The awareness of radon danger and health risk has been growing steadily in Canada over the past the decade or so. With this increased awareness, provisions for radon mitigation have been added to the National Building Code and have been included in new construction since 2016.
New houses, commercial buildings, and even many additions to existing buildings, are now required to have a rough-in for a future radon mitigation system. RADONreduction is specialized in residential radon mitigation in Calgary and surrounding area, so that will be the focus of this blog post.
Radon mitigation involves creating a negative pressure (slight vacuum) under the concrete basement floor, known as the slab, using piping and a specialized radon fan. The soil gas is drawn to a collection point where it is safely exhausted to the atmosphere. In a house built before 2016, this would involve coring or jackhammering a hole through the slab, removing some of the sub-slab fill to create a “suction pit” where a pipe would be inserted through the slab and sealed around. Another hole is required to be put through the sidewall as the exhaust point. Between the slab suction point and the exhaust point there will be piping and a specialized radon fan. The fan will be “sucking” the soil gas through the sub-slab fill (generally gravel in and around Calgary) and venting it outside before it can enter the home. The addition of the rough-in is intended to improve the efficiency of a radon mitigation system as well as ease of installation and cost reduction.
A rough-in to meet minimum building code involves a few things, including a “Schedule 40”, or thick-walled, 100mm (4”) pipe stub is to be protruding above the slab at least 300mm (1 foot) and labelled “Radon”. This is intended to be the suction point of the radon mitigation system. Below the slab that same pipe attaches to a 90-degree elbow which usually has a perforated pipe attached to it (often weeping-tile) that is meant to run to the approximate centre of the house’s footprint.
To me, the other components of the building code for radon are even more important than the above. There is a requirement for sub-slab fill of at least 100mm (4”) of clean gravel without a lot of fine particulates. This specific clean gravel is known to builders as “radon rock”. This gravel layer is very porous due to the gaps between all the gravel, making it easy to draw the radon gas through. Over top of this gravel layer is a polyethylene sheet membrane that is sealed to the footings all around the foundation. Any penetrations through this sheet such as tele-posts, plumbing stacks, floor drains, and so forth are also sealed. This membrane creates an air-tight barrier between the house and the area below the slab.
A common misconception is that the membrane stops radon from entering the house or building. This is absolutely false as radon is an inert gas and can easily pass through the membrane. The membrane is intended to allow a negative pressure to be created below it and be contained to the sub-slab area where the radon gas is. If air from the building itself is drawn down below the slab due to gaps, cracks, openings, or unsealed penetrations, this can have a number of negative consequences to the homeowner. These consequences include energy penalties from losing room-air that has been heated or cooled (at a great expense these days) being sucked down below the slab and exhausted to the atmosphere along with the radon gas. Any loss of sub-slab negative pressure will also reduce the efficiency and effectiveness of the radon mitigation system due to the fact that the negative pressure will be weakened or lost and therefor reduce the area treated by the radon mitigation system.
Another negative implication of a poor seal between the house and the sub-slab area is that air-loss from the house can create a negative pressure within the building. A negative pressure inside the home can cause back-drafting of combustion appliances like hot water heaters and fireplaces that are not directly vented outside. Back-drafting can actually cause air from outside to be drawn into the home through exhausts such as hot water tank flues and fireplace chimneys, bringing the combustion exhaust (and carbon monoxide) back into the home causing a potentially deadly situation for the occupants.
The addition of provisions for radon mitigation to the building code is a great step in the right direction for protecting people from this deadly gas. Common issues with radon rough-ins, along with some easy fixes, and variations of radon rough-ins will be explored in further blogs. Please feel free to reach out to find out additional information or to schedule a free, no-obligation quote to install a radon mitigation in your house.
