FIELD NOTE · SUPPLEMENTAL SET
Saturated soil, unnamed membrane: the amenity deck specification
ISSUEDJULY 11, 2026DRAWN BY THE NIGHTLY SWEEP
The waterproofing membrane on an amenity deck is examined once, closely, and then never seen again, and the 2025 California Building Code, in force since January 1, 2026, prescribes waterproofing by material and by thickness for a basement floor under hydrostatic pressure, and prescribes none for the deck over a lobby. So the membrane over an occupied lobby is chosen by a person.
What the code fixes is everything stacked on top of that sheet. The General Services Administration's planted roof guidance sets out, above the membrane, a protection and moisture management layer, a root barrier membrane, a separation layer, insulation, a drainage layer of geocomposite or granular mineral, filter fabric, growing medium and the planting itself, placed by several different trades on somebody else's schedule. That list starts at the membrane and leaves out the vapor barrier GSA draws under the sheet in all four of its roof types.
Chapter 15, which governs roofs, runs Section 1501 through Section 1513, and not one of those sections is titled waterproofing. Section 1805.3 governs the surface nobody stands on, and it is specific: for floors, rubberized asphalt, butyl rubber, fully adhered or fully bonded HDPE or polyolefin composite, or not less than 6-mil PVC, and for walls, 40-mil polymer-modified asphalt or 6-mil polyethylene, among other approved materials. Where the water goes and how the assembly burns are fixed too; the sheet is left open, and the architect or the waterproofing consultant closes it in a specification written long before anyone orders a roll.
GSA sorts planted roofs by growing medium, extensive at 3 to 6 inches, semi-intensive at 6 to 12 inches, intensive above 12 inches. It also measured wet weight, per ASTM E2397, for two of its own recommended profiles: 20.06 psf for the 3-inch single-course extensive one and 42.23 psf for the 6-inch multi-course one it files as semi-intensive, numbers GSA says should be used only as a guide. The second is not the first with more soil on it. It carries one more inch of growth media, 4 inches against 3, and the rest of the difference is a 2-inch drainage course, a capillary fabric and heavier plants the shallow profile does not have at all. Media depth is a landscape architect's decision landing on a structural engineer's sheet.
Table 1607.1 adds the people: 20 psf of live load on a roof not intended for occupancy, 100 psf on a roof area used for assembly purposes, and live load reduction is not permitted there. The load side did not move in this cycle. Section 1606.5 and those rows read the same in the 2022 edition, and the part of this subject that did move sits in the referenced standards chapter instead, under the drains.
The planted roof assembly pulled apart, deck at the bottom, with layer order and media depths from General Services Administration planted roof guidance, Table A3 for wet weight by profile, and loads from 2025 CBC Section 1606.5 and Table 1607.1.
Under the 2025 cycle California runs on ASCE/SEI 7-22 with Supplement 1, named in the referenced standards chapter of the building code, where the 2022 edition ran on ASCE 7-16. Rain load already counted the static head at the secondary drainage inlet plus the hydraulic head above it at design flow, so drain sizing has been inside that number for cycles. What ASCE 7-22 adds is a third term, a ponding head taken from the deflection of the roof under unfactored rain plus dead load, which puts deflection inside the rain load rather than leaving it to a separate ponding-instability check. So the stiffness of the deck and the size of the drains now land in the same figure, and the saturated media Section 1606.5 makes the engineer count twice is part of the dead load doing the deflecting.
4 in. MAXIMUM SHORT-TERM HYDROSTATIC HEAD IN A FLOOD TEST, ASTM D5957-98(2021) 24 hours MINIMUM AGE OF THE MEMBRANE BEFORE THAT WATER GOES ON, 48 HOURS BELOW 50 DEGREES F 2 percent THE STEEPEST SLOPE THE FLOOD TEST GUIDE COVERS, 20 MM PER METER
What closes when the overburden goes on is the clean window, not the technique. GSA states that low-voltage leak detection can be performed before and after the green roof is installed on appropriately designed green roofs, by charging the wet medium over the membrane and letting that charge travel through the moisture in the vegetated cover to any penetration. IIBEC agrees the low-voltage method can troubleshoot through different types of overburden, then prices it: much more difficult and challenging than testing exposed membranes, with significantly reduced reliability. Before the overburden, a scan costs a clear deck; after it, a scan costs whatever has to come off to reach the sheet, drainage course, growing medium and planting included.
