What Is Fire-Rated Drywall?

Both Type X and Type C are fire-rated, but they're not identical:

1. Type X, most common, contains glass fibres in the core, typically 5/8" thick, achieves 1-hour rating in standard wood-stud or steel-stud assemblies
2. Type C, proprietary blend with vermiculite added to the glass-fibre core, slightly higher fire performance, typically used in 2-hour and 3-hour rated assemblies, costs roughly 30% more than Type X.

In typical GTA residential construction, Type X 5/8" handles every 1-hour rated assembly required by OBC Part 9. Type C shows up in commercial and multi-residential where 2-hour ratings between dwelling units are required.

Ontario Building Code mandates fire-rated drywall in specific assemblies:

1. party walls between attached dwelling units (townhouses, semi-detached, multiplex), minimum 1-hour rating, often 2-hour
2. garage-to-house walls, 1-hour rated assembly between an attached garage and any habitable space
3. ceiling between a garage and a room above, 1-hour rated
4. any wall enclosing a furnace room or service room above a certain BTU rating
5. common corridors in multi-unit residential, minimum 1-hour rated walls and ceilings
6. shaft enclosures, stairwells, elevator shafts, and mechanical chases require 1-hour or 2-hour ratings depending on building height
7. public corridors in mixed-use buildings.

In a typical Toronto single-family home with an attached garage, fire-rated drywall is required on all garage walls and ceiling shared with the house, that's usually the only fire-rated assembly. In a townhouse or multiplex, the party walls between units use 1- or 2-hour rated assemblies.

A 1-hour rating isn't achieved by drywall alone, it's the entire assembly that gets tested and rated. The Underwriters Laboratories of Canada (ULC) maintains a directory of tested wall and ceiling assemblies with documented fire ratings. A typical 1-hour wood-stud party wall assembly: 2x4 wood studs at 16" o.c., 5/8" Type X drywall on each side, fasteners at 8" o.c. on edges and 12" o.c. in the field, joints taped and finished.

Change any element (different fastener spacing, thinner board, different stud spacing) and the rating doesn't apply. GTA drywall contractors install to specific ULC assembly numbers, usually documented on the architectural fire-rating schedule. We screw, tape, and finish to the spec, including pre-rocked deadeners and service penetrations sealed with rated firestop products.

Even the right drywall installed wrong fails inspection:

1. standard 1/2" board substituted in a rated location, the most common rejection reason
2. screw spacing greater than the tested assembly specifies, usually 8" on edges, 12" in field for Type X
3. joints not correctly taped and mudded, open joints fail the rating
4. electrical boxes back-to-back through a rated wall without firestop putty
5. penetrations (plumbing, ducts) without rated firestop sleeves
6. recessed lights cut directly through the rated ceiling without rated covers
7. battens or furring strips changing fastener depth.

For a 1-hour rated assembly to deliver 1 hour of fire protection, every detail matches the tested assembly. That's why fire-rated work is more expensive than standard drywall, the install procedure is more demanding, not the material.