Ventilation required?

Scenario: Two story home, two car garage, front 1/2 of garage has attic space above it that is not shared with anything else…just 200 sf or so of dead space. Attic wall on back side that is shared with livable space is insulated. There’s soffit vents on two sides but no gable vent, ridge vent or other passive venting up high to discharge the hot air. Is there a requirement for ventilating that size & type of attic space? The IRC seems to be silent on it. I’m sure many of us would recommend it but is there any requirement?

Generally, the attic space above a garage does not require ventilation.

Jeff…is that a personal opinion or can it be backed up anywhere? I thought there was a size, i.e a square footage minimum, but I can’t find it anywhere. This is just for my own and another inspector’s curiosity and future reference.

Opinion based on experience and research in the UBC. I can’t say whether this also applies to the IRC.

The UBC classifies a garage (attached or detached) as a Type U Occupancy. Basically, the UBC defines a Type U Occupancy as a “utility” type room/space, which includes garages and other “non-living” spaces.

I have never seen attic-ventilation requirements that apply to Type U Occupancies.

OK, good deal…I’ll drill down some on the UBC and IBC.

that still doesn’t address the excessive shingle wear and curl in the un-vented space…imho…

Yes, I agree…the inspector that had originally asked my opinion on this noted exactly that on his report today. There’s definitely reasons to add ventilation but I was/am hoping for something tangible that a builder can relate to. As I investigate the IBC I see and agree with Jeff…maybe. One section, 1203.2, of the 2003 IBC that is not Occupancy specific says that ventilation is required. So, I don’t have the final answer from a code standpoint just yet.

I like all roof cavities to be vented, but if the attic is not insulated (such as…above a garage) I don’t make a big deal out of it. It’s the insulation application that will cause attic cavities to become ovens.**

IBC-2003 & 2006 Section 1203** - Ventilation

1203.2 Attic spaces. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof framing members shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain and snow.

Blocking and bridging shall be arranged so as not to interfere with the movement of air. A minimum of 1 inch (25 mm) of airspace shall be provided between the insulation and the roof sheathing. The net free ventilating area shall not be loss than 1/150 of the area of the space ventilated, with 50 percent of the required ventilating area provided by ventilators located in the upper portion of the space to be ventilated at least 3 feet (914 mm) above eave or cornice vents with the balance of the required ventilation provided by eave or cornice vents.

sorry Mike i’m not a code inspector …just use my experience in construction since 1968

There is such a thing, and it’s called “good practice”! A building code, as many have said here, is only a minimum standard, and not necessarily a primer of good practice. One should not need a code to realize that any enclosed wood structure needs ventilation. However, ventilation is more art than science, and perhaps the soffit vents are enough, or perhaps there is a ventilation path to a ridge vent above the insulated space.

From a practical standpoint it should be vented…if for no other reason because of the heat that builds up from underneath which in turn will diminish the service life of the shingles.

Amazes me why a builder would spend an extra $600.00 on architectural shingles yet save $40.00 by not adding ridge vent over the garage…what a moron.

What alarms me is where the right slope of the garage roof dumps into vertical wall over the foyer…amazes me why architects design homes to fail.

Is this a vinyl sided home with a brick veneer on the front.



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code is the minimum, the shingle manufacture will want to see ventalation or there will be no warranty, not that it is easy to work through a roofing warranty.

No, not exactly. This is a Hardie sided home with a brick veneer on three sides.

Now, there’s an interesting angle. Owens-Corning literature states “Regardless of the deck used, the roofing installer must ensure that the attic ventilation meets or exceeds FHA Minimum Property Standards.” Now, if I knew what that standard stated…

Agreed. And the garage will be a sauna. The IRC doesn’t distinguish between attic types to my knowledge. Venting is required per the IRC. I write it up recommending ventilation when I see it.



403-1.2 Attic Space

a. Cross ventilation shall be provided for each
separate space. Ventilation openings shall be
protected against the entrance of rain and
b. The ratio of the total net free ventilation
area to the area of ceiling shall be not less
than 1/150, except that the ratio may be 1/300
(1) A vapor retarder having a transmission
rate not exceeding one perm is installed
on the warm side of the ceiling;
(2) Between 25 and 50 percent of the required
ventilating area is provided by vents
located in the eaves or cornices with the
balance of the required ventilation
provided by ventilators located at least
3’-0" above the vents in the eaves or
cornices; or
(3) The attic space is accessible and
suitable for future habitable rooms or
walled-off storage spaces have at least
50% of the required ventilating area
located in the upper part of the
ventilated spaces as near the high point
of the roof as practicable and above the
probable level of any future ceiling.

Other info:,1827948&_dad=portal&_schema=PORTAL

“Where defective design work contributes more than 50% of the roofing failures, defective workmanship accounts for about 30% of the total roofing failures. Most of these errors by contractors are due to ignorence about the consequences of their actions and absence or poor supervision.”

Carl G. Cash in Roofing Failures

This is good book but hard to find. Cash was a very knowledgeable roof consultant and worked closely with experts in many areas of roofing. He was involved in developing ASTM protocols for testing roofing materials.

Having only intake vents without any exhaust vents will create a sauna in that space area above the garage. This will lead to humidity build up, which will ultimately lead to mold. Although this mold is contained to that one area, the continuous high heat and humidity will cause damage to the roof decking. Also, having this ventilation imbalance (intake but no outake) will cause the shingles to fail sooner. They call this the hot roof effect (No ventilation in the attic space. They also use the term hot roof when closed cell insulation is used). Unfortunately, this is all too common amongst construction companies. Their roof IQ is quite low and I have seen some odd places where they placed outake vents. My home is a prime example of toxic black mold formation from having only intake vents and no exhaust. It is a deathly design.