Gil Stengel on sun 21 sep 97
I'm here with Brad Schwieger, from Ohio University. Brad is on sabbatical
this year and has just completed a kiln in his home studio. He doesn't
have email access right now, so I'm posting a question for him.
In Brad's studio, his new kiln is a hard fire brick chimney passing
through a standard composite roof. Wooden trusses and sheating etc. He
is wondering how much clearance to roof members is appropriate for his
chimney and further, how to flash such a unit weathertight. The chimney
passes through his roof about four feet above the arch of his kiln. The
kiln is softbrick construction, downdraft, built for standard cone ten
reduction work. The chimney itself is hard brick, 41/2 inches thick as it
passes through the roof.
I'll collect and pass on any information to Brad.
Gil Stengel
email: gstengel@macomb.com
WWW: http://homepage.macomb.com/~gstengel
June Perry on tue 23 sep 97
The best thing to do is check with the local ordinances. It differs from
place to place. When I built a wood kiln when I lived in Santa Barbara I got
the specs from the city and then had a local metal sheetworking company make
me the kiln hood and exhaust pipes, flashing etc.. In my case I remember that
I could be 2" away from flammables if I used rather expensive heat shielding
material. There were very specific measurements for the size of the hood and
how far out it should come from the kiln on all sides, etc. I also had to
have a double exhaust chimney. I took a photo from one of my kiln building
books to the metal shop and they fabricated that shape using the recommended
measurements from the country.
I would definitely advise checking with the county and following the specs.
If anything goes wrong down the line, that could be your protection if you
need to make an insurance claim. Also, make sure you insurance covers your
kilns etc.
Regards,
June
Ric Swenson on tue 23 sep 97
There very well may be a local building code that covers chimney flue
clearances from combustible trusses and joists, etc. Talk to a local mason
or carpentry contractor to find out the code (s)....BEFORE you do the
work....(unless you are open to the building inspector coming later to
inspect....and requiring you to do it over. ! ) I suggest you also make a
scale drawing of the distances you use....so that if the flashing covers up
much of what you have done...you have a record of exactly how you did it.
Get on the phone and do some research for regs. in OHIO....maybe different
in other locales....?
Minimum air space away from hot surface ought to be 6 to 8 inches.....if
you can make use of some insulating ceramic fiber blanket or board (
"FiberFrax" or "KaoWool".) you might even feel safer. I would.
The double wall stainless 4 ' long, 12" dia. duct that passed through the
roof of my studio in Anchorage was 8 inches from any wood surface...and all
exposed wood surfaces were covered with 1" thick Kaowool blanket
The flashing was made up by a tinsmith....(ah...."aluminumsmith?)....he
came....he looked....he measured....he went away and made the aluminum
flashing....we installed it....making it water tight to the roofing..which
had been cut back 8 inches also. The flashing went up the stack about 2'
(Anchorage has been known to get a little snowfall, sometimes...)
A 'tinner ' usually works for a roofing contractor, and they might give you
particular "advice" for your pitch and composition of roof.....
The stack ....chimney probably must go about 4' above the highest point of
your roof peak....mine was a flat roof...I went up 4' anyway.
I was worried about the heat...so...believe it or not...I attached a meat
thermometer where I could see it as the kiln fired the first time....just
to seee what the temperature actually measured....If I remember
correctly...it got to about 175 degrees at the height of the fire.....that
was on the hot side of the fiber blanket....which is pretty much
"thermally opaque"...so I knew the joists were safe from the heat.
Hard brick will transmit heat pretty well, so err on the side of caution,
if err you must. A downdraft flue ....as it passes through a roof 10-15
feet above...will be quite a bit cooler than an updraft Olsen 24 which I
was firing.
HTH
Happy potting! (and firing!)
.......Ric
At 11:51 PM -0400 9/21/97, Gil Stengel wrote:
>----------------------------Original message----------------------------
>I'm here with Brad Schwieger, from Ohio University. Brad is on sabbatical
>this year and has just completed a kiln in his home studio. He doesn't
>have email access right now, so I'm posting a question for him.
