Scottish Passivhaus social housing - the results are in!

Ahead of the Scottish Passivhaus equivalent policy consultation, we have compiled an overview of feedback and post-occupancy monitoring of a range of Scottish Passivhaus social housing schemes.

Closeburn, Dumfries & Galloway

Residents of Closeburn Passivhaus homes: It’s really really warm. It’s the middle of October. It’s cold outside but inside it’s really nice. We haven’t yet had to put the heating on.”

The Closeburn project comprises 3 terraced Passivhaus certified properties in the village of Closeburn in Dumfries & Galloway, owned by Nith Valley Leaf Trust and designed by John Gilbert Architects . A post-occupancy evaluation study has been undertaken and includes Indoor Air Quality (IAQ) monitoring, MVHR evaluation and thermographic studies. Many thanks to John Gilbert Architects for sharing the as-yet unpublished research data.

IAQ

The indoor air quality, including air temperature (internal and external), Relative Humidity (RH) and CO₂ concentrations in bedrooms and the living-rooms were measured with specialist sensors.

CO₂ monitoring findings: Carbon dioxide (CO₂) is used as a proxy to establish if an indoor space is well ventilated and if the indoor air quality is acceptable. CIBSE guides and Building Regulations in Scotland recommend sufficient renewal of air to avoid exceeding 1000 ppm of CO₂. Levels below 1000ppm indicate good indoor air quality. CO₂ concentrations were monitored from December 2020 to February 2021. It was found that CO₂ concentrations remained between 550ppm and 900ppm which confirms that indoor air quality was very good throughout the monitoring period and never exceeded the maximum recommended thresholds. This also means that the results meet best practice guidance for IAQ and Building Regulations recommendations.

Indoor temperature and RH findings: Temperature levels remained within the recommended thresholds throughout the day and the monitoring period (20 to 22.5*C). The RH results are slightly lower than the recommended RH thresholds, reaching sometimes 30 to 35% RH, but stayed most of the time within 35 and 45% values. This means that the indoor air is slightly dry and might compromise comfort levels for the tenants. These results helped Nith Valley Leaf Trust to review and changed the ASHP heating system settings.

Thermography

The internal thermographic images reveal even surface temperatures across the building fabric, in red, orange and yellow colours. This indicates that there are no visible gaps and thermal bridges in the insulation and airtightness layers, which minimises heat loss and and building performance issues. Internal surface temperatures are generally around 18 to 20°C, as predicted in thermal bridging calculations. The study did not find any noticeable signs of thermal bypass or other related building performance issues.

Occupant Survey

Residents of Closeburn Passivhaus homes: The house is lovely. We absolutely love it. It’s still a bit mindblowing to think this is where we actually live.”

A structured occupant survey was conducted, looking at the way the occupants are using the properties, evaluating usability and comfort levels in each of the three properties

The tenants confirmed during the occupant survey that the houses were generally comfortable, and that temperature and indoor air quality were acceptable during day and night.
Building occupiers mentioned that they found it difficult to get used to the less reactive heat pump systems, with lower radiator temperatures (note – heat pumps are not a Passivhaus requirement, but an optional low carbon technology). This required multiple training sessions with the systems’ manufacturer.
CO₂ sensors were fitted in the master bedroom by the Nith Valley Leaf Trust, to allow residents to confirm when CO₂ concentrations are below/ above the recommended 1000ppm threshold.

MVHR monitoring

The ventilation system in these properties, consists of a centralised MVHR system providing fresh air to bedrooms and living room and extracting polluted air from the kitchen and bathrooms. The system was evaluated by measuring the air flow at each MVHR grille. The door undercut gaps (air transfer) and the sound level pressure in each room were also measured, and compared with commissioning sheets, design values and Passivhaus recommendations.

The checks found that the airflow measurements and sound level pressure findings complied with Building Regulations and met Passivhaus recommendations. The three systems were balanced and performing as shown in the design specification provided by the MVHR supplier.

