What Are Common Attic Ventilation Problems in Apartment Buildings?

If you manage an apartment, condo, or townhome community and discover mold or rotten roof decking in one building, how do you know the problem isn’t hiding in the others too? Are you worried that even though the roofs look relatively normal from the outside, poor attic ventilation is quietly trapping moisture and allowing mold and rot to spread undetected?

At RoofSmart, we recently encountered this exact situation while inspecting an apartment community in the Greater Seattle area. What started as an inspection for potential roof leaks uncovered mold, rotten decking, and significant attic ventilation problems. Once we realized the same conditions could exist elsewhere in the community, the project eventually grew into roof replacements and ventilation improvements across 13 buildings.

In this case study, I’ll show you the hidden damage we discovered, why poor attic ventilation contributed to problems throughout the complex, how firewalls made correcting the airflow more complicated than a typical roof replacement, and the custom attic ventilation systems we used to give each attic section the airflow it needed and help prevent the mold and moisture problems from returning.

Common Attic Ventilation Problems in Apartment Buildings

What hidden damage is common in an apartment building with poor attic ventilation?

Recently, I got called out to do an inspection on the roof of an apartment building. The owner wanted me to check out some potential leak spots and wanted a new roof installed. Another estimator at RoofSmart, Chris Koeing, joined me for this inspection.

While we were out there, we confirmed that the attic ventilation system was messed up and discovered mold and several soft spots in the roof, which indicates that there’s rotting plywood that will need to be replaced.

Here are some examples of the state of the attic during our inspection:

There was also some damage that wasn’t obvious until the roofing crew started tearing off the roof:

This is a community where it's basically a bunch of condos and townhomes that are, for the most part, actually owned by the people who are living there. But there's one big board (like an HOA) for the whole community.

This was a great board to work with because they were super concerned about the mold that we found in the first building. They were worried about the health of people living there, especially because they knew that kids were living in that building.

We explained to them that the roof can appear fine on the outside even though it’s hiding catastrophic damage within the attic. This was the case with the roofs on these apartment buildings.

We also told them that to get rid of the mold we’d need to do mold remediation, remove the rotten plywood, and make sure that the attic ventilation actually worked.

They asked if it was possible that other buildings also had these same issues. We said yes because we had the same concern, and we ended up replacing the roof on 13 buildings in total in that apartment complex.

Each one of them had the following issues:

• Mold in the attic
• Soft spots on the roof
• Poor attic ventilation
• Old, worn-out asphalt shingles

How do you update the attic ventilation in an apartment building with a firewall?

After the HOA board approved our suggestion to do a full roof replacement for all 13 buildings, here was the plan we created for each building to fix the ventilation and get the roof in good condition again:

• Mold remediation in each attic

• Updating attic ventilation

• Replacing rotten roof decking as needed

• Installing new asphalt shingles on each building

After following all of these steps in each building, we’d be able to assure the HOA board that the roof is in excellent condition and is set up to prevent mold from returning.

The biggest challenge on this job was dealing with the firewalls in the attics. Because there were firewalls in each building that basically cut the attic into two halves, each half required a unique, custom ventilation plan.

Here’s an overview of the attic ventilation plan we came up with for the attics in these apartment buildings:

Each unit had its own unique needs that required tweaking the plan a bit, but this is the basic foundation that each one was working from.

Here’s a breakdown of the main types of ventilation used in this plan:

• Ridge Vents: Used on the side of the firewall with the ridge
• RVO Vents: Installed in areas with no ridge
• O'Hagin Vents: Used in sections with no eave for sufficient airflow
• B144 Vents: Placed in lower areas
• Bird Blocks: These are the intake vents installed around the outer perimeter of the roof

In some cases, the bird blocks were blocked to make sure that the O’Hagin vents could do their job as intake. Also, there are some sections that needed to be curtained off from everything else so that they could function as their own mini attic.

All of this was carefully planned and installed to ensure that every part of each attic had the right amount of airflow according to building code and that none of the vents would cause the others to short-circuit and fail.

Ensuring that your attic has proper ventilation and airflow is the best way to protect it from collecting excess moisture that rots the wood or invites mold growth. This is extremely important to keep in mind when living in a damp, rainy area like Seattle.

The firewall also made the mold remediation a longer task because the crew had to enter each unit separately instead of being able to do the whole attic from one entry point.

We sent out multiple crews to work on this project, and they completed everything in about 1 month. We left a storage container for our tools on-site while working on the project and had to be careful not to park in anyone’s assigned spot due to limited parking.

The HOA board was happy with the final results and relieved to know that their tenants were finally protected from the mold.

What are the most common attic ventilation problems in Seattle apartment buildings?

This project showed just how much damage poor attic ventilation can hide. What began as an inspection for potential leaks ultimately uncovered mold, rotten roof decking, and ventilation problems across 13 buildings.

Because firewalls divided the attics, some sections had no ridge, and others lacked adequate eave intake, we had to treat different areas as individual ventilation systems. Ridge vents, RVO vents, O’Hagin vents, B144 vents, and bird blocks were all placed strategically to provide the necessary airflow without short-circuiting one another.

Whether you’re responsible for one home or an entire community, attic ventilation problems can be easy to overlook until you discover mold, moisture, or rotten decking. Sometimes the problem is that the ventilation was designed or installed incorrectly in the first place.

Read our article “What’s Wrong With My Attic Ventilation? Common Mistakes Roofers Make” to learn which attic ventilation mistakes we commonly find on Seattle-area roofs and how those mistakes can prevent your attic from getting the airflow it needs.