What space should we reserve now for an all-electric commercial building?
Reserve a workable system, not an empty plant-room rectangle. Before the concept plan freezes, coordinate heating and hot water plant, storage, electrical supply, airflow, maintenance access and replacement routes. Test the roof as a shared resource for plant, solar panels and safe access. The required dimensions come from the engineers' load estimates and equipment options. The architect's task is to protect those envelopes until the team has enough evidence to confirm or reduce them.
This article is about new buildings. For existing commercial buildings, see our article on deep energy retrofits.
Why the space question arrives late
An electric heating strategy can change where the building needs space. The GBCA/Cundall guide identifies larger plant areas, airflow and electrical infrastructure as considerations when replacing gas heating with heat pumps [1]. This is a coordination warning, not a universal area multiplier. Plant type, loads, heat source, storage and redundancy determine the actual envelope.
The Energy Efficiency Council's commercial electrification roadmap identifies physical constraints and electricity network capacity as barriers raised in stakeholder consultation [2]. That work concerns existing buildings. Our inference for new buildings is practical: test those constraints before floor plates, risers and roof allocations make an alternative difficult.
The trade that sets the plant size: storage or peak demand
Hot water storage can allow a smaller heat pump to serve a short demand peak; the GBCA/Cundall guide describes this alternative to matching boiler peak capacity [1]. But daily energy demand alone does not size the system. Ask the hydraulic and mechanical engineers to test the demand profile, usable storage, recovery between peaks and output at the design conditions. Include heat losses, any backup heating and the agreed resilience requirement.
The physical test is an energy balance: heat supplied plus usable stored heat must meet demand over each critical period. A tank that covers the first peak but cannot recover before the next is not a complete solution. Ask for the heat-pump thermal output and electrical input separately. The electrical engineer then checks coincident building demand, including backup plant, cooking and EV charging where relevant. Compare the options by area, height, weight, airflow, electrical capacity and whole-system cost.
Air-source heat pumps need an outdoor air path that prevents harmful recirculation; a large room is not enough if its openings cannot provide the required airflow. Screens and acoustic treatment must work with that airflow. Water- or ground-source options have different interfaces. Low-temperature heating also affects the heat emitters, so confirm the operating temperatures and coil or terminal-unit sizes with the mechanical engineer [1].
The roof is contested
Draw one coordinated roof plan showing plant footprints, airflow and exhaust zones, PV layout, shading, access, fall protection and replacement lifting zones. Reserve section heights as well as plan areas. A clear rectangle on plan may be unusable once a screen, duct, parapet or maintenance clearance is included.
Have the building surveyor and energy consultant identify the applicable renewable-energy and EV provisions for the project's jurisdiction, building class, approval date and compliance pathway. Record the adopted NCC edition and any variations; Part J9 is one place to check [3]. Then have the electrical engineer confirm the layout and network interfaces. Do not allocate roof space to plant simply to minimise a solar requirement.
An allowance is provisional until its engineering assumptions are checked. Confirming the design does not make the required plant area available for another use: release only surplus space after the coordinated design shows it is no longer needed.
The spatial reservation matrix
Use this matrix in the concept coordination meeting. Every row needs a zone ID on plans and sections, a named technical owner, the current basis (allowance or calculated option), and the evidence required before the envelope can be reduced. Keep required operating, maintenance and replacement space protected after the system is selected.
Element and zone ID | Reserved envelope, including clearances | Assumption, owner and design status | Evidence before reducing the reservation |
|---|---|---|---|
Space-heating plant (zone ID on plans) | Plant, airflow paths, acoustic treatment, operating clearances and heat-emitter space | System options, design-condition output, recirculation and noise. Mechanical engineer; acoustic specialist where needed. State allowance or calculated option | Selected system and coordinated operating envelope confirmed; release surplus only |
Hot water plant and storage (zone ID) | Tanks, pumps, insulation, access, drainage and structural load | Demand profile, usable storage, recovery and backup strategy. Hydraulic/mechanical engineer; structural engineer checks loads | Demand and recovery checked; option selected; loads and maintenance space coordinated |
Roof allocation: plant, PV, access and exhaust (roof zone IDs) | Plant zones with airflow clearances, height-safety and maintenance paths, exhaust discharge zones, PV array area, shading | Whether a PV provision applies, which option, and the array layout. Owner: electrical engineer and energy consultant, with the building surveyor | Coordinated roof plan and section confirm plant, PV, access and future replacement |
Electrical supply and network connection (zone IDs) | Substation, main switchboard, risers, cable routes | Coincident demand, backup plant and load-control assumptions; network capacity and connection conditions. Electrical engineer | Supply strategy supported by network advice; keep connection conditions and lead times in the programme |
Electric vehicle charging (zone IDs) | EV supply, controls and distribution space where required | Electrical engineer to confirm applicable provisions, charging assumptions and demand-control strategy | Charging layout, distribution routes and any demand-management assumptions coordinated |
Commercial kitchens and food tenancies | Electric cooking, exhaust risers and discharge | Tenancy cooking assumptions and electrical allowance. Owner: leasing lead with the electrical and mechanical engineers | Tenancy mix and cooking strategy agreed |
Access and replacement routes | Paths, lifting zones and openings for the largest item | Largest item size, crane or lift strategy, replacement interval. Owner: mechanical engineer | Replacement route verified through plans and sections, including access and lifting constraints |
When the big plant room is the wrong answer
A central plant room is not always the best answer. The guide identifies direct electric heating as an option for very low heating demand, and local hot water for low distributed demand [1]. That does not mean resistance heating is more energy-efficient than a heat pump. It means low annual use can change the trade-off between plant complexity, distribution losses, space and cost. Compare the complete system and its peak electrical demand. Reduce avoidable loads first, while maintaining the required ventilation, comfort and hygiene performance.
Illustrative scenario, not a real project. A concept roof has a generous plant rectangle but no section or airflow path. When screens, solar panels and maintenance routes are added, the air-source option no longer fits. Moving it into a basement does not solve the problem unless the engineer can design a suitable air path, acoustic treatment and access route. The missed decision was not plant-room area; it was whether the complete system could operate in the reserved envelope.
Next step
Ask the services team for two or three feasible options before concept sign-off. For each, show the load basis, plant and storage envelope, structural loads, airflow, coincident electrical demand and replacement route. Mark unresolved items on the drawings with an owner and decision date. Keep provisional space until that owner provides the agreed evidence; keep the final operating envelope for the life of the building.
For a large electrical load, the next constraint may be the connection rather than plant-room area. See the grid-capacity decision guide for the distinction between supply agreements and connection capacity.
When comparing cooling options, test the full heat path using the cooling and water-balance questions rather than treating the equipment label as a complete system description.
Sources
- GBCA and Cundall, with the NSW Government and CEFC, A practical guide to electrification: For new buildings (April 2022), sections on space heating, domestic hot water and the all-electric plant room.
- CEFC and Energy Efficiency Council, A roadmap to reduce emissions in commercial buildings (January 2026).
- NCC 2025 Volume One, Part J9, J9D5 and its limitations.
Questions or corrections: contact Makao.
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