affecting a roost needs a licence. A survey in September can mean waiting until the following May.
All wild birds are protected while nesting, broadly March to August, which limits clearing vegetation, roof work and demolition. On coastal roofs, gulls are protected too. Plan the timetable backwards from the survey calendar, not forwards from your preferred start date.
In the book Chapter 12: Ecology and the Calendar →
Specifying and choosing a builder
How do I write a specification for builders?
A specification is a written description of the work: what is to be done, to what standard and with which materials. For each part of the work record the grade, the notes that remove ambiguity, the allowance and the product. Write each item as a list of attributes rather than a sentence: “grey kitchen, mid range” produces three quotes for three kitchens.
The test for every line: if this were done badly, could I tell by looking once it is finished? If not, write the detail, such as the number of coats of paint or how a worktop’s cut edges are sealed. Write it before you ask for prices, give it a version number, and send any change to every builder.
In the book Chapter 13: Write the Specification First →
When do I need building regulations approval?
Building regulations apply if the work affects the structure; installs or alters heating, hot water, drainage or electrics; replaces a window, external door or rooflight; renovates a wall, floor or roof between heated rooms and the outside; changes the ventilation; or changes the use of part of the building. Like-for-like repair and cosmetic work usually fall outside them.
There are two equally valid ways to get work signed off: a registered installer under a competent person scheme certifies it, or you apply to building control with a building notice or full plans. Either way, keep the certificate, because a buyer’s solicitor will ask for it. Planning permission and building regulations are separate approvals.
In the book Chapter 14: Building Regulations: What Your Work Triggers →
How many quotes should I get from builders?
Three, all against the same written specification, sent on the same day with the same deadline. Three is enough to see the range and spot one that is out of line; with two you cannot tell which is the odd one.
When one quote is much cheaper, find what it assumed less of: materials, coats of paint, making good, scaffolding or waste. Check whether it is a fixed quote or an estimate, count the provisional sums and ask what each is based on, and ask how long the price holds.
In the book Chapter 17: Getting Quotes and Choosing a Builder →
How do I check a builder before hiring them?
See the public liability insurance certificate, not just a mention of it. Check trade registrations (Gas Safe, the electrical schemes, FENSA) on the scheme’s own register. If it is a limited company, check Companies House, and search the register of county court judgments. Call two references from recent similar jobs, see finished work in person if you can, and get a written quote against your specification.
Walk away if they knocked on your door, will not put anything in writing, want a large payment up front or offer a cash discount, press for a quick decision, cannot show insurance or references, or say permissions are not needed for structural, drainage or electrical work.
In the book Chapter 17: Getting Quotes and Choosing a Builder →
Should I tell a builder my budget?
Usually yes, as a realistic range, with the specification fixed. The specification is your protection, not secrecy. A builder who knows the budget can say early that the job cannot be done for the money, or suggest alternatives that meet it, which saves everyone time.
What never helps is taking one builder’s price to another and asking them to beat it. It turns pricing into an auction, tells every builder what kind of client you are, and builders talk to each other. If a quote is higher than expected, ask what is driving the cost and whether a change to the specification would bring it down.
In the book Chapter 15: How You Start Is How It Runs →
What should a written agreement with a builder include?
Thirteen things: who and where; the work, by referring to your specification; the price and any provisional sums; payments tied to completed stages; retention, the defects period and warranties; start and finish dates; how changes are agreed; materials and standards; subcontractors and waste; insurance; who pays if site conditions differ from what was assumed; how either side can end the agreement; and how disagreements are resolved. Sign it before work starts.
Match the document to the job. A signed one-page letter is far better than nothing for small work. For most home projects, the JCT Home Owner contract suits well and includes adjudication. A builder who flatly refuses to put the price, timetable and payment stages in writing has told you something important.
In the book Chapter 19: The Written Agreement →
Who is responsible for the builder’s waste?
You are, more than most people expect. Under the waste duty of care, a householder must make sure waste leaving the property goes only to a registered waste carrier. If waste traced to your address is dumped and you cannot show you took reasonable steps, the penalty can be yours, and paying someone in good faith does not count.
Check the carrier’s registration on the public register (the Environment Agency’s for England, Natural Resources Wales’s for Wales), write down the number, and keep the waste transfer notes. Agree in writing who removes waste, whether it is in the price, and whose waste the builder’s skip takes. A skip on the road or pavement also needs a council permit.
