How to Keep Roof Joists From Freezing (And Why It's Bad)

Keep Roof Joists From Freezing

When the weather gets cold, you may notice that the joists in your attic freeze. Especially for new homeowners, this can be very concerning and raise many questions regarding the safety of the beams freezing and how to prevent it from happening in the future.

Frozen roof joists do not impact the stability of the structure in any way, but once the temperature rises in the attic, the melting ice can cause water damage and mold. To prevent your home’s roof joists from freezing, lower the moisture levels in the attic by sealing all bypasses and air leaks.

Frozen roof joists are usually not something you must worry about, but they can cause a lot of damage if ignored. Let’s take a closer look at why roof beams freeze, why frozen joists can cause damage to your home, and how to prevent it going forward.

Why Do the Roof Joists in Your House Freeze?

Roof joists freeze because of two interacting factors in your attic:

  • Below-Freezing Temperatures
  • High Moisture Levels

Roof joists often freeze during the winter when moisture and low temperatures combine in the attic of your home. Elevated moisture levels in the air permeate the wood, and water collects on the outside of the beam. Below-freezing temperatures freeze the moisture-laden joists solid and often leave a layer of ice or frost on their surface.

Insulating your attic can only do so much to retain heat in your home. It is common for attics to reach temperatures below freezing quite regularly during the winter in most places. The factor that you can more easily control is the moisture levels in your attic.

Moisture gets into your attic through a variety of entrances. Barring a hole in your roof that lets in water, most moisture collects in attics from heated air escaping from the central portion of the home. Improper ventilation can worsen the problem by not providing enough airflow to allow the moisture to escape the attic.

roof in the winter

Why Is It Bad If Your Home’s Roof Joists Freeze?

The process of roof joists freezing does not cause any significant damage or issues to the structural integrity of the beams. However, once the temperature rises above freezing and the frozen joists thaw, the resulting water can cause considerable damage.

  • Mold - One of the biggest concerns after frozen beams thaw out and drip water is the possibility of mold. Mold spores can circulate the house and cause severe health issues, not to mention the cost of treating the mold and replacing any damaged materials.
  • Water Damage - Water damage comes in many forms, from simple cosmetic issues to structural damage. Water can leak through the ceiling of your home and cause spots on the drywall. It can also cause the joists and sheathing in your attic to warp.
  • Wet Insulation - Insulation can lose up to 40% of its R-value insulating effectiveness when it gets wet. Ineffective insulation can increase heating and cooling costs in your home, plus damp insulation is a prime location for mold growth.

How to Prevent Roof Joists From Freezing

Now that you know a little about why roof joists freeze and how it can cause roof repairs to be expensive, you're probably wondering how to prevent it from happening. Below are some of the most effective methods to help stop your home’s roof joists from freezing during cold weather.

Ensure No Exhaust Fans Vent Into the Attic
Your home should not have any exhaust fans that vent into the attic. All exhaust vents should make it to the house's exterior to ensure all moist air makes it outside and doesn't accumulate inside the structure.

There are usually at least a few exhaust fans that you should check, including the kitchen exhaust fan, exhaust fans for each bathroom in the house, and clothes dryer vents. Exhaust fans venting into the attic is not a problem in most up-to-code dwellings, but it’s always good to check, especially if your home is older.

Block All Attic Bypasses
Attic bypasses are any air leaks from the central part of the home into the attic. Heated air from the central portion of the house is often quite humid, so it’s essential to block all holes where it can escape into the attic space.

Openings into the attic, such as a whole house fan, are prominent places to seal during winter, but you can often find holes where moist air can escape into the attic in many other less-obvious areas. Any time something passes through the ceiling or upper wall plates, it’s a good idea to seal around the opening. Wire holes, furnace vents, and plumbing vents are the most common openings.

You can block attic bypasses using various materials, but spray foam works best in most situations.

Improve Attic Ventilation
Ventilation alone will not do much to stop your home’s joists from freezing, but air circulation in the attic can help move humidity out of the confined space. Improving your attic ventilation can help, but stopping the moisture from getting into your attic in the first place is much more effective in preventing your joists from freezing.

Once you've thoroughly sealed all attic bypasses and places where air could escape the interior of your home into the attic, then you can consider improving attic ventilation. There are many types of vents that you can add to enhance air circulation, with ridge roof vents and soffit vents being some of the most common.

Final Thoughts

While not inherently harmful to your home, frozen roof joists can cause severe water damage and mold issues once the temperature rises. Be proactive about preventing your beams from freezing by taking action while the temperature is warm.

Ensure no exhaust fans from clothes dryers, bathrooms, or kitchens vent into the attic and release moisture-laden air into the space. Seal up all attic bypasses or holes where air from the central part of the house can get into the attic. Combined with adequate attic ventilation, these measures will ensure as little moisture as possible remains in the attic space.

The less humid the air is in the attic, the less water will freeze in and on the roof joists, causing problems when it thaws. If you're concerned about your roof during cold temparatures, contact your local Portland roofers.

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