Mulberry Harbour Phoenix Caissons at Portland Harbour is a Grade II listed building in the local planning authority area, England. First listed on 17 May 1993. Caisson. 4 related planning applications.
Mulberry Harbour Phoenix Caissons at Portland Harbour
- WRENN ID
- quartered-shingle-winter
- Grade
- II
- Local Planning Authority
- Constituency
- South Dorset MP: Lloyd Hatton (Lab)
- Country
- England
- Date first listed
- 17 May 1993
- Type
- Caisson
- Address
- Mulberry Harbour Phoenix Caissons at Portland Harbour, Opposite Castletown Pier, Isle of Portland, Dorset, DT5 1BD
- OS grid reference
- SY 687 747
- Coordinates
- 50.57133, -2.44284
- Source
- Historic England listing
Description
The Mulberry Harbour Phoenix Caissons at Portland Harbour are two 'Phoenix' caissons from 1944, moored end-to-end. Each caisson is constructed from reinforced concrete and weighs 7,000 tons (7,113.8 tonnes).
They are rectangular in shape, measuring 12.19 meters long, 9.14 meters wide, and 12.19 meters high. The caissons have a monolithic appearance, with concrete walls that rise above a wider concrete base, which provides a walkway around each caisson. At the center of each end, there is a vertical concrete pier with an opening that allows passage along the walkway. This pier can be used for ladder access to the roof, and there are fixed ladders at the adjacent ends, along with a gangplank connecting the two caissons.
Steel railings are present at parapet level, and the roofs feature fixings for former 40-mm Bofors light anti-aircraft guns mounted on squat towers. Internally, the caissons are divided into several open transverse chambers that can be flooded to sink them to the sea floor, allowing them to function as a breakwater.
Local climate
Mulberry Harbour Phoenix Caissons at Portland Harbour receives an average of 840 mm of rain a year. This makes it wetter than 55% of listed buildings in the UK. Its exposure to wind-driven rain is greater than that of 77% of listed buildings.
It experiences an average of 13 freeze-thaw cycles a year, fewer than 88% of listed buildings. Of these, 5 follow at least 1 mm of rain in the preceding 48 hours. Average temperatures at this location have risen by 0.3°C per decade since 1991.
Averages for 1991–2020; temperature trend 1991–2025. Figures describe the wider area (a grid cell of roughly 10 km), not the individual site. Contains modified Copernicus Climate Change Service information 2026.
More on this building
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- Full EPC report — heating system, energy costs, size, glazing, construction etc.
- No sale records on file
- Related listed building consents — 4 applications
- Detailed attributes — period, style, materials, features
- Flood risk assessment
- Radon risk assessment
- Weather exposure and heating demand — rain and frost month by month and year by year, wind direction, solar and humidity
Matched applications, energy data and sale records are assembled automatically and may contain errors. Flag incorrect data.
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