Durock under corrugated steel for heat shield on walls: 1/4" vs 1/2" Durock?

[MaybeErnie]

I'm into the final stages of building a hearth for a stove. For wall protection and rustic look, I was planning on just using reclaimed corrugated metal panels with 1" spacers to get the necessary open space between the wall and shield. However, now I don't think that the metal alone is sufficient because the used panels I see aren't generally heavy gauge steel (24 gauge or better) and they are also full of holes and imperfections. Consequently, I'm thinking that I should use Durock as the primary first layer (again, with spacers) and then screw the steel panels over it.

My question is whether I can get away with 1/4" Durock for this or if it would be too flexible and fragile for this application. Do I need to stick with 1/2"?

 

[Highbeam]

The question really is whether any wall shield at all is required by your install manual. If you are outside of the minimum clearance to combustibles then you can use bare plywood if you want. Anything else is just aesthetic.

If your stove manual specifically requires a particular insulative value for a specific wall shield then start with that requirement.

Typically walls get 1/2" durock when attaching to studs. This due to stability between the studs so you don't have a wavy wall.

 

[MaybeErnie]

Yes, unfortunately I do need the wall heat shield.

In order to keep the costs manageable, this project is happening in phases. Initially, we'll be using an older, unlisted Lopi stove with the intent to replace it with a newer listed stove sometime in the next couple of years. Accordingly, I'm over-building the hearth and wall protection to meet the specs for an unlisted stove. I framed the hearth so that once we have a more efficient stove that requires less clearance, I can downsize the hearth without disrupting the framing or tile. Also, we kind of like the look of the weathered corrugated steel as it fits the house style, so we'd probably go with that, whether it's installed as a spaced-out heat shield or merely as a cool "patina" directly on the sheetrock behind the stove.

 

[Murray01]

How To Reduce Wood Stove Clearances

How to reduce non certified wood stove clearance to combustible requirements using heat shields.

www.canadianchimney.com

The above link is for Canada, what I understand is US regulations are a bit more relaxed than Canadian standards but not sure so verify/check for clearances.

If you plan on putting tiles/bricks on at some point then you would need 1/2” cement board for rigidity. If it’s only ever going to be recycled corrugated metal panels then I wouldn’t think rigidity isn’t as much of a concern.

One thing I’ve learnt on this form and discussions with inspectors is follow your owners manual to a Tee. The inspector I talked to uses the owners manual and chimney spec's to verify that installation meets or exceeds their stated minimum clearances.

 

[MaybeErnie]

Thanks to everyone for your input and advice!

The tricky part of this project is that we don’t know what the final stove will be, so I figure the best thing to do for now is to overbuild and err on the safe side. Hence the need for the wall shield, although it may not be necessary given the low clearances required for efficient new stoves. The stove pipe, chimney pipe and ceiling box will all be Duravent Duratech double wall with the proper clearances, but given the cost of that stuff, we’re putting off the stove purchase for a while.

 

[Highbeam]

It doesn't hurt a thing to overbuild. You found an unlisted Lopi? Or do you mean uncertified? There are some Lopi experts here that can maybe find the required clearances to combustibles if that info exists anywhere.

I know it's illegal to install an uncertified stove in WA. I wouldn't worry so much about the stove police as I would about the risk of no insurance in the event of a fire.

 

[MaybeErnie]

I guess I mean that it predates the UL certification. I think it’s from 1982, but can’t remember the model name.

I did tell our insurance agent about the woodstove and they didn’t seem too concerned. Still, I am trying to build this thing out so that there are no safety issues that would arise in an inspection. I also had a professional from a local fireplace retailer come out so that we could review the plans together.

 

[Highbeam]

With how cheap a modern noncat can be, like a drolet, Id be inclined to find a modern stove. Even used. I paid 600 or so dollars for my NC30 from home depot about 12 years ago. Would much rather have that installed in the home than an unlisted 1982 thing.

That said, it might not be in the cards for you right now. Sounds like you'll do the best you can.

 

[MaybeErnie]

Too many home remodeling projects happening at once – ha ha! I’m going to finish up this hearth and chimney install and then I will start watching for deals closely again. I’ve seen a couple of tempting bargains, but they got away from me.

Thanks again for your input!