Chimney Termination Requirements (Origin)

[LSaupe]

It is widely known that in many municipalities that a chimney must terminate at least 3 feet above a flat roof line or 2 feet above any structure within a 10 foot radius.

Anyone know where these numbers come from? Is it a spark issue, or aerodynamic (proper drafting drafting around obstacles) issue? If so, can anyone point me to some references that explain this?

Hope you all are making some good Btu's this weekend,

Larry S.

 

[elmoleaf]

Actually, it must be a minimum of 3' high at it's highest point where it exits the roof (flat or any slope), and at least 2' above any structure within a 10' radius as you describe.
For a typical code citation of the requirements, see the International Residential Code, section R1003.9 ( http://www.rumford.com/code/IRC06.html)

I don't know of any good online explanations, but I believe you're correct that it's about safety and draft issues. If not high enough, hot flue gases and sparks have a chance to start burning nearby materials.

 

[fossil]

The source document it NFPA 211, which has been widely adopted as code. NFPA 211 simply states the standard without an explanation of how they arrived at it. Rick

 

[webbie]

It is a somewhat arbitrary MINIMUM which may give decent results if everything else is in order.

But when it comes to solid fuel - you only have to look at proper chimneys in Britain and Europe to see that they often have to be higher than this....for proper results. Sometimes it is draft, sometimes it is keeping smoke from your neighbors windows, etc.

 

[LSaupe]

Thanks for the reply's here on this.

Hypothetical... let's say you ran across a wood stove installation (chimney running up along the side of the house and around the edge of a sloping roof). If the stack was only 2 feet above the edge of the roof (2 feet where it passes the plane of the roof), aside from not meeting code rerquirements, is that a safety issue or a performance issue?

 

[jtp10181]

Safety... sparks or embers or hot gasses could heat the roof and start it on fire.

Performance... the chimney is on the low end of the roof and I am assuming much shorter than the peak. The appliance may decide the inside of the house makes a better chimney.