Constructing a Protected Alcove

[p301]

Ok so after much deliberation i've settled on the hearthstone shelburne for a wood stove. I'm planning out my alcove and am running into some questions about the protected surfaces that will need to be located most likely on all three walls and the ceiling and how they will interface with each other. If anyone has any experience and could help me out on this one id greatly appreciate it. I know the bottom of all the vertical walls are to have a 1" air space with a 1" opening top and bottom (the sides will be closed) should the interior corners be closed off from each other so each wall is its own ventilated air space, or should they all be connected so there is one large U shaped ventilated air space that is all connected either one is easy enough to do

Secondly i'm trying to wrap my head around how the ventilated air space on the ceiling will work. The ceiling will be flat but id like to possibly add an arch in the front for aesthetics. Should the openings for the air gap be on the left and right side of the stove or front and back side of the stove or does it not matter? Or if i install an arch should the opening for the air gap be on the back side of the ceiling facing down and then show somehow on the vertical surface of the arch (Id rather not do it this way) Do i need to worry about heat being trapped behind the arch which will maybe hang down slightly below the ceiling and cause the temps to rise to a dangerous level at the ceiling?

Again any help is greatly appreciated i'm not concerned about the work just about making sure everything is done safely and correctly

 

[begreen]

The wall shields can touch in the corners to create a big U shaped shield. It's the free, vertical convection of air behind the shields that is important. That's why the gaps at top and bottom are important. The ceiling shield also needs to permit the free convection of air. Would it be possible to have vent slots above the arch?

 

[p301]

begreen That is a perfect idea to have the vents above the arch. I didnt see how just a flat shield with an air gap would allow convection mounted horizontally.

Would you happen to know if there is any product to use as a fireproof sheathing with a higher R value to mount over the exposed 2x4's for the walls and ceilings before i create my air gap. i know sheet rock is perfectly ok but i would like the piece of mind of using some kind of insulated fireproof board instead if possible. As an added benefit id save 1/2" on each side to the nearest combustable. I'm tring to stay away from durorock as i dont want to add the weight to my cantileverd alcove being i will already have one layer and cultured stone creating the protected surface, and the stove itself

 

[begreen]

You can use Durock NexGen, it's lighter than sheetrock.

 

[p301]

thanks begreen that solves that problem. I was reading the NFPA 211 they talk about not using the screws and spacers directly behind the stove and I guess in an alcove to the sides as well. I guess they are worried about the heat transferring through the screw and causing pyrolisis on the wood its secured to? In a small alcove that seems like it would be a pretty large percentage of the area with no screws or spacers especially if that wall will be holding cultured stone. How is everyone handling that situation? i couldn't find anywhere that said this requirement didn't have to be met if the cultured stone covered the screw head although i think it would dissipate the heat pretty significantly.

 

[begreen]

Yes, that is the worry, though I think it's a bit overblown, especially behind cement board and a layer of concrete (cultured) stone.

 

[p301]

So i guess guys are just ignoring that requirement? If it was just sheet metal thats one thing but It seems crazy to leave possibly a 30" x 30" space not secured to the wall thats holding up stone! Maybe some kind of perforated spacer in those areas so the spacer doesn't have the screw retain the heat and is open to the convection process of the air gap?

 

[begreen]

According to a testing report I read several years ago pyrolysis occurs fastest with small fragments or shavings of wood. The tiny shank of a screw that is shielded into solid wood seems like a low risk issue when it's well protected. I too would be concerned about properly supporting the weight of the wall with concrete on it.