When house-hunting to relocate to Bristol, Ian and his partner Corinne were looking for a mid-century property as a renovation project, but one that also had the potential to be thermally upgraded to a high standard. They found a house near Westbury on Trym in the north of the city, which has since undergone a ‘deep retrofit’
As a building performance researcher, Ian was keen to demonstrate the benefits of a fabric first approach, focusing on energy reduction and improving occupant comfort. Longer term, the aim is to reduce carbon emissions, through the installation of micro-generation and solar thermal technologies. Achieving 69% carbon savings through fabric measures alone has been a significant achievement so far given the house, as inherited, already had undergone fairly recent boiler and window replacements (not factored in the CO2 emission reduction calculation). Furthermore, the house has been extended, increasing the treated floor area by almost 25%.
In his work, Ian has been part of the technical team involved with progressive changes to the Building Regulations for Part L (energy) and Part F (ventilation). When it came to providing an evidence base for informing retrofit standards, he was surprised at how little data was available to chart the benefit of thermal upgrade measures. In part, this helped to inform the decision to retrofit an existing property, rather than the original plan for a new-build.
Ian has installed temperature, humidity and CO2 sensors, meters, sub-meters and data loggers throughout the home to record long-term energy and environmental data. Monitoring has been in progress since October 2013 and Ian will be able to discuss performance-related findings during open days. Follow the progress and findings as they are published: www.fourwalls-uk.com/blog.
The house was built in 1962 and is located of the fringes of Blaise Castle Estate: a woodland park in the northwest of the Bristol. Properties from this era tended to have a large amount of concrete elements, which can be the cause of significant thermal bridges. One of the key challenges of the planned retrofit was to eliminate, or minimise these thermal weak points. The house is built into a slope, which brought about another set of thermal challenges.
The house had only one previous owner and had been very well cared for by them. However, it was in need of modernisation: it still had the original electrical and heating systems (except for the boiler which had recently been replaced). Many of the original single-glazed windows had been progressively replaced by the original owner, but the house was largely uninsulated, except for a thin layer of scattered vermiculite in the loft – just enough to prevent condensation.
An interesting aspect of this retrofit is the use of external (or internal is some areas) insulation applied over a cavity wall. Usually the reserve of solid wall properties, Ian was determined to demonstrate that EWI and IWI are equally applicable to cavity wall properties, providing that the cavity has been treated correctly. The result is that the house has been super-insulated, achieving U-values for walls of between 0.1 and 0.17 W/m2.K, for the roofs between 0.1 (loft) W/m2.K and 0.14 W/m2.K (extension flat roof), and 0.13 W/m2.K for the new floor. The new triple-glazed windows have a U-value of 0.9 W/m2.K, and the airtightness has been improved by around 90% through the inclusion of a detailed air barrier strategy as part of the design. Thermal bridges relating to the concrete gutters and original balcony have been addressed by replacing them with thermal bridge-free structures. Subsequently, the house now has a measured annual heat demand of <2,500 kWh/year (approximately £100/year), down from 22,000 kWh/year (approximately £1000/year).
The works also included the addition of a low energy side extension, and conversion of the storage area on the lower ground floor into a kitchen/diner. Ian and his partner work from home, so the extension included the creation of a new studio, and the old kitchen has been converted into a study.
Full details of measures installed:
External wall insulation has been applied to the entire envelope: both original and the extension. Windows throughout are timber-framed and triple-glazed. The result is that all walls, roofs and floors have exceptionally low heat loss properties. Good indoor air quality is maintained by the heat recovery ventilation system, ducted to each room in the house. This strategy means that the house needs to be as airtight as possible to ensure all air entering and leaving the house (in winter) goes through the heat exchanger. Airtightness test results were 17.5 m3/hr/m2@50Pa for the original house, which has reduced to 1.8 m3/hr/m2@50Pa during the renovation works. The plan is to reduce the air permeability further still.
Other features include:
Re-wiring included the installation of 100% sub-metering for the electrical circuits, which will be monitored over the long-term to help target further energy reductions. Gas and water consumption are also monitored, as are temperature, relative humidity and CO2 concentrations. The data logger for these sensors and a weather station collects data every 5 minutes.
For more detailed information, visit the low energy buildings platform http://www.lowenergybuildings.org.uk/viewproject.php?id=389
The comfort levels throughout the year.
The cavity was filled using a high-performance polystyrene bead (EPS) prior to the application of external wall insulation. We did this for a number of reasons:
1. To help insulation value overall – i.e. original, uninsulated cavity had a U-value of appr. 1.4 (W/sq.m K). Cavity insulation (CWI) reduced this to appr 0.4.
2.To reduce thermal by pass potential for external wall insulation (EWI) layer. This is 100% essential. Without CWI, warm air escaping from the house would effectively use the empty cavity as a chimney (hot air rises) and out to atmosphere. So without CWI, the EWI would be useless. CWI+EWI give an overall U-value of appr 0.12.
We have some areas where EWI was not possible (<10% of available wall area of house). In these areas, we still have CWI, but switched to internal wall insulation (IWI). These walls have a U-value of appr. 0.17, but beware there is a higher risk of interstitial condensation, so either select a system with good vapour control layer (and that this is put in very well and sealed), or is diffuse open, such as wood fibre with lime plaster.
To read more, go to the home page and type in a topic into the search bar – I have tried to tag each entry so that everything is searchable. I also need to post more updates on recent performance when I get time!
We used polystyrene bead (EPS – extruded polystyrene), as opposed to mineral fibre, for two reasons:
a) EPS flows exceptionally well compared to fibre – we needed to ensure no/little air movement in the cavity.
b) Should there be a risk of interstitial condensation during certain times of the year (the moisture models showed this as a very small risk in October) then EPS will not get damaged, or absorb moisture and transfer this into the wall (damp problem). Mineral wool can absorb moisture and ultimately degrade.