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Need carpentry advice, framing a fireplace hearth


feralfreak

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I'll second the impact driver, best tool I've purchased, it makes framing with screws, which I prefer (no squeaks), much much easier.

Make sure that if you go with screws, that they are rated for construction, I normally use either deck screws, or GRK. In your case you might be able to screw all the way through your new framing into the sub floor to hold it down instead of toe nailing.

Don't skimp on the construction adhesive, it's pretty inexpensive and as wddleme said, you can always return the extra. I recently replaced the stringers for a set of stairs, and ended up using 5 tubes of adhesive to glue down the treads and risers.

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Sounds like you're on the right track now :D All the details are on the tile forum I mentioned including backer screws, their use and spacing. I don't like the "Hardie backer" as I've seen it delaminate over time :o I prefer the cementitious board for backer but Hardie should work OK here.

As to the treated lumber it's use is limited by code to only where it is mandated and in places outside of the habitable building envelope. It makes no difference whether the masonry in question is concrete, block, brick, or mortar, for they all collect and retain moisture which will cause rot in untreated wood; that's why only treated may make direct contact with it, and that is how the code is worded, interpreted, and applied. It's all in the ICBO and other building codes, look it up if you don't believe me. This stuff is my daily bread-and-butter and I've been doing it all for over 35 years now. In my current working radius I deal with 6 different code jurisdictions each of which uses a different version of code standards or who have added some of their own heightened requirements to a standard code. Some things are contradictory being required in one place while being prohibited in another. It's insane but that's how it works in my business :screwy: And there's the usual situation of how strictly they are applied since each inspector must interpret them and apply any allowable variances at their own discretion. If they want to make your life miserable they can because nobody and no house is perfect and they can always find a reason to fail you if they want to, which a few of them do just to show you how powerful they are. Luckily most are sensible and willing to bend as long as the intended goals of that part of the code are being met adequately.

Legally, work like this requires a permit and inspection due to it being considered safety-related (Fire code) so that must be my 'official' recommendation. But having said that, as long as your work meets or exceeds the code requirements and nobody of authority discovers the lack of total legality now or in the future, you can do it DIY without worry as the end result will be the same either way B) No guessing and no less than

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I understand Bettypooh's code comments on PT.....that said, in practical application for subfloors to tile applications with backer board I've never seen it used interior....however, make sure you have exterior grade leftover, not an interior plywood (eg from a leftover cabinet project or such....check the labeling).

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Back in the old days before treated lumber, best practice was to use a rot-resistant wood species or to isolate with heavy felt;or roof shingles where masonry contact was necessary. Hardly ever a problem but sometimes. Sills take a beating because. that masonry is always in contact with the ground so it wicks moisture up from there. Unless you have a groundwater issue, fireplaces tend to be drier so even though there's still ground contact it isn't normally a problem there. Codes are meant to protect you but some of them border on being absurd. Were it not for the legal ramifications there are several things I'd ignore as useless or stupid but you have to play their game their way so you do.

Bettypooh

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  • 2 years later...

Well, i managed to get some done on my hearth, no subfloor on it yet but have a look,where i sistered joists i accidentally cut a hair short, but i secured a sister joist with a good amount of 2 1/2 inchx9 deck screws, end screws (and on a sistet joist 2 toenail screws) are 3 1/2 x 10, my cuddly Buster wanted to help out, silly bear was using the wrong tool

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Please be careful! If that is a wood burning fireplace in particular you have placed combustible building materials to close! You might be better off using metal studs and HardieBacker. Consult your local building codes for minimum to combustible material, your local building codes should be available for free online. Even if it is a prefabricated gas fireplace the manufacturer has a minimum distance to combustibles and that information could be found on their website.

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Wood studs won't matter, but you should a cement backer board over plywood for strength. Here's a few pics of a fireplace I built in our house a few years back.

First, the old brick covered wood stove, which got the house way too hot.

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Then, how it looked after a partial tear-down

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Framing of the new gas fireplace.

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Here's a side view in progress, showing the recess for the TV above the mantle

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The left side is now completed. The cabinet below the bookshelf contains a 15" subwoofer, and the THX equipment

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Here's the final view, after several years. Notice how the cherry wood darkens over time.This gas fireplace allows a lot more flexibility with the cabinetry design than a wood-fired box. Yes, this was all built to code and the manufacturers guidelines. There are several hidden airducts for cooling, and several PVC pipes for cable runs.

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I plan to usecement board over the hearth subfloor, gotta have something to mud the tiles to, the fireplace is a zero clearance one, one thing im wondering right now is, which do i lay down first?  The 3/4 plywood  (i have to be strategic with the cut out to fit it around the fireplace in front, use what I take from the front cut out to fill in the back by a couple inches) or the 7/16 osb (a full sheet, never been cut)

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If you use 1/2 inch backer board, the OSB is all you need. What is your stud spacing on that hearth? That looks like about a foot. That is GIFs enough for supporting 7/16 OSB, so save your plywood for something more interesting. 

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I drew the hearth out since I wasn't sure exactly how to answer the question, i seem to have different spacings (probably not very good but im all i can afford haha),we have some backer board but its 1/4 inch, been here since before we got here, 2 2'x4' sheets the squatters left, cost is a factor 

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If you are using the 1/4 inch backer board, then you need the extra strength of the plywood. Also, make your breaks between the backer boards as close to being over studs as you can. That will help when you mortar on the tile.

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18 hours ago, WetDad said:

If you are using the 1/4 inch backer board, then you need the extra strength of the plywood. Also, make your breaks between the backer boards as close to being over studs as you can. That will help when you mortar on the tile.

I hadnt considered where the breaks land, but i will now. Another advantage i think to the combination of plywood and osb will be a little more surface for the edge tiles, should those be placed first or the flat area? Im kinda leaning towards doing the edges first so the flat area tiles cover the top of the edges but ive never done this before 

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