The vent pipe should be run up to a point where the top end is at least a foot or so above the roof.
For example, a 6-inch (152 mm) diameter Type B vent must extend above a simple gabled roof only 1 foot (305 mm) for roofs having up to 6/12 pitch, if the terminal is not within 8 feet (2438 mm) of a vertical surface such as an upper-story exterior wall.
3-2-10 Rule Explained
Explained, the chimney pipe must be a minimum of three feet above the roof but also two feet taller than anything within ten feet. The portion of the rule stating the pipe needs to be 2 feet above anything within 10 feet is where most people get confused.
The international code for vents require a minimum of 6” extension above the roof. The codes in the USA are normally equal from state to state and require them to be 12 inches above the roof.
(a) No gas vent shall terminate less than five feet in vertical height above the highest connected equipment draft hood outlet or flue collar. (b) No type B-W gas vent serving a vented recessed heater shall terminate less than twelve feet in vertical height above the bottom of the heater.
CLEARANCES AND ENCLOSURES
Selkirk Type B Gas Vents 3 through 24 inch sizes must be installed with ONE INCH MINIMUM AIR SPACE CLEARANCE TO COMBUSTIBLES! 26 through 48 inch sizes require TWO INCHES MINIMUM AIR SPACE CLEARANCE TO COMBUSTIBLES. These clearances are marked on all gas carrying items.
A connection between a vent pipe and a vent stack or stack vent shall be made not less than 6 inches (152 mm) above the flood level rim of the highest fixture served by the vent. Horizontal vent pipes forming branch vents shall be not less than 6 inches (152 mm) above the flood level rim of the highest fixture served.
The International Plumbing Code (IPC), requires plumbing vent pipes to extend vertically at least 152 mm (6 in.) above a roof, per Section 905.5, "Vent Connections and Grades." Additionally, vent pipes must be at least 305 mm (12 in.) away from a vertical surface.
Vent terminals extending through a wall shall terminate at least 6 inches (152 mm) above the roof and the opening shall face upward. Vent terminals shall not terminate under the overhang of the building. Air admittance valves are not approved for venting of plumbing fixture traps.
The vent stack should terminate as close to the roof as possible, reducing exposed vent stack area. However, a very short vent stack is at risk of being buried in snow. The vent stack should extend 20 cm above the roof, wrapped in rigid foam insulation and a metal collar to reduce the potential for frost.
This rule means that your chimney's shortest side needs to be at least 3 feet above the roof penetration, and its top has to be 2 feet higher than any part of the building that's within 10 feet.
Optimize Chimney Height - Taller chimneys lead to better draw. If at all possible, extend the height of your chimney to help improve the chimney draw. Consider Using a Chimney Cap - A chimney cap helps to prevent debris buildup and downdrafts caused by adverse weather conditions.
Double wall flue pipes have to be installed in accordance with the manufactures installation instructions. ( generally clearance to combustibles is 6 inches. ) Single wall flue pipes have to comply to CSA B365 requirements. ( generally clearance to combustibles is 18 inches. )
Type B vents must be equipped with their own special chimney caps. If the cap is damaged or lost, it should not be substituted with something not recommended by the manufacturer. The clearance required from combustible materials is printed on the flue's exterior metal surface, and is generally 1 or 2 inches.
Properly installed, the vent cannot come apart through vibration, and offers protection against vent failure or fire hazard. Type B Gas Vent is designed for negative pressure applications and flue gas temperatures not exceeding 400°F above ambient for Category I appliances.
A universally accepted guideline for roof ventilation is the 1/150 ventilation rule. According to this rule, a roof must have ventilation that is at least one square foot for every 150 square feet of attic or crawl space. A minimum of 13.3 square feet of ventilation is needed for a 2,000-square-foot attic.
The vent pipe should be run up to a point where the top end is at least a foot or so above the roof.
Appliances designed for natural draft venting and incorporating integral venting means shall be located so that a minimum clearance of 9 inches (229 mm) is maintained between vent terminals and from any openings through which combustion products enter the building.
Roof vent pipes are not only exposed to the sun, but also to thunderstorms, rain, snow, and more. Therefore, they are more likely to get damaged before their age. However, to increase their durability by up to 20 years, you may cap the roof pipe vent.
Extensions of vent pipes through a roof shall be terminated at least 2 feet above the roof surface and shall be properly flashed. Where the roof is used for any purpose other than weather protection, the vent pipe shall extend at least 7 feet above the roof surface and shall be properly supported.
Tips for Installing Vent Pipes
When installing a revent pipe, the horizontal portion must be at least 6 inches above the fixture's flood level or to the highest point water can rise. For example, the flood level for a sink is its rim or overflow hole.
Vent pipes must be installed so they stay dry. This means that they should emerge from the top of the drainpipe, either straight vertically or at no less than a 45-degree angle from horizontal, so that water cannot back up into them.
How much clearance (vent height) your roof vent needs depends on the pitch of your roof and the climate zone you live in. These applications are for when Exhaust Vents are installed less than 2 feet below the peak of the roof. 3/12 roof pitch or greater: 1” or 2” tall collar is recommended for all climate zones 1 - 8.
3 Vent Connection Height Above Fixtures. Connections between any horizontal vent pipe, including individual vents, branch vents, relief vents, circuit vents or loop vents, and a vent stack or stack vent shall be made at least 6 inches above the flood level rim of the highest fixture on the floor level.
A single-walled vent pipe should be six inches away from any combustible material, and a double-walled vent pipe should be one inch away.