fireplace mantel design

[tim vadas]

I'm trying to design a fireplace mantel, and while i like the look of what i came up with (inspired by this: http://www.woodweb.com/galleries/pro...osts/2111.html), i'm not sure about parts of the construction. IMG_5003.jpg

attached is a sketch, hopefully it's dark enough to get an idea, but generally it's similar to the link, except that i'm just doing the fireplace surround. My existing fireplace has about 3" brick + 2" slate as the hearth, and brick surrounding a nearly flush insert, that is flush with the drywall adjacent to it. There is a section of concrete block that i'll be covering with the mantel. The total width of the surround is 60", height about 54". I don't want the surround to be too proud of the wall, though i'll probably bring it out about 1-2" to account for the wall straightness and give the mantel more support. I plan on using quartersawn white oak.

My main concerns are attaching to the wall, and supporting the mantel piece.

To attach the mantel, i was planning on attaching three corbels to the surround, dovetailed both on the surround and into the mantel. The surround wood thickness is only 3/4"-7/8", so not a lot of thickness for a beefy dovetail, but i could also use glues and screws (into end grain, not the best but some additional support) in the back. The corbels are only 4-6", so i figured wood movement is negligible? I had planned on solid piece of wood for the mantel, 1.5" thick, and i haven't decided how wide, at least 6". It's white oak, so it's heavy. I'm a little worried about supporting the mantel on the three corbels. I'm not opposed to also securing the mantel to the wall somehow. Any suggestions on this? Any problems you see?

To attach the whole surround to the wall, i had planned on screwing it to some board i attach to the wall behind it. I'd want screws hidden, so i was thinking of going in through the side and plugging the holes when i'm done. I'm not adverse to hiding screws on the front either because i was thinking about pegging some of the joints, anyway. I could do some kind of cleat, but then i'm not sure how to tie that in with the mantel piece depending on how i attach the mantel.

any comments or tips are appreciated. Thanks!

[Brian W Smith]

Class "A",new construction?

[Jamie Buxton]

I'm afraid I can't read the details in your drawing. But one thing you should pay attention to is the building-code requirements for spacing from the fireplace opening to flammable materials surrounding it. IIRC, for the first six inches around the opening, no combustible materials. For the next six inches, combustible materials can protrude no more than 1/8" for each 1" of distance from the opening.

There's a pretty good book called Making Mantles by David Getts. He covers many practical issues, like design, and how to hook the thing to the wall. http://www.amazon.com/Making-Mantels...els+david+gets

[tim vadas]

Brian, i'm not sure what class "A" means. This is my existing house, not new construction. I checked the codes for the fireplace and woodstove insert, so all the clearances are met.

I'll check out the book.

[Brian W Smith]

Look up a class "A" diagram.A side elevation is what you need to look at.Look right where the metal damper gets layed into FP on the front.This is usually(strong wording that comes from 40 years in the field)...where a FP gets the hottest.

Touchy subject.Masons don't want to talk about it......inspectors "can't" talk about it......mantle builders are usually ignorant about it.You want to be dang careful,not only about meeting,well intention'd codes....but also about how your mantle interfaces with this heat.

A digital temp gun is a mighty handy,gadget to some,bit of "kit" to have around.We use ours for some pretty obscure things.......some of which include shooting certain HVAC conditions.See if you can borrow one and shoot the front of your FP with it,"on the boil".You are looking for any significant spikes.Use a flashlite and stick your noggin up in the firebox and examine exactly how the flame front is effecting the outside surfaces......right where you're proposing the mantle.

Mantles appear to be straight fwd design.....and they should be.But you're basing design on a criteria that you may not have control over.The building codes are pretty good,but they really drop the ball on FP's.They(folks who write/change the codes)never fully "get" the firebox.They extended the hearth,and have workable clearances for chimney...but they don't address the area that causes the most issues(throats,quality firebox design).It's like plumbing codes in this way.They address areas that are easy to inspect,but leave a lot on the table(check venting codes on plumbing sometime,guy who wrote them can't even explain it?).Best of luck.

[Jamie Buxton]

Look up a class "A" diagram...

Link please?