Ventilated Attics And Rafter Spaces
The Irc Does Not Require Ridge Vents
Ridge vents are commonly seen on many homes, but they are not required by the International Residential Code . The IRC does state that ventilation is required, but not specifically ridge vents.
All states follow IRC regulations, but some states make their own adaptations based on factors like climate that can influence how ventilation needs to be achieved or maintained. Thus, your states local residential code may stipulate the use of ridge vents, specifically, so you should always check these regulations before finalizing your ventilation plans.
Determining The Current Code Adopted
It is important to know the building code that is adopted in the jurisdiction having authority. While not all jurisdictions require a permit for roofing work, repairs or replacements will need to comply with the applicable code in effect at the time of the repairs or replacement. Similarly, the building code that was in place at the time of the original construction or when the roof cover was last replaced should be known in order to verify compliance of the roof cover. Users should contact the authority having jurisdiction if there are questions. This would commonly be the building department or building inspection department of the village, town, city or county in which the building is located. Qualified building officials and building envelope specialists are both useful contacts to help determine local area requirements and if new-to-market products are acceptable.
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What Roof Ventilation Is Required By Code
Now that we know ridge vents are not required by the IRC, and we know that some roofs are even exempt from the ventilation requirement entirely, lets look at what the IRC does stipulate regarding ventilation because this will apply to the majority of homes.
Section R806.1 of the International Residential code states that enclosed attics and rafter spaces that have a ceiling attached directly to the underside of the rafters must have cross ventilation for each space, this means there should be openings on either side.
Furthermore, the vents must be protected so as to not allow rain or snow to enter through them. After all, ventilation shouldnt compromise weatherproofing because this would lead to a whole new set of issues!
The ventilation openings must meet the following criteria:
- They must have a minimum opening of 1/16 .
- They must not exceed 1/4 .
- Any ventilation opening that has a diameter larger than 1/4 must be covered with a corrosion-resistant screen with an opening diameter between 1/16 and 1/4 .
- All vents must open directly outside.
- All vents must be protected from birds, rodents, snakes, and other small animals.
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Variances In Local Requirements
Today, most jurisdictions that have adopted building and/or residential codes use some edition of the IBC and/or IRC. However, older buildings have been built to a variety of building codes or in some cases to no building code. Consequently, it is important to know which code was adopted and enforced when the building was permitted.
Some local building codes establish a threshold that requires the roof structure to be evaluated for conformance with the latest building code provisions when more than a certain percentage of the roof is being replaced or if remodeling exceeds a certain threshold. Main Wind-Force Resisting System loads have changed less over the years than C& C loads. Therefore, it is more likely that the roof-to-wall connections, roof sheathing attachment and roof covers are under-designed, than is the roof structure when compared with current design loads and construction practices. This also means that when re-roofing there are opportunities to improve the roofs wind performance by following best practices for roof-to-wall and sheathing attachment.
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Is Roof Venting Required By Code
Keeping this in view, is a ridge vent required by code?
If you plan to install insulation on your attic floor, then most building codes require that the attic be vented. If a roof has only soffit vents and no ridge vents, most codes require 1 square foot of net free ventilation area for every 150 square feet of attic floor area.
Also, how much venting does a roof need? For most, the requirement is 300 to 1, meaning one square foot of ventilation is required for every 300 square feet of attic floor. That one square foot is then divided equally between intake and exhaust. Even with all the same type of vent, you need to have them in proportion to your intake vents.
Similarly one may ask, are roof vents necessary?
Ventilation benefits a roof when it’s hot outside as well. Unventilated or poorly ventilated attics don’t have an escape route for the heat that builds up. This buildup of heat can damage your shingles from the inside out. An evenly vented roof will allow the hot air to escape keeping your roof and attic cooler.
When should you vent your roof?
In summer, the sun heats air in the attic. In winter, heat from your home warms attic air. In either season, good venting occurs when cool air can enter the attic near the eaves and exit near the peak. Ideally, half of the vent area should be low and half high.
Gas Fired Water Heater Chimney Codes In The Us
See the National Fuel Gas Code, Chapter 24, Fuel Gas, that includes discussion of venting requirements in Section G2427 p. 360, Venting of Equipment .G2427.3 Design and construction. A venting system shall be designed and constructed so as to develop a positive flow adequate to remove flue or vent gases to the outdoor atmosphere.
