Formatted Title
Distributed and Optimized Sub-Slab Venting (DOSSV)
Background/Objectives
Active soil depressurization (ASD) is the most used remediation technique for radon for existing buildings in the USA. Guidelines and standards for new building construction have been adopted that depending on the jurisdiction require passive radon mitigation systems to be installed, that still can be converted later to active systems if the inclusion of the passive system does not yield low radon concentrations during a radon test. These passive systems are designed with gravel and radon/moisture barriers under the concrete slab and sealing of the lowest floor to minimize occasional radon entry. However, these passive and active systems are by their design continually, or intermittently, "mining" soil gases. This is because the fresh air is intended to come from the outside and travel under the footings of foundation walls where it will mix with the radon laden air in the plenum after which it is actively removed by a fan. The problem is that this technique, because it applies a stronger vacuum on the sub-slab soil than the stack effect on the basement slab in the winter, also can draw radon and VOC contaminants in from elsewhere under the building. This is especially a problem in Karst areas, or Karst-like circumstances even in areas that are not generally known to have a Karst type geology. Such effects can be made worse by occasional high winds, barometric pressure changes, or situations where buildings are located on a side of a hill, or over man-made or natural, coarse, sub-terraneous material. The number of buildings that were thought to have been mitigated properly but that are found not to remediate successfully, are expected to grow with the use of continually measuring home consumer devices that can monitor buildings day and night, through weather cycles, and all seasons. The objective is to provide a higher quality protective system than ASD in new home buildings to the occupants that can guarantee low radon in the building, starting with an improved design of the parts below the concrete slab.
Approach/Activities
The new design model, DOSSV, implementing radon and soil gas mitigation features during new construction of residential homes and buildings will be discussed. It is based on controlled sub-slab ventilation of an aggregate filled space (plenum) below the concrete slab under a building with a controlled minimum amount of air from a known source. This type of sub-slab ventilation in new building construction will be able to operate with a lower vacuum than standard ASD systems and allowing fresh air to enter directly reducing the problem of continual, or intermittent "mining" of radon or VOC contaminants for the soil gasses from below the building. The installation of these DOSSV systems uses similar materials as standard ASD systems, lowering the threshold for its implementation, but does rely on proper design and implementation, making a need for inspections of work during the building process necessary. The DOSSV design model promises to accomplish lower final radon levels and soil gas contaminants and lower energy losses than are possible with active soil depressurization mitigation methods for similar size buildings. It also requires fewer discharge vent pipes for larger buildings. Before construction begins, during the architectural phase, specific calculations will help optimize the design. For a less optimal design the efficiency can also be calculated.
Results/Lessons Learned
As of this moment theory has been developed and calculations have been done to predict the exact pressure-ventilation characteristics and the effectiveness to lower radon concentrations. Due to regulatory requirements DOSSV has not been implemented yet. Pilot projects are currently being discussed. The latest data from ongoing pilot projects will be discussed at the conference.