ASHRAE 90.1 (Energy Standard for Buildings Except Low-Rise Residential Buildings) is the baseline energy code for commercial construction in most of the United States. The IECC commercial provisions reference ASHRAE 90.1 as a compliance path, and many jurisdictions adopt it directly. Plan reviewers checking energy code compliance on commercial projects are checking ASHRAE 90.1 requirements whether the jurisdiction formally adopts the IECC or ASHRAE 90.1 itself.
ASHRAE 90.1 offers three compliance paths: prescriptive (Section 5-10), performance (Section 11 with Appendix G energy modeling), and the Energy Cost Budget method (Section 11 without Appendix G). Most projects use the prescriptive path for at least part of the building because it requires straightforward documentation on the drawings rather than a full energy model. But even prescriptive compliance has enough detail to generate plan review comments on nearly every commercial project. These are the errors that come up most often.
Compliance path selection
Mixing compliance paths without documentation
ASHRAE 90.1 Section 5.1 allows the use of the prescriptive path for the building envelope while using the performance path for HVAC and lighting, or vice versa. This is called a "mixed compliance" approach and it is permitted, but the energy code compliance form must clearly indicate which compliance path applies to each system (envelope, HVAC, service water heating, power, lighting).
The most common error is not including a completed energy code compliance form (COMcheck or equivalent) in the drawing set, or including one that does not specify the compliance path for each system. Plan reviewers need to know which path the designer is using before they can verify the specific requirements. A drawing set that does not include an energy compliance form or that notes "complies with ASHRAE 90.1" without specifying the path will be returned as incomplete.
Envelope: insulation and fenestration
Incorrect climate zone or insulation values
ASHRAE 90.1 Section 5 (Building Envelope) prescribes minimum insulation values for walls, roofs, floors, and below-grade surfaces based on the climate zone. ASHRAE 90.1 Table 5.5-1 through 5.5-8 list the requirements for each climate zone (1 through 8) and each construction type (mass wall, steel- framed wall, wood-framed wall, metal building wall, etc.). The insulation value is expressed as minimum R-value for insulation or maximum U-factor for the overall assembly.
| Component | Common error | What the reviewer checks |
|---|---|---|
| Roof insulation | Using R-value for insulation alone, not assembly U-factor | Assembly U-factor per Table 5.5-x matches climate zone requirement |
| Steel-framed wall | Ignoring thermal bridging through steel studs | Assembly U-factor accounts for framing factor, not just cavity R-value |
| Below-grade wall | Omitting insulation entirely on below-grade portions | R-value per Table 5.5-x for applicable depth below grade |
| Slab-on-grade floor | Not insulating slab perimeter in climate zones 4+ | Perimeter insulation R-value and depth per Table 5.5-x |
| Continuous insulation | Calling out ci on drawings but not specifying R-value | Specific ci R-value and location (exterior, interior, or integral) |
The most consequential envelope error is using the wrong climate zone. ASHRAE 90.1 Figure B-1 and Table B-2 map every U.S. county to a climate zone. A project in Denver (Climate Zone 5B) has significantly different insulation requirements than a project in Phoenix (Climate Zone 2B). A designer who uses Climate Zone 4 values for a Climate Zone 5 project will undersize the insulation on every assembly. Plan reviewers verify the climate zone on the energy compliance form against the project address.
Fenestration area and U-factor errors
ASHRAE 90.1 Section 5.5.4.2 limits the total fenestration area (windows, curtain wall, storefront) to a maximum percentage of the gross wall area. For the prescriptive path, the maximum is 30% for vertical fenestration (40% with tradeoffs per Section 5.5.4.2.3). Skylight area is limited to 3% of the gross roof area (5% with daylight controls per Section 5.5.4.2.4).
Plan reviewers calculate the fenestration area ratio from the architectural elevations and floor plans. The most common error is exceeding the 30% fenestration area ratio on a prescriptive compliance path without switching to the performance path or providing the tradeoff documentation per Section 5.5.4.2.3. A building with a glass curtain wall on two facades may have a fenestration ratio of 50% or more, which cannot comply prescriptively without the tradeoff option or a performance path energy model.
Fenestration U-factor and solar heat gain coefficient (SHGC) must also comply with the prescriptive tables. Plan reviewers check the window schedule on the architectural drawings for the specified U-factor and SHGC values and compare them against ASHRAE 90.1 Table 5.5-x for the applicable climate zone. A common error is specifying a U-factor that meets the requirement for fixed windows but not for operable windows, which have a higher U-factor due to the frame construction.
HVAC efficiency
Equipment not meeting minimum efficiency requirements
ASHRAE 90.1 Section 6.4.1 requires that HVAC equipment meet minimum efficiency levels specified in Tables 6.8.1-1 through 6.8.1-16. The tables cover unitary air conditioners, heat pumps, chillers, boilers, furnaces, and other equipment types. The minimum efficiency depends on the equipment type, capacity, and in some cases the heating fuel type.
The most common error is showing equipment on the mechanical schedule that does not include the efficiency rating (EER, IEER, SEER2, COP, AFUE, or thermal efficiency depending on the equipment type). Without the efficiency value on the drawings, the plan reviewer cannot verify compliance. Another frequent error is specifying equipment that meets the federal minimum but not the ASHRAE 90.1 minimum, which may be higher for certain equipment types and capacity ranges. Plan reviewers cross-reference the equipment model number and efficiency rating on the mechanical schedule against the applicable ASHRAE 90.1 table.
