What type of material should be used to seal open spaces between the chimney wall and combustible building materials?

Sealing open spaces between the chimney wall and combustible building materials is crucial for fire safety and structural integrity. The correct choice, non-combustible material, is used because it can effectively resist heat and prevent the spread of fire from the chimney to adjacent structures. Non-combustible materials include products like steel, masonry, or certain types of cement-based sealants. These materials ensure that in the event of a fire within the chimney, there is a lower risk of igniting nearby combustible materials, which could otherwise lead to a fire hazard.

Using a wood-based material or plastic sheeting would pose significant risks, as both can easily ignite and contribute to fire spread. Fiberglass, while somewhat fire-resistant, may not provide the same level of protection or structural integrity as dedicated non-combustible materials in this context. Thus, non-combustible material is the safest and most effective choice for sealing around chimneys in order to enhance safety and compliance with building codes.