Fireblocking (aka firestopping) is very important to control the spread of fire from one room to another and one floor to another. During the construction of a building, voids are created, either by design or by the creation of holes to allow electrical and plumbing to run between wall systems and floors. These voids must be filled so that oxygen does not encourage the spread of fire.
What is the Correct Method for Firestopping?
Various materials are allowed for fireblocking. Depending on local codes, this fireblocking material may be as simple as filling the void with paper, rockwool insulation or fire-rated caulking.
We have found that inspectors in one jurisdiction want only rockwool for fireblocking, while others allow for unfaced fiberglass. Some inspectors allow the voids to be filled with toilet paper. Why the variety of opinions?
The idea of fireblocking is to prevent the drafting of fire. When oxygen is able to bleed from one room/floor to another, then the fire will spread. The material, itself, is inconsequential if the idea is to simply stop drafting. However, some believe that the idea of fireblocking is more than stopping the drafts. They believe that the material must be fire-rated.
Ultimately, the correct method is the one outlined by local codes. Therefore, this article is simply informative, not prescriptive. According to the 2003 Michigan Residential Code, unfaced fiberglass IS one of the correct materials to use for fireblocking.
R602.8.1 Materials. Except as provided in Section R602.8, Item 4, fireblocking shall consist of 2-inch (51 mm) nominal lumber, or two thicknesses of 1-inch (25.4 mm) nominal lumber with broken lap joints, or one thickness of 23/32-inch (19.8 mm) wood structural panels with joints backed by 23/32-inch (19.8 mm) wood structural panels or one thickness of ¾-inch (19.1 mm) particleboard with joints backed by ¾-inch (19.1 mm) particleboard, ½-inch (12.7 mm) gypsum board, or ¼-inch (6.4 mm) cement-based millboard. Batts or blankets of mineral wool or glass fiber or other approved materials installed in such a manner as to be securely retained in place shall be permitted as an acceptable fire block. Batts or blankets of mineral or glass fiber or other approved non-rigid materials shall be permitted for compliance with the 10 foot horizontal fireblocking in walls constructed using parallel rows of studs or staggered studs. Loose-fill insulation material shall not be used as a fire block unless specifically tested in the form and manner intended for use to demonstrate its ability to remain in place and to retard the spread of fire and hot gases.
R602.8.1.1 Unfaced fiberglass. Unfaced fiberglass batt insulation used as fireblocking shall fill the entire cross section of the wall cavity to a minimum height of 16 inches (406 mm) measured vertically. When piping, conduit or similar obstructions are encountered, the insulation shall be packed tightly around the obstruction.
Please check with your state’s requirements for their standards as they relate to fireblocking.