A hood system installed as part of new construction is planned alongside the building’s structure, roof design, and mechanical systems from the start. A hood retrofitted into an existing building has to work around decisions that were made for an entirely different purpose — often years or decades before anyone imagined a commercial kitchen would occupy the space. That mismatch creates specific technical and cost challenges that don’t exist in new construction.
Every Type 1 hood system requires a duct that exits through the roof, terminating with a properly designed exhaust fan and discharge configuration that meets California mechanical code clearance and discharge direction requirements. In an existing building, this means cutting a new penetration through a roof structure that was never designed with that opening in mind.
This creates a cascade of considerations: structural evaluation to confirm the roof framing can accommodate the penetration and support the added weight of exhaust equipment, roofing membrane repair and waterproofing around the new penetration, and in many California jurisdictions, a required engineering review before the penetration is approved. Buildings with certain roof types — particularly older buildings or those with limited structural capacity — can require significant additional structural work to safely support a new hood system.
In new construction, duct routing from the hood to the roof is planned as part of the building’s overall design, typically running through space designed to accommodate it. In a retrofit, that duct often has to route through existing ceiling space, around structural elements, electrical and plumbing systems that were installed for a different purpose, and sometimes through multiple building levels depending on where the kitchen sits relative to the roof.
This routing challenge can meaningfully affect where your cooking line can actually be positioned within your layout — sometimes constraining equipment placement more than an owner initially expects, because the most efficient workflow layout on paper may not align with a duct route that’s structurally and financially feasible in the existing building.
As we’ve covered in our broader hood ventilation guide, makeup air is a required component of a compliant exhaust system — replacing the air your hood removes from the kitchen. In new construction, makeup air ductwork and equipment are planned into the building’s mechanical design from the start. In a retrofit, finding space for makeup air equipment and ductwork within an existing building’s mechanical infrastructure is frequently one of the more difficult technical puzzles of the project, particularly in buildings with limited roof space or mechanical room capacity already committed to other systems.
A retrofit hood project typically requires new electrical circuits for exhaust fans and hood lighting, coordinated with whatever electrical infrastructure already exists in the building. As we’ve discussed in the context of overall utility infrastructure assessment, older buildings frequently have electrical panels with limited remaining capacity — meaning a hood retrofit project can trigger a broader electrical panel upgrade that wasn’t part of the original project scope until the infrastructure assessment revealed it.
Given how much a hood retrofit depends on a building’s existing structural, roof, and mechanical conditions, this is exactly the kind of assessment that should happen during your site selection process — not after you’ve signed a lease and started design. A space that looks promising for your concept can carry hidden hood retrofit costs that only become apparent once a mechanical engineer or hood contractor actually evaluates the roof structure, existing mechanical infrastructure, and available duct routing paths.
At Northbay Restaurant Design, evaluating hood retrofit feasibility as part of our early site and infrastructure assessment includes:
