What devalues a house is anything that hands a buyer a cost, a legal risk or fewer ways to fund and resell it: flood risk, Japanese knotweed, a defective construction type, a low EPC, work without planning permission, work without building regulations approval, a short lease, a restrictive covenant and missing information.
The positive version is what protects value: a house a buyer can insure, borrow against, let or live in, with paperwork that answers their solicitor before they ask.
In short
- Nine problems cut what buyers will pay, and each one below rests on an official source for how it works.
- A low EPC, missing sign-offs, a short lease and missing information can often be fixed or started before you sell.
- Flood risk and a defective construction type are hard to fix, so evidence and realistic pricing matter most.
- In Scotland the seller of most homes must give a buyer a Home Report within nine days of being asked.
If you would rather have the answer for your own house, get a free desktop valuation: send us the address and you will have an evidence-backed range within 24 hours. We introduce properties to investor buyers, and a desktop valuation is not a survey.
We found no official source that puts a percentage on any of these, so this guide sets out how each problem works and whether you can fix it. The fixability grades are our own judgement, not an official rating.
Flood risk and knotweed on the land
1. Flood risk
The Environment Agency’s long term flood risk service shows the risk for an area in England from rivers, the sea, surface water, reservoirs and groundwater. It does not say how likely an individual property is to flood. In Scotland the equivalent is SEPA’s flood maps.
The cost for a buyer is insurance. Flood Re, a scheme insurers can use behind the scenes on a home insurance policy, only covers homes built before 1 January 2009. A buyer who cannot get affordable cover has a reason to offer less or walk away.
Fixable before a sale: no, because the location cannot change. A current insurance schedule that includes flood cover shows cover can be found, though the buyer will still need a policy of their own.
2. Japanese knotweed
GOV.UK guidance for England says you do not legally have to remove Japanese knotweed unless it is causing a nuisance, but you must stop it spreading off your land, and treatment usually takes at least 3 years. RICS surveyors reporting on a home follow the RICS professional standard Japanese knotweed and residential property, which sets the management approach by risk level.
Fixable before a sale: partly. Start treatment early, so a buyer finds a programme under way rather than a problem nobody has dealt with. Answer the property information form truthfully either way, because hiding knotweed from a buyer can lead to a claim against you after the sale.
How the house was built and altered
3. A defective construction type
Section 528 of the Housing Act 1985 lets the Secretary of State designate a class of buildings as defective where their design or construction is defective and, because that became generally known, the value of some or all of the homes has been substantially reduced.
Other non standard methods are not designated but can still narrow the buyer pool, because in our experience some lenders will not lend on them. Our guide to unmortgageable property covers which problems can be cured.
Fixable before a sale: rarely. Know your construction type and keep the documents for any repair already done.
4. A low EPC rating
GOV.UK says you must order an EPC before you market a property. It rates the property from A to G, is valid for 10 years, and in Scotland must also be displayed in the property.
A rating of F or G is a cost for any landlord buying in England. Since 1 April 2020 landlords cannot let a property covered by the rules if it is rated below E unless they have a valid exemption, with a cost cap on the required improvements of £3,500 including VAT.
Fixable before a sale: often. The EPC lists the steps to improve the rating, and a new assessment records the result.
5. Work without planning permission
In England, the planning guidance on enforcement says building work substantially completed on or after 25 April 2024 generally becomes immune from enforcement after 10 years, against 4 years for work completed before that date. Deliberate concealment can extend those limits, and until a breach is immune a buyer takes on the risk of an enforcement notice. None of this applies to a listed building, because the same guidance says there is no time limit on listed building enforcement, unconsented work can be an offence and listed building consent is not granted after the event.
Fixable before a sale: often. A retrospective application under section 73A of the Town and Country Planning Act 1990 can regularise the work, but the same guidance says you get only one opportunity to obtain permission after the event, either through that application or through an appeal against an enforcement notice.
6. Work without building regulations approval
GOV.UK warns that without approval you will not have the certificates of compliance you may need when you sell, and that the building control body could make you pay to fix faulty work.
Fixable before a sale: usually. Regulation 18 of the Building Regulations 2010 lets an owner apply for a regularisation certificate for unauthorised work carried out on or after 11 November 1985. The certificate is evidence, not conclusive evidence, that the work complies. The same GOV.UK page points readers in Scotland to separate rules.
Leases, covenants and missing paperwork
7. A short lease
GOV.UK says that when 80 years or less remain on a lease, the cost of extending it increases significantly. A buyer prices that cost in, as our guide to short lease flat pricing sets out.
Fixable before a sale: yes, if you qualify. The same page says a flat lease may be extended by 90 years and a house lease by 50 years.
8. A restrictive covenant
A covenant in the title can limit how the land is used or what is built on it, so past work that breaches one becomes the buyer’s problem.
Fixable before a sale: sometimes. In England, section 84 of the Law of Property Act 1925 lets the Upper Tribunal discharge or modify a restriction on grounds including that it is obsolete, that it impedes reasonable use of the land, or that those with the benefit have agreed, and it can order compensation.
In Scotland, section 90 of the Title Conditions (Scotland) Act 2003 gives the Lands Tribunal for Scotland power to discharge or vary a title condition.
9. Missing information
The government’s home buying and selling reform roadmap refers to estate agents’ existing responsibilities under the Digital Markets, Competition and Consumers Act 2024 to give buyers relevant information, and says it will publish guidance on material information.
The sales pack it anticipates includes tenure, council tax band, EPC rating, known covenants, building safety information and search results. That sales pack is a proposal, not yet law, and the government does not expect these measures to apply in Scotland, which already has the Home Report system covered below.
Fixable before a sale: yes. Gather those documents before you list, because a gap found late gives a buyer a reason to renegotiate.
Selling in Scotland
mygov.scot says the Home Report has three parts: a single survey and valuation, a property questionnaire and an energy report. The seller or agent must provide it within nine days of a buyer asking.
What that changes
The questionnaire covers alterations, extensions and notices that might affect the home, so several problems above can be in front of a Scottish buyer before an offer.
Which problems you can fix first
| Problem | Fixable before a sale | The step to take |
|---|---|---|
| Flood risk | No | Have the insurance schedule ready |
| Japanese knotweed | Partly | Start treatment early |
| Defective construction type | Rarely | Keep construction and repair documents |
| Low EPC rating | Often | Make the EPC’s recommended improvements, then reassess |
| No planning permission | Often | Retrospective application or enforcement appeal, not both |
| No building regulations approval | Usually | Regularisation certificate |
| Short lease | Yes, if you qualify | Lease extension |
| Restrictive covenant | Sometimes | Tribunal application to discharge or modify it |
| Missing information | Yes | Gather the documents before listing |
Our view: a problem a buyer finds for themselves gets priced on their own estimate of the risk, while one you have already dealt with, with the paper to prove it, leaves them far less to guess.
What this means if you are selling
Work through the nine problems before you set a price, and start any fix before you market the house, not after an offer. Fix what can be fixed, gather the evidence for what cannot, and price anything left against what a buyer will have to do about it. If the house is already on the market and not moving, our guide to why a house is not selling covers price, condition and the current market.
If you want to know what your house is worth with these problems priced in, get a free desktop valuation: send us the address and you will have an evidence-backed range within 24 hours, yours whether you sell or not.
This is general information, not advice on your situation, so take independent legal and survey advice before acting. Sources were checked on 16 September 2026.