Thread: Combustion air garages

In my area, Tampa Florida, I routinely see combustion air ducts run through garage ceilings that terminate inside of the attic space above the garage. This would seem to me to be in violation of IRC 309.1.1, 309.1.2, and 309.2. Your thoughts and comments will be appreciated. If someone could paste those codes that might help this thread.

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Originally Posted by Tom McDonnell

In my area, Tampa Florida, I routinely see combustion air ducts run through garage ceilings that terminate inside of the attic space above the garage. This would seem to me to be in violation of IRC 309.1.1, 309.1.2, and 309.2. Your thoughts and comments will be appreciated. If someone could paste those codes that might help this thread.

SECTION R309
GARAGES AND CARPORTS
R309.1 Opening protection. Openings from a private garage
directly into a room used for sleeping purposes shall not be permitted.
Other openings between the garage and residence shall
be equipped with solid wood doors not less than 13/8 inches (35
mm) in thickness, solid or honeycomb core steel doors not less
than 13/8 inches (35 mm) thick, or 20-minute fire-rated doors.

R309.1.1 Duct penetration. Ducts in the garage and ducts
penetrating the walls or ceilings separating the dwelling
from the garage shall be constructed of a minimum No. 26
gage (0.48 mm) sheet steel or other approved material and
shall have no openings into the garage.

R309.1.2 Other penetrations. Penetrations through the
separation required in Section R309.2 shall be protected by
filling the opening around the penetrating item with
approved material to resist the free passage of flame and
products of combustion.

R309.2 Separation required. The garage shall be separated
fromthe residence and its attic area by not less than 1/2-inch (12.7
mm) gypsum board applied to the garage side. Garages beneath
habitable rooms shall be separated from all habitable rooms
above by not less than 5/8-inch (15.9 mm) Type X gypsum board
or equivalent. Where the separation is a floor-ceiling assembly,
the structure supporting the separation shall also be protected by
not less than 1/2-inch (12.7 mm) gypsum board or equivalent.
Garages located less than 3 feet (914 mm) from a dwelling unit
on the same lot shall be protected with not less than 1/2-inch (12.7
mm) gypsum board applied to the interior side of exterior walls
that are within this area. Openings in these walls shall be regulated
by SectionR309.1. This provision does not apply to garage
walls that are perpendicular to the adjacent dwelling unit wall.

If the vent pipes are terminating in the attic then it is wrong. This would be just like a chimney into the attic if a fire broke out in the garage.

Originally Posted by Scott Patterson

If the vent pipes are terminating in the attic then it is wrong. This would be just like a chimney into the attic if a fire broke out in the garage.

Not vent pipes, combustion air, which are allowed to open to the attic provided the attic is properly ventilated.

Originally Posted by Tom McDonnell

In my area, Tampa Florida, I routinely see combustion air ducts run through garage ceilings that terminate inside of the attic space above the garage. This would seem to me to be in violation of IRC 309.1.1, 309.1.2, and 309.2. Your thoughts and comments will be appreciated. If someone could paste those codes that might help this thread.

Tom,

First thing is you should be in the FBC-Residential, not the IRC.

Section thing is here are those sections:
- R309.1 Opening protection.
- - Openings from a private garage directly into a room used for sleeping purposes shall not be permitted. Other openings between the garage and residence shall be equipped with solid wood doors not less than 13/8 inches (35 mm) in thickness, solid or honeycomb core steel doors not less than 13/8 inches (35 mm) thick, or 20-minute fire-rated doors.
- - R309.1.1 Duct penetration.
- - - Ducts in the garage and ducts penetrating the walls or ceilings separating the dwelling from the garage shall be constructed of a minimum No. 26 gage (0.48 mm) sheet steel, 1-inch (25 mm) minimum rigid nonmetallic Class 0 or Class 1 duct board, or other approved material and shall have no openings into the garage.
- R309.2 Separation required.
- - The garage shall be separated from the residence and its attic area by not less than ½-inch (12.7 mm) gypsum board applied to the garage side. Garages beneath habitable rooms shall be separated from all habitable rooms above by not less than 5/8-inch (15.9 mm) Type X gypsum board or equivalent. Where the separation is a floor-ceiling assembly, the structure supporting the separation shall also be protected by not less than ½-inch (12.7 mm) gypsum board or equivalent.

As I envision your description, the ducts run from inside the garage where the water heater is and go into the attic.

If that is the case, my question is "WHY?" The garage is not a "confined space" which would need that.

More information is needed.

Jerry

Agreed. If the garage only houses a water heater that averages around 32000 to 36000 BTU/h then then in most caes the mathematical equation BTU/h divided by20=Cubic feet of required air volume works. But, if you throw in a gas furnace or 2 and maybe a gas clothes dryer (22000 BTU/h then it almost never works even in a three car garage.