>
>In Brad's studio, his new kiln is a hard fire brick chimney passing
>through a standard composite roof. Wooden trusses and sheating etc. He
>is wondering how much clearance to roof members is appropriate for his
>chimney and further, how to flash such a unit weathertight. The chimney
>passes through his roof about four feet above the arch of his kiln. The
>kiln is softbrick construction, downdraft, built for standard cone ten
>reduction work. The chimney itself is hard brick, 41/2 inches thick as it
>passes through the roof.
>
>I'll collect and pass on any information to Brad.
>
>
>Gil Stengel
>email: gstengel@macomb.com
>WWW: http://homepage.macomb.com/~gstengel
R i c S w e n s o n,
P.O. Box 4 9 4
North Bennington, VT U. S. A.
0 5 2 5 7 - 0 4 9 4
Days ( 8 0 2 ) 4 4 2 - 5 4 0 1 ext. 4 6 2 1
or fax ( 8 0 2 ) 4 4 2 - 6 1 6 4
email: rswenson@bennington.edu
"If you are going to teach a bear to dance....
...... be prepared to dance until the bear gets tired."
( old Russian proverb.)
*************************
John Baymore on tue 23 sep 97
------------------
.....snip.....
In Brad's studio, his new kiln is a hard fire brick chimney passing
through a standard composite roof. Wooden trusses and sheating etc. He
is wondering how much clearance to roof members is appropriate for his
chimney and further, how to flash such a unit weathertight.
......clip......
You will find all sorts of recommendations about this issue in the various
books on kiln building, and you'll fine little exact concensus. A lot of
this is very site specific. The source for the =22proper=22 minimum =
distance
is ultimately going to be the local building authorities that have
jurisdiction anyway. This doesn't say that this distance they tell you is
at all correct, just that you won't have trouble with the =22powers that =
be=22
if you use their clearances =3Cg=3E. If their clearance recommendations =
seem
too close for you (and you have FAR more experience with fuel fired kilns),
go bigger. Then you'll look good and conservative to them..... which is a
nice place to be.
Wood as it is exposed to repeated heating well below it's ignition point
begins to dry out and eventually =22char=22. As this happens, the ignition
point (of each specific wood) keeps decreasing (to a final minimum). So
the roof penetration point for kilns in wooden frame buildings is an area
that deserves a lot of attention and monitoring.
I have used a clearance of 18=22 for the roof structure members framing the
penetration point of an uninsulated hardbrick chimney in a wooden frame
structure many, many times. Joists and cross members need to be built up
as per building code for the snow loading and roof pitch specified in your
area. So for a 9 x 9 ID chimney (18 x 18 OD) , the opening is framed to 54
inches square. No sheathing is extended into this area. No matter what
the other part of the roof is made of (particle board, ply, etc.), this
area is then sheathed over with aluminum corrugated sheeting. The
clearance from the edges of the aluminum roofing to the actual brickwork
can then be pretty tight.... couple of inches.
As to the flashing itself, I have used standard aluminum flashing many
times on hardbrick chimneys on gas kilns with very good luck. At the
distance you describe, it shouldn't be too hot on the cold face of the
chimney for the aluminum to stand up well. If you want to get fancy, you
can create a vent right around the chimney at the high point of the roof
penetration.
First, form a lower frame around the chimney that is atached to the sloping
roof that sort of sticks up like an L and is made watertight with roofing
cement at the attachment point.
There should be a standard cricket on the upper side to deflect the water
run off coming down the roof. The vertical side of this L shape might be
about 8-10 inches in height with the horizontal side being a few inches.
Inverted over this, coming down at a slope off of the chimney is a flange
that is NOT attached to the lower box which is attached to the roof. This
piece sort of looks like the hood that might be built over an updraft kiln.