G2427.6.5 Gas vent termination. A gas vent shall terminate in accordance with one of the following:
1. Above the roof surface with a listed cap or listed roof assembly. Gas vents 12 inches in size or smaller with listed caps shall be permitted to be terminated in accordance with Figure G2427.6.5, provided that such vents are at least 8 feet from a vertical wall or similar obstruction.
All other gas vents shall terminate not less than 2 feet above the highest point where they pass through the roof and at least 2 feet higher than any portion of a building within 10 feet .
G2427.7.3 Termination. Single-wall metal pipe shall terminate at least 5 feet in vertical height above the highest connected equipment draft hood outlet or flue collar.
Single-wall metal pipe shall extend at least 2 feet above the highest point where it passes through a roof of a building and at least 2 feet higher than any portion of a building within a horizontal distance of 10 feet .
An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe.
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Distances: How Far Can The Plumbing Vent Piping Be Located From A Plumbing Fixture
As we discuss at PLUMBING DRAIN NOISE DIAGNOSIS, if the horizontal distance between a plumbing fixture and the vertical vent piping is too great, the fixture may not drain properly, producing slow drainage or gurgling noises.
Poor drainage is not just an annoyance, it can be unsafe since there is also the risk that the poorly vented plumbing fixture will lose the water from its plumbing trap, then permitting sewer gases into the building.
As we show in Carson Dunlop Associates’ sketch, the distance allowed between a plumbing fixture and the vertical vent piping varies between a minimum and maximum as a function of the pipe diameter.
Summary Of Good Venting Practices For Gas Fired Water Heaters
Water heaters must be vented using a listed and approved venting system that provides adequate size, height, and draft.
Otherwise such vents may be unsafe, venting combustion products, including dangerous carbon monoxide, into the building.
Illustrations of proper gas fired water heater venting using Type B- double wall vent pipe through a roof or through a chimney include details for the flue vent connector such as the requirement of a minimum vent connector upwards slope of 1/4″ per foot of horizontal run.
These illustrations are adapted from WHIRLPOOL RESIDENTIAL GAS WATER HEATER MANUAL retrieved 2018/03/05, original source: http://www.whirlpoolwaterheaters.com/media/99595/100263111.pdf
Watch out: regarding these clearances, see the SAFE GAS B-VENT CLEARANCE DISTANCES CLARIFICATION by Charles Buell near the end of this article.
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Does An Attic Have To Be Vented
Ventilating attic spaces is often viewed as a technical requirement for steep-slope roof assemblies, as well as a building code requirement. However, since the 2009 edition of the IRC, attics can be designed to be either vented or unvented. So, the decision to vent an attic space is not dictated by building code it really is a design choice.
Requirements for unvented attics can be found in Section R806.5 of the 2018 IRC. This section contains an extensive list of requirements and conditions that have to be met in order to have an unvented attic. This article will not discuss them, but readers are encouraged to familiarize themselves with those requirements.
How A Lot Does A Roof Vent Value
Roof & Ridge Vent Prices
Putting in a roof vent prices between $300 and $650 on common, together with labor and supplies. Actual charges depend upon the sort, dimension, and variety of models you select to put in. Ridge vents value $2 to $3 per linear foot. Roof vents are available a wide range of kinds and vary from $10 to $500 every.
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Attic Vent And Insulation Clearances
With the installation of attic insulation being very common practice now to achieve energy compliance, it is important to make sure that the roof vents providing attic ventilation is not blocked my the insulation. To ensure that vent openings are not blocked by insulation, the code requires the insulation to be held back from the vent openings a minimum of 1 inch.
The same is applied to enclosed rafter spaces. When ventilation is provided to rafter spaces, not less than a 1 inch space shall be provided between the insulation and the roof sheathing. This clearance must be maintained throughout the rafter space as well as throughout the attic for all types of openings providing attic ventilation.
What Kind Of Roof Vents Are Finest
Generally, we suggest soffit vents for consumption and a ridge vent for exhaust. For houses that cant have a ridge vent, field vents are typically the second most suitable choice for exhaust. And for houses that cant have soffit air flow, youll find that fascia vents to be your second finest wager.
