FIRE-SEPARATION COMPLIANT STAIRS REQUIRED
The attic stair unit in the garage is required to be fire-resistance compliant or improved to meet the minimal separation requirements set forth in IRC R302.5 and R302.6:
R302.5 Dwelling/garage opening/penetration protection. Openings and penetrations through the walls or ceilings separating the dwelling and attics from the garage shall be in accordance with Sections R302.5.1 through R302.5.3.
Built-in folding ladders provide a convenient means of access to attic areas and are becoming increasingly popular for utilizing (unintended) storage space above garages. Unfortunately, people who install these ladders are generally unaware of fire separation requirements. Thus, with almost all of these installations, fire safety standards are inadvertently violated.
The partition wall between a house and an adjoining garage is typically covered with ½ or 5/8 inch drywall, to slow the spread of a garage fire to the dwelling. If the garage attic and house attic are not also divided by a firewall or fire-separation rated assembly, then the garage ceiling becomes part of the fire separation and must also be finished with 1/2 inch drywall. The access cover on a folding ladder is a mere sheet of ¼ inch plywood. When installed in a garage ceiling, this thin wood membrane replaces a portion of the fire-resistant drywall board, thereby breaching the required fire separation.
NOTE: The flame spread ratings for ½” gypsum board (drywall of Sheetrock) and ¼” Lauan plywood are not equivalent. The higher the rating the faster the material burns.
The rating for ½” gypsum board is 20. See:
https://www.usg.com/content/dam/USG...eetrock-gypsum-sheathing-submittal-WB2380.pdf
The rating for ¼” Lauan plywood is 150. See:
http://sfm.dps.louisiana.gov/doc_woodproducts.html
Many, if not all, attic stair manufacturers sell units that will fulfill the fire separation requirement. The fire retardant plywood door panel is chemically treated to provide slower ignition, low flame spread, lower smoke production, and has self extinguishing features (burning ceases when ignition source is removed or exhausted.) Class A, or 1, pressure treated plywood is approved by building codes throughout the US for specific applications within fire resistant buildings as an equal alternative to non-combustible construction.
Memphis Folding Stairs, et al., advertises a "Firegard" option. FireGard® XF - Antimony Trioxide Flame Retardant.
To recap, a garage ceiling pull-down ladder is allowed by the IRC only under two circumstances: if the firewall is continuous above the ceiling separating the attic spaces between the garage and house, or if the pull-down ladder unit itself is UL-rated for installation in a fire-separation ceiling. IT CANNOT BE MADE ANY CLEARER.
There are roughly 7,000 fires in attached residential garages in the US every year. Do not become a statistic.
See:
https://www.usfa.fema.gov/downloads/pdf/statistics/v14i12.pdf