Ordering constraint checks in the right sequence

Run the free checks before you view the site, the paid checks before you make an offer, and the season-bound surveys the moment the site is under offer. That ordering is the whole trick. Most self-builders lose money not because a constraint was hidden, but because they found it in the right order and acted on it in the wrong one, paying for a topographical survey on a plot that a two minute flood map check would have ruled out.

Here is a sequence that works for a plot of one to five houses, with the reasoning behind each stage.

An hour of free checks, before you visit

None of these cost anything, and together they eliminate a large share of unsuitable sites.

1. The national planning data service, for conservation areas, article 4 directions, green belt, listed buildings, national landscapes and whatever else the authority has published.
2. The Environment Agency flood map for planning, for flood zones 2 and 3, and the surface water risk map alongside it.
3. The MAGIC map, for sites of special scientific interest, priority habitats, ancient woodland and agricultural land classification.
4. The National Heritage List for England, for listed buildings and scheduled monuments on or near the site.
5. The council's policies map, for the settlement boundary, allocations and local designations.
6. The council's planning register, for the site's application history, including refusals and their reasons.
7. The coalfield map, if the site is anywhere near a former coalfield.
8. Historic mapping and aerial imagery, for filled ground, former industrial use, ponds and lost buildings.

Two of these deserve more attention than they get. Planning history tells you what the authority has already decided about this land, which is the closest thing to a preview of the answer. And historic maps reveal made ground and former uses that turn into a contamination budget later.

Record each check with its date. You will be asked.

Checks worth paying for before an offer

Once a site survives the free stage, spend money in this order.

A title check from HM Land Registry, for the title register and plan, costs a few pounds and shows restrictive covenants, rights of way and whether the seller owns the access. A covenant against building can defeat a site that has planning permission, and it is not a planning matter, so nobody at the council will mention it.

Pre-application advice from the local planning authority. Fees are published per council and banded by scheme size. For a small residential site this is usually the best value item on the list, because it produces a written officer view on principle, scale and the documents the application will need.

A water company enquiry for sewer records and a capacity view, which tells you where the public sewers run, whether they cross the site, and whether there is capacity to connect.

A mining report where the coalfield map indicated a risk area.

A walkover by an ecologist, which at the right time of year gives you a preliminary view of habitats, potential for protected species and the likely biodiversity baseline. It is the least costly way to find out whether your programme is about to meet a survey season.

Checks that can wait until the site is secured

Detailed ground investigation, topographical survey, drainage design, utilities capacity applications and structural surveys of any existing buildings are all necessary, and none of them tells you whether to buy. Commission them once the site is under offer or exchanged, subject to planning where the deal allows.

The exception is anything season-bound. Waiting for those is what costs a year.

Season-bound checks that dictate the programme

Ecology survey windows are fixed by biology, not by the programme, and they are the most common cause of delay on small sites.

Mandatory biodiversity net gain applies to small sites from 2 April 2024, which means a habitat baseline assessed with the statutory metric, a ten per cent uplift and a 30 year management commitment for most schemes. The baseline is a botanical exercise and it is season-bound, so a site bought in November with a spring start is already committed to a summer survey. A Preliminary Ecological Appraisal in the first weeks after exchange is the move that keeps the programme intact, and the metric work in a Biodiversity Net Gain Assessment has to be completed by a competent person under the Environment Act 2021 regime.

The constraints that change the price rather than the design

Some findings do not alter what you build. They alter what it costs, and they should go straight into the offer.

• Community Infrastructure Levy liability, where the council charges it, with the self-build exemption claimed correctly and before work starts
• planning obligations under section 106 on sites above the local threshold
• biodiversity net gain delivered off site through units or credits, where the site cannot accommodate the uplift
• nutrient or water neutrality mitigation in affected catchments, which in some areas is the largest single abnormal, and which our note on water neutrality and how a scheme proves it covers
• coal mining remediation, grouting and capping, covered in mine entries, permits and coalfield planning conditions
• contamination remediation, following a Land Contamination Phase 1 desk study and any intrusive phase that follows

Each of these is quantifiable before purchase, at least approximately. A site that works at the asking price minus the abnormals is a site. One that only works if the abnormals vanish is not.

A worked sequence for a small site

Illustrative only, for a plot with outline permission for two houses in a village:

Week one, the free checks. Flood zone 1, outside the conservation area, inside the settlement boundary, no listed buildings within 100 metres, one refusal in 2016 for four houses on highway grounds.

Week two, title check reveals a right of way in favour of the neighbouring farm across the proposed access, and the pre-application response confirms that two dwellings are acceptable in principle but that the access needs visibility splays the current layout cannot achieve.

Week three, the ecologist's walkover identifies a hedgerow of moderate condition and a small pond 80 metres away, so a newt assessment is needed within the spring window.

The offer is revised to reflect the access works and the ecology programme. Purchase completes in February, the newt sampling runs in May, the application is submitted in July.

That sequence costs a few hundred pounds and about four weeks. The alternative, which is buying first and finding the right of way afterwards, costs considerably more.

Recording what you checked

Keep a single table with one row per check: what was checked, the source, the date, the result and a link or file reference. It takes minutes to maintain, it goes into the planning statement as evidence that the site was appraised properly, and it is the document that protects you if something was searched for and was not there at the time.

This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Enter your postcode on PlanScope to run an automatic constraint check against a site and see which reports it points to.