Do you have to install all of the chimney?

[williaty]

Stay with me here, I know that sounds like an absolutely astonishing question, but there's a valid inquiry behind it.

In spring, we're having our roof replaced with a standing seam metal roof. Poking a penetration through such a roof after it's installed is a big no-no. So that's really our only chance to put a chimney in if we ever want a wood stove. However, we just did the budget for the year and there's no way to afford a wood stove this year. Is it possible to install the cathedral ceiling support box and whatever has to go on the outside of the roof in order to allow the roofer to flash/water seal the penetration, yet not install anything else?

I'm hoping that you guys will say the cathedral ceiling support box plus the exterior pipe can be installed, capped off to air-seal it with some insulation stuffed in the pipe for the next year, and then we can just add the interior pipe from the inside at a later date.

Does it work that way or are we out of luck?

 

[begreen]

Yes, you can install the chimney and support box and delay installing the stove and stove pipe. If you want the stove pipe to go straight up though it really helps to know specifically which stove is going in so that alignment and clearances are correct. Note that we see several installations on metal roofs that are done after the roof is in place. They can be done afterward. What's important is to use a good flashing and install it correctly. By far the most recommended flashing is ICC Excel's metal roofing flashing.

 

[Oldman47]

I have already done about what you are contemplating. I am building a new home and recognized the need for a chimney for a future stove. I wanted to get the chimney done while the area was easily accessible. What I did was install the chimney from the ceiling support all the way up through the roof and even installed to the chimney cap. I used the criteria for 2 feet above the nearest 10 foot object and the minimum 3 feet above the roof penetration just as if I was about to connect to a stove. To avoid trouble with my existing heating system I stuffed the chimney full of Roxul to plug up that heat leak path. When I am ready to install the stove, probably next month, I will remove the Roxul and use the stove connector pipe to make my connection to the chimney. It is not a perfect solution because I do get a bit of air leakage through that dead ended chimney but it is working pretty darned well to limit my heat losses through the hole the chimney creates.

 

[begreen]

One can also tape a plastic bag over the opening to stop heat leakage.

 

[Oldman47]

That should stop air leakage but I also wanted the insulation value.

 

[Hogwildz]

You can absolutely install the stack after the new roof is put on. The flashing detail is going to be the same as when doing it while installing the roof. In either case, it is best to try and plan the penetration through the roof in the panel away from a seam. And yes, you can run what you need to have it done at time of the new roof, and just cap the top till you're ready to install the stove.

 

[Hogwildz]

That should stop air leakage but I also wanted the insulation value.

Sealing it off until it is ready for use will stop air flow, and pretty much heat loss with no air flow. Unless you plug the whole thing with Roxul, your insulating value will be minute.
Sometimes it is best not to overthink some things.

 

[Dakotas Dad]

Just out of curiosity, why is it OK to cut a hole in the roof now, but not later?

 

[williaty]

Just out of curiosity, why is it OK to cut a hole in the roof now, but not later?

Because they can work through the roof deck with no panels installed, then custom-fit each panel to the chimney as they work past it. If they come back later, they have to take up a big enough portion of the roof to give them access to the roof deck for the support install, then modify the existing pieces to fit around the chimney, then flash it properly. It's easier, cheaper, and more likely to be dry if they do it on the first go.

 

[Dakotas Dad]

Having gone through a roof or two.. That's not how we do it here.

The chimney support is attached to your ceiling joists, the chimney system just passes through an opening created at the time of installation. Flash, collar, add exterior roof brackets as/if needed.

 

[begreen]

Sometimes this depends on the interior ceiling construction and desired finished look. Both methods work. If the intent is for the chimney to be roof supported, the flanges can be bent over and nailed to the roof deck before the metal roof is installed. This works well when there is only one ceiling joist to nail or screw to.

This is from DuraVent's install instructions:

 

[Hogwildz]

Because they can work through the roof deck with no panels installed, then custom-fit each panel to the chimney as they work past it. If they come back later, they have to take up a big enough portion of the roof to give them access to the roof deck for the support install, then modify the existing pieces to fit around the chimney, then flash it properly. It's easier, cheaper, and more likely to be dry if they do it on the first go.

Someone's filling your head with garbage.