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gas pipe under concrete slab

stealman's picture

I am building a building which is on a concrete slab. I want to put a gas line for propane under the slab. Can I do this? If so what material should i use for the pipe and what stipulations are there when doing this?

Thanks for the help

You sure can - the pipe just (post #206331, reply #1 of 13)

You sure can - the pipe just has to be rated for burial and where it comes through the slab it has to have something that prevents the concrete from direct contact - a little piece of sill seal foam or even cardboard duct-taped around the pipe is used a lot.  Now it seems everyone is using the stainless steel flex line for gas lines.   I'm not sure how deep under the slab the line needs to be - there is probably a standard depth that helps to provide separation between this and the other stuff buried under the slab but I can't recall what we did the last time.

 

Beer was created so carpenters wouldn't rule the world.

And, of course, make sure any (post #206331, reply #2 of 13)

And, of course, make sure any fill is well-compacted, so it won't shift and cause the pipe to break.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Yes, you can, but the (post #206331, reply #3 of 13)

Yes, you can, but the code requirements are different than others have advised.

No code allows you to run unsleeved gas pipe under-slab inside a building.

You must sleeve the gas line with a larger sized pipe--say, pvc--beginning outside the building and all the way inside and up thru the slab. At the inside termination of the sleeve, the annular space between the sleeve and the gas line must be sealed to prevent leaking gas from entering the building. The outside sleeve must have a vent that rises above ground, and vent must turned down and screened to prevent entry of bugs, debris and water.The gas pipe itself must be rated for underground burial.

The reason for the sleeve is to prevent leaking gas originating at an underground leak from following the pipe and filling your building with gas. This is especially dangerous because the odorant (mircaptin, similar to rotten onion) added to propane and natural gas will be absorbed by soil, and you would not be alerted to the leak by the typical smell of gas.

Around here (post #206331, reply #4 of 13)

we use 2" PVC conduit starting underground outside the building, and coming up through the slab inside... but the pipe (yellow polyethylene, similar to PEX in terms of working properties) is direct-buried between the tank and the beginning of the conduit. I've never seen anyone do a vent riser outside. Personally I like to run the conduit almost all the way to the tank, in case there's ever a need to pull new pipe, but that's not required, and in some cases the pipe would be too long to be pull-able anyway. 

To some extent, an unvented (post #206331, reply #5 of 13)

To some extent, an unvented conduit defeats the purpose of having a conduit. The vented conduit provides a direct path for a gas leak to escape to the outside where, not only is it more likely to leak harmlessly, but the odorant will still be present, which increases the likelihood of the leak being detected.

The purpose of the vent is not so much to protect the pipe as it is to direct any leak out from under the building, and to prevent a leak from following along the trench to inside the building. As the gas passes thru soil, the odorant is absorbed, but not as it passes thru the conduit. 

This actually happened in a nearby town a few years ago when a leaking underground  propane line sent gas alongside the line that went under a restaurant, where it collected in the crawlspace. Ignition was probably from an electrical spark at the sealed-combustion furnace located in the same crawlspace. The resulting explosion and fire destroyed much of the building, but no one was in the building at the time.

Whoever is responsible for inspecting the installations you mention has dropped the ball, along with the installers, because all of the nationally-recognized fuel gas codes in the country require the vent on the outside, and they also require positive sealing of the annular space between the pipe and the conduit inside the building.

Thinking about the last one I installed (post #206331, reply #6 of 13)

and realize I didn't describe it correctly. This is a case where the tank is buried in front of the house but the regulator is on the back of the house. The poly line travels through a conduit under the slab to get to the regulator, and of course never emerges in the house, but pops up next to the house. The regulator has a nipple into the wall cavity, and CSST takes off from that nipple and heads back under the slab through a different conduit. That conduit emerges inside the base cabinet for the cooktop. There's a third conduit from there to a gas fireplace insert. All of the poly and CSST was pulled into place and connected (and of course tested) at the end of the project. The only conduit end that's buried is at the tank. It's hard for me to imagine a leak that wouldn't vent to the atmosphere with odorant intact, but I'm not sure.

I'm going to read up on the code and ask the inspector about it. He knows all of the details of everything in my experience, so I would be curious to know if there's something he is not enforcing.

