Appeal 33637

OSSC 1812

Section 1812.2.1 – Subfloor Preparation. A layer of gas permeable material shall be placed under all concrete slabs and other floor systems that directly contact the ground and are within the walls of the living spaces of the building, to facilitate future installation of a sub-slab depressurization system, if needed.

Section 1812.2.2 – Soil-gas-retarder. A minimum 6-mil polyethylene or equivalent flexible sheeting material shall be placed on top of the gas-permeable layer prior to casting the slab or placing the floor assembly to serve as a soil-gas-retarder by bridging any cracks that develop in the slab or floor assembly and to prevent concrete from entering the void spaces in the aggregate base material.

Section 1812.2.5 – Passive sub-slab depressurization system (basement or slab-on-grade). In basement or slab-on-grade buildings, sub-slab soil exhaust system ducts complying with Section 1812.2.6 shall be installed during construction…

Section 1812.2.6 – Sub-slab soil exhaust system ducts (SSESD). SSESD’s shall be provided in accordance with this section and shall run continuous from below the soil-gas-retarder to the termination point described in section 18.12.2.6.5…

Omit ventilation portion of the radon mitigation system for Building C. Existing radon levels in the existing Barbur Rentals Building were tested and are very low.

Building C, which is below the water table will have a radon barrier that is incorporated into the waterproofing membrane. At Building C, the low levels of radon found on the site will remain in the water underground and will
be prevented from entering the building by the radon barrier. Radon will be greatly reduced from the tested current low levels where no radon barrier is present. We have specified two competitive waterproofing membranes, both of which have been tested for radon control. I have included the product data for the two products, with the radon test results highlighted for your review.

Due to the high water table, any radon in the soil will enter the water and it won’t dissipate into the atmosphere until that water is exposed to air. So to mitigate the radon, we have to create “air” under our building. This means we have to dewater under the building in perpetuity.

To accomplish this mitigation, the radon collection pipes under the slab would need to be sized to collect water and air (each pipe would be sized to be collect water but be at least half full of air). We can’t collect air without collecting water so that means we would probably end up delivering thousands of gallons of water/hour into the storm sewer. That water would result in a huge stormwater charge. It could also lower the water table in the neighborhood, which could affect adjacent properties including Safeway.