Originally Posted by Tom McDonnell

Jerry

Agreed. If the garage only houses a water heater that averages around 32000 to 36000 BTU/h then then in most caes the mathematical equation BTU/h divided by20=Cubic feet of required air volume works. But, if you throw in a gas furnace or 2 and maybe a gas clothes dryer (22000 BTU/h then it almost never works even in a three car garage.

Tom,

Yeah, but ... you are in Tampa ... a gas furnace or 2?

And a clothes dryer in the garage? They still doing that there?

Also, where I said this:

Originally Posted by Jerry Peck

As I envision your description, the ducts run from inside the garage where the water heater is and go into the attic.

I left off the end of what I was thinking (glad you brought this back up): Those combustion air duct would need fire dampers at the garage ceiling and some type of control to shut the gas appliance down when the fire damper activated.

I typed just so much then must have started thinking about something else.

That means that, yes, the "separation" is 'still required', even with those ducts meeting the requirements for duct, because the ducts open to the garage. Meeting that separation will be difficult, so it makes sense to go out through the garage wall instead. Which also changes the calculations for the combustion air.

Jerry

Thanks.

Most commonly I see 1 gas furnace and 1 gas water heater located in the garage. Clothes dryers? Not so much but occasionaly on an older home. It's not the norm but occasionaly, on a large house I'll see 2 gas furnaces and a large water heater.

To shed more light on the combustion air vent design-1 -12 inch round metal pipe roughly 1.5 feet in length installed in the garage ceiling covered by an AC return register with non-movable louvers. The pipe terminates in the attic space.

Again, my thought on this is that yes this provides the necessary combustion air but violates the living space/garage separation requirements. Furthermore, in the event of a garage fire, this opening will pull that fire into the attic in no time at all and with a vengence because obviously the draft would be incredible.

Nonetheless, this is what's being done on a routine and regular basis. I'm guessing that once an incident happens the finger pointing will start. Similar to the 1/4" to 1/2" stucco debacle of '04, or the aluminum wiring debacle in '73, or the hardboard siding one in 80's.

It just doesn't make good sense to me that no one recognizes that an opening to attic from the garage is a just bad idea and a dangerous one at that. But that's the way it is.

Tom,

I see three simple solutions to that installation problem (the fire damper and shutting down the gas appliances is not really a good solution, but less expensive to add after-the-fact as now installed). You would not want the fire damper to close and the appliances to stay on as that would create its own hazard.

Solution #1 (during construction): Install two roof goose neck type exhaust hoods and connect each of the two combustion air ducts to them, seal the connection. The combustion air is now no longer open to the attic, as long as the ducts were at least 26 gage, they would not need to be wrapped in gypsum board.

Solution #2 (during construction): Install the combustion air ducts out through the wall.

Solution #3 (during construction): Install 1/2" gypsum board on a truss which aligns with the garage house wall to continue the separation up to the roof sheathing. This way they could just cut holes in the garage ceiling ... oh ... wait ... they are already 'just cutting holes in the garage ceiling ...

Originally Posted by Tom McDonnell

Jerry

Thanks.

Most commonly I see 1 gas furnace and 1 gas water heater located in the garage. Clothes dryers? Not so much but occasionaly on an older home. It's not the norm but occasionaly, on a large house I'll see 2 gas furnaces and a large water heater.

To shed more light on the combustion air vent design-1 -12 inch round metal pipe roughly 1.5 feet in length installed in the garage ceiling covered by an AC return register with non-movable louvers. The pipe terminates in the attic space.

Again, my thought on this is that yes this provides the necessary combustion air but violates the living space/garage separation requirements. Furthermore, in the event of a garage fire, this opening will pull that fire into the attic in no time at all and with a vengence because obviously the draft would be incredible.

Nonetheless, this is what's being done on a routine and regular basis. I'm guessing that once an incident happens the finger pointing will start. Similar to the 1/4" to 1/2" stucco debacle of '04, or the aluminum wiring debacle in '73, or the hardboard siding one in 80's.

It just doesn't make good sense to me that no one recognizes that an opening to attic from the garage is a just bad idea and a dangerous one at that. But that's the way it is.

Sounds like you are on the right track and have a firm grasp on the concept of separation.
If you are seeing this on new construction or newly permitted work, this may be a good time to take some of Jerry's advice from a while back; call the AHJ and ask them about what you are seeing and what their thoughts are on the subject. This may be something they never considered and once questioned they may have a light bulb come on realizing the danger they have been allowing.
You might just save some lives.

Thanks Jim. That's good advice.