In the book Chapter 18: Agreeing the Small Stuff →
Running the job
Do I need a party wall agreement for an extension?
If the work is covered by the Party Wall etc. Act 1996, you must serve notice on the neighbour. It applies mainly to work to a shared wall, some new walls on or near the boundary, and digging close to a neighbour’s foundations. The notice periods are two months for work to a party wall and one month for excavation or a new boundary wall, and they run from the day the notice is served, so serving late simply moves your start date.
If the neighbour agrees in writing, the work can go ahead once the notice period ends. If not, surveyors are appointed to agree a party wall award, which can add a few months. In flats, the Act can apply to floors and ceilings too. Start the process four to five months before you want to begin.
In the book Chapter 20: Before Day One →
Should I move out during a renovation?
Moving out is usually the better choice if the work involves the only bathroom, the only kitchen for more than a short time, structural work overhead, a full rewire or asbestos removal. Staying is often possible but costs more than people expect: a job that takes eight weeks in an empty house can take twelve in an occupied one, and the quote rises for protection, cleaning and phasing.
Price both options before you appoint the builder. If you stay, agree a phasing plan, set house rules in writing, insist on proper dust partitions, and set up a temporary kitchen before the old one comes out.
In the book Chapter 21: Living Through It, and the Order of Work →
How should I pay a builder?
In stages, each tied to a specific piece of work being completed and checked, never to dates or time passed. The rule that matters: the total paid should never run ahead of the value of the work done. Keep a running total at every site visit, so that if the builder stopped tomorrow you would have paid for less than you have received.
A deposit is reasonable only for materials ordered specially for your job, backed by the supplier’s invoice. A general request for cash on account can be an early sign of a builder in difficulty. On larger jobs builders are sometimes paid monthly on a valuation, which needs someone qualified to value part-finished work.
In the book Chapter 22: Managing the Build →
What is retention on a building job?
Retention is a percentage held back from each payment, commonly about 5%, as security for putting right defects. A typical arrangement releases half at practical completion and the rest at the end of the defects period, once any reported defects have been fixed. Agree the percentage, the defects period and the release dates in writing before work starts.
On a modest job with a sole trader, retention can be out of proportion and cost you the builder you wanted; your legal rights apply either way. On larger jobs, or wherever defects would be hidden and expensive to reach, it is worth having.
In the book Chapter 22: Managing the Build →
Finishing
What is snagging, and how do I do it?
Snagging means inspecting the finished work and listing everything that is incomplete or not to the agreed standard. Do it before the final payment, in daylight, with the specification on paper, and allow two to three hours for a full refurbishment. Go room by room in a fixed order: floor, walls, ceiling, joinery, services, fittings.
Operate everything: every socket, tap, radiator, window, door, lock and fan, the shower at full temperature, and the boiler through heating and hot water cycles. Number and photograph each item as you list it, write it precisely, and agree a date for finishing in writing. Keep any disputed item separate rather than holding up the whole payment.
In the book Chapter 23: Snagging, Handover and Retention →
What certificates should I get when building work is finished?
Depending on the work: the building control completion certificate, the electrical installation or minor works certificate, Gas Safe notification and commissioning records, a FENSA or equivalent certificate for windows and doors, the structural engineer’s calculations, any party wall award, and product warranties with proof that they were registered. Add manuals, paint and tile references, and the positions of hidden pipes and cables.
Make the handover pack a condition of the final payment and say so in the agreement. These documents are difficult, sometimes impossible, to obtain later, and their absence usually comes to light when you sell or remortgage. Keep them in the project file for at least fifteen years.
In the book Chapter 23: Snagging, Handover and Retention →
What can I do if defects appear after the builder has left?
The end of the defects period is not the end of your rights. The defects period is whatever your contract says, usually months. Underneath it, your consumer rights require work done with reasonable care and skill; a claim for breach of contract can generally be brought within six years, or twelve if the contract was a deed; and the Building Safety Act 2022 extended the Defective Premises Act to fifteen years for claims arising since 28 June 2022, including work to existing homes by a business.
Report defects in writing with photographs as they appear, and inspect before the defects period ends. Keep the project file, because it is what makes a claim provable. Take advice if a builder disputes a defect.
In the book Chapter 16: Warranties, Defects and Avoiding Disputes →