unsupported chimney

[John Dirks Jr]

This is an upcoming inspection so I don't have any details or measurements yet. I'm a bit concerned by the looks of this.

What are some general rules and guidelines about chimney support that might apply in this case? What are sources to back up opinions?

Thanks

[Scott Patterson]

This is an upcoming inspection so I don't have any details or measurements yet. I'm a bit concerned by the looks of this.

What are some general rules and guidelines about chimney support that might apply in this case? What are sources to back up opinions?

Thanks

I thought all masonry chimneys are to be self supporting?

[Bruce King]

There is a table in the IRC for lateral bracing I think.
IRC Table R606.8 ?

Sorry, I don't have it handy.

Height is limited to something like 10 times the longest width unless properly braced. Also depends on the wind rating for your area.

[Scott Patterson]

There is a table in the IRC for lateral bracing I think.
IRC Table R606.8 ?

Sorry, I don't have it handy.

Height is limited to something like 10 times the longest width unless properly braced. Also depends on the wind rating for your area.

That section is for walls.

The section that covers chimneys is R1003

R1003.3.1 Vertical reinforcing. For chimneys up to 40
inches (1016 mm) wide, four No. 4 continuous vertical bars,
anchored in the foundation, shall be placed in the concrete,
or between wythes of solid masonry, or within the cells of
hollow unit masonry, and grouted in accordance with Section
R609.1.1. Grout shall be prevented from bonding with
the flue liner so that the flue liner is free to move with thermal
expansion. For chimneys more than 40 inches (1016
mm) wide, two additional No. 4 vertical bars shall be
installed for each additional 40 inches (1016 mm) in width
or fraction thereof.

R1003.3.2 Horizontal reinforcing. Vertical reinforcement
shall be placed enclosed within 1/4-inch (6 mm) ties, or other
reinforcing of equivalent net cross-sectional area, spaced
not to exceed 18 inches (457 mm) on center in concrete, or
placed in the bed joints of unit masonry, at a minimum of
every 18 inches (457 mm) of vertical height. Two such ties
shall be installed at each bend in the vertical bars.

R1003.4 Seismic anchorage. Masonry and concrete chimneys
and foundations in Seismic Design Category D0, D1 or D2 shall
be anchored at each floor, ceiling or roof line more than 6 feet
(1829 mm) above grade, except where constructed completely
within the exterior walls. Anchorage shall conform to the
requirements in Section R1003.4.1.

R1003.4.1 Anchorage. Two 3/16-inch by 1-inch (5 mm by
25 mm) straps shall be embedded a minimum of 12 inches
(305 mm) into the chimney. Straps shall be hooked around
the outer bars and extend 6 inches (152 mm) beyond the
bend. Each strap shall be fastened to a minimum of four
floor joists with two 1/2-inch (13 mm) bolts.

That is about all that really covers chimneys....

[John Dirks Jr]

It turns out that the house chimney was the one to worry about. 72" wide with a roof sloping into it and no cricket. It was a brick masonry chimney and the entire exterior side had recently been parged with concrete and that was beginning to crack up from the crown and downward. Water stains were in the firebox and the hearth extension projected only 12" into the room.

The roof to chimney junction was gooped up with sealer and there was water damaged sheathing around the penetration seen from the attic.