CAUSE & ORIGIN INVESTIGATIONS: MASONRY CHIMNEY FAILURES
https://sites.google.com/site/metropolitanforensics/cause-origin-investigations-masonry-chimney-failures
We inspected
many failed masonry chimneys this past winter.
This blog briefly reports some of the results of the cause & origin investigations.
Photo 1: Failed masonry chimney. Note
the TV antenna attached to the chimney. The antenna contributed to the
tortional twisting of the mortar joints and fracturing of several bricks,
leading to the chimney failure in just few years. TV antennnas should not be mounted on
chimneys.
Masonry
chimneys are structures which provide ventilation for hot flue gases or
smoke from a boiler, stove, furnace or fireplace to the outside
atmosphere. A flue liner is a secondary barrier in a chimney that
protects the masonry from the acidic products of combustion and helps prevent
flue gas from entering the house.
Unfortunately
chimneys are the least-inspected and least-maintained parts of the home. Regular
chimney maintenance is essential to prevent damage, deterioration and future
high-cost chimney repairs. Furthermore,
improper flashings, incorrect/missing sealant or worn/damaged flashing around
the chimneys are common causes for roof leak.
The
flashing of the chimney refers to the overlapping layers of metal (e.g.,
aluminum, copper or galvanized steel) sheets that safeguard against water where
the roof and chimney meet. Some of the
flashing should be located underneath of the roof shingles, and should travel
up the sides of the chimney to provide seamless protection for this vulnerable
area. This is not always done, leading
to roof and chimney damage.
The
most common problem we observed was water penetration into the chimney
structure. During the cold winter months, the masonry
materials deteriorate when exposed to freeze/thaw cycles. During these cycles, moisture that has
penetrated the chimney freezes and expands, causing damage to the individual
chimney components: mortar, bricks, concrete blocks, concrete crown, etc.
Water
penetration can cause interior and exterior damage to a home and masonry
chimney including:
•
Spalling, pitting or efflorescence on the brick surface
•
Cracking or crumbling of the cement blocks
•
Rusted damper assemblies and fireplace doors
•
Deteriorated metal or masonry firebox assemblies
•
Rotting adjacent wood and damaged wall coverings
•
Water stained or damaged walls and ceiling
•
Clogged clean out port
•
Stained chimney exterior
•
Deteriorated exterior mortar
•
Cracked or deteriorated flue lining system
•
Leaning or collapsed chimney structure
•
Chimney settlement
PHOTO 2: Heavily deteriorated
chimney crown. Note the lack of rain
cap, the deteriorated mortar joints and the organic growth inside and on the
exterior of the chimney.
Why is there water penetration inside the
chimney structure? The simplest
explanation we can give is that the chimneys are not properly designed,
constructed and/or maintained. Very
rarely have we seen a chimney that is properly constructed. By far the most deficient area is the chimney
crown (or chimney cover as some people call it) and the flashing around the
chimney.
Most of the
time the chimney’s crown is incorrectly constructed using the
wrong concrete thickness or is flat. At
other times we observed that the chimney had no rain cap. The lack of rain cap and/or a flat crown, in
combination with lack of maintenance, allows water to enter the chimney from
the top and cause water damage due to the freeze thaw cycles. This is a slow deterioration process and it
starts when the chimney is built.
PHOTO 3: Heavily deteriorated
chimney crown and chimney structure.
Note the lack of rain cap, the deteriorated mortar joints and the black
stains.
The chimney
cover ideally is designed to protect the chimney from the rain and to shed rain
water away from the chimney by tapering it and extending its drip line
to at least 2 inches beyond the side of the masonry surface (the drip
overhang); a drip groove is also recommended to shed water past the plane of
the four chimney walls. The proper
chimney cover should be constructed of Portland cement-based mixture and cast
or formed with a downward slope so it directs the water away from the flue to
the edge of the cover.
When
water/moisture enters the chimney it will freeze and expand during the winter
months, damaging the brick, cement block, mortar, stucco and perhaps the
flue liner. Freeze-thaw damage cycles
take many years to develop, are a long-term occurrence and they are not sudden
or accidental events.
PHOTO 4: Spalled brick pieces that had been
coated with stucco. The brick spalled
and fell off the chimney along with the stucco.
Spalling is when the
face of the brick breaks apart. The reason for the brick’s deterioration can be
a result of many different things, but more often than not, it is the result of
water freezing and thawing internally, which weakens the brick. Another reason is poorly made mortar
(stronger than the brick). We often see
spalling in bricks that have been coated with paint, stucco, etc. Coating the brick can lead to accumulation of
salts beneath the brick surface (sub surface efflorescence) that can cause
flaking of the brick.
Metropolitan Engineering,
Consulting & Forensics (MECF)
Providing Competent, Expert
and Objective Investigative Engineering and Consulting Services
We
know you need to process damage claims quickly and knowing the facts is now
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(PFIS) feature:
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starting at $499 per chimney or roof inspection (volume discounts are also
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·
10-State
Coverage Area
P.O. Box 520
Tenafly, NJ 07670-0520
Tel.: (973) 897-8162
Fax: (973) 810-0440
E-mail: metroforensics@gmail.com