Deep Energy Retrofit of the Vogelweelde Neighbourhood, Halle

Halle, Belgium Construction and Development, Target groups of housing
Responsible Housing Award



Character of the estate

The neighbourhood has an open, green character, obtained by tree-lined streets with green verges and footpaths, as well as open front yards. The backyards of the single-family homes are accessible via footpaths. The inner area between the apartment buildings on Leeuwerikenlaan and Merellaan has been filled in with collective open space, including a playground. The district comprises two major construction phases, namely the southern part of the Leeuwerikenstraat was built with 98 homes in 1955 by the contractor Vande Kerckhove.

The second phase from 1959 included the further development of the northern district of this axis with 100 residential units, mainly grouped in apartment buildings that are located at an angle. All homes were designed by local architect Albert Pinson. Sober two-storey semi-detached houses under tiled saddleback roofs, linked into rows of mainly four single-family houses (or eight apartments) that are slightly offset from the building line. The brick volumes, opened by rectangular window openings, show great uniformity, despite the presence of a five-type variety. This results in variation in detailing and use of materials, especially in the elaboration and framing of the partially linked entrance doors.

Situation before implementation

After multiple smaller renovation projects focusing on individual parts of the envelope such as windows and doors or roofs as instructed by the Flemish Society for Social Housing (VMSW), WPZ decided to focus on a full energetic renovation that would first be trialled on an estate close to their headquarter (the Vogelweelde).

Typical problems for these homes where double glazing is installed is that the indirect consequences could not be managed. For example, the installation of double glazing changes the cold point causing moisture to build up on walls which are at a lower temperature due to cold bridges.

Poor overall thermal performance of the building envelope meant that residents of homes were more exposed to other characteristics – for example, an end of terrace shaded location meant these residents would find it harder to heat their homes during winter.

Issues tackled

Besides the challenges of the pandemic, which resulted in periods of stop-start work, it was essential that the residents remained in their homes while the renovation was carried out to avoid putting pressure on other areas of the housing stock. This meant that the health, safety and well-being of residents were paramount during the renovation and strict standards of conduct were applied to everyone on-site supported by outstanding resident liaison at every stage.

Actors involved

  • Flemish Society for Social Housing (VMSW)
  • Woonpunt Zennevallei
  • Knauf


The energy-saving results will be announced in early 2022, but already improvements of 26% have been recorded by Knauf Energy Solutions (KES) megawatt hour technology following the installation of the loft installation system.

A key benefit is the savings for tenants on their energy bill, with an estimated average annual saving of almost 800 euro. Given the evolution of gas prices, we would expect the savings to be even higher with this project.

Measurement of energy performance before and after the project to verify if the promised energy performance had been delivered in practice. A key benefit is that it ensures that the contractor has achieved what they promised and can be held to this promise in a contractual warranty, as agreed between Woonpunt Zennevallei and Knauf Energy Solutions.

This insight into how the investment really performs also enables Woonpunt to know what the real return on investment is for deep energy retrofit projects and helps inform future decisions regarding improving the energy performance of the housing stock and decarbonisation of the heating supply.

Real performance monitoring also offers key insights at the pre-monitoring phase, to show how disadvantages of poor thermal performance are unevenly distributed i.e. residents in homes with different orientations and types may find it more difficult to heat their homes, pay more for their heating bills, than other residents even though their houses are notionally the same standard in EPB calculations.


Why it works

The project benefitted from two types of innovation:

1) Implementation of the project according to a one-stop-shop approach

The project was the first of its kind in Belgium for residential housing owned by the social housing companies, where the resident engagement, design, works, and quality control were brought together by a single contractor. This was made possible by a special tendering approach developed by Woonpunt Zennevallei (see below)

2) Measurement of real energy performance, before and after works had been completed

This was the first large scale renovation project to use KES negaWatthour technology. This means that for the first time a social housing company can really know the real energy performance delivered by the renovation rather than relying on the EPC calculation.

3) Energy performance backed up by a contractual warranty

While common in other sectors, this is the first time any project we are aware of in the social housing sector has been backed up by a contractual warranty, meaning that if the promised performance isn’t delivered in practice, then Knauf Energy has to investigate and correct a potential problem.

Tools used

Woonpunt Zennevallei developed a new type of tendering to procure the deep energy retrofit of the Vogelweelde neighbourhood. Until recently social housing companies tendered for energy renovations according to a design – bid – build approach. This would entail one tender for works and another for design, leading to huge amount of time and administrative burden in preparing these projects. With this new, ‘design and build’ type tender, it means that we can procure energy renovations in a much more time-efficient way.



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