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Toilet drain line outside the building

SDS

Registered User
Joined
Dec 30, 2020
Messages
97
Location
Washington State, USA
Single-family home built in 2012 under the IRC

The homeowner added an unpermitted 3rd story half bath...toilet and sink, sometime after the home was built. This toilet room is located on the inside of an exterior wall and they ran the waste line to the outside of the wall, then along the wall for about 20' (sloped) before it drops vertically down to tie into the underground sewer line. This line is fully exposed for it's entire length outside the building and they painted it with something the same color as the house.

There is a cleanout and a vertical vent line up at the toilet room end of the line...say, 16-18 feet up in the air. The vent line terminates just below the gable eaves. The homeowners would like to insulate it and soffit it into a protective enclosure rather than remove the half bath and drain line if possible.

P2603.5 Freezing states that plumbing lines shall not be installed outside the building unless adequate provisions are made to protect it from freezing, but it doesn't elaborate on minimum R-value required

The WSEC references min. duct insulation of R-8 as well as R-6 for mech piping, but I can't find any specific minimum for plumbing.

What would be an acceptable min. R-value for a plumbing drain line outside the building?
 
Sewer generally doesn't freeze as it doesn't "hold" water....Do you have a minimum sewer frost depth where you are?

I should've been more specific in my OP...P2603.5 states that water, sewer or waste pipes cant be installed outside the building where winter design temp is below 32*...we're at 22* here, so it cannot be outside unless insulated, but I cannot find anything specifically saying to what R-value it is to be insulated.
 
I think that they did not list an R-value because it really varies by location as to what is necessary. Given that, the code writers intended for the determination to be made by the building official.

I would think you could get away with a fairly low R value, since the sewer doesn't hold water like steveray said. Also consider where the heat that your insulated chase is capturing is coming from, and how well heat from the house will be able to get into the chase to keep the pipe warm. Fortunately, you don't have to keep the pipe at room temperature.

The more heat that can get in there from the house, the less insulation you will need.
 
IECC R403.4 requires R-3 insulation for hydronic piping, and R403.5.2.3 requires R-3 insulation for hot water piping located outside the conditioned space. I'd probably feel better with R-6 or 8.
 
This is what I'm thinking also...which would be an R21 in this case.
I think that is overkill since you don't have to keep the pipe at a minimum of 68 degrees like you do the interior of the house. If you keep it at 33 degrees or above, it'll never freeze. Consider that the heat from the house will transmit through the pipe, since part of the pipe is in a conditioned area.

However, it is completely up to the local jurisdiction, and you can certainly justify R21 that way if you feel it is necessary.
 
Insulating a soffit or chase installed outside of the thermal envelope without a heat source is almost pointless. There are two things to consider here: 1) What does "outside the building mean"? Does it mean outside the thermal envelope? Or outside the building envelope? 2) What does "protected from freezing" mean?

I agree that waste pipes don't hold water and they are not subject to freezing to the extent that other pipes are, but I would also say that every time water runs down that pipe, it runs down the outer diameter, and leaves liquid water in small amount. Could this build up in prolonged, extremely cold temps? Would this build up be enough to disrupt flow and create a LOG jam? Who wants to be responsible for that?

Consider a heat trace inside the chase with insulation.
 
If it hasn’t frozen yet it probably never will. A jalapeño pepper pizza once a month during the winter should keep it open.
 
I recall traveling in the UK and Scotland years ago how so many masonry buildings routinely had cast iron dwv on exterior of buildings. How else do you add plumbing to a small masonry row house?
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I should've been more specific in my OP...P2603.5 states that water, sewer or waste pipes cant be installed outside the building where winter design temp is below 32*...we're at 22* here, so it cannot be outside unless insulated, but I cannot find anything specifically saying to what R-value it is to be insulated.
I don't see where your code requires insulation, it's just that they cannot be outside.
Is this do for roof down spouts too?
 
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