How this guide defines the area
For this guide the area is the Isleworth Riverside conservation area in the London Borough of Hounslow, a single designation of about 155.8 hectares. More than half of that land is also part of the Syon Park registered park and garden, so the figures below describe a mix of parkland, historic buildings and housing rather than a purely residential district.
Two features dominate the record: a concentration of high-grade listing connected with Syon, and a large share of the conservation area inside Flood Zone 3. Both are explained with their sources below, and the Hounslow guide gives the borough-wide picture.
Isleworth Riverside on the public record
Every statement below links to the public record it comes from; sources were re-checked on .
The conservation area and its documents
Planning.data.gov.uk records the conservation area under Hounslow reference HSLCA05, with a designation date of 11 November 1972 and a mapped extent of about 155.8 hectares.
Hounslow lists its conservation area appraisals and maps on one download page, and the council's Isleworth Riverside appraisal is the document to read before changes to an elevation, roof or boundary wall are planned.
No conservation-area Article 4 direction for the riverside is listed in the Article 4 data on planning.data.gov.uk, and since that is not confirmation from Hounslow, the council's appraisals page is checked before a permitted development right is relied on.
Syon and the listed entries
When queried on 1 November 2026, the NHLE listed-building data returned 57 list entries within the boundary: 46 at Grade II, 5 at Grade II* and 6 at Grade I.
The Grade I entries are Syon House, the Syon House Conservatory, the Syon Park Boathouse, The Pavilion, Floras Column, Syon Park, the Gate Lodge to Syon House and the Syon Park Entrance Lodges and Gates, London Road.
At Grade II* the list adds the Church of All Saints, Garvin House, Gumley House (Convent), The London Apprentice Public House and the Gates to Syon Lodge.
The scheduled monument London's Early Porcelain Industries: The Isleworth Pottery also lies within the boundary, and works to the monument itself fall under scheduled monument consent, handled through Historic England rather than the council.
Syon Park, a Grade I registered park and garden, overlaps about 82.67 hectares of the conservation area, which is more than half of its mapped extent.
With six Grade I entries and a Grade I landscape in one boundary, the Syon Park register entry is read with the appraisal before any visible alteration is designed.
Flood zones and where the water comes from
Of the conservation area, 68.7% lies in Flood Zone 3 on the Flood Map for Planning kept by the Environment Agency, and a further 3.6% in Flood Zone 2.
The map attributes most of that Flood Zone 3 land to a source it labels the sea: 36.3% of the area is shown from the sea alone, 32.0% from rivers and the sea together and 0.4% from rivers alone, according to the same planning map.
Nearly all of the Flood Zone 2 land, 3.5% of the area, is also attributed to the sea on the Flood Map for Planning, with 0.1% from rivers and the sea combined.
Flood zones assume no defences and are drawn for planning rather than for individual properties, so each address also goes through the long-term flood risk service, which covers surface water too.
For a purchase in Flood Zone 3, the inspection looks for past water entry, floor and threshold heights, airbricks and any resilience measures, and the Flood Map for Planning is where the flood risk assessment that an extension here is likely to need begins.
Gravel, silt and alluvium over clay
The BGS geology viewer maps London Clay Formation bedrock, clay and silt, at all five sample points across the conservation area.
Its 1:50,000 superficial deposits layer shows Kempton Park Gravel Member sand and gravel at three points, alluvium of clay, silt, sand and peat at one, and Langley Silt Member clay and silt at the other.
Alluvium is variable and can include soft or compressible layers where peat is present, so where the mapped superficial geology is alluvium or silt, distortion in older walls and floors is compared with long-term settlement before a cause is suggested, and drains are tested because leaks can soften fine soils or wash material out of gravel.
Housing in two nearby LSOAs
The VOA's council tax stock tables for 2025 count about 1,740 dwellings in LSOAs E01002667 and E01002686, two statistical areas that approximate the riverside rather than follow the conservation-area line.
