# Exterior Chimney Chase Code And Best Practices, Above And Below The Roofline--Ventilation, Insulatio



## Renovation (Jan 8, 2011)

Hi Folks,

How's that for a searchable title?

I've been researching exterior chase construction, and thought I'd pass on what I've learned.

I'm planning to optimize the draw of my exterior chimney by enclosing it, and bringing the chase below the roofline into the building's heated envelope, and insulation the portion above the roof. 

The toughest question was whether to vent the portion above the roofline.  From what I've seen, the standard practice is to leave the upper chase both unsealed and uninsulated, with a vent at the top to release whatever moisture enters from the loose construction.  For example, here's Simpson's DuraTech chase-top flashing, which has a 13" hole for a 10" OD 8" ID Class A chimney pipe:

http://www.northlineexpress.com/item/5SP-9630/8-Simpson-DuraTech-Chase-Top-Flashing-9630

I wanted to do better, insulating the upper chase to hold heat and improve draw, to keep that big 8" wide flue from stalling with a cat stove's sometimes slow and cool flue gases.  As I said above, venting is SOP, but is it necessary?  Is it legal and advisable to seal a tight, sealed, and insulated chase, or might there be problems?

My research says that sealing is beneficial and legal.  I'll include the evidence below, and a link to it's source, in case it's useful.  Please feel free to make any comments or corrections.

It also has some interesting discussion of metal versus masonry flues, and chimney fires, which I included for general interest.  I'll have to break it into parts, because of the character limit. :/


Best,

George

From The Journal of Light Construction:

http://forums.jlconline.com/forums/showthread.php?t=47395



> Old 04-10-2009, 11:51 AM
> tucker tucker is offline
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## Renovation (Jan 8, 2011)

> Old 04-12-2009, 09:18 AM
> tucker tucker is offline
> Veteran Contributor
> 
> ...


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