8, MAIRWEN, Cefn, St Asaph, Denbighshire, LL17 0HB Data via plota.co.uk

31/2026/0154/LP - Certificate of Lawfulness for a Proposed Use / Development Approved

Proposal

Tystysgrif datblygiad cyfreithlon ar gyfer estyniad unllawr arfaethedig i gefn yr annedd / Lawful development certificate for a proposed single storey extension to rear of dwelling Data via plota.co.uk

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View original council record ↗Last checked 1 Oct 2026, 01:43

Application progress

✓

Received

25 Mar 2026

✓

Approved

18 May 2026

Approved on 18 May 2026 · Dirprwyedig/Delegated · Last checked 1 Oct 2026

Documents 7

Site constraints 5

Agricultural land, grade 3a

Best and most versatile land (grades 1, 2 and 3a). Source: the Predictive Agricultural Land Classification Map (Defra and Natural England, 2025; the Welsh Government's Predictive ALC Map 2 in Wales), a model rather than a site survey. A site survey can differ.

Where development of farmland is needed, policy prefers poorer land over the best and most versatile (grades 1, 2 and 3a). Three sources: Natural England's post-1988 field surveys, which are definitive where they exist; the Defra predictive map for England (2025) and the Welsh Government predictive map, modelled from the soil map with 3a and 3b split; and the 1970s provisional map, which planners and other services still show, coarser and with grade 3 undivided. Where the provisional and predicted grades disagree, treat the predicted grade as the current estimate and expect an application to carry its own survey.

Special area of conservation about 167 m away: Coedwigoedd Dyffryn Elwy / Elwy Valley Woods

Work nearby can need a habitats assessment.

Harm to a protected site is only accepted where there is no alternative and an overriding public interest.

Radon affected area, class 5

An estimated 10 to 30% of homes reach the radon action level. Indicative for the 1 km square, which takes the highest class found in it; a radon test gives the answer for a building.

From the British Geological Survey and UK Health Security Agency indicative atlas. Under building regulations, as the BRE guide BR 211 (2023) sets out, new buildings and extensions need basic radon protection from class 3 in England and Wales and from class 2 in Scotland, and full protection from class 5. The class at the site itself, from the detailed BGS map, decides which.

UKHSA radon ↗

SSSI about 167 m away: Coedydd ac Ogofau Elwy a Meirchion

Natural England may need consulting, depending on what is proposed.

Sites of special scientific interest are the best wildlife and geological sites in the country. Development likely to harm one is rarely permitted.

National infrastructure project about 1054 m away: North Wales Wind Farms Connection

The site is about 1054 m from the project boundary. Electricity line, decided. The project page says whether consent was granted. Also within 2 km: Mona Offshore Wind Farm (decided, about 1261 m); Awel y Môr Offshore Wind Farm (decided, about 1954 m); SP Mid Wales (Electricity) Connections Project (SP Manweb) (at pre-application, about 1504 m).

Nationally significant infrastructure projects (power stations, electricity lines, pipelines, major roads and railways, harbours, airports and reservoirs) are consented by a Secretary of State under the Planning Act 2008, after an examination by the Planning Inspectorate, rather than by the council. The boundary is the one the Inspectorate consults on and can change as the scheme does. Projects are shown within 2 km of the site.

Planning Inspectorate project page ↗

Not affected

Outside flood zones 2 and 3 · No scheduled monument at the site

Checked on 6 October 2026. The pin for this application is the centre of its postcode rather than the building, so distances to nearby designations are measured from the postcode and can be out by the width of the postcode area. Historic England, the Environment Agency, Natural England, the Planning Inspectorate, the British Geological Survey and UK Health Security Agency (radon, contains BGS materials © UKRI) and council datasets, Open Government Licence. A boundary can run through a site and the council holds the definitive record: confirm with the council before relying on this.

Building

Floor area89 m² (958 sq ft)

Energy ratingF (24 out of 100), could reach B

PropertySemi-detached house, 5 habitable rooms

Built1930 to 1949

HeatingElectric storage heaters

WallsCavity wall, as built, no insulation (assumed)

From the energy performance certificate lodged in March 2014, the latest held for this property, matched to this application by its address. The building may have changed since. View the certificate

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Important details

Council: Denbighshire
Application type: Certificate of Lawfulness for a Proposed Use / Development
Postcode: LL17 0HB
Received: 25 Mar 2026
Validated: 25 Mar 2026
Ward: WD31 - Trefnant
Parish: Cefn Meiriadog CC (31)
Case officer: Show
Target decision: 20 May 2026
Decision: Certify
Decision date: 18 May 2026
Decision level: Dirprwyedig/Delegated
Applicant: Show
Agent: Show

How this decision compares

Decided in 54 days from validation, about the council's usual 55 days. Approved, as 89% of extensions here are.

This one54d

Council55d

UK55d

55%decided within 8 weeks

89%approved

207decided in the last year

Plota live figures for extensions decided by Denbighshire in the last twelve months, from validation. Denbighshire decision record →

Consultation & key dates

Statutory expiry: 20 May 2026

Historical activity at this location

4 nearby applications on record - archival context, not part of the live application.

Within ~100m

Nearby activity

2021 Approved

2 Mairwen, Cefn, St. Asaph, Ll170Hb

Tystysgrif datblygiad cyfreithlon ar gyfer codi estyniad cefn unllawr / Lawful developmen…

31/2021/1041 7 Dec 2021

2020 Approved

4 Mairwen, Cefn, St. Asaph, Ll17 0Hb

Dymchwel sied, codi estyniad i ochr yr annedd a chodi garej ar wahan i'r cefn / Demolitio…

31/2020/0149 15 Apr 2020

2019 Approved

7, Mairwen, Cefn, St Asaph, Ll17 0Hb

Codi estyniad porth unllawr ar blaen y ty / Erection of single storey porch extension to…

31/2019/0260 10 May 2019

2017 Approved

7, Mairwen, Cefn, St Asaph, Ll17 0Hb

Tystysgrif datblygiad cyfreithlon ar gyfer codi estyniad un llawr i gefn yr annedd / Lawf…

31/2017/0175 12 Apr 2017

Energy performance: Energy performance certificates from the Energy Performance of Buildings Register, Ministry of Housing, Communities and Local Government. Contains public sector information licensed under the Open Government Licence v3.0. © Crown copyright 2026.