# Confused about non combustible wall construction.



## JF1977 (Nov 21, 2015)

I have been reading through this forum looking for advice on how to build non combustible wall protection. I have a few questions I am still not sure about. I had two ideas in mind, one is steel studs placed horizontal faced with 1/2 inch cement board then another layer of vertical studs and cement board. The other is cement board spaced with porcelain spacers. The steel stud seems much stronger since I would like to cover the cement board with a stone veneer.
1. If using metal studs to space out cement board will they transfer heat to the drywall they are protecting? 
2. The NFPA 211 states not to have fasteners behind the stove, but in a corner install where exactly would be considered behind the stove.
3.Would layering horizontal steel studs faced with cement board then vertical steel studs faced with cement board double the r value or just be over kill.


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## begreen (Nov 21, 2015)

Welcome. What stove is this for and is the goal to achieve a clearance reduction?

A proper wall shield must have clear vertical convection behind the wall shield. The supports for the cement board should all be vertical. One simple method is to snap off long 3" wide strips from the 1/2" cement board. Double them up to make 1" thick vertical firring strips to support the wall shield. Be sure to leave a 1" gap at the bottom of the wall shield and keep it open at the top,


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## JF1977 (Nov 21, 2015)

Yes it is for clearence reduction on a Pine Barren Piney 1 in my work shop. I am also rebuilding the hearth that my Hearthstone Phenix sits on.


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## begreen (Nov 21, 2015)

With a proper ventilated wall shield (open top and bottom) the rear corners clearance can be reduced to 12".


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## coaly (Nov 21, 2015)

Also NO supports in centerline behind stove.
Normally the shield is supported on a few bricks with air space under it for intake. This supports weight, so the wall fasteners only hold it upright.

https://www.hearth.com/econtent/index.php/articles/stove_wall_clear
https://www.hearth.com/what/clearancesprimer.html


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## coaly (Nov 21, 2015)

The top link for some reason doesn't load right now. It's a good article and used often.
Here is a table from NFPA 211 with heat shield details;
https://www.hearth.com/talk/wiki/nfpa-wall-clearance-reductions/


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## JF1977 (Nov 21, 2015)

Would leaving a larger air gap be bad say maybe a 3 inch


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## begreen (Nov 22, 2015)

3" shouldn't be an issue.


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