Project Context
This walkthrough uses a representative new-build acute care hospital in a high-seismic state: about 280 beds and 320,000 SF, reviewed by California’s Department of Health Care Access and Information (HCAI, the agency formerly known as OSHPD) and designed to the FGI Guidelines.
Healthcare is one of the most demanding estimating environments. State plan review, the FGI Guidelines, ASHRAE 170 ventilation requirements and infection-control rules all create cost that does not exist in a comparable office building. The estimate has to be built room by room and code section by code section, not by square foot.
What the Estimate Needs to Answer
On a project like this, the mechanical estimate is usually built (or independently checked) to find scope gaps before bid. The key questions are:
- How much seismic restraint does the mechanical and plumbing work need, and is it shown or only specified?
- What does ASHRAE 170 require, room by room, and does the equipment schedule actually deliver it?
- What infection control risk assessment (ICRA) measures apply to mechanical work next to occupied areas?
- What medical gas piping, alarms, and third-party verification are required under NFPA 99?
Typical Challenges
1. Seismic Restraint of MEP Systems
In California hospitals, nonstructural components (ductwork, piping, conduit and equipment) must be braced for seismic forces under the California Building Code, which references ASCE 7 Chapter 13. The bracing design is often delegated to the contractor and shown only in the specifications, so it is easy to leave out of a takeoff.
A seismic restraint takeoff typically covers:
- Transverse and longitudinal sway braces on duct and pipe runs that exceed the size or weight thresholds in the approved bracing system (many contractors use an HCAI pre-approved bracing system, identified by an OPM number)
- Vibration isolators with seismic snubbers or restrained isolators for air handlers, fans, pumps and chillers
- Flexible connections where piping and ductwork cross building seismic joints
The quantity depends on run lengths, duct and pipe sizes and the brace spacing in the chosen system, so it is counted from the drawings rather than applied as a percentage. National unit costs rarely include this work at California hospital levels, so it needs its own line items.
2. ASHRAE 170 Room-by-Room Ventilation Matrix
ASHRAE 170 (Ventilation of Health Care Facilities) sets, for each space type, minimum outdoor-air and total air changes per hour (ACH), the required pressure relationship to adjacent areas, filtration efficiency, and design temperature and humidity ranges. California adopts its own version of these requirements through the California Mechanical Code, so the estimator works from the edition the project is designed to.
Instead of a CFM-per-square-foot allowance, the estimate uses a matrix with one row per room. The fields that drive cost:
| Field captured per room | Why it drives cost |
|---|---|
| Space type (e.g. operating room, airborne infection isolation, patient room, soiled utility) | Sets the required ACH, pressure and filtration |
| Minimum outdoor-air and total ACH | Sets supply CFM, terminal unit size and duct size |
| Pressure relationship (positive / negative / none) | Requires dedicated exhaust, tight construction and room pressure monitors |
| Filtration requirement | Sets final-filter banks, housings and pressure drop, which affects fan selection |
| Temperature / humidity range | Can require humidifiers, reheat and dedicated cooling |
Once the matrix is built, it is checked against the air handler and terminal unit schedules. A mismatch, such as an isolation room drawn without a dedicated exhaust fan, becomes a pre-bid RFI.
3. ICRA Measures for Mechanical Work
When construction happens next to occupied patient areas, the infection control risk assessment sets the class of precautions. At the higher classes, mechanical work typically includes:
- Isolating or sealing HVAC returns and supplies that serve the work area
- Maintaining the work area at negative pressure with HEPA-filtered negative air machines, exhausted outside where possible
- Capping and sealing open ductwork and equipment openings during storage and installation
- Temporary filtration on units that stay in service near the work zone
These items are usually priced as their own Division 01 or Division 23 line items because they are real labor and equipment, not overhead.
4. NFPA 99 Medical Gas Piping
Medical gas and vacuum systems (oxygen, medical air, vacuum, nitrous oxide, nitrogen, WAGD) are labor-intensive. A typical takeoff includes:
- Copper tube cleaned for oxygen service (ASTM B819, Type K or L), with joints brazed under a nitrogen purge unless the adopted NFPA 99 edition and the specifications allow another joining method
- Zone valve boxes by zone, gas and floor, and source valves at each riser
- Master alarm panels (NFPA 99 requires at least two, in separate locations) and area alarm panels for each monitored zone
- Outlets and inlets counted from the room-by-room medical gas schedule
- Installer qualifications (ASSE 6010) and independent third-party system verification by an ASSE 6030 certified verifier before use
Third-party verification is often left out because it is performed by a separate firm; it belongs in the estimate either way.
Applicable Codes and Standards
- ASHRAE 170 – Ventilation of health care facilities (as adopted by the California Mechanical Code)
- NFPA 99 – Health Care Facilities Code (medical gas and vacuum systems)
- California Building Code (Title 24, Part 2) and ASCE 7 Chapter 13 – seismic design of nonstructural components
- FGI Guidelines – design and construction of hospitals
- SMACNA – duct construction and seismic restraint guidance
- ASSE 6010 / 6030 – medical gas installer and verifier qualifications
Software Workflow
| Software | Purpose |
|---|---|
| PlanSwift | Duct, pipe and equipment quantities from PDF sheets |
| Bluebeam Revu | Markups, room matrix cross-checks, RFI log |
| Trimble Accubid | Labor units and material pricing for mechanical scope |
Common Estimating Risks
| Risk area | Why it matters | Mitigation |
|---|---|---|
| Seismic restraint left to “by others” or a percentage | Large, labor-heavy scope that is rarely drawn | Count braces from runs and the chosen bracing system |
| Filtration or exhaust under-specified in schedules | Equipment and fan changes after award | Build the ASHRAE 170 matrix and compare it to schedules |
| ICRA measures treated as overhead | Unpriced labor, equipment and schedule | Price ICRA as specific line items |
| Medical gas verification omitted | System cannot be put in service without it | Include third-party verification in the base estimate |
Takeaways
- National averages do not fit California hospital work. Seismic restraint and state review add cost that has to be counted, not factored.
- Ventilation is priced room by room. ASHRAE 170 cannot be estimated from square footage.
- Infection control is measurable scope. It belongs in the estimate as labor and equipment.
How We Apply This on Real Bids
When a contractor sends us hospital drawings, we follow the same order: code-driven scope first (seismic, ventilation, infection control, medical gas), then quantities by CSI division, with every unresolved item listed as a question for the design team. See our HVAC estimating and MEP estimating services, or pricing for fee ranges.