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Ventilation Openings For Attic Spaces
We discussed earlier about how ventilation openings must also be protected from rain, snow, birds, rodents, and similar creatures while still providing enough opening to properly vent. So let us discuss how these openings are required to be protected.
The ventilation openings must be at least 1/16 inch to no more than 1/4 inch. If the openings are larger than 1/4 inch, then material such as corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl or similar material with openings not less than 1/16 inch and no more than 1/4 inch shall be provided.
Whichever one of these is used it is important to exercise care to ensure that the vent openings remain unobstructed while providing protection to prevent entry of unwanted visitors.
Also it is important to note that all required attic ventilation openings shall open directly to the outside air.
Asphalt Shingles On Slopes Of Less Than 1 In 3
- Except for the first 2 courses, coverage shall be not less than 3 thicknesses of shingle over the entire roof, disregarding cutouts.
- A starter strip shall be installed along the lower edge of the roof so that it extends approximately 12 mm beyond the eaves and rake of the roof and fastened along the bottom edge with nails spaced not more than 300 mm o.c.
- Starter strips shall be laid in a continuous band of cement not less than 200 mm wide.
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Design Pressure Coefficients For Roof Zones
Wind produces different magnitudes of pressure acting on the surfaces of a building due to the buildings geometry, and can create small areas of higher pressure on a surface while at the same time other areas on the same surface experience lower pressures. Because geometric variations can be quite large, Component and Cladding design pressure coefficients decrease as the area over which the pressure acts increases. Building codes generally divide roofs into three zones: perimeter, corner, and field . Zoning can also vary based on roof slope and geometry . For low-slope roofs, wind pressures typically have the greatest magnitude at the roof perimeter and corners. Steep-slope roofs have the greatest pressures in the perimeter and corners, as well as the roof peak and eaves. Other geometric discontinuities may have increased pressures as well, especially those at greater height on the structure. These pressures can be positive or negative depending on the direction of the wind and the geometry of the building. This is reflected in building code provisions by dividing the roof into zones and specifying different design pressure coefficients, GCp, for the various zones.
How To Calculate The Amount Of Ventilation You Need
Please note: the following provides advice for homes with ventilated attics. There are some styles of vaulted ceiling homes or flat roof homes that have ventilation spaces within the roof itself, and no attic. These ventilation needs are calculated differently.
The key to proper ventilation of your roof and attic is balance: the amount of space you devote to intake must be equal to the amount you allow for exhaust, and these must be calculated according to the size of your attic and slope of your roof.
You can calculate attic ventilation requirements by determining the square footage of your attic floor , and compare that to the total required net free area . Vents are rated by their net free area, or the amount of space for air to flow in or out. This helps make it easy to calculate how many vents you need for your attic, once youve determined your requirements.
If your attic floor has a vapor barrier, you will need one square foot of NFA per every 300 square feet of attic floor area . If there is no vapor barrier, double it to one square foot of NFA for every 150 square feet of attic floor space . These are broad guidelines, so be sure to check with your local building code.
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Making Water From Air
Most homeowners and builders believe that attics should be vented. If you walk down to your local lumberyard and lean on the counter, the employees and nearby customers will offer a variety of opinions about why attics need to be vented. Unfortunately, its highly unlikely that the statements you hear will be true.
Here are the four most common reasons people suggest to explain the practice of venting attics:
- To reduce the chance of moisture build-up in the attic or condensation on the underside of the roof sheathing.
- To make roofing shingles last longer.
- To lower cooling bills during the summer.
- To reduce the chance of ice dams.
Although attic ventilation is sometimes able to contribute in a very small way to addressing the problems on this list, there are much better solutions to all four problems than ventilation.
What does the code require?
If you plan to install insulation on your attic floor, then most building codes require that the attic be vented.
The standard code formula requires 1 square foot of net free ventilation area for every 300 square feet of attic floor area, assuming that half of the ventilation openings are located in the lower half of the attic and half near or at the ridge. If a roof has only soffit vents and no ridge vents, most codes require 1 square foot of net free ventilation area for every 150 square feet of attic floor area.
Ought To I Open My Attic Home Windows In The Summertime
In case your attic appears to get as sizzling as your automotives inside on a heat, sunny day, you most likely want higher attic air flow. Simply as you may crack open a automotive window to forestall such extreme warmth in your automotive, you should utilize air flow within the attic to cut back the warmth achieve.
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