Passive house certification typically happens at the end of detailed design, when drawings are complete enough for an energy modeler to run a full simulation. The problem: the decisions that determine whether passive house is achievable envelope area, glazing ratio, building orientation, form factor are all made at concept stage, long before any simulation is run.
What Passive House Actually Requires
- Airtight envelope with thermal bridge-free detailing
- High-performance glazing with solar control adjusted to orientation
- Mechanical ventilation with heat recovery (MVHR)
- Heating and cooling demand below 15 kWh/m²/year
- Form factor ratio of envelope area to treated floor area below roughly 0.7 for compact buildings
Why Form Factor Is Set at Concept Stage
Form factor is a direct function of building geometry. A compact, cubic massing has a low form factor and performs well passively. A complex building with many external corners, wings, and large floor-to-ceiling glazing has a high form factor and requires more insulation, better glazing, and more careful detailing to achieve the same heating demand. By the time detailed design starts, form factor is already fixed.
What Brox's Energy Check Does
Brox runs a simplified energy model on each concept's massing not a full PHPP simulation, but a proxy calculation that estimates heating demand, cooling demand, and solar gain from orientation, envelope area, glazing ratio, and climate zone. Concepts that pass a passive-house-equivalent target are flagged as passive-ready. Concepts that require significant additional measures are flagged with the gap and the primary constraint.
What to Do With the Flag
A passive-ready flag from Brox means the massing is geometry-efficient enough that passive house performance is achievable with standard passive-house detailing. It is not a certification but it is a meaningful early filter that tells you which massing option to develop in detail if passive performance is a priority.
Tip
If passive house is a target, specify it explicitly in your brief. Brox will weight massing scoring toward lower form factors and flag any concept where passive house would require glazing reductions that materially change the building's character.
Check Passive Performance at Brief Stage
Brox scores every concept for energy performance before you commit to a massing so passive house decisions are made when they are cheapest to make.
Brief a Passive-Ready Concept →
