Merkins Avenue, Dumbarton
Overview
This was the second phase of ongoing refurbishment work carried out by Bellsmyre Housing Association, which owns 150 properties in a housing estate on the outskirts of Dumbarton. The housing described in this study was built in 1956 and contains 42 flats entered by seven closes. The Association acquired the properties from Scottish Homes in 1992.
The tenements were gutted to provide 40 high quality units with enhanced energy efficiency, gas central heating and door entry systems. Concrete balconies were cut back and used to support new bay windows. There was full tenant engagement throughout involving weekly meetings, decanting and re-housing on site for some tenants. A difficult-to-let unpopular scheme was transformed into a popular development with low turnover and low vacancy rates.
The construction comprises external walls of no-fines concrete, pitched roofs and solid concrete floors. Heating was by electric fires.
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Approach
The original flats were very energy inefficient and reliant on electric fires and storage heaters for heating. Energy efficiency was enhanced by rendered 60mm polystyrene external cladding, 30mm expanded polyurethane insulation to close walls, 150mm mineral fibre to roofs, enclosure of balconies, 100mm ground floor insulation, new timber windows with 12mm double glazing and full gas fired central heating with combination boilers. The concrete construction required ceilings to be lowered and floors raised for services installation. This has produced SAP ratings of 82 for top floor flats and 97 for first floor flats, and reduced heating bills by 80%.
There have been some difficulties: the void behind the bay window has created draughts, the external insulation is not strong enough to hold satellite dishes and is subject to vandalism, and the original boilers have been replaced by cheaper and more reliable and efficient alternatives.
Roof
Before refurbishment:
Uninsulated loftAfter refurbishment:
150 mm mineral fibre
External Walls
Before refurbishment: 103 mm no-fines concrete (250 mm on third floor)
After refurbishment: 6 mm render and 60 mm expanded polystyrene to existing walls, plus 50 mm cavity and 12.5 mm plasterboard internally
Close Walls
Before refurbishment: Uninsulated
After refurbishment: 9.5 mm plasterboard and 30 mm polyurethane composite board applied to existing wall
Ground Floor
Before refurbishment: Uninsulated
After refurbishment: 18 mm chipboard over 100 mm insulation
Windows
Before refurbishment: Single glazing
After refurbishment: Replacement timber-frame double glazing (12 mm gap) with draught-stripping
Ventilation
Before refurbishment: Uncontrolled
After refurbishment: Draught-stripped windows with bathroom and kitchen extract fans (time-switch controlled)
Heating
Before refurbishment: Electric fires
After refurbishment: Gas-fired central heating with combination boiler (fan-assisted flue), programmer, room thermostat, and TRVs
Hot Water
Before refurbishment: Electric immersion heaters
After refurbishment: Supplied from the combination boiler system
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A SAP analysis was carried out for the flats before and after refurbishment. The Table gives the results for the two flat types estimated to have the highest and lowest SAP ratings after refurbishment. The analysis showed that excellent SAP ratings were achieved, above those which could be typically expected for refurbishment. Annual space and water heating costs were estimated to reduce by 84% for the top floor 1-bed flat and 79% for the first floor 3-bed flat. Corresponding CO2 emissions were estimated to have reduced by 58% and 26% respectively.
Top Floor 1-Bed Flat
SAP rating
Before: 1
After: 82
CO₂ emissions (tonnes/year)
Before: 6.5
After: 2.7
First Floor 3-Bed Flat
SAP rating
Before: 32
After: 97
CO₂ emissions (tonnes/year)
Before: 5.0
After: 3.7
U-values
Roof: 0.25 W/m²K
Walls: 0.45 W/m²K
Ground floor: 0.45 W/m²K
Fuel Costs
Estimated reduction: 80%
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At a meeting with the Association’s development committee it was clear that the tenants were very pleased with the refurbished housing, but that the high standard had been achieved not through the Association’s own knowledge but because an architect had been employed who was experienced in refurbishment. However, for future refurbishment projects the Committee is likely to use the SAP energy rating as a design tool. This will include asking the architect to achieve a specified minimum SAP energy rating value.
There have been some difficulties: the void behind the bay window has created draughts, the external insulation is not strong enough to hold satellite dishes and is subject to vandalism, and the original boilers have been replaced by cheaper and more reliable and efficient alternatives.
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