DASMA TDS 173 - Garage Doors and Ventilation

An attached garage can be a pathway for carbon monoxide to enter living space if the air barrier between the garage and the house is not adequate. At the same time, a garage door that is too tightly sealed can trap fumes inside the garage during warm-up cycles. DASMA TDS 173 addresses both sides of this problem.

What this data sheet says

TDS 173 discusses how garage door design affects air movement in attached garages and what role the door plays in CO safety and code-required separation.

"Garage doors are not airtight, and they are not intended to be the primary barrier between the garage and the home. The wall and ceiling between the garage and the living space must provide the required fire and air separation."

Key points from TDS 173:

• Garage doors are not designed to be airtight. Bottom seals, side seals, and top seals reduce air infiltration but do not eliminate it. The door is not the primary CO barrier.
• IRC R302.5 and R302.6 require the wall and ceiling between an attached garage and the living space to provide a specific fire-separation assembly. That separation also serves as the air barrier against CO migration.
• Ventilation within the garage. The code does not require mechanical ventilation in residential garages, but natural ventilation through the door perimeter and any vents is assumed. Installing a very high-performance door with extremely tight seals in an unventilated garage warrants attention to CO risk during warm-up cycles.
• Bottom seal condition matters for air quality. A deteriorated bottom seal allows outdoor air and rain to enter the garage. But it also allows fumes to pass out of the garage through the bottom gap, which is not always undesirable in an unventilated attached garage.
• CO detectors. TDS 173 reinforces the recommendation to install CO detectors in homes with attached garages, regardless of door seal quality.

When it applies

TDS 173 is relevant to several common situations:

• Adding a tight weatherseal package to an older door. Upgrading from a worn-out bottom seal to a high-performance seal system improves energy efficiency but reduces the casual ventilation path through the door perimeter. If the garage has CO sources, the upgrade should be paired with a CO detector.
• Permit review for attached garages. Plan reviewers sometimes ask about ventilation provisions for attached garages. TDS 173 clarifies the role of the door versus the wall-ceiling assembly.
• Winter warm-up in Colorado. Warming up a car in an attached Denver garage for even a few minutes without the door open can produce dangerous CO concentrations. This is the most common residential CO exposure scenario on the Front Range.

What this means for you

Do not warm up a car inside a closed attached garage, ever. The bottom seal will not protect you. Modern vehicles still produce CO at startup, and garage volume is small enough for CO to reach dangerous levels in minutes.

Install a CO detector in the garage and in the adjacent living space. This is the single most effective mitigation for the risk TDS 173 addresses.

Replacing a worn bottom seal is still the right call for energy efficiency. The ventilation argument is not a reason to keep a deteriorated seal. Fix the seal; add a CO detector; open the door before starting the vehicle.

G Brothers can inspect and replace bottom seals and side seals during any service call and can advise on seal options appropriate for Denver's temperature range.

Full text and source

Download DASMA TDS 173 from the official TDS index at https://www.dasma.com/technical-data-sheets/.

This entry applies to residential attached garages with sectional doors. Detached garages and commercial buildings have different ventilation and CO considerations.