This is SDB’s first project for Dacorum Council and was won under competitive tender on a quality and cost basis. It is a traditional contract with the architects as contract administrator as well as designer.
The scheme is for a block of nine two bedroom flats on three floors plus roof level plant room built to PassivHaus standards including certification just outside Hemel Hempstead in £1.4m. It is the first PassivHaus scheme to be constructed by Dacorum and one of three projects that represent the first new council housing by the borough for 25 years.
It consists of a single skin blockwork structure covered in insulated render with a top floor plant room. This form of construction combined with an internal parge coat provides a continuous airtight layer around the building punctured only by the windows and services. The communal heating system further restricts the penetrations to the area of the plant room.
The windows are triple glazed Passivhaus certified units by EcoHaus with a u value of 0.7. The heating and ventilation services consist of MVHR system supplemented by a small gas boiler to raise the air temperature where required. The tenants are unable to control this individually but are provided with a panel heater should they need additional heat. Hot water is supplied from a central storage system fed by solar panels on the roof and supplemented by a second larger boiler with the flats also having an immersion heater as reserve. Particular consideration was given to the risk of overheating given the airtight nature of the building with all internal services being comprehensively insulated to avoid any heat loss which might contribute to internal temperatures.
One of the key challenges for any Passivhaus scheme is achieving the required airtightness and this is the area that many UK schemes have fallen down on. Not only does it require careful detailing, particularly around windows and other junctions but it also needs an unusually high standard of workmanship and attention to detail.
The final air test has just been completed on the Nokes and the target was achieved comfortably. The biggest challenge on this scheme was not the airtightness but the heating and ventilation controls and installation. The ventilation system was installed by an outside specialist but the communal heating system was installed using the company’s own labour. One of SDB’s great advantages is the extent of this direct labour force which includes operatives who have been with the company for many years having risen from apprentice or junior. The site manager on this project who has on a range of projects including PassivHaus new build as well as a Retrofit for the Future project at Hawthorn Road started as a young carpenter and has worked his way up to senior site manager. He is also now our low energy building specialist and PassivHaus champion.
- ADDRESSThe Nokes, Gadebridge, Hemel Hempstead, HP1 3LF
- CLIENTDacorum Borough Council
- ARCHITECTChambers Goodwin Partners
- ENGINEERSBellamy Wallace Partnership
- CLIENT REPRESENTATIVEChambers Goodwin & Partners
- M&E CONSULTANTSWarm Company Ltd
- CONTRACT SUM£1.4m
- COMPLETION DATE14/04/2015