Multifamily Common Area HVAC Title 24 Requirements
Common area HVAC in a multifamily building follows Sections 160.2(c), 160.3 and 170.2(c): outdoor air sized to the larger of 15 cfm per person or an area rate, MERV 13 filters, tested ducts, and acceptance tests before an occupancy permit. Equipment serving only the dwelling units follows separate rules.
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Sizing the outdoor air
Equation 160.2-H sets the outdoor airflow for a common-area zone at the larger of 15 cfm per person or the Table 160.2-B area rate times the floor area. Corridors default to 5 people per 1,000 square feet and 0.15 cfm per square foot, so a 1,000 square foot corridor works out to 75 cfm by people and 150 cfm by area. The 150 governs.
Filters and ducts
- Filters: MERV 13, or the matching AHRI 680 particle efficiency, in nominal 2 inch depth or 1 inch sized for 150 feet per minute face velocity, with gasketed racks. This covers supply air through ducts over 10 feet, supply-only ventilation and the supply side of balanced systems.
- Duct leakage: a new duct system on a constant-volume, single-zone system under 5,000 square feet, with over a quarter of its duct surface outdoors or in unconditioned space, must test at 6 percent of nominal airflow or less. Other duct systems follow California Mechanical Code Section 603.9.2.
When you replace a unit
Section 180.2(b)2B sends new or replacement components through the equipment, sizing and fan power rules of Section 170.2(c)1, 2 and 4. A noncompliant thermostat is replaced with a demand responsive type, and a new duct system is at least 75 percent new material. Expanding an existing system leaves the existing equipment alone (Exception 1 to Section 180.2).
Tests before the occupancy permit
Section 160.3(d)1 requires acceptance tests under Nonresidential Appendix NA7 by a certified mechanical acceptance test technician: outdoor air (NA7.5.1), constant volume single zone controls (NA7.5.2), new or altered ducts (NA7.5.3), economizers, DOAS, HRV or ERV (NA7.5.4) and demand control ventilation (NA7.5.5). The first three certificates are NRCA-MCH-02-A, 03-A and 04-A.
Zone thermostat ranges and shut-off controls are on multifamily temperature control. Systems serving only dwelling units and shared kitchens or laundries for units that lack them may follow the dwelling-unit rule instead. Related pages: multifamily HVAC, common area lighting, acceptance testing before final, mechanical acceptance tests and the multi-family service.
Common Title 24 Questions
- Do apartments need Title 24?
- Does a duplex need Title 24?
- Do triplexes and fourplexes need Title 24?
- Which Title 24 forms does a multi-family project use?
- What is an LMCC certificate?
- How much does a multi-family Title 24 report cost?
Frequently Asked Questions
Common area. The Multifamily Compliance Manual says spaces used by building managers and maintenance staff are common use areas, so Sections 160.2(c) and 160.3(a)2 apply.
A certified mechanical acceptance test technician, whose certification number goes on the Certificate of Acceptance under Section 160.3(d)3.
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