Question of the Day - #56 If it Walks Like a Duct!

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Question of the Day - #56 If it Walks Like a Duct!

Postby RDavidson » Wed Nov 26, 2014 7:19 pm

Minnesota Mechanical Code section 512 regulates subslab soil exhaust systems. So does proposed MR sections 1303.2400 thru 2403. The Minnesota Mechanical Code refers to the conduit for exhausting radon from subslab locations to the outside as a “duct” and repeatedly refers to this conduit as a duct. It does not meet the definition of a vent or a pipe. When ducts occur in buildings constructed under the Minnesota Building Code (IBC), they receive special attention. They cannot be provided with fire dampers. They are required to be installed in a shaft having a rating as required by IBC section 707.4.

Now there is an opinion that has floated in that refers to these radon ducts as “PVC plumbing pipe (that) is not currently put into shafts, it is fire stopped at floors”. Is a radon duct a “plumbing pipe”? Do we sometimes play fast and loose with definitions? Or are they intended to be ignored?

Why is this even an issue? Because radon systems may be required in multistory buildings that contain dwellings or in mixed occupancy buildings that contain dwellings or in buildings that are required to have a fire resistive rating.

If you choose to route the radon duct from its origin in a floor slab through several floors or occupancies of a building to the exterior, how must it be treated? You may be penetrating occupancy separations or fire-rated floor/ceiling or roof/ceiling assemblies. There are no other methods for penetrating these assemblies for these ducts other than via a shaft.

Whether you believe that each dwelling in an apartment house must have its own passive radon system and duct or if one duct can be used for the entire building, the fact remains that each portion of the floor that is in contact with earth must be ventilated and when you have a first floor laced with footings for bearing walls you will have a lot of different areas. How do you extend the riser into the ceiling space above? Load bearing walls will have footings under them. You will likely need to have a non-load bearing wall to extend the riser through. Then you could connect it to a horizontal run of hundreds of feet to the main riser if you believe that meets the code.

Some folks have suggested vehemently that it is a vent and not a duct. If you feel comfortable with that opinion and can defend yourself given the definitions and the rules in the code, go for it. What does all of this confusion do to the idea of uniformity?

What is your view on how these ducts should be handled in mixed occupancy and fire rated situations? Keep in mind that the IBC was not developed to address radon ducts since the only radon rules that exist in the I-Codes are in the IRC and DLI has chosen to expand their use to all residential uses. There are no exceptions in the IBC for radon ducts. All ducts are treated the same.
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