Expert: Bart Ogden - 10/18/2009

Question
QUESTION: Dear Bart,

I just had my entire roof top chimney re-built.  The old chimney had an overhang consisting of the cap and the first one or two rows of brick.  To my surprise, the new chimney was built with no overhang.  My contractor said this is the best way to disperse the water and that overhangs are prone to deterioration.  Can you weigh in on this, is it acceptable to not have an overhang?  Also, can you explain the difference between a cap and a crown.  Often these terms seem to be used interchangeably.

Thanks in advance for your help.
James

ANSWER: Hi James,

A CONCRETE chimney crown should be constructed with the following:  

1.  Bond Break between crown and chimney
2.  Expansion joint between flue tile and crown
3.  Drip Edge on bottom of extension
4.  Steel or Fiber Reinforcement
5.  Sloped Construction to shed water

Specifically, from the Brick Institute of America:

See:  Technical Notes 19B - Residential Chimneys - Design and Construction
Rev [June 1980] (Reissued Apr. 1998)

www.bia.org  Click on Technical Notes on left side of page. Click on Technical Notes 19B.




Thanks for using AllExperts.Com and good luck with your project.

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney, Inc.
Wichita, KS
Voice 316-265-9828
Fax 316-265-9890
www.HomeSafeKS.com

CSIA Certified Chimney Sweep #2653
CSIA Certified Dryer Exhaust Technician #10
NFI Certified Wood Specialist
NFI Certified Gas Specialist
NFI Certified Pellet Specialist
NFI Master Hearth Professional
NCSG Technical Advisory Council Member

Advice given is general in nature. Local laws and ordinances may govern and/or supersede the information and recommendations provided. Final determinations are the responsibility of a local professional with first-hand knowledge of the situation, and the AHJ.

Note: Dissemination, distribution or copying of any part of this email or its attachments is prohibited without the expressed permission of the sender.




---------- FOLLOW-UP ----------

QUESTION: Hello Bart,

Thank you for your timely response and reference to www.bia.org.  This information was invaluable and got my project back on track.  If you could be so kind, I have a few clarifying questions on the information I reviewed.

What is a drip edge on the extension?  How is this different from a simple 90 degree edge?  Can the extension/overhang consist of corbeled chimney brickwork (last two courses about 5/8") and a concrete cap overhang beyond this (about 1 3/8" for a combined overhang from the chimney face of about two inches?

Again, thank you.
James

Answer
Hi James,

The "drip edge" is a groove appx 3/8" deep in the bottom of the overhang of the crown that allows the water to drop off the crown before it runs back to the chimney structure.  It is located appx 1" from the outside underneath edge of the crown overhang.

The overhang on the chimney crown should be appx 2".  The edge of the crown should be no less than 2" thick.

Thanks for using AllExperts.Com and good luck with your project.

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney, Inc.
Wichita, KS
Voice 316-265-9828
Fax 316-265-9890
www.HomeSafeKS.com

CSIA Certified Chimney Sweep #2653
CSIA Certified Dryer Exhaust Technician #10
NFI Certified Wood Specialist
NFI Certified Gas Specialist
NFI Certified Pellet Specialist
NFI Master Hearth Professional
NCSG Technical Advisory Council Member

Advice given is general in nature. Local laws and ordinances may govern and/or supersede the information and recommendations provided. Final determinations are the responsibility of a local professional with first-hand knowledge of the situation, and the AHJ.

Note: Dissemination, distribution or copying of any part of this email or its attachments is prohibited without the expressed permission of the sender.