gable vents

Originally Posted By: Rafael
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hi again


on a home as small as about 900 sqft in rectangular shape, is it requierd


to have to vents on each side of the house or can you just have one gable vent on the whole house?Does it have to due with age also


Originally Posted By: phinsperger
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preferably located as close to the eaves as possible. Most often this is done through sofit vents. Ensure the sofit vents are not obstructed by insulation. Min 1 sqft venting for every 150 sq ft


2) An exhaust preferably located as close to the ridge as possible. Min 1 sqft venting for every 150 sq ft

This gives you a total of
Min 1 sqft venting for every 300 sq ft


You should have a min (more would be better) of 3 sq ft

You can use sofit venting in combinination with a gable vent.

When only gable vents are used, the best solution would be to have one at each end to facilitate the flow of air across the attic space. It does not work as well as sofit venting as because its effectiveness is more determined by wind movement. Sofit/ridge venting is more effective because it is determined by convection.


Age can be a factor in that if it is a much older house it may not have a continuous air barrier under the insulation. If there is no other venting other than the gable vent, it could be pulling the "intake" air from the living space of the house. I'm not sure where you are so I don't know the climate conditions, but this can result in moisture build up in the attic (possibly leading to mold and wood decay), high heating/cooling costs, interior humidity problems.


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Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: ekartal
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If you only have one gable there will no ventialtion at all - zero. Soffit and (entire) ridge as Paul mentioned is best. Soffit and roof vents work well too, but having soffit, gable AND ridge venting will actually have a negative impact. The poor air won’t know which way is up. icon_wink.gif


Erol Kartal
ProInspect


Originally Posted By: aslimack
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I liken the 1 gable vent to trying to blow into a glass with your face pressed up against it making a seal. No where for the air in the glass to displace too. Not gonna work.


Adam, A Plus


Originally Posted By: Joe Funderburk
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Quote:
1) An intake preferably located as close to the eaves as possible. Most often this is done through sofit vents. Ensure the sofit vents are not obstructed by insulation. Min 1 sqft venting for every 150 sq ft

2) An exhaust preferably located as close to the ridge as possible. Min 1 sqft venting for every 150 sq ft

This gives you a total of
Min 1 sqft venting for every 300 sq ft


Paul, I have a question about vents. I'm not an expert on it, but I don't understand your math. My ciphering says the above total ventilation would be 2 sq. ft. / 150 sq. ft. Isnt' that in excess of the requirement?

Then another question: you seem to say "intake" and "exhaust" ventilation are required. My rerecollection of the standard is that it simply specifies "ventilation" and specifies the sq. footage requirements (1/100). Please let me know if I'm wrong.


--
Thanks,

Joe Funderburk
York County, SC
Alpha & Omega Home Inspection, LLC
jfunderburk@aohomeinspection.com
www.aohomeinspection.com

Originally Posted By: gbell
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ROOF VENTILATION


806.1 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. Ventilating openings shall be provided with corrosion-resistant wire mesh, with 1/8 inch (3.2 mm) minimum to 1/4 inch (6.4 mm) maximum openings.

806.2 Minimum area.
The total net free ventilating area shall not be less than 1 to 150 of the area of the space ventilated except that the total area is permitted to be reduced to 1 to 300, provided 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 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 to 300 when a vapor barrier having a transmission rate not exceeding 1 perm (57.4 mg/s ? m2Pa) is installed on the warm side of the ceiling.

806.3 Vent clearance.
Where eave or cornice vents are installed, insulation shall not block the free flow of air. A minimum of a 1-inch (25.4 mm) space shall be provided between the insulation and the roof sheathing at the location of the vent.


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Greg Bell
Bell Inspection Service

Originally Posted By: phinsperger
This post was automatically imported from our archived forum.



Joe Funderburk wrote:


Paul, I have a question about vents. I'm not an expert on it, but I don't understand your math. ...


Oopps! ![icon_redface.gif](upload://f7DX2EWhmUfsDapWaYT3oJHMCj1.gif) Your right. I meant to divide the 1 sq ft not the 300 sq ft.

Upper (exhaust) = .5 sq ft per 300 sq ft
Lower (intake) = .5 sq ft per 300 sq ft



Joe Funderburk wrote:

Then another question: you seem to say "intake" and "exhaust" ventilation are required. My rerecollection of the standard is that it simply specifies "ventilation" and specifies the sq. footage requirements (1/100).


This is of course Canadian code but I read Greg Bell's post of 806.2 to accomplish practically the same thing.

Quote:
9.19.1 Venting
9.19.1.1. Required Venting
(1) Except where it can be shown to be unnecessary, where insulation is installed between a ceiling and the underside of the roof sheathing, a space shall be provided between the insulation and the sheathing, and vents shall be installed to permit the movement of air from the space to the exterior.
9.19.1.2. Vent Requirements
(1) Except as provided in Sentence (2), the unobstructed vent area shall be not less than 1/300 of the insulated ceiling area.
(2) Where the roof slope is less than 1 in 6 or in roofs that are constructed with roof joists, the unobstructed vent area shall be not less than 1/150 of the insulated ceiling area.
(3) Required vents are permitted to be roof type, eave type, gable-end type or any combination thereof, and shall be distributed
(a) uniformly on opposite sides of the building,
(b) with not less than 25% of the required openings located at the top of the space, and
(c) with not less than 25% of the required openings located at the bottom of the space.
(4) Except where each roof joist space referred to in Sentence (2) is separately vented, roof joist spaces shall be interconnected by installing purlins not less than 38 mm by 38 mm on the top of the roof joists.
(5) Vents shall be designed to prevent the entry of rain, snow and insects.
(6) The unobstructed vent area required in Sentences (1) and (2) shall be determined in conformance with CAN3-A93, "Natural Airflow Ventilators for Buildings".


Incidentally, There is no reason why you would want to have the split between upper and lower anything other than 50/50. The code allows for a variation (to a point) to permit practical construction.


--
.


Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: lewens
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Paul


You still did it backwards


You need 2 sq ft per 150 sq ft of roof area.



Just my usual 12.5 cents


From The Great White North Eh?
NACHI-CAN
www.aciss-brant.com
www.certifiedadulttrainingservices.com/

Originally Posted By: phinsperger
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That means 1 square foot of total vent space for every 300 square feet of ceiling area. Right?


9.19.1.2 (3)(b)(c) with not less than 25% of the required openings located at the top of the space
Now that 1 sqaure foot is to divided up between the upper (exhaust) and lower (intake). It can be 75/25, 60/40 etc. but 50/50 is optimal.

So 1/2 sq ft upper and 1/2 sq ft lower. Correct?

I admitt I was a bit too fast on the keyboard and made an error the first time but I think this is right.

Tell you what Larry, I'll bet you a drink at the meeting on Sept 14 that I'm correct ![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)


--
.


Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: Rafael
This post was automatically imported from our archived forum.



thanks for evrybodies input and sorry , i should of posted this in exterior.