Missing economizer requirement
ASHRAE 90.1 Section 6.5.1 requires air-side economizers on individual cooling systems with a capacity of 54,000 Btu/h (4.5 tons) or greater in most climate zones. The exceptions are limited: Climate Zone 1A is exempt, and certain system types (dedicated outdoor air systems, systems with energy recovery meeting specific effectiveness thresholds) have modified requirements.
Plan reviewers check every packaged rooftop unit, air handler, and split system on the mechanical schedule with a cooling capacity of 54,000 Btu/h or more. If the unit does not have an economizer and the project is not in an exempt climate zone, the reviewer will flag it. The error is frequently a rooftop unit schedule that specifies the cooling capacity and efficiency but does not indicate whether an economizer is included. In some cases the designer specifies a unit model that is available with or without an economizer option but does not indicate which configuration is being used.
Lighting power density
Exceeding the lighting power density limits
ASHRAE 90.1 Section 9.2 requires that the connected lighting power in a building not exceed the limits calculated using either the building area method (Table 9.5.1) or the space- by-space method (Table 9.6.1). The building area method provides a single watts-per-square-foot allowance based on the building type. The space-by-space method provides different allowances for each room type (office, corridor, lobby, restroom, etc.) and is typically more generous for buildings with diverse space types.
| Building type | LPD allowance (W/sf) | Common error |
|---|---|---|
| Office | 0.79 | Exceeding with decorative or task lighting not included in calculations |
| Retail (general) | 1.06 | Not accounting for accent and display lighting in total LPD |
| School/university | 0.87 | Lab and shop spaces calculated at classroom rate |
| Hospital | 0.96 | Operating rooms and imaging suites at whole-building average |
| Warehouse | 0.48 | Exceeding with high-bay fixtures in sorting/shipping areas |
The most common error is not providing a lighting power density calculation on the electrical drawings. The calculation must show the total connected lighting wattage, the building area (or the area of each space if using the space-by-space method), and the resulting watts per square foot. Without this calculation, the plan reviewer cannot verify that the lighting design complies. A lighting plan that shows fixture types and locations but does not include a wattage schedule or a LPD summary will be flagged.
Not accounting for lighting controls
ASHRAE 90.1 Section 9.4.1 requires automatic lighting controls in most spaces, regardless of the compliance path. These are mandatory provisions, not prescriptive tradeoffs. Required controls include occupancy/vacancy sensors in enclosed offices and classrooms (Section 9.4.1.1), daylight responsive controls in daylight zones adjacent to vertical fenestration and skylights (Section 9.4.1.4), and automatic time-based controls (scheduling) for all non-dwelling unit spaces.
The error is showing a lighting plan with fixture types and locations but not showing the control zones, sensor locations, or daylight zones on the reflected ceiling plan or lighting control plan. Plan reviewers check that every enclosed office has an occupancy or vacancy sensor shown on the drawings, that sidelighted and toplighted daylight zones are identified with automatic dimming or switching controls, and that a time-based control schedule is referenced. Missing lighting controls documentation is one of the most frequent energy code comments on commercial projects.
Mandatory provisions
Missing mandatory requirements regardless of compliance path
ASHRAE 90.1 Sections 5.4, 6.4, 7.4, 8.4, and 9.4 contain mandatory provisions that apply to every project regardless of whether the prescriptive or performance path is used. These include insulation installation quality requirements, air barrier continuity, duct sealing and insulation, pipe insulation, service water heating efficiency, transformer efficiency, and lighting controls. Designers using the performance path sometimes assume that the energy model satisfies all requirements, but the mandatory provisions must be met independently.
The mandatory provisions that generate the most plan review comments are: air barrier continuity (Section 5.4.3.1, requiring a continuous air barrier across the building envelope with all joints and penetrations sealed), duct insulation (Section 6.4.4.1, requiring minimum R-6 or R-8 insulation on supply ducts depending on location), and pipe insulation (Section 6.4.4.2, requiring insulation on piping conveying fluids above 105F or below 60F). Plan reviewers check that these items are called out on the drawings or in the specifications even when the project uses a performance path energy model.
Commissioning requirements
Not addressing commissioning on the drawings
ASHRAE 90.1 Section 6.7.2 requires commissioning for HVAC systems in buildings larger than 50,000 square feet or with a total mechanical system capacity over 600,000 Btu/h. The commissioning requirements include functional performance testing of HVAC controls, economizer operation, air and water balance, and equipment capacity verification.
The plan review comment is not that the commissioning has not been completed (it cannot be completed before construction). It is that the drawings do not include a commissioning specification or a reference to a commissioning plan. Section 6.7.2.1 requires that the construction documents include the commissioning requirements. A mechanical drawing set that does not reference commissioning on projects that exceed the threshold will be flagged. The fix is typically a note on the mechanical general notes sheet referencing the commissioning specification section and identifying the systems to be commissioned.
Catching ASHRAE 90.1 errors before submittal
ASHRAE 90.1 compliance spans the architectural drawings (envelope insulation, fenestration area and performance), the mechanical drawings (HVAC efficiency, economizers, duct insulation, commissioning), the electrical drawings (lighting power density, lighting controls, transformer efficiency), and the plumbing drawings (service water heating efficiency, pipe insulation). The errors that generate the most revision cycles are the ones that require coordination between disciplines: an envelope insulation specification on the architectural drawings that does not match the U-factor on the energy compliance form, or a lighting plan that shows fixtures but not the control zones required by the energy code. Reviewing the architectural, mechanical, and electrical drawings against ASHRAE 90.1 in a single pass catches these cross-discipline coordination gaps before the plan reviewer does.