A specification has to impose the order: membrane down, the 24 hours ASTM asks for, the flood test, the scan across the wetted sheet, then protection and root barrier and drainage, then the media, then the planting. None of that is scheduled anywhere. The waterproofing contractor detailing every drain, penetration, edge and transition is working inside a window the general contractor controls, since the schedule decides when the deck is clear, when the test water goes on, and when the landscape crew starts placing media.
Nothing schedules the membrane. No re-test interval, no inspection cycle, no service life, and the fire code official who can require a maintenance plan for the vegetation under that same section has no equivalent lever for the sheet beneath it, which by the time anyone is looking for it is under a drainage course, several inches of growing medium and a planted terrace.
A wet ceiling in the parking level below is produced a long way upstream of the crew that rolled the sheet out and the landscape contractor who filled the planters over it. The decision sits in the specification, where a membrane the code declines to name gets selected against a stack whose weight the code insists on weighing twice, and where the flood test and the scan are either written into the sequence or left out of it. Chapter 15 names no membrane for it. Section 1805.3 names 6-mil PVC for a basement floor.
What the code fixes is everything stacked on top of that sheet. The General Services Administration's planted roof guidance sets out, above the membrane, a protection and moisture management layer, a root barrier membrane, a separation layer, insulation, a drainage layer of geocomposite or granular mineral, filter fabric, growing medium and the planting itself, placed by several different trades on somebody else's schedule. That list starts at the membrane and leaves out the vapor barrier GSA draws under the sheet in all four of its roof types.
Chapter 15, which governs roofs, runs Section 1501 through Section 1513, and not one of those sections is titled waterproofing. Section 1805.3 governs the surface nobody stands on, and it is specific: for floors, rubberized asphalt, butyl rubber, fully adhered or fully bonded HDPE or polyolefin composite, or not less than 6-mil PVC, and for walls, 40-mil polymer-modified asphalt or 6-mil polyethylene, among other approved materials. Where the water goes and how the assembly burns are fixed too; the sheet is left open, and the architect or the waterproofing consultant closes it in a specification written long before anyone orders a roll.
Wet soil, and the same soil dry
Section 1606.5 runs two sentences, and they count all landscaping and hardscaping material on a vegetative or landscaped roof as dead load, weight that has to be computed twice, once with the soil and drainage layers fully saturated and once with them fully dry, because the two conditions load the structure differently and the more severe one governs. Two sentences decide more about this deck than the waterproofing section Chapter 15 does not have.GSA sorts planted roofs by growing medium, extensive at 3 to 6 inches, semi-intensive at 6 to 12 inches, intensive above 12 inches. It also measured wet weight, per ASTM E2397, for two of its own recommended profiles: 20.06 psf for the 3-inch single-course extensive one and 42.23 psf for the 6-inch multi-course one it files as semi-intensive, numbers GSA says should be used only as a guide. The second is not the first with more soil on it. It carries one more inch of growth media, 4 inches against 3, and the rest of the difference is a 2-inch drainage course, a capillary fabric and heavier plants the shallow profile does not have at all. Media depth is a landscape architect's decision landing on a structural engineer's sheet.
Table 1607.1 adds the people: 20 psf of live load on a roof not intended for occupancy, 100 psf on a roof area used for assembly purposes, and live load reduction is not permitted there. The load side did not move in this cycle. Section 1606.5 and those rows read the same in the 2022 edition, and the part of this subject that did move sits in the referenced standards chapter instead, under the drains.
The planted roof assembly pulled apart, deck at the bottom, with layer order and media depths from General Services Administration planted roof guidance, Table A3 for wet weight by profile, and loads from 2025 CBC Section 1606.5 and Table 1607.1.
Water that does not leave the roof
Section 1502.1 sends roof drainage design to Section 1611 and to Chapter 11 of the California Plumbing Code, and Section 1502.2 requires secondary emergency overflow drains or scuppers wherever the perimeter construction stands high enough to entrap water if the primary drains allow buildup. Water that cannot leave is water the deck holds, and water the deck holds is load, which is how a drainage drawing turns into a structural one.Under the 2025 cycle California runs on ASCE/SEI 7-22 with Supplement 1, named in the referenced standards chapter of the building code, where the 2022 edition ran on ASCE 7-16. Rain load already counted the static head at the secondary drainage inlet plus the hydraulic head above it at design flow, so drain sizing has been inside that number for cycles. What ASCE 7-22 adds is a third term, a ponding head taken from the deflection of the roof under unfactored rain plus dead load, which puts deflection inside the rain load rather than leaving it to a separate ponding-instability check. So the stiffness of the deck and the size of the drains now land in the same figure, and the saturated media Section 1606.5 makes the engineer count twice is part of the dead load doing the deflecting.
