Cement board attachment to fireplace rim

[sc204]

I appreciate the answers receeived so far, so time for another question.
My fireplace calls for 11 inches of clearance above it in front. It comes with a 12" x 60" non combustible board to fit that area. As I am going to be facing the whole fireplace with ledgestone, I was planning to just use cement board over all the framing.
My question is how to attach the cement board to that upper lip of the fireplace. It is a 1/2" lip probably about 1 1/4" tall.
Thanks

 

[Corey]

Interesting conundrum. A bit hard to say without knowing make, model, etc. Are you sure "...11" clearance in front..." means above the firebox? not actually in front of the fireplace (ie extending out to the floor) or maybe means 11" above the fireplace to anything sticking out - like a mantle?

When I installed my gas fireplace, I believe the clearance was more reasonable, like 2 or 2-1/2 inches, so I just let the board run a bit long without worrying about any solid attachment. Then it got a 12" porcelain tile, anyway - so that really beefed up the rigidity.

If you have to keep that 11 inch span, I guess the way I would go about it would be to mock up the cement board on the ground, but using a 2x4 in place of the metal lip. Go in and 'pre screw' the cement board to that 2x4 so you get the layout and counter-sinking for all your screws. Then put the cement board in place on the actual fireplace and mark where you placed the screws, drill some pilot holes and re-install the screws.

Alternately, guess you could just hang that piece of cement board and screw through the front. Then you kind of hope the screw will pierce the metal flange and that it will get enough grip on the flange to properly countersink the screw before tearing out of the metal flange. Though again, a bit hard to say without having an idea of the thickness of the flange, the screws you want to use, etc.

Maybe with this bump, others with more knowledge than I will chime in!

 

[sc204]

Thanks for the reply. These are the 2 pages from the manual where I got the 11 inches.

 

[Lennox65]

Use a metal stud on it's edge across the width of the opening. Cut notches to attach it to the wood framing on both sides. Screw through the flange into the metal stud and then attach the non com board.

 

[sc204]

I did go with the metal stud. Just screwing into the flange might have worked out by drilling pilot holes. The cement board screws seemed to bite in pretty well. The metal stud will add additional support.