VOA counts are rounded to the nearest 10, and in these two areas the build-period split is 26.4% from 1919-1939, 23.6% from 1945-1972, 23.0% from 2000 onwards, 16.7% from 1973-1999 and 7.5% from before 1900.
Flats and maisonettes make up 49.4% of dwellings and terraced houses 39.1%, with 9.8% semi-detached and 1.1% detached, in the VOA property-type figures.
Only 17.8% of these dwellings sit in council tax bands F to H on the VOA band table, and the largest single band is D at 39.7%.
With almost a quarter of the stock built since 2000 and about half of it flats on these VOA tables, a purchase here may be in a newer block, where the lease and service charge history matter as much as the fabric.
Service guides published for Isleworth
The guides in the first column apply one type of instruction to this part of Hounslow; the second column links the general page for each service.
Other guides close by
The Hounslow guide covers the wider borough, and the neighbouring guides for Twickenham, Richmond, Kew and Chiswick describe their own conservation areas, ground and housing.
Questions about the riverside records
How much of the conservation area is in Flood Zone 3?
On the Flood Map for Planning, 68.7% of the conservation area is in Flood Zone 3 and 3.6% in Flood Zone 2, mostly attributed to the sea or to rivers and the sea together. These zones ignore defences, so look up the address itself on the long-term flood risk service.
Does being in a flood zone mean a house will flood?
Not necessarily. A planning flood zone describes the chance of flooding from rivers or the sea if defences were absent, across an area rather than for one building. What matters for a particular property is its floor levels, its history, local defences and its drainage, which is why an inspection looks for evidence on site.
Which Grade I buildings stand inside the boundary?
Six Grade I entries appear in the NHLE data, and every one of their names refers to Syon: the house, its conservatory, the boathouse pavilion, Floras Column, the gate lodge and the entrance lodges and gates. A further five entries are Grade II*, and 46 are Grade II.
How much of the designated land is registered parkland?
About 82.67 hectares of the 155.8-hectare conservation area overlaps the Syon Park registered park and garden, which is Grade I, so more than half the designated land is also a registered landscape. Homes near it can raise questions about the park's setting as well as conservation-area ones.
What kinds of homes are found around the riverside?
Across the two LSOAs behind these figures, VOA data for 2025 show 49.4% flats or maisonettes and 39.1% terraced houses, with build periods spread from 1919-1939, at 26.4%, to 2000 onwards, at 23.0%. The stock covers every period, so the right questions differ widely from one address to the next.
What should I gather before asking about a riverside property?
The address, your reason for the instruction, any flood search or insurance information you already hold, the lease for a flat, and planning or building control references for past works. If you know of earlier water entry, treatment work or underpinning, mention it, because it changes where the inspection concentrates.
How we work on an instruction
Hampstead Chartered Surveyors is a RICS-regulated firm (RICS Regulated Firm No. 923064) working from its registered Hampstead NW3 office. The firm does not claim premises, staff or completed instructions in an individual locality, and it does not treat a neighbourhood name as evidence about a particular building.
An instruction starts with the full address, the decision the client faces and the documents already available, such as leases, drawings, notices or earlier reports. The scope, fee and inspection date are confirmed in writing only after that review, and access to roofs, lofts, basements or common parts is agreed before the visit.
Reports include RICS Level 2 and Level 3 home surveys, building and defect investigations, party wall appointments, reinstatement cost assessments, contract administration and schedules of condition. Each report records what was inspected, what could not be seen and what further investigation the evidence supports.
Public datasets such as the conservation-area register, the National Heritage List for England, British Geological Survey mapping, the Environment Agency flood map and Valuation Office Agency housing statistics describe areas rather than individual properties. They frame questions before an inspection; they never replace it.
Reviewed by Savas Bulduk BSc (Hons) MRICS, Director & Chartered Building Surveyor at Hampstead Chartered Surveyors & Building Consultancy. Last reviewed: . Our people · RICS firm record