Thread: Single wall metal pipe

OK, can you tell I'm studying the IRC?

I'm trying to understand the difference between G2427.7.4 and 2427.7.6

The first (G2427.7.4) says that single wall pipe shall be used only for runs directly from the space in which the appliance is located through the roof...

The second (2427.7.6) says that single wall pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic....

Based on the first, I envisioned a water heater in the attic. Reading the second, I'm now unsure. So I'm trying to "see" this in my head. I'm not having much luck considering my head is a large, cavernous void.

Thanks in advance,
Bruce

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Closet inside house with flat roof and no ceiling.

Of course, though, that would have to be an older home before energy codes kicked in, otherwise there would be insulation up there .. or ... a newer home where the builder tapered the ceiling up to the roof where the single wall goes through, with the tapered walls being insulated.

Of course, though, the cost to achieve the second defeats any cost savings of not using Type B vent.

Originally Posted by JB Thompson

OK, can you tell I'm studying the IRC?

I'm trying to understand the difference between G2427.7.4 and 2427.7.6

The first (G2427.7.4) says that single wall pipe shall be used only for runs directly from the space in which the appliance is located through the roof...

The second (2427.7.6) says that single wall pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic....

Based on the first, I envisioned a water heater in the attic. Reading the second, I'm now unsure. So I'm trying to "see" this in my head. I'm not having much luck considering my head is a large, cavernous void.

Thanks in advance,
Bruce

JB:

Here is the commentary for your answer:

G2427.7.4 (503.7.4) Limitations of use. Single-wall metal
pipe shall be used only for runs directly from the space in which
the appliance is located through the roof or exterior wall to the
outdoor atmosphere.
[1]Single-wall metal pipe is further restricted by this section
to only two applications. It can run from the appliance
directly to the outdoors through an exterior wall
or it can run from the appliance directly to the outdoors
through a roof. Single-wall metal pipe cannot pass
through any floors, interior walls or partitions and cannot
pass through attics or concealed spaces. This
means that the appliance served must be in a space
with an exterior wall or in the same story as the roof.

So does "passing through an attic" mean the same as "originating" in an attic?

I'm not trying to be a semantics nazi (or even a smart aleck), but I'm not as versed to the code writer's meanings as some of you.

Thanks,
Bruce

Originally Posted by JB Thompson

So does "passing through an attic" mean the same as "originating" in an attic?

I'm not trying to be a semantics nazi (or even a smart aleck), but I'm not as versed to the code writer's meanings as some of you.

Thanks,
Bruce

JB: It means originating somwhere other than the attic and then passing through the attic. If it originates in the attic then it can be used to penetrate the roof.

Originally Posted by A.D. Miller

JB: It means originating somwhere other than the attic and then passing through the attic. If it originates in the attic then it can be used to penetrate the roof.

I agree

I have heard others say it cannot even start in the attic but I never read it that way.

Cannot originate in an attic and cannot pass through an attic (okay - change "cannot" to "not allowed to", we know it "can" be done because we see it done - just not "allowed").

From the 2006 IRC. (underlining is mine)
- G2427.7 (503.7) Single-wall metal pipe. Single-wall metal pipe vents shall comply with Sections G2427.7.1 through G2427.7.12.
- - G2427.7.1 (503.7.1) Construction. Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 inch (0.7 mm) thick, or other approved, noncombustible, corrosion-resistant material.
- - G2427.7.2 (503.7.2) Cold climate. Uninsulated single-wall metal pipe shall not be used outdoors for venting appliances in regions where the 99-percent winter design temperature is below 32ºF (0ºC).
- - G2427.7.3 (503.7.3) Termination. Single-wall metal pipe shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood outlet or flue collar. Single-wall metal pipe shall extend at least 2 feet (610 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm) (see Figure G2427.6.4). An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe (see also Section G2427.7.8, Item 3).
- - G2427.7.4 (503.7.4) Limitations of use. Single-wall metal pipe shall be used only for runs directly from the space in which the appliance is located through the roof or exterior wall to the outdoor atmosphere.
- - G2427.7.5 (503.7.5) Roof penetrations. A pipe passing through a roof shall extend without interruption through the roof flashing, roof jack, or roof thimble. Where a single-wall metal pipe passes through a roof constructed of combustible material, a noncombustible, nonventilating thimble shall be used at the point of passage. The thimble shall extend at least 18 inches (457 mm) above and 6 inches (152 mm) below the roof with the annular space open at the bottom and closed only at the top. The thimble shall be sized in accordance with Section G2427.10.15.
- - G2427.7.6 (503.7.6) Installation.Single-wall metal pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic, inside wall, concealed space, or floor. The installation of a single-wall metal pipe through an exterior combustible wall shall comply with Section G2427.10.15. Single-wall metal pipe used for venting an incinerator shall be exposed and readily examinable for its full length and shall have suitable clearances maintained.