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Question about roof flashing on Tiny House on Wheels

 
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Hey everyone!

So I have a quick question. I am installing a wood stove through my 3/12 roof, my tiny house is already legal height limit and I am trying to avoid going higher than the peak of my roof.

My question is, how high is a Selkirk or ICC roof flashing for low pitched roofs, meaning how much height does it add before the double wall insulated chimney pile comes out of it. My idea is to have a small 2-3” piece sticking out of the flashing after the collar and add another piece which would be removable for transport but I need to make sure that this added height near the eaves doesn’t add too much height.

Can anyone help me with this?
 
gardener
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That's a relevant question ... and looking through Selkirk docs there isn't a definitive height above roof given.  I think this is generally because a) generally it doesn't matter and b) there is some variation based on pitch and roofing material.  But it is going to be high enough to ensure water flow can't rise up into it ... so at least several inches.

I _think_ the one we have sits about 6" above the shingles.  With a 3/12 roof  you'd need to be at least two feet horizontally away from the peak.  If you can aim for the middle of the roof then you'd have a full 12" to play with.  A side benefit of being further down the roof ... generally you'll want a support strut from the chimney to the high side of the roof.  If you are placing this on the wall of the peaked side then there is no where to put the strut : (

But here are two question for you ... what is the sizing of your system?  The smallest cathedral roof penetration from Selkirk is for a 6"  pipe.  6" seems kinda big for a tiny house.  Also, given the small volume of a tiny house I would go with a back vent on the stove and an external chimney just to not give over that volume to a stovepipe.  Of course, an external chimney probably has to go on either end so as not to exceed width limits (although, if its external I think its not such a big deal to disassemble once or twice a year to shrink your width down.  Also MUCH easier to clean and inspect an external chimney.
 
pollinator
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I think you can make it work if mounted straight up the outside wall, but I agree with Eliot that out the wall is probably easier.  Waterproofing a chimney flashing through a metal roof is a pain in the @$$. We either put it just off the peak so the top edge of the flashing is under the ridge cap, or split that piece of metal so all the pieces shingle together (don't do it this way if you can help it)
 
Michael Kalman
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Thanks guys! I was going with a 6” because all the 4” kits are out of stock until January and I need it soon so I’m adapting my 4” up to 6”,

I’m planning on doing this at the eaves, do you think going out the wall will cause creosote build up? The problem going out the back is that I need my stove 4” from the wall and I don’t think I can make that happen by going out the back and through the wall, can I?

Also, I cannot have the stove pipe go to the peak because the stove is placed by the side of the house near the eaves of the gable roof. I’m paranoid about the rubber/silicone pipe boots and cutting a slit into my roof also makes me nervous too.
 
Eliot Mason
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Michael:

A pic or diagram might help.

But Scott is right - and I didn't even think it - is that going through the roof really complicates - and compromises - the roofing.  For something which moves, and flexes, I'd really prefer to have as few roof penetrations as possible.  You are also creating additional complications around the vapor seal at the highest and most vulnerable to water condensation area.  Going out the side is significantly easier to flash and seal.

Its possible that going from a 4" to a 6" will accelerate your draft and make it harder to control the burn.  6" is also more expensive than the 4".

Exiting out the rear and through the wall is easy and you can definitely get the stove 4" from the wall - there is a thimble that goes in the wall and you just run a pipe from the stove to the thimble.  The neat thing is that you generally have a T at the base of the external stack, creating a straight path from the top to the bottom - just open the cap at the bottom and anything in the pipe falls out.  Super easy to run a brush up or just tap on the pipe and see what shakes loose.

Can't speak to the relative accumulation of creosote in external vs external chimney.  But I'll say this ... in the unlikely event of a chimney fire, would you prefer it indoors or outdoors?
 
R Scott
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If you put it at the eave, you put the flashing down first, bend up the sides where the ribs will land, then cut an upside down "U" in the tin.  Put a piece of closure at the top edge of the flashing. You can shingle a piece of flat flashing under it to extend to the eave but probably won't need to.  I would use snow and ice dam or self sealing window tape under it just to triple make sure you don't leak.
 
Michael Kalman
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Hey Eliot,
I'm concerned that the double wall pipe would go to my wall thimble, would that be safe? Does it just go to the wall and out the house? After it goes outside the house, it would have to extend past the eaves in order to avoid putting a hole through the roof, right? I think this is bad for a tiny house on wheels as I'd have to disassemble it all for moving or the whole pipe might go flying down the road. Would it be possible to leave the sections of insulated chimney pipe to be able to be disassembled for transport? Is this possible?


Hey Scott,
That's my thoughts, to cut an upside down "U" and slip in the flashing and tuck in some butyl flashing tape and then caulk it as well. I'm paranoid that water would want to find its way in because its at the eaves.

To you all, do you think going for 6" is okay with a cast iron damper installed?
 
Eliot Mason
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Michael:

I think if it comes out the back its a double wall.  If it comes out the top, then I think single wall is ok, but you have to have something like a 3' vertical rise before adding an elbow and moving through the wall.

Much info at http://supervent.com/sitecore/content/global-configuration/selkirk/products/chimney/supervent-usa

And huh, at least in that line 6" is as small as it gets. You need to go to the "Direct-Temp" line to get 4", and that comes with the bonus of providing a source of fresh air to the stove (if your stove is equipped for it).

As to the tiny house and mobility question ... this is really a personal preference.  How often is this going to be moved?  the number of straps can always be increased so secure it, and I think its not super hard to disassemble the pipes either - but yeah, I wouldn't want to do it more than 2x a year.  Its just a matter of starting at the top and working your way down - you might have two to four screws every 3-4 feet connecting the sections. The insulated pipe is just twistlock so its really easy to take apart.  I'm more worried about it being mounted on a sidewall and becoming too wide (and smacking something) than I'm worried about the wind.

Note that insulated pipe is fine.  If you go with single wall, then you would need to have an non-flammable surface on the wall (this goes for interior and exterior).

 
Michael Kalman
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Thanks Eliot!

I'm leaning towards a roof exit, but can someone get me an accurate measurement and their model of roof flashing?

I have to get this ordered soon
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