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IsoKern Fireplace Issues

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XR250

XR250

Structural
Jan 30, 2013
5,987
I recently worked on a large residential renovation. The plans showed a wood framed fireplace with a sheet metal flue liner. No call out were made to the type of fireplace insert.
Apparently they installed this - It weighs about 2000 lbs when all is said and done. They are having issues with the firebricks cracking.
By the numbers, there is enough wood structure beneath it, however, it is installed where there is a flush girder that is slightly higher than the adjoining joists. My suspicion is this and the deflections in the floor system are causing the problems. I am working on a fix with the contractor.

He has not asked me for any money yet to help offset his costs. My feelings are this...

1) I had never even heard of these things prior to a couple of weeks ago. Every fireplace insert I have designed for (as far as I know) was a lightweight metal thingy.
Is it incumbent on me to be familiar with all fireplace insert technology?
2) It was not called out on the plans so how was I to know I needed to design for a 2k load. If I had known, I would have simply added a large masonry pier under it.
3) Should the contractor have asked me, "hey, we are putting 2k of masonry on this floor, is it designed for it"?
4) What responsibility does the Arch. have in this?

Apparently, Isokern has two models - one designed for a slab and one for a wood foundation. Seems like a wood foundation is a