Longmeadow, Annan

Loreburn Housing Association has undertaken some invaluable like-for-like comparative research on 4 Passivhaus properties versus 4 near-identical layout homes built to SHQS Silver standard. The study included two sets of 2 semi-detached bungalows and 2 terraced 2-storey houses of very similar layout and built by the same contractor. However, the specification of windows, heating and ventilation is obviously very different between the two standards.

A few stand-out observations have come out of the as-yet unpublished research report 'Post-occupancy comparison of building performance in Passivhaus and SHQS Silver Standard Homes in Scotland' written by Briony Munro at Loreburn Housing Association.

Mould risk was a performance indicator in which Passivhaus properties dominated consistently higher rankings. The MVHR units appeared to play a contributing role in managing fluctuations in CO₂ and humidity levels within Passivhaus properties, although one Silver Standard home (Property F) did achieve good ventilation through opening windows. As the method of opening windows was under the discretion of each respective tenant, it could be concluded that the MVHR units in Passivhaus properties played a role in maintaining consistently sufficient internal conditions to negate the risk of mould without the need to rely on tenants to open windows.
Overall Passivhaus properties did perform better than Silver Standard homes, however, occupant usage was by far a bigger determinate of post occupancy building performance than the building standard. Property B was a prime example of optimal use of a Passivhaus property, and the data reflected the benefits of passive design when utilised as intended. With the exclusion of this property, the other properties studied performed relatively similarly overall.

Niddrie Road, Glasgow

Resident of Niddrie Road retrofit: “I wish all the homes were like this one. I have been very happy since I moved in and I don’t need to worry about the energy bills”

A deep retrofit aiming to meet the EnerPHit (Passivhaus retrofit) standard has been undertaken on a four-storey sandstone fronted tenement block of eight small flats on behalf of Southside Housing Association. The project has been extensively studied and evaluated.

Technical performance of the building with tenants in situ has been underway (and is still continuing) comparing theoretical with actual performance and seeking to understand why any such deviations in performance may occur. A series of interviews was undertaken with tenants post-occupancy in their newly retrofitted flats

Technical performance

The Niddrie Road, Glasgow: Tenement retrofit evaluation interim report found:

"The dwellings appear to be performing [better than] the targeted levels of consumption. This low energy use does not appear to have been at the expense of thermal comfort, with good average indoor temperatures, generally within the Enerphit performance targets throughout this period. The dwellings internal air quality/ventilation remained below 1000ppm CO₂ for the monitoring period, and there was no evidence from this monitoring of the MVHR systems being switched off or otherwise failing. At this stage there are no obvious concerns about presence of interstitial moisture in the construction. This will require on-going monitoring as conditions may change over time. There were some initial technical problems and delayed maintenance completion with the heat pumps. There are clearly lessons to learn for more efficient and effective training in the use of different aspects of the ‘kit’ in the properties though as time went on there was also evidence of satisfaction with the homes and their warmth and affordability."

Occupants' feedback

The Niddrie Road, Glasgow: Tenement retrofit evaluation interim report found:

"Initial findings suggest that the resident are enjoying a marked improvement in the thermal comfort of their living space compared to their previous address, but that they are still learning how best to use the heating and cooling controls in their new home (although this includes working together co-operatively to help each other do so). It was too early to say anything definitive about their energy costs.

Occupants’ feedback on the indoor environment, energy use and overall satisfaction was collected on first visit to each flat. Occupants reported overall satisfaction with all the aspects of the home, particularly the low energy bills. Several of the occupants reported not having to pay for electricity during the period of the energy rebate from the Government between October 2022 and March 2023. From a fuel poverty and affordability perspective, this was very positive for occupants as this suggests that the monthly energy bills were below £66.00 even with particularly high energy prices and that some of this credit may have even rolled out to the further months."

Quotations from the interviews included the following:

“I wish all the homes were like this one. I have been very happy since I moved in, and I don’t need to worry about the energy bills”
“The house was too warm during winter, but after a visit from the engineers to look out to my boiler everything was good. I haven’t had any problems since then”
“My house is comfortable and cheap to heat”

The Niddrie Road retrofit appears to be very successful in providing dwellings that are very low energy, comfortable, healthy, with high degrees of occupant satisfaction.