Four inches of standing water, held for a day
ASTM D5957-98(2021), the standard guide for flood testing horizontal waterproofing installations, applies to surfaces sloped not more than 2 percent, which the standard writes as 20 mm per meter, and covers fully adhered sheet membranes, fluid-applied membranes and loose-laid sheets on parking garages and plaza decks over habitable spaces or elevated structures. The trade did not wait for a code section. Per ASTM's published scope, the test ponds water to a short-term hydrostatic head of not more than 100 mm, 4 inches, and is not run within the first 24 hours after installation, or for at least 48 hours where temperatures sit below 10 degrees C, 50 degrees F. A structural engineer should review the substrate's load capacity before anyone floods the deck.4 in. MAXIMUM SHORT-TERM HYDROSTATIC HEAD IN A FLOOD TEST, ASTM D5957-98(2021) 24 hours MINIMUM AGE OF THE MEMBRANE BEFORE THAT WATER GOES ON, 48 HOURS BELOW 50 DEGREES F 2 percent THE STEEPEST SLOPE THE FLOOD TEST GUIDE COVERS, 20 MM PER METER
A wetted membrane, and the day it is covered
IIBEC Technical Advisory 018-2019, updated in 2021, states that scanning platforms must make direct contact with the membrane, so they cannot be used on assemblies covered by pavers, garden or ballast that cannot be readily removed. Nothing in it requires the scan to precede the overburden. Physics does that. Low-voltage methods read a wetted membrane; the high-voltage method sweeps a broom-like electrode across a dry one, and neither suits black EPDM unless specialized conductive primers are used, while high-voltage results are affected by varying membrane thickness in fluid-applied systems.What closes when the overburden goes on is the clean window, not the technique. GSA states that low-voltage leak detection can be performed before and after the green roof is installed on appropriately designed green roofs, by charging the wet medium over the membrane and letting that charge travel through the moisture in the vegetated cover to any penetration. IIBEC agrees the low-voltage method can troubleshoot through different types of overburden, then prices it: much more difficult and challenging than testing exposed membranes, with significantly reduced reliability. Before the overburden, a scan costs a clear deck; after it, a scan costs whatever has to come off to reach the sheet, drainage course, growing medium and planting included.
A specification has to impose the order: membrane down, the 24 hours ASTM asks for, the flood test, the scan across the wetted sheet, then protection and root barrier and drainage, then the media, then the planting. None of that is scheduled anywhere. The waterproofing contractor detailing every drain, penetration, edge and transition is working inside a window the general contractor controls, since the schedule decides when the deck is clear, when the test water goes on, and when the landscape crew starts placing media.
Vegetation on a schedule, membrane on none
The fire code schedules the part of this assembly that grows: Section 317 of the 2025 California Fire Code is titled Vegetative and Landscaped Roofs. In the 2024 International Fire Code text that edition is built on, as reproduced by UpCodes, Section 317.2.1 requires supplemental irrigation to maintain hydration and keep dry foliage to a minimum, and Section 317.2.2 requires excess biomass, overgrown vegetation, leaves and dead or decaying material to be removed at regular intervals not less than two times per year.Nothing schedules the membrane. No re-test interval, no inspection cycle, no service life, and the fire code official who can require a maintenance plan for the vegetation under that same section has no equivalent lever for the sheet beneath it, which by the time anyone is looking for it is under a drainage course, several inches of growing medium and a planted terrace.
A wet ceiling in the parking level below is produced a long way upstream of the crew that rolled the sheet out and the landscape contractor who filled the planters over it. The decision sits in the specification, where a membrane the code declines to name gets selected against a stack whose weight the code insists on weighing twice, and where the flood test and the scan are either written into the sequence or left out of it. Chapter 15 names no membrane for it. Section 1805.3 names 6-mil PVC for a basement floor.