Thread: Firebox support is plywood

1994 Colonial with wood-burning fireplace. Looking up the clean-out from the basement, I could see plywood supporting the firebox. I recommended a chimney sweep clean and make corrections. They called in the local building inspector who thought it was metal. My picture shows knotty plywood, and don't mind disagreeing with anyone on the matter.

I've always called it out for removal due to fire hazard, though it must be a very difficult job and not sure anyone actually does... What do others say in this situation?

P1070653-small.jpg

I always call it out and call for level 2 inspection by a pro.
Let them sort it out!
I've seen them like that and toasted.
Fireplace is not useable until repairs are made also goes in my report.
if I can't see up from the bottom I check with an awl through the cleanout
good catch!
And there are still inspectors out there that don't use cameras

Yep, once you catch one fireplace like this, you'll take pictures looking up from the ash dump cleanout every time you see one. Looks like they ran the subfloor over and just buikt over top of it. Like Wayne, I've found some charred up ones too. The fireplace is unusable in it's present condition and would likely require major deconstruction and rebuilding to be usable.

Here's what I say:

The hearth support is improper as currently installed. The hearth is supported by wood (form materials were never removed). All of the wood forms should have been removed prior to use. I recommend having this support system evaluated (make sure the hearth extension can support itself) and corrected (remove wood) as needed to help avoid fire.

Could you see anything at all from the top? What was the base there? Perhaps it was a plywood form used to pour a concrete slab. As such, it would be very difficult to remove after the pour.

Originally Posted by Rich Goeken

Could you see anything at all from the top? What was the base there? Perhaps it was a plywood form used to pour a concrete slab. As such, it would be very difficult to remove after the pour.

You can do surgery on the foundation of the firebox or you could blow it out from the hearth-up then install a factory built fireplace right on the hearth and leave the plywood there. Just an option.

Thanks for all the comments. Seems unanimous. It's amazing what you can see taking pictures up the clean-out (haven't seen anything looking back yet...)

I ran into this problem earlier this month. It was in the house my wife was selling, so I had a dog in the fight, so to speak. My initial thought was that the plywood would only extend an inch or so beyond the opening at the top of the ash pit and that the concrete was placed against the CMU most of the way out to the edge of the outer wall of the pit. I could not imagine that they would build the fireplace and thirty some feet of chimney founded on a piece of plywood (between the pit wall and the base of the fireplace.)

I spoke with three masons what had two to four decades of experience each in the area. They all confirmed that this was not an uncommon practice twenty-five to thirty years ago; it wasn't the best way to do it, and they cannot do that now, but it shouldn't be a safety problem. The sheet of plywood would be slightly larger than the opening and there would be 6 or 7 inches of concrete between the edge of the plywood and the outside and the ash pit. The single sheet of plywood is in a box that is intended to receive ash, some charcoal from unburned wood, and probably the occasional ember. It is unlikely that the plywood would ever be ignited by ashes falling through the ash dump, and if it was, it would not generate enough heat so that it could be felt on the outside of the ash pit.

The buyer was somewhat satisfied with this explanation, but asked for $2,000 to have a mason cut out an opening in the ash pit, remove the plywood and tooth in new CMU.

A jar full of Formosan termites would have that plywood outa there in a month or two.

Then light a fire in the ashpit, and burn em up.

From my archives.

Great photos, Nick. I think in this case, a picture is truly worth a thousand words! Thank you for sharing! -Don

Originally Posted by Bob Arledge

I ran into this problem earlier this month. It was in the house my wife was selling, so I had a dog in the fight, so to speak.

Just curious.... how are you involved in any way as an inspector in a house that your wife is selling?

...

Should this wood also be removed? This is in crawlspace under wood-burning masonry fireplace.

Added yellow to show plywood I'm asking about.

Separate question...what are your thoughts on corbeled smoke chambers....should they be parged smooth? How do you word your comment if so?

Thanks