South Wales · Subsidence Risk
Subsidence risk in Swansea: what to check before buying
Swansea bedrock is Carboniferous Coal Measures across most of the city, interbedded sandstones, mudstones and coal seams of the South Wales coalfield. Superficial deposits include glacial till and alluvium along the Tawe. Mining is the dominant ground-stability factor.
Last updated: 6 May 2026. Editorially reviewed: 20 May 2026.
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Check subsidence signals for a UK address in 15 seconds
BGS clay susceptibility, building age, tree context and the things to ask your surveyor.
Run a free previewBGS clay susceptibility for Swansea
BGS GeoSure rates clay shrink-swell susceptibility as low to moderate across Swansea, much lower than south-east England. Clay-driven subsidence is uncommon as a buyer issue compared to mining.
BGS GeoSure publishes shrink-swell susceptibility ratings at 1:50,000 scale, covering the whole of Great Britain. Most insurer subsidence-risk models begin with this dataset. Conveyancers' environmental searches use BGS data plus mining and contamination layers to produce a per-address report.
Trees, drainage and other risk factors in Swansea
Mining subsidence and steep slope stability are the dominant Swansea factors. Trees on glacial till are a moderate-secondary risk.
Three checks the survey should cover:
- Tree species, distance from foundations, and any TPO (Tree Preservation Order)
- Drain condition and any documented leaks (CCTV survey if older clay drains)
- Crack pattern: BRE Digest 251 categories 0–5 with width, location, and direction
Mining-era subsidence in Swansea
Heavy historic coal and metal mining across Swansea and the wider South Wales coalfield. The Coal Authority CON29M report is essential on every Swansea property, the South Wales coalfield is one of the most heavily mined regions in the UK. Your conveyancer orders it during conveyancing.
What subsidence means for your mortgage and insurance
Lenders treat historic, stabilised subsidence as standard if there is a structural engineer's report and any underpinning is documented. Active subsidence triggers retentions, specialist insurer placement, and in some cases lender refusal until remediation is complete and stable.
Insurance is the bigger ongoing constraint. A property with a prior subsidence claim sits in a constrained insurer market. The existing insurer typically continues cover but new business placement is harder. Disclosure of any prior claim is required on the seller's TA6 form.
How to check your specific address
City-wide context is orientation. Per-address checks before offer:
- 1Pull the BGS shrink-swell susceptibility for the postcode (free at bgs.ac.uk/datasets/geosure).
- 2Order a Coal Authority CON29M report if the property is in a historic coalfield boundary. Your conveyancer arranges this.
- 3Read the TA6 form for any prior subsidence claim, structural movement, or insurance involvement.
- 4Commission a RICS Level 3 (Building Survey) for any property over 60 years old in a high-clay-susceptibility area.
Run the check
Check subsidence signals for a UK address in 15 seconds
BGS clay susceptibility, building age, tree context and the things to ask your surveyor.
Run a free previewFrequently asked questions
Is subsidence common in Swansea?
Swansea bedrock is Carboniferous Coal Measures across most of the city, interbedded sandstones, mudstones and coal seams of the South Wales coalfield. Superficial deposits include glacial till and alluvium along the Tawe. Mining is the dominant ground-stability factor. BGS GeoSure rates clay shrink-swell susceptibility as low to moderate across Swansea, much lower than south-east England. Clay-driven subsidence is uncommon as a buyer issue compared to mining.
Will subsidence affect my mortgage in Swansea?
Lenders treat historic, stabilised subsidence as standard if a structural engineer's sign-off is in place. Active or progressive subsidence triggers retentions, specialist insurer placement, and in some cases lender refusal until remediation is complete.
What should the survey cover for subsidence in Swansea?
Mining subsidence and steep slope stability are the dominant Swansea factors. Trees on glacial till are a moderate-secondary risk. The surveyor should record any cracks (BRE Digest 251 categories), assess proximity of trees and drains, and recommend a structural engineer's report where category 2+ cracking or active movement is suspected.
Keep going
Related Swansea buyer pages
- Flood risk in Swansea , the other major environmental check before offering.
- Full property check in Swansea , 12 public-data checks for any Swansea address.
- Subsidence monitoring on a survey , what surveyors mean by "monitor for movement" and what to do.
- Evidence of movement , the broader category surveyors use for cracking patterns.
Editorial review
Editorial owner: BiteRight Ltd, operator of MyPropertyScan. We review buyer guides against UK public property datasets, RICS survey wording, lender requirements, and common buyer questions.
Pages are updated when source coverage, property-risk guidance, survey cost assumptions, or product checks materially change. Methodology and dataset limitations are explained on the MyPropertyScan methodology page.
Sources used
We use UK public and specialist sources where they are available. Public datasets can be incomplete, delayed, or missing for some addresses. Treat them as a starting point, not as a replacement for professional advice.
Source standard: preference goes to official government datasets, statutory bodies, professional standards, and primary dataset publishers. We cite the source family on the page and explain coverage limits rather than filling gaps with unsupported estimates.
General information only. Not legal, mortgage, insurance, or surveying advice. Always confirm with your own surveyor, broker, and conveyancer before making decisions. MyPropertyScan is operated by BiteRight Ltd.