The type of installation you (post #206331, reply #7 of 13)

The type of installation you describe is covered in the IFGC fuel gas code, section 404.6.2 (2009 edition), and the way it was done is correct, provided that both ends of the indoor conduits terminate in an accessible place, and that the annular space is NOT sealed at either end.

In this case, a leak would be directed to the accessible point of termination, with no loss of odorant, and no way for the leaking gas to accumulate underground and find its way to some other exit point inside the house.

Definitely check with the (post #206331, reply #8 of 13)

Definitely check with the inspector what they are looking for.  No one code is used the same everywhere - it just isn't.

 

Beer was created so carpenters wouldn't rule the world.

International Residential Code (post #206331, reply #9 of 13)

The IRC encompasses the other codes into it, and the IRC Chapter 24, and the Fuel Gas Code are identical.  The parenthises refer to the Fuel Gas Code numbering.

G2415.12 (404.12)  Piping Underground beneath Buildings.  Piping installed underground beneath buildings is prohibited except where the piping is encased in a conduit of wrought iron, plastic pipe, steel pipe, or other approved conduit material designed to withstand the superimposed loads.  The conduit shall be protected from corrosion in accordance with Section G2415, and shall be installed in accordance with Section G2415.12.1, or G2415.12.2 

The commentary on this section indicates that the conduit is to vent gas in the event of gas pipe failure, and to prevent superimposed loads from the building damaging the gas pipe. 

In practice, the tricky part is the "designed to withstand superimposed loads".  The "designed" means it must be engineered.  In most seismic zones, it is less expensive to not run the line below the slab, and run it up the exterior wall, and into the attic space instead.  Because, the design costs money, and the conduit itself gets impractily large, running it under the slab becomes more costly than building it into the attic. 

G2415.12.1 (404.12.1) Conduit with One End Terminating Out-doors.  The conduit shall extend into an occupiable portion of the building and, at the point where the conduit termiates in the building, the space between the conduit and the gas piping shall be sealed to prevent the possible entrance of any gas leakage.  The conduit shall extend not less than 2 inches beyond the point where the pipe emerges from the floor.  Where the end sealing is capable of withstanding the full pressure of the gas pipe, the conduit shall be designed for the same pressure as the pipe.  Such conduit shall extend not less than 4 inches outside the building, shall be vented above ground to the outdoors, and shall be installed to prevent the entrance of water and insects.

The commentary indicates that the purpose is to vent any leaking gas out doors. 

G2415.12.2 (404.12.2) Conduit with both ends terminating indoors.  Where the conduit originates and terminates within the same building, the conduit shall originate and terminate in an accessible protion of the building and shall not be sealed.  The conduit shall extend not less than 2 inches beyond the point where the pipe emerges from the floor. 

Commentary:  This method allows piping to run between any two points in the building without a vent run to the outdoors and without sealing the ends of the conduit.  The 2 inch rise is to prevent liquids and debris from falling into the conduit.  The ends of the conduit are not to be sealed so as to allow any leakage to be noticed by the occupants, the same as leakage would be noticed anywhere else in the structure.  If the conduit ends were sealed, there would be no evidence of a piping defect, no matter how severe the defect, possibly leading to a major leak in the event of conduit or end seal failure. 

Spot on. In practice, the (post #206331, reply #10 of 13)

Spot on. In practice, the plastic pipe in conduit is run from the 1st stage regulator, underground to the 2nd stage regulator at the building, from whence it is run by copper or black iron pipe to the fixtures. I haven't seen any installations where the fuel line is under the concrete floor in a building. Much less expensive to have the runs under the floor(basement or crawl space) or in the walls.

Not likely you'd see (post #206331, reply #11 of 13)

copper or black iron under a slab, because it would be quite hard to pull either of those materials through a conduit. It's done with CSST quite often, though.

Gas pipe setup under the slab ! (post #206331, reply #12 of 13)

Now a days,it is possible to implement the propane gas ducts under the slab using some expertise housing therapies.The ducts should be durable and must not be too brittle. Following the standard depth of burial avoiding the bare contact with sorroundings,setup the ducts from corner to corner of slab wolud be the best practice.The setup should be supervised by the experts for security purposes.

(No subject) (post #206331, reply #13 of 13)


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

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