waste line under insulation board or on top
LarryY
| Posted in Construction Techniques on
Here’s my plan for the garage/dwelling floor. From the top of the slab downward: 4 inches reinforced (rebar grid) concrete, over top 4 inches of gravel, then 6 mil plastic, 2″ insulation board, over 3″ sand. Waste line leading to the septic tank will be under the slab. Does the horizontal (with 1/4″ per foot slope) waste line need to be a minimum depth below say the top of a garage slab? I’m trying to figure out whether the 3″ waste line would be above the 2″ insulation board or below. Thanks.
Replies
If you're inland at all I'm assuming it can freeze there. The waste line should be under the insulation.
(Just out of curiosity, what sort of waste line to a septic is only 3"?)
Agreed--the drain line ought to be under the insulation not only for freeze-protection, but it will also allow you to bury it an any depth you'd like or need. Trying to keep it above the insulation would limit the bury depth.
The sizing of the lines will meet "code", and will certainly be adequate for your needs, both for the garage and for the future house.
"Code" is, unfortunately, a moving target, depending on where you live. There's no such thing right now as a "national plumbing code" in the sense of having one code that applies everywhere in the nation. There are two main plumbing codes that compete with each other, the UPC and the IPC, but regardless of which one is selected as the code in any jurisdiction, these codes are still subject to local amemdments and, sometimes, the whims of individual inspectors.
In our jurisdiction, for example, there's an amendment that requires a minimum 4" to be run into every building, even a small shop/garage like yours. It's not a bad idea in some ways, but, OTOH, the code is intended to be a minimum standard, not best practice.
My point is: always check first with your local inspector on Q's like this, because none of us here are likely to know all the details of local practice and inspector expectations/prejudices.