Exposed roof installation question

[ChillyNoMore]

Hello all! I have read through many of the posts here and have learned *so* much, but I still have a few questions before I am ready to tackle the chimney installation (6" Class A) for my new Scan 61 wood stove.

The biggest puzzler is the best way to support the chimney given that my ceiling is the roof. Specifically, the roof/ceiling is 2"x6" tongue and groove boards spanning exposed rafters that are 6' on center. There is 2.5" of rigid foam insulation above the T&G boards and then I'm assuming a layer of plywood topped off with "4-ply hot built-up roof system" (per the roofing company). See the picture below...

I have read through the Simpson DuraTech installation guide and there seem to be three possible options:

1) Square ceiling support box (9438A or B): cut a 12" by 12" square hole in the ceiling/roof, slide the box down into the hole, cut the corners of the box that extend above the roof, fold the resulting flaps down on the roof and screw them into the plywood (or through the foam into the T&G boards?) Finish by sealing the flanges with large quantities of roofing tar and cap with roof flashing and storm collar.

2) Reduced clearance square ceiling support box (9436B): same as the option #1, but only make a 10"x10" hole? When can the reduced clearance box be used? For 6" class A chimney, that would only provide 1" of clearance, by my math...

3) Roof support (9463): cut a 12" diameter round hole in the ceiling/roof, screw the support brackets into the roof, and again flash like crazy. Cover the 2" gap around the chimney pipe with roof flashing above and trim collar below.

The instructions refer in each case to framing in the opening, but I don't know how to do that given how the ceiling/roof is constructed. Are the plywood and boards alone sufficient to support the weight of the chimney? Will I have issues with the T&G boards that will be unsupported once the hole is cut in the roof?

Also, which of these options will be the easiest to seal against air and water infiltration?

Which approach will be easiest for an experienced DIY-er?

Thanks in advance for your guidance -- I really appreciate it.
(FYI, I did put a call into Simpson technical support but they are backed up on calls for at least 48 hours.)

 

[Hogwildz]

Hello all! I have read through many of the posts here and have learned *so* much, but I still have a few questions before I am ready to tackle the chimney installation (6" Class A) for my new Scan 61 wood stove.

The biggest puzzler is the best way to support the chimney given that my ceiling is the roof. Specifically, the roof/ceiling is 2"x6" tongue and groove boards spanning exposed rafters that are 6' on center. There is 2.5" of rigid foam insulation above the T&G boards and then I'm assuming a layer of plywood topped off with "4-ply hot built-up roof system" (per the roofing company). See the picture below...

I have read through the Simpson DuraTech installation guide and there seem to be three possible options:

1) Square ceiling support box (9438A or B): cut a 12" by 12" square hole in the ceiling/roof, slide the box down into the hole, cut the corners of the box that extend above the roof, fold the resulting flaps down on the roof and screw them into the plywood (or through the foam into the T&G boards?) Finish by sealing the flanges with large quantities of roofing tar and cap with roof flashing and storm collar.
Your would have to cut the insulation out and frame around the opening with 2" x 4"s and plywood etc to get your 2.5" space filled, then fold the flanges over onto the 2x4 and screw the flanges to the wood. The foam aint going to support squat, and will merely mush when you screw to it.

2) Reduced clearance square ceiling support box (9436B): same as the option #1, but only make a 10"x10" hole? When can the reduced clearance box be used? For 6" class A chimney, that would only provide 1" of clearance, by my math... Not sure on this one

3) Roof support (9463): cut a 12" diameter round hole in the ceiling/roof, screw the support brackets into the roof, and again flash like crazy. Cover the 2" gap around the chimney pipe with roof flashing above and trim collar below. I believe the roof support it for between 16" &/or 24" rafters, don't think it will work in your situation.
Looks like option 1. How much pipe you going to have out that support box up top?

The instructions refer in each case to framing in the opening, but I don't know how to do that given how the ceiling/roof is constructed. Are the plywood and boards alone sufficient to support the weight of the chimney? Will I have issues with the T&G boards that will be unsupported once the hole is cut in the roof?

Also, which of these options will be the easiest to seal against air and water infiltration?
You would use a standard flat roof base flashing on the roof surface, and have to flash it in with either hot tar (built up roofing) or it could be donw in torch down modified, by someone who has lots of exerpience with torch down.

Which approach will be easiest for an experienced DIY-er?
It looks like those part numbers are for Duravent flue pipe. Call their tech and ask what is best for an exposed ceiling flat roof, and which parts would be needed.
They should have a detail for doing your type install.

Thanks in advance for your guidance -- I really appreciate it.
(FYI, I did put a call into Simpson technical support but they are backed up on calls for at least 48 hours.)
Sorry just read this part.

Are you sure those tongue and groove boards are only 2" x 6" ers? I done plenty of decks like that and they were more like 3" & 4" x 6" boards.
You ain't spanning 6' rafters with only 2" x 6"ers, they will sag between the rafters. If they are 3 or 4" thick, they will support that ceiling support no problem.

What is that seam in the decking at the right of the picture? Does the T&G just end and butt to plywood, or is that more discolored T&G with a cut across it?

 

[ChillyNoMore]

Thanks for your blazingly fast response Hogwildz!

Where I can see an exposed end of the T&G, it does indeed seem to be only 2"x6". It looks like it is maybe 1.75" thick, but definitely not more than 2". (This place was constructed in the mid-'60s and more than one person has commented that it is unclear how it is still standing!) What looks like a seam in the picture is from where I pulled down a cabinet that was attached to the ceiling and the T&G had not been sealed.

Just to clarify your framing recommendation, are you saying to cut out the insulation between the plywood roof deck and the T&G ceiling and replace it with a ripped down 2"x4" on edge? Or, would you suggest enlarging the roof opening by 1.5" on each side and then framing back in to the 12"x12" box opening? I believe the trim collar is 2" wide so it might just cover the 2"x4" so it won't be visible from below.

Is is true that sealing the flashing with hot tar is not DIY friendly? Are there any options that I can do myself that will work until I'm ready to tackle the whole roof? I got a quote from the local roofing company, and they want $250 just to roll the truck to do a little torchdown repair.

Regarding the chimney height, that is another area where I could use some guidance. The roof is 2/12 pitch so the code (as I understand it) only requires 44" above the roof deck. However, the Scan 61 manual "suggests a total minimum height of 15', measured from the floor level on which the stove is installed." The stove itself is 3' high and the room height is only 8', so that would imply over 7' of Class A chimney. Does that sound right or should I start with less chimney and add more if I have draft problems?

Finally, since I'm new to burning wood, would you recommend that I get a stove adapter with a damper to have more control over the fire? Or are these only needed if the chimney is super-long? (I have read on this forum that folks have had problems with the DuraTech 8679 not fitting correctly.)

Hope you don't mind all the questions!

 

[ChillyNoMore]

Hi again,

A gentle bump in the hopes of getting some additional advice...