107 Niddrie Road is a pre-1919 red sandstone tenement in Govanhill in the south side of Glasgow owned by Southside Housing Association. It consists of eight one-bedroom flats and a communal close and back court.
This project was designed to the EnerPHit methodology (Passivhaus for retrofit) and features ultra high levels of insulation and airtightness combined with new heating and ventilation systems. These measures will drastically reduce energy bills for the tenants while providing them with a comfortable and healthy internal environment.
Design Brief
The EnerPHit method was chosen because it is the most robust strategy worldwide to reduce carbon emissions and protect tenants from fuel poverty. Southside Housing Association (SHA) commissioned this groundbreaking retrofit which was supported by Scottish Government, Glasgow City Council and the housing association themselves. The whole building was in a parlous state internally and externally and had been vacant for a couple of years. It was also, unusually, in the single ownership of SHA which gave us a unique opportunity.
The design approach was three fold: i) building repairs and conservation of the tenement, ii) energy efficient measures and iii) improved layouts and upgraded finishes such as new kitchens and bathrooms.
Design Process
We have upgraded the building fabric to minimise the heating demand by ensuring the whole envelope is wrapped in high levels of insulation, minimising thermal bridging and ensuring there is a continuous airtightness line, including continuity at all key junctions (eg. at eaves level, windows etc.) General building repairs have been carried out including a repair / restoration of the sandstone street facade.
Four flats are heated by individual air source heat pumps (ASHP) which take heat from the external air and uses it to provide hot water for radiators and domestic hot water. The four upper flats are heated by new efficient combi gas boilers.
All eight flats have their own mechanical ventilation heat recovery unit (MVHR) installed above the ceiling in the bathrooms. These extract moist / stale air from kitchens and bathrooms while bringing in fresh air from the outside. The heat exchanger transfers the heat from the stale air to the fresh to minimise heat loss which reduces the heating demand.
The upper six flats have wastewater heat recovery units installed to the bath / shower so heat can be recirculated back into the hot water system to reduce the water heating demand.
Urban Response
It is crucial that we safeguard Glasgow’s sandstone tenements for future generations but we also have to face the pressing needs of addressing climate change and fuel poverty. This balance can challenging to achieve.
In this project the energy efficiency demands have been as rigorous as it is possible to be, and to achieve them we opted to externally insulate the rear facade of the block and side gable – which is far more effective thermally – but to internally insulate the street-facing facade.
Internal insulation means that the external look of a building is retained, but it also introduces a number of technical risks, mostly to do with moisture, that most people are unaware of, and which can threaten the actual fabric of the building we are trying to conserve. In this project, we used lime plaster internally for airtightness and vapour permeable woodfibre insulation to minimise the moisture risk, but even with these measures, there was a decay risk to the floor joists in the street-facing walls, so we removed the joist ends to ensure that our drive to create energy efficient properties does not lead to failure of the building fabric in years to come.
All new windows are Passivhaus certified triple glazed but have been carefully proportioned to reflect the traditional window split of the sash and case typically installed in tenements. Internally there is very little evidence of the energy efficient measure and in most cases you would never know they are there now internal finishes have been installed.
Sustainability
We have specified natural building products where possible at Niddrie Road.
This is because such materials do not contribute to the poor indoor air quality which is found in most modern homes, but also because they have lower embodied energy and carbon than most conventional building materials. They also tend to be vapour permeable and hygroscopic, thereby helping to reduce the wider moisture risks associated with very airtight buildings.
Conventional chemical timber treatments were avoided which saved money and significantly reduces the chemical load on occupants whilst still ensuring that timber components in the building are safeguarded.
The heating demand has been reduced to 25.9 kWh/m2/year through a fabric first approach which is approximately 90% lower than that of a similar sandstone tenement. The lower four flats are fossil fuel free as they use zero carbon technologies (ASHP).
Overall the project demonstrates the potential to conserve Glasgow’s beautiful stone heritage whilst creating flats which will cost less to heat than a new build equivalent, using a range of natural, low embodied materials. The properties are being monitored by the University of Strathclyde in combination with an extensive evaluation of the design and build process by CaCHE in the coming year or so.