Nov 16, 2015

Installing the wood stove chimney and cutting the roof.



Well, it’s time to work on the chimney. A big and very scary step (for me). Scary, because since we’ve shingled the roof—we’ve had a few good rain storms and the roof stood up to the challenge. Now, we’ll be making a hole in this well-built roof—and hopefully the right sized hole and in the right location J To back up a bit. You can buy all your chimney pieces a la cart.  Or, DuraVent sells a basic kit that has all the components you need to go through the roof—just need to buy the actual chimney pipes separate. The kit has a square support box with trim, attic insulation shield with collar, roof flashing with collar and a chimney cap. For what it’s worth—the best deal on it was at Tractor Supply Company along with the 24ga stainless steel triple walled chimney pipe. What sucks is that for such a potentially hazardous install, the instructions could be better. Furthermore, I found some videos on youtube that help, but not one that answers all questions. So here goes.

Although I don’t have my stove yet, the maker gave me the location of the 6” chimney opening on top of the stove. We first mocked up the measurements on the floor. We calculated the 13” clearance from the back (12” needed clearance + 1” for approximate cedar thickness to be safe). Then it was 5.25” from back of the stove to the start of the pipe. Pipe was 6” diameter which would make a 3” radius. Anyway—that was the center point of our pipe (13” + 5.25” + 3” = 21.25” from framed wall). Then, looking up—we decided to use a truss that was already there to support the chimney support box. We dropped a plumb bob from the truss down to the floor so that we had that location marked. We could then tell the left/right location of the stove chimney opening. Once we had all those marked, we went in the opposite direction. From the center of the stove pipe mark on the floor, we dropped a plumb bob from the ceiling until we could locate the place on the roof that aligned with our center mark. Once we had it—we put a screw through the roof. That was our center of the roof opening. Also, since we had the distance from the wall measured (13”), we reflected that on to the truss and now knew where our support box will sit.

Calculating clearances and stove placement on the floor to put in the chimney.
Plumb Bob(on left) and marking locations on the floor.


Next, we had to frame around the support box on the trusses. We simply held the box in place and framed around without actually attaching the box permanently yet. 

Framing around the chimney support box to hang it.
Chimney Support Box

Next would be to cut the hole in the roof. As careful as we were about this, hind sight is 20/20 J Because the directions call out for a 2” clearance all around the chimney, and the chimney is 6” in diameter, we summed it up to 6+2+2=10” diameter. I was also aware that the roof hole should be an oval going from eave to peak, not a circle. So, from the center screw we put in earlier, we measure a radius of 5” and marked it on the inside of the roof. I then used a spade drill bit and drilled 4 pilot holes. We made a mistake in our calculations here—but more on that later.

Marking the roof opening for the chimney and drilling starter holes.
Guide holes.

Then, using a Sawzal, I cut around the marked oval from inside of the building and we had a hole in the roof. All while cutting the hole—one of my buddies was up on the roof making sure nothing went wrong.
We have a hole in the roof for the chimney to go through.
Hole in the roof.

With a little careful further trimming, we were able to get our Stainless Steel, triple walled chimney through the roof opening. Once we accomplished that—we could secure the support box in place. The one thing about the support box is it should protrude 2” below the finished ceiling. Since we don’t yet have a ceiling—we made it 3” to be sure (to accommodate the cedar). Because of the size of the support box, nailing it to our framed support was tricky, so right or wrong, the guy on the roof helped my secure it by using the roof opening to reach in for the air nailer and putting 2 nails per side of the box making sure we had a 3” drop from the truss along each side. One of the places where the instructions failed me was here.  The kit came with an insulation shield. It’s a piece with a rectangular bottom to fit around the support box, and a piece of circular flashing slightly higher above.  The flashing is not sealed and has a gap. So I understood this piece as something that prevents the insulation from falling in to the hot support box. It also gets capped with a collar. But in my situation, the support box extends almost half of the height of my small attic and the insulation shield won’t fit. Further, the insulation should rest below the top of the support box for me—however a mouse or whatever can make its way in to the uncapped support box. So, though we did not use the insulation shield that came with the kit—I will need to go back and frame something up to seal that support box.

Now, back to the mistake I hinted at which I realized after everything was assembled. The triple wall chimney piece all together comes out to 10” diameter. Same as the opening we made in the roof. This takes away the 2” clearance we added to the 6” stove chimney on all sides and leaves me with 0” clearance. I figured that out once everything was done of course! I will need to go in now and find a way to expand the hole without taking anything apart.

Now back to our schedule programming. Once we could get the chimney through the hole and we had the support box framed and secured in place, we were on the roof trying to get the chimney flashing piece lined up correctly. We cut a few shingles around the top of the flashing to carefully line up over the flashing.

Cutting the shingles so they lay well around the chimney flashing.
Cutting away shingles to lap over the flashing.

This is the 2nd place the instructions failed me. The flashing needs to tuck under the shingles on the top side and sit over the shingles on the sides and bottom. The directions say to only nail the top, or the top and sides ( I forget) but on a tar and flat roof—they say to nail on all sides. The videos I’ve seen I saw it nailed on all sides—which is what we did. However, not before applying flashing silicon generously all around the bottom side(laying on the roof) of the flashing.  We used regular roofing nails to nail the flashing and caulked all the nail heads with the flashing silicon.  We also caulked a few shingles we lifted and used a level on the side of the chimney to make sure the chimney was level. Finally, we ran a bead of flashing silicon all around the perimeter of the flashing to make sure no water gets in.

3rd place where the instructions failed me is sealing the chimney. From watching some video, I remembered to put a special high heat silicon around where the chimney met the flashing. Then I put the collar over it, then sealed the top part of the collar. So in a way, the collar was sealed on both sides-- top and bottom. From the instructions—it’s hard to gather if what I did was correct or not. However, I think it’s right as the flashing I had was not the “Vented” kind and with snow piling on the roof, it would melt when the chimney got hot and would drain inside into the sauna—so I think I did the right thing.

Finally, we made sure our chimney stood at least 2’ from the highest point of the roof (should be within anything 10’ away—but I got trees—I hope they don’t count.)

With that, we put the chimney cap on that came with the kit and called it a day.

We have a completed chimney on the roof.
Look at that chimney!

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