Attic ventilation requirement

[Sifu]

The code requires cross ventilation of attic spaces and specifically indicates that where the ceiling is applied directly to the rafters (sloped ceilings) the rafter spaces must be ventilated. In the last few days I have run across a number of installations that did not provide baffles. Of course arguing ensued when I wrote corrections. I decided to check my premise. The code for insulation clearance says "where eave or cornice vents are installed" and indicates a 1" air space. It does not require eave or cornice vents.

So in one case, a shed roof, cathedral ceiling on the inside, I asked for what I used to install back in my builder days: either a side-wall vent at the top or roof vents with cross ventilation within each 2x12 rafter along with eave ventilation and baffles thus providing the entire roof with cross ventilation.

In another case, an addition with the rafter tie/CJ installed higher up on the rafter forming a sloped portion of ceiling. The eaves stuffed tight with fiberglass and the rafters blown in with cellulose and no baffles. I required baffles.

The code asks for ventilation, indicates a reduction when a percentage is installed in both the upper and lower portions of the attic and indicates eave vents may not be required. So to my question: Is there code language indicating where ventilation must come from? In the first case could it all come from the eave with none at the top? And in the second case could the eave ventilation be left out, thus negating the need for the 1" air space?

IMO cross ventilation indicates that ventilation must "cross" the roof, which would mean top and bottom given that heat rises. Since nobody here actually has a code book I usually have to defend my corrections (to my BO) with code language or good interpretations and I am having trouble finding solid ground in that respect.

Any thoughts are appreciated.

 

[Gregg Harris]

Can you use 2009 IBC 1203.2 Attic spaces

 

[Sifu]

Technically no. I am limited to 2006 IRC but if it presents good evidence to support either position I'll incorporate it into my own opinion. (since nobody else here bothers to read a code book how would they know anyway?) I went through 09 IRC for help today but not 09 IBC. I'll check it tomorrow. Does it offer something different than the earlier versions?

 

[Gregg Harris]

It give a description of cross ventilation from eves and cornice vents and upper ventilation of the area being vented. And yes it is new verbiage.

 

[Keystone]

Our industry can be trying and most don't care for it to begin with, by inserting a code where it is not in effect is not the way to go and only goes to substantiate the bias some may feel.

 

[Gregg Harris]

Can you use 2009 IBC 1203.2 Attic spaces

1203.2 is the same verbiage as 2009 IRC 806.2 I skipped it earlier, it basically matches what you have stated

 

[north star]

+ +

Sifu,

This is one link to one manufacturer explaining the need for a balanced

ventilation system......Hope this helps!

FWIW, while the IRC doesn't specifically mention "the thermal effect",

it is a very important component in the ventilation process.

http://www.cor-a-vent.com/pdf/balancedventilation.pdf



Typically, larger sized gable vents [ side vents ] are required to fully

ventilate the entire attic space........If only the gable vents are used, then

a mechanical means of ventilation may be necessary to achieve a balance

of the flow, which is why the soffit and ridge venting methods are

preferred......Not sure that you could sell this idea to your BO though!



+ +

 

[Sifu]

I received a call from the insulation installer. Large regional installer, been doing it for thirty years all over the place etc., etc. He sent me an article making the case for eliminating the air space in dense packed vaulted ceilings with cellulose insulation. The article appears to based on 20 year old studies and for a different region of the country, though it does make compelling arguments, mostly based on the density of the material and the added difficulty of moisture to pass through it.

Another thing, I found in the 2006, IRC Q&A the following (condensed): Q-Does the code require soffit ventilation? A-No. Soffit ventilation is optional. Q-If soffit vents not installed is 1" air-space required? A-No.

Based on that I think the answer to my OP is that I made a mistake based on having good code to back it up. I still think balanced air flow and cross ventilation is the intent and ideal but the Q&A seems pretty clear. Couple that with the industry article and I think I'll have to let the cellulose install pass.

 

[steveray]

R806.1 Ventilation required.

Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space.......

Hence...if each rafter bay is seperated (by drywall)....each one needs cross ventillation....(high and low).....which would require the 1" airspace (baffle) to ensure airflow

 

[Gregg Harris]

Steveray That would be my contention.

 

[Sifu]

I agree that cross ventilation is the intent but how does one explain the Q&A? Would you require the air-space in a dense packed cellulose ceiling like the one described? Oh, and what does the statement from keystone mean?

 

[steveray]

I think Keystone is just empathizing with your position (new codes, old contractors).....I know(believe) there are some exemptions in the newer codes for the crazy foam....if one of them applies to the cellulose as well then great.....but I need to require it under the code WE are on...

I agree that cross ventilation is the intent but how does one explain the Q&A? Would you require the air-space in a dense packed cellulose ceiling like the one described? Oh, and what does the statement from keystone mean?

