How do you vent an exhaust through a roof?

Venting an exhaust system through the roof is a common requirement for many homes and buildings. Kitchen range hoods, bathroom fans, clothes dryers, furnaces, water heaters, and other appliances all require proper exhaust ventilation to the outside. Installing a roof vent allows dangerous or unpleasant exhaust gases to be released high above the building where they can dissipate safely. This prevents the accumulation of carbon monoxide, moisture, grease, and other byproducts inside the structure.

Planning the Vent Installation

Properly planning a roof venting project is crucial to ensure the system functions correctly and safely. Here are some key steps to take before starting the vent installation:

• Determine the required CFM (cubic feet per minute) airflow rating for the exhaust appliance based on manufacturer specifications. This influences vent duct sizing.
• Select a vent termination kit rated for the exhaust type. Roof vents are available in various materials like galvanized steel, stainless steel, or plastic.
• Choose a location on the roof surface that aligns with the appliance exhaust location.
• Make sure the planned vent location meets all building code requirements for clearance from windows, air intakes, etc.
• Have necessary roofing materials on hand if flashing installation is needed.
• Inspect the attic space above the exhaust location if accessible.

Taking these preparatory steps allows you to identify any issues and have all required materials before starting. This helps the roof vent installation go smoothly and safely.

How to Cut a Hole in the Roof

Once you’ve mapped out the vent location, the next key step is cutting a hole through the roof sheathing. Here is the basic process:

1. From inside the attic, locate your planned vent position and mark a outline on the underside of the roof sheathing.
2. Drill a pilot hole somewhere inside the outline.
3. Insert a reciprocating saw blade into the pilot hole from underneath.
4. Carefully cut along the outline with the reciprocating saw, making sure to avoid any roof rafters or supports.
5. Double check the opening size matches the required dimensions for your vent.

Wear protective eyewear and gloves when cutting the roof hole. Try to limit cutting debris falling into the attic space below. Have someone outside watch and call out your saw position to avoid cutting in the wrong spot.

Installing the Roof Vent

Once the roof vent hole is cut, you can install the actual vent termination kit:

1. Apply a ring of roofing cement around the hole underneath to seal it temporarily.
2. Slide the roof flashing or boot flange up under the shingles above the hole.
3. Secure the flashing to the roof deck using roofing nails.
4. Seal any gaps between the flashing and shingles with additional roof cement.
5. Twist-lock the vent cap into the flashing or attach with screws per manufacturer instructions.
6. Apply more roof cement around the top and edges of the flashing.

Be extremely careful when on the roof to avoid falls. Wear shoes with slip-resistant soles. Follow all safety procedures when working at heights.

Running the Exhaust Ductwork

Once the roof vent termination is installed, the next step is connecting the exhaust ductwork:

1. Run rigid metal ducting from the appliance up through the attic to the roof vent.
2. The duct should be as straight and smooth as possible with minimal bends.
3. Connect duct sections together securely with screws and tape.
4. Support the horizontal duct spans with metal strapping every 4-6 feet.
5. Insulate the ductwork to reduce condensation buildup.

Proper duct installation is crucial to achieve the rated airflow for venting combustion gases or moisture as needed. Follow all manufacturer instructions for material, slope, and support.

Completing the Installation

Once the exhaust vent and ductwork are fully installed, complete the project with these remaining steps:

• Caulk exterior holes or gaps around the vent flashing.
• Attach mesh screen spark arrestor if combustible exhaust.
• Test appliance operation and confirm adequate airflow.
• Make any duct adjustments needed to maximize airflow.
• Seal attic opening around duct with firestop caulk or insulation.
• Clean up all tools, materials, and debris from project.

Your appliance exhaust is now safely vented through the roofline and ready for normal use. Be sure to follow any manufacturer instructions for testing or adjustment specific to your appliance.

Key Safety Tips

Properly installing a roof vent requires working safely at heights, cutting holes in the roof, and handling potentially hazardous exhaust gases. Here are some key safety reminders:

• Use fall protection like harnesses when on the roof.
• Never work on a wet, icy, or damaged roof surface.
• Wear heavy work gloves when handling sheet metal.
• Turn off power to appliance before starting work.
• Follow all building codes for roof penetrations and clearances.
• Have a fire extinguisher and first aid kit available.
• Carefully ventilate work area if dealing with combustion exhaust.
• Monitor carbon monoxide levels if applicable.

Never compromise safety to complete the installation faster. Preventing injuries or hazards should always be the top priority.

Hiring a Professional

While a DIY enthusiast can install their own roof vent in many cases, hiring a professional is highly recommended for several reasons:

• They have extensive experience locating rafters and avoiding roof damage.
• They can properly integrate the vent with your roofing shingles and materials.
• They have safety training for working at heights and fall prevention.
• They may be needed to obtain any required building permits.
• Your home insurance may require a licensed contractor for coverage.
• They can identify and follow all applicable building codes.
• Professional installation gives you peace of mind that the job is done right.

Even if you want to try DIY venting, having a roofer inspect your planned location first is wise. Get professional help if you have any doubts or concerns about safely completing the installation.

Cost to Install a Roof Vent

The total cost to have an exhaust vent professionally installed through your roof can range from $200 up to $1000 or more depending on several factors:

• Roofing materials – Asphalt shingles are cheaper than slate or tile roofs.
• Vent type – Simple passive vents are less than powered exhaust fans.
• Vent size – Larger vents for high-capacity fans cost more.
• Vent material – Plastic is cheaper than stainless steel.
• Height and pitch of roof – Steeper roofs are more complex and expensive.
• Attic – Easy attic access lowers cost vs. cramped spaces.
• Ductwork – Long or difficult duct runs add cost.
• Professional vs DIY – Hiring a contractor costs more but is safer.

Get multiple quotes to find the best value. The lowest bid may not reflect complete professional service. An experienced contractor charges more but often saves money by doing the job right the first time.

Alternative Venting Options

While venting exhaust systems through the roof is very common, it is not the only option in all cases. Here are some alternative venting methods to consider:

• Wall venting – Install a vent cap directly through an exterior wall instead of the roof when possible.
• Soffit vents – Vent through the eave overhangs along exterior walls.
• Dryer vent box – Conceal a dryer vent behind an exterior wall-mounted vent box with louvered grill.
• Remote roof venting – Use a small roof vent with a fan and duct from appliance on lower floor.
• Air admittance valves – Install one-way valves to vent flows into the attic instead of outside.
• Condensing venting – Modern high-efficiency appliances can vent moisture into drain pipes.

Consider all options and determine what works best for your specific appliance, site conditions, and building layout. Involving an experienced contractor early on ensures the best venting solution.

Conclusion

Installing a roof vent for gas, moisture, or exhaust discharge involves careful planning, safety precautions, roof penetrations, and ductwork skills. While a DIY project is possible in many cases, the safest option is hiring a professional roofing contractor unless you have extensive experience. They have the expertise to complete the installation to all code requirements without risking roof damage, hazardous exhaust buildup, or personal injuries from falls or other hazards. Investing in a professional installation gives you peace of mind that this critical ventilation project is handled correctly.