Question on construction / wood working ?

Question on construction
I have seen a few posts on chimneys recently in this group.
What is the general rule on chimneys in terms of height ?
How much higher than the roof do they have to be ? Can they be in line with the roof ?
Is there a law on this ? especially in N. California ?
Thanks Jessica
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snipped-for-privacy@gmail.com wrote:
> What is the general rule on chimneys in terms of height ?
Check with the building dept in your area.
Definitely covered by local building codes.
Lew
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snipped-for-privacy@gmail.com wrote:

I can't speak about the laws of the state of California, but there is a law of physics that you will regret ignoring. The chimney must be several feet (I'd say at least 2) higher than the highest point of the roof. The reason is that when the wind blows, the air "stacks up" on the upwind side of the roof, creating a high pressure region there. If your chimney is lower than the peak, certain wind conditions will force smoke back down the chimney. Ever wonder why old factories had such tall smokestacks? In general, the taller the chimney the better it draws.
DonkeyHody "Even an old blind hog finds an acorn every now and then."
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It would be good to go higher but it is not necessary. The chimney on my house is not the tallest point and has worked well for 25+ years.
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All the references, and my own experience, show that it needs to be at least 2' higher than any point within 10' in order to get a proper draft. Doesn't matter whether what's within 10' is a tree or a roof line.
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All the references, and my own experience, show that it needs to be at least 2' higher than any point within 10' in order to get a proper draft. Doesn't matter whether what's within 10' is a tree or a roof line.
Yeah, I know referenced do call for that but I believe that with those specs you are pretty much insured to have a good draft. However as with my house and the several in the neighborhood that are built like mine the chimney is not taller than the peak of the house. Perhaps the specs will work in "any situation" and my set up works if the roof is like mine.
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Charlie,
That also happens to be the building code in most parts of the country (using one of the three national codes.)
Measure the highest point within 10' from the chimney, make the top 2' higher than that.
Old guy

All the references, and my own experience, show that it needs to be at least 2' higher than any point within 10' in order to get a proper draft. Doesn't matter whether what's within 10' is a tree or a roof line.
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I believe this is a function of distance from the peak. Over a certain distance, I don't believe you have to maintain a height higher than the peak.
--

-Mike-
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On 19 Jan 2007 15:08:14 -0800, snipped-for-privacy@gmail.com wrote:

You should ask in alt.construction, alt.building.construction or even alt .homerepair
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Don't forget to take into account anything that is around your building----other buildings trees etc that can create a down draft in your chimney.
wrote:

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snipped-for-privacy@gmail.com wrote:

In my area, the topmost of the chimney had to be at least 10 feet horizontally away from the nearest roof plane. Tom
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That would pretty well eliminate having a fireplace in a house.

horizontally away from the nearest roof plane. Tom

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CW wrote:

Why would you say that? Although I'd agree with the "2 feet higher" spec, do you think it wouldn't draw? Tom
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As stated, no roof could be within a 10 foot radius of a chimney. That pretty well limits you to a free standing chimney away from the house, assuming you have a roof. You left something out.

Why would you say that? Although I'd agree with the "2 feet higher" spec, do you think it wouldn't draw? Tom

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CW wrote:

I'm trying to figure what I might have left out to cause you to conclude this. As stated, the "topmost" or cap of the chimney (Maybe that's it: Not the chimney per se) was to be a minimum of 10 feet in a horizontal axis from the nearest roof plane. Sorry about the miscommunication, I thought I was clear. Tom
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Isn't the chimney right next to the nearest roof plane? :) We know what you meant, but look at the literal translation of what you wrote.
More formally is can read: provide a minimum of 2 feet clearance to all roof surfaces and structures within 10 feet of the chimney and 3 feet above the highest point that the chimney penetrates the roof (i.e. the side of the chimney furthest up the roof slope). This is a national code, outlined in section FG503.5.4 of the International Fuel Gas Code.
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Nope, see the 2, 3, 10 rules here http://www.usinspect.com/car/0104TechJargChimneyHeight.asp
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There are ground rules dictated by the laws of physics.
The 'usual case form' of which are usually included in local building codes.
That said, there _are_ ways to make a chimney work in 'unconventional situations.
In the house I grew up in, when we remodeled and added a fireplace, the chimney top was around 10 foot below the neighbor's roof-line (about 14 feet away), below two roof peaks on our house (8 feet, and 15 feet away), and there was a large locust tree (estimated 20 ft taller), less than 4 feet away.
The brick-mason _refused_ to build it, until the architect had a lengthy discussion with him ; he *knew* -- from years of experience -- that that fireplace would never draw right.
He would have been right, but the architect knew what he was doing, and had already ordered, what was then called a 'draft inducer' -- a -big- (entirely passive) 'pot' that installed on the top of the chimney, and more than made up for the 'obstacles' surrounding the chimney. As I recall, we _did_ have to get a 'variance' from the city allowing the construction, since it _was_ contrary to code standard.
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