 

[Sifu]

After reading the 06, 09 and 12 IBC, the 06, 09 and 12 IRC and the 06 Q&A I have come to the following conclusion: The 06, 09, 12 IRC say the same thing...."where eave vents are installed" and the 06 Q&A clearly says they are not required and if not required then neither is the 1" air space, so IRC=eave vents not required and if not present then 1" air space not required. 06, 09, 12 IBC clearly requires cross ventilation, each edition a little different but all indicating that some of the ventilation must come from upper portions and the remainder from eave or cornice, so IBC=eave vents required therefore cross ventilation and air-space required. I don't like my own conclusion but I don't inspect what I like or don't like. I guess its just another case of a little lower standard for 1 and 2 family residentials.

 

[mtlogcabin]

Eave and cornice vents are used to meet the ventilation requirements. They are not "required" they may be part of the ventilation design.

R806.2 Minimum area.

The total net free ventilating area shall not be less than 1/150 of the area of the space ventilated except that reduction of the total area to 1/300 is permitted provided that at least 50 percent and not more than 80 percent of the required ventilating area is provided by ventilators located in the upper portion of the space to be ventilated at least 3 feet (914 mm) above the eave or cornice vents with the balance of the required ventilation provided by eave or cornice vents. As an alternative, the net free cross-ventilation area may be reduced to 1/300 when a Class I or II vapor barrier is installed on the warm-in-winter side of the ceiling.

 

[Big Mac]

The code states that cross ventilation is required. I know of no exception to that. If the client does not wish to use eave vents, there are other products out there that can be placed on the roof at the low end of roof systems to allow ventilation into the lower potion of the individual rafter spaces. They are similar to a roof to wall vents but are designed to be placed ont he sdurface of the roof. Another option would be to place roof jacks over every other rafter so as to allow ventilationinto each bay.

Another way to provide cross ventilation in an open attic would be to use gable end vents.

There are options, but the easiest means is to just provide eave vents at the bottom and a ridge vent at the top.

 

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[steveray]

2009 Requires it........

SECTION R806 ROOF VENTILATION

R806.1 Ventilation required. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain or snow. Ventilation openings shall have a least dimension of 1/16 inch (1.6 mm) minimum and 1/4 inch (6.4 mm) maximum. Ventilation openings having a least

 

[Sifu]

I think 2009 Options it as well, R806.3 "where eave or cornice vents are installed". R806.1 instructs how the openings are made, not where. Understand I think its an exceedingly bad idea to not vent the underside of the roof in this condition but I don't believe codes support it. ICC publishes the Q&A just to answer questions like this, and they did. If the correct amount of ventilation is provided for the size of the roof by gable vents then the cross ventilation has been provided. I agree that the code says "where ceilings are applied directly to the underside of roof rafters" and that doesn't get accomplished here but I can't reconcile that with the Q&A.

 

[steveray]

Sifu...read 806.1 first....."shall have cross ventilation for each separate space".....then you go to the how.....if each space vents with gable vents like an open attic, great...if you have a cathedral ceiling or otherwise compartmentalize the bays, then you probably need eave vents and then you need an airspace...

 

[north star]

$

steveray,

Please keep in mind that Sifu is already fighting a

daily uphill battle with his BO; as well as, the

contractor community, ...so, if the IRC doesn't

specifically call for something [ in writing ], he

won't be able to require it, regardless of

the actual functionality of it......In this case,

proper ventilation of the attic spaces.

FWIW, the "balancing / ventilation" of the air

inside an attic is a no brainer, but that is not

clearly worded in the IRC.

$

 

[steveray]

NS...I understand Sifu's position and am not envious......bottom line is, those individual rafter spaces need to be ventillated,,,,how is it being accomplished? I agree that the baffles are not always required, (like in an open attic or shed with no insulation) but it is a venting option to be chosen and implemented properly by the applicant.....

 

[tmurray]

It should be fun to replace those 25yr shingles in 5-7 years.... Gotta love hot roofs

 

[Sifu]

I am not using my ever increasingly precarious position as an excuse here. As I said I agree the spaces should be ventilated. My quandary is with the Q&A where the question is asked and answered. Notice I said should be ventilated, not must, since the code doesn't spell it out and the Q&A does....in the opposite. Believe me, if I had absolute code on this I would absolutely not accept it.

 

[Big Mac]

Soffit ventialtion may or may not be the same as eave vents in concealed spaces where individual bays are the concern. Soffit vents could be into an enclosed soffit system that does not even communicate with the attic space. The soffit vents (aka eave vents) referred to could also be eave vents for an open attic condition that could be cross ventilated without the use of eave vents.

As previously noted, there are ways to provide cross ventilation even in individual rafter spaces without using eave vents placed between rafters or trusses at the wall line. The code does require cross ventilation, it just allows some flexibilty as to how you might achieve it.