Can You Vent a Dryer Into the Attic?


Venting your dry outside through a wall in your home requires quite a bit of work, skill, and time. Seeing as how heat rises anyway, is venting into the attic a safe alternative?

The International Residential Code states that you must not vent a dryer into the attic. Building code permits a dryer vent to run through the attic, but it must not terminate there. In addition to being a potential fire hazard, venting into the attic would result in moisture problems, which leads to mold and rot forming.

There is a lot of legislation surrounding dryer vents, which you must comply with to protect you and your family and to ensure you don’t invalidate your home insurance.

In this article, I’ll cover:

  • The dangers of venting into an attic
  • Why venting through your roof is the safer option
  • Step-by-step guide on how to vent through the roof
Bathroom Exhaust Fans

6 Dangers of Venting a Dryer into an Attic

The following issues of attic venting apply to both electric and gas clothes dryers:

1. Length of Duct

A major restriction may be the distance from your dryer to your attic. Manufacturers consider 35 feet of ducting as the physical limitation for most clothes dryers. With longer ducting, you are putting a lot of strain on the machine, which decreases the efficiency and health of your dryer.

2. In-Direct Path

Any detours the dryer’s exhaust needs to make before reaching the outside air will reduce the machine’s efficiency. 90-degree ducting bends are equal to adding an extra five feet to the length of the duct.

3. Condensation

Part of the reason for keeping the ducting short is condensation. Attics can reach freezing in the winter and have the effect of condensing the moisture on the inside of the metal duct before it exits your home. These droplets will gather and roll back down the pipe as streams of water into the back of your dryer.

4. Build-Up of Lint

Water condensate from the top of the duct can cascade to the base of the duct and trap lint in the middle of the pipe. Even if the lint escapes into the attic, it will build up in clumps and form potential fire hazards.

Residential codes restrict some venting practices, such as laying ducting longer than 35 feet and venting into attics. So, you need to check your local building codes for legal methods of ducting.

6. Building a Home for Rodents

A widespread practice when venting into an attic is to leave the pipe or duct open for better airflow and to prevent blockages. This opens up a perfect habitat for rodents to nest in, and the balls of lint that collect around the vent make fantastic nesting materials.

Venting a Dryer Through the Roof

Though not the best method, you may find that you have no choice but to make a hole in your roof for venting. Roof vents are a safe and efficient method of exhausting dryers without windows or exterior wall access.

Pros:

  • Efficiency – The shortest distance to the outside may be through the roof; this is better for efficiency and building codes.
  • Condensation – A short and direct duct means that more water vapor will condense outside rather than against the walls of the ducting.
  • More Considerate – If you are surrounded by neighbors, they may not like to hear the buzzing of your machine or the smell of the exhaust. A roof vent offers a venting position the furthest away from your neighbors.
  • Prevents Blow-Back – Roof vents are less prone to directional winds, which can blow back exhaust into the duct.
  • Safer – Reduces the build-up of vapors that create dangerous molds and wood rot in your attic. Noxious gases stay outside of your home, and you do not end up with balls of lint in the attic.

Cons:

  • Leaking Roof – By cutting a hole in your roof, you are giving the rain an entry point. Even with the best techniques and materials, you will never seal the vent up as well as if it was a solid roof.
  • Appearance – Depending on the exit hole, you may find that you do not like the look of a chimney sticking up through the middle of your roof. It may also cause issues with your local building regulator’s Roofing Codes.
  • Height – If allowed, most building codes need the exhaust pipe to extend at least 12-inches above the height of your roof. This makes the chimney cap more noticeable and gives storms more surface area to tear away at.
  • Cost – Installing a duct through your roof is more complex since you need to seal the hole and try to make it waterproof again. You may even need a tailor-made chimney crown to preserve the aesthetics of your home.
  • Maintenance – If your local codes allow you to put a vertical dryer vent through your roof, they may come with a proviso. The roof vent may require annual maintenance by a professional vent cleaner.

How to Vent Your Dryer Through the Roof

It is easy to over-complicate the task of installing a dryer vent in your roof; you want to make it look neat and avoid destroying your insulation.

Drilling a hole through your roof to install a vent should be simple, which it is if you follow these steps:

  1. Mark up – It is worth spending time planning where the hole is going to come through. Consider, will the duct need to be longer than 35 feet? Will it hit a support beam? Is there another object on the roof that will be in the way of the vent?
  2. Plan the duct path. For the best airflow, you want to try to run the duct with the least number of turns from the back of the dryer to the roof vent.
  3. When you are happy with the placement, cut a hole for the shape and size of ducting you are using. For tiled roofs, remove the tiles from around where you want the vent to sit on your roof.
  4. Cut a hole through the roof insulation with a utility knife and use a jigsaw to cut a duct-sized hole through the support board. If you have tiles cut them so that they fit around the hole.
  5. Raise the shingles so that you can slide the vent cap beneath them. Use scrap wood to hold it out the way.
  6. Spread roofing tar between the vent shield and the roofing deck. Put the pipe of your vent cap through the hole you made.
  7. You may want to secure it with nails, then spread more tar over the shielding and the roof.
  8. You want to have the shingles or tiles overlap the vent’s shielding for better rain flow.
  9. Go back into your attic and secure the duct to the vent pipe. You may want to use a hose clip to tighten the connection.
  10. A cold pipe will condense the water vapor to the inside of the duct before it reaches the outside air. Consider lagging the metal duct pipe to reduce the action of the cold air in your attic on the water vapor.

Graham Walsh

I want to share everything I know about home improvement in order to help you. Whether you're a home enthusiast or an industry professional, I have the information that you need.

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