Class A install, ventilation?

lab17 · Oct 22, 2012

After some serious consideration and info from the forums I made a decision and now have a question on install.
I'm installing a class A chimney for my Osburn Stratford. The 6" Dura-vent chimney I got with the unit from the dealer. Reading the install this chimney (Simpson dura-vent) requires ventilated roof flashing, and rafter protectors which the dealer never brought up as being required.
1. I have galvanized metal around, can I use that as my rafter protectors putting it outside the clearance requirements and attaching it to the rafters?
2. I have 2' of attic space which the chimney passes through (firestop and attic insulation shield will be here) then into a 6' chase above roof line (uninsulated) with a metal chase cap. The chase is open to the attic where the chimney breaks the roof plane into the chase so some venting does go into the attic. Do I need to have a vented chase cap or put vents on the chase side to accommodate the required ventilated roof flashing requirement by the Dura-vent chimney?
Thanks

DAKSY · Oct 22, 2012

You building inspector will tell you whether your install meets code, & whether or not you need the vented flashing.
As far as the chimney in theattic goes, I would build a box out of aluminum or galvanized steel that meets the Clearance to Combustibles (CTC) & that runs from the ceiling firestop to the under side of the roof flashing. That will keep ANYTHING from getting into the CTC zone. I WILL say that whenever we received a ventilated roof flashing from our vendors, & installed it with the holes in it, we always had to return to the jobsite, as those vents leak during a heavy rainstorm, whether it's from the rain getting DIRECTLY into the slots or it was splashing off the roof & getting up under the storm collar. We started using aluminum tape, inside & out, to seal the vents from leaking & never had an issue...YMMV

lab17 · Oct 23, 2012

Thanks DAKSY
I will be getting some aluminum tape to the seals and the air intake as well. Once it stops raining here I will be able to open it all up again and finish.

begreen · Oct 23, 2012

If you use the M&G DuraVent roof flashing it will not have ventilation slots to cover up. Instead they have a better design IMHO that uses self-draining indents in the flashing cone that go right up under the storm collar. I have never had a leak with this system.

lab17 · Oct 23, 2012

I was looking at that and thinking this design makes way more sense, my issue is how to connect it to the top of the chase which is 3'x2'. Any ideas.
Top picture is of the chase top.
Bottom picture shows the ceiling into the attic then into the open chase. you can see the quality cut and frame job the original installer did of the prefab I'm replacing.

EatenByLimestone · Oct 23, 2012

http://www.chimneyproductsdirect.co.uk/index.php?page=product&pid=67&cat=3&range=19

Matt

DAKSY · Oct 23, 2012

lab17 said:
I was looking at that and thinking this design makes way more sense, my issue is how to connect it to the top of the chase which is 3'x2'. Any ideas.
Top picture is of the chase top.
Bottom picture shows the ceiling into the attic then into the open chase. you can see the quality cut and frame job the original installer did of the prefab I'm replacing.

You definitely want to box in the Class A from the under side of the roof sheathing to the sheetrock ceiling below with aluminum or galvanized sheet. You also want to replace the chase top with one made from aluminum sheet & with an aluminum collar that's siliconed in place.That one one your chase now is galvanized & that was what was used 15 - 20 years ago, but you can see that the galvanization has failed & since its thin-walled it'll rot thru. Matt shows you one that you can buy or you should be able to go to a local hearth shop that does install & have them fabricate one that will fit your particular chase top dimensions. I've probably built 25 or 30 of them & they have never leaked...

dorkweed · Oct 23, 2012

So far, so good with my "supervent" from Menards with the ventilated flashing. I caulked and pulled the storm collar down as far as I could upon install over the cone of the flashing, and then caulked (high temp silicone) some more on top of the storm collar/class A seam. No problems...............................yet !!!

Clearcutter · Oct 24, 2012

I just finished a similar install of the Enerzone version of your Stratford.
I also used Selkirk Supervent and the flashing supplied is the vented kind with slots. So far so good, it's been up about three weeks now with no sign of leakage yet... I live on Vancouver island so if it's gonna leak I'll find out!! We have had around 150mm of rain since its been up.
As far as the Rafter protection goes I used 4" angle tin and lined the 14" x 14" framed box going through the ceiling with the attic insulation shield on top of the framing and a flat piece of tin below the framing as a FireStop. I don't have a picture on my phone but will post one when I get home.

lab17 · Oct 25, 2012

Thanks for the advice. I did box in the chimney from ceiling to chase with galvanized. Talked to one local shop they only do galvanized custom chase tops so I'll be checking with others for someone who does aluminum. Good to hear on the flashing, picked one up and will install when we get a couple dry days in a row.

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