Chimney Repair & Installation Flashcards

Under the IRC, a masonry chimney must extend at least how far above the highest point where it passes through the roof?

Answer: 3 feet

The 3-2-10 rule requires 3 ft above the roof penetration and 2 ft higher than anything within 10 ft.

Using the 3-2-10 rule, a chimney must be at least 2 feet higher than any part of the building within what horizontal distance?

Answer: 10 feet

The chimney must be 2 ft above any portion of the building within 10 ft horizontally.

A cricket (saddle) is required on the upslope side of a chimney when the chimney's width parallel to the ridge exceeds:

Answer: 30 inches

IRC R1003.20 requires a cricket when the chimney dimension parallel to the ridge exceeds 30 inches.

When repointing deteriorated chimney mortar joints, old mortar is typically removed to what depth?

Answer: About 2 to 2.5 times the joint width

Standard practice removes mortar to roughly 2 to 2.5 times the joint width, usually 1/2 to 3/4 inch, for a sound bond.

Why is using a very hard, high-Portland mortar to repoint soft, older brick a problem?

Answer: It forces moisture and stress into the brick, causing spalling

Mortar should be softer than the brick so the joints, not the brick faces, absorb movement and moisture stress.

Which type of product is recommended for waterproofing exterior chimney masonry?

Answer: Vapor-permeable silane/siloxane repellent

Vapor-permeable repellents shed liquid water while letting vapor escape, preventing trapped moisture damage.

Counter flashing on a masonry chimney is best secured by:

Answer: Setting it into a reglet cut into the mortar joints

Counter flashing is let into a reglet in the mortar joints and sealed so it overlaps the step flashing.