The flashing is inserted into the brickwork of the chimney the same way as
is done on standard redbrick, just not quite as far. This flange has a
vertical wall that overlaps but does not attach to the part fixed to the
roof itself. The overlap should be about 4-5 inches. The clearance
between the two flanges should be about 1-2 inches or so.
This creates an opening all around the chimney that allows the cold face of
the chimney to have a good cooling airflow along it, venting out of the
roof at the top. The two vertical offset walls prevent water from coming
in, but let air out through an S shaped path tha is formed around all sides
of the chimney..
Making this complex shape takes time, but it keeps the heat from collecting
in the pocket formed by the framing and roofing around the penetration
point. This is a frequently cited area for causing the few reported kiln
fires that actually do occur.
So much depends on the circumstances of the installation, it is hard to
make recommendations without seeing the site and discussing the situation
fully. Another route here, and possibly the better depending on the
site, is to switch to commercial high temperature venting units at the roof
penetration point. A phone call to the insurance company that insures the
kiln building might be prudent, to get their opinion, since they will be
the ones who will decide if the roof penetration was done correctly if
there ever is a fire.
Being told you are not covered AFTER the fact is a real bitter pill.
These units come with specifications for roof penetrations, and hardware
that makes the job much easier. And often the .....time is money......
factor is important too.
To my knowledge, in all the site built kilns I have been involved with over
the 20 or so years that I have been consulting and installing them, there
never has been a fire.
Best,
.....................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40Compuserve.com
Arturo M DeVitalis on wed 24 sep 97
You might also check out Nils MFT approach using sleeves inside
galvanized chimney sections which fit through a standard off-the-shelf
roof collar and don't require any special attention since the chimney is
not hot at that point.....(that is one long sentence, which my english
teacher told me never to do!)
Malone & Dean McRaine on thu 25 sep 97
I set my roof on fire and had to hose it down while firing my wood fastfire
at around 2200F because of inadequate clearance & heat leaks in the chimney.
So much smoke I didn't notice the charring of the rafters. I filled in
around the roof framing with ceramic fiber and had no more trouble. I'd have
a sheet metal flashing fabricated and put fiber on all exposed wood if it
was me.
Stay cool
Dean
Teri Seeley on fri 26 sep 97
Malone & Dean McRaine wrote:
>
> ----------------------------Original message----------------------------
> I set my roof on fire and had to hose it down while firing my wood fastfire
> at around 2200F because of inadequate clearance & heat leaks in the chimney.
> So much smoke I didn't notice the charring of the rafters. I filled in
> around the roof framing with ceramic fiber and had no more trouble. I'd have
> a sheet metal flashing fabricated and put fiber on all exposed wood if it
> was me.
> Stay cool
> Dean
I had a similar problem during the first firing of my Minnesota
Flattop. In this case, however the problem was caused by **too much**
insulation. I had literally packed the space between the chimney and
the roof with fiber insulation: the latter lost the airspace it depends
on for its insulating properties and actually began to conduct heat.
Fortunately I caught the problem before any major damage was done.
I too had to resort to hosing the roof and spraying the inside rafters
with water to prevent further charing and fire.
During the second firing I left a 6" air gap between the layers of
insulation around the chimney and around the rafter space and had no
problems.
Bill
--
Theresa and William Seeley 410 486-3171 (voice)
Villa Nova Pottery 410 484-6273 (fax)
4015 Buckingham Rd. Baltimore, MD 21207
"186,000 miles/second is not just a good idea - it's the law!"
paul m wilmoth on thu 2 oct 97
Dear Gil,
On my wood kiln with a hard brick chimney I have allowed six
inches around the stack. For added precaution I stapled kaowool to the
wooden trusses. This was an extra concern but as I have found to be
unnecessary - better to error on the side of caution however.
I have a tin roof over the kiln so flashing was easy. For a
sheating and shingle structure he may want to put a galvanized exterior
flue around the chimney as it goes through the roof so that it has an air
space for drawing cool air between the exterior of the chimney and the
galvanized section, then he can flash normally around it.
good luck -- Paul
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