Is it better to vent a bathroom fan through the roof or side of the house?

When installing a bathroom fan, one of the most important considerations is how to route the venting. The two main options are venting the fan through the roof or venting it through the side of the house. Both methods have pros and cons that homeowners need to weigh when deciding where to vent their bathroom exhaust fan.

Page Contents

1 Factors to Consider When Venting a Bathroom Fan
2 Conclusion

Factors to Consider When Venting a Bathroom Fan

Here are some of the main factors to think about when deciding whether to vent the bathroom fan through the roof or the side of the house:

Vent length – A shorter vent pipe is always better for maximum air flow and efficiency. Roof vents are often shorter.

Accessibility – Roof vents may require getting up on the roof to service them. Sidewall vents are easier to access.
Appearance – Roof vent requires a visible pipe on the roof, which some homeowners dislike aesthetically.
Moisture – Sidewall vents allow moisture buildup inside vent pipe. Roof vents minimize moisture buildup.

Insulation – Both venting methods require insulation around the ductwork to prevent condensation buildup.
Installation – Roof venting is more complex. Side venting is easier in most cases.
Cost – Side vents tend to be less expensive to install overall.

Let’s explore each of these key considerations in more detail…

Vent Length

An important factor when installing a bathroom fan is keeping the length of the vent as short as possible. Long vents reduce airflow, decreasing the exhaust fan’s effectiveness. Long vents also tend to accumulate more moisture.

Roof vents provide the most direct path outside, giving the shortest possible vent length. The fan can be installed on the ceiling and then vented straight up through the attic and roof. This keeps the venting very short and direct.

Sidewall vents tend to require a longer vent pipe run. The pipe needs to be routed from the fan to the exterior wall, likely with horizontal runs to get to the outside. This often increases the vent length significantly compared to a roof vent.

Accessibility

Roof vents can be more difficult to access for cleaning and servicing compared to sidewall vents. With roof venting, a professional may be required to get up on the roof to service the vent cap and pipe. Sidewall vents are readily accessible from inside or outside the house.

Easy accessibility is an advantage of sidewall vents. They allow do-it-yourself cleaning of the vent pipe and replacement of the vent cap if needed. No special equipment is required like with roof vents.

Appearance

Roof vents require a visible pipe running up the side of the roof. Some homeowners dislike the utilitarian look this can give the home’s exterior. Sidewall vents have no exterior visible venting.

So for a cleaner look with no visible roof venting, sidewall vents provide a hidden exhaust solution. Although the vent cap is visible on the outside of the house, there is no pipe running up the roofline.

Moisture Accumulation

Moisture buildup is a primary concern with bathroom fan venting. Warm, humid air condenses as it travels through the vent pipe to the outside. This can lead to mold and moisture damage over time.

Roof vents are less prone to moisture accumulation since the vent pipe is short and runs straight up with no horizontal sections. Sidewall vents often have horizontal pipe sections where moisture can gather.

Properly insulating sidewall vent pipes is critical to prevent condensation issues. But roof vents are simpler and limit chances for moisture to gather in the ductwork.

Insulation Needs

Any venting method needs to be properly insulated to prevent condensation problems within the vent pipe. Fiberglass duct insulation or plastic flexible ducting should surround the entire vent pipe run.

For roof vents, the section in the attic should be insulated to provide an adequate vapor barrier. With sidewall vents, any horizontal pipe sections in unconditioned spaces should be carefully insulated.

If the vent pipe is not properly insulated, condensing moisture can lead to mold growth and damage to walls and ceilings.

Installation Complexity

Cutting through the roof, flashing, and roofing work make roof vents more complex to install. Sidewall vents involve simpler exterior wall penetration and finishing.

Proper roof vent installation requiresroofing expertise to weatherproof the pipe penetration and prevent any leaks. Mistakes during roof venting can easily lead to serious roof leaks or other issues.

Sidewall venting has fewer construction challenges and risks. The biggest steps are cutting through the wall cleanly and sealing up the exterior penetration.

Cost Comparison

Due to the construction work and materials involved, roof vents tend to cost more to install than sidewall vents. The table below compares typical installation costs:

Vent Type	Cost Range
Roof Vent	$400 – $700
Sidewall Vent	$100 – $350

This cost range can vary based on the home’s construction and complexity involved. But sidewall vents are generally the more affordable and simpler option.

Conclusion

Ultimately, both roof and sidewall venting can work well for venting a bathroom fan. Sidewall vents make the most sense for ease and cost in many situations. But roof vents are a good choice when the shortest, most moisture-resistant vent path is preferable.

Homeowners should consider all the factors and installation requirements when deciding the best venting method for their specific bathroom. Getting professional input is also wise to ensure proper ventilation and prevent problems.

With good planning, insulation, and installation, both roof or sidewall vents can effectively remove moisture and odors from a bathroom. Proper airflow and duct sealing are critical to prevent moisture issues in surrounding walls and ceilings and provide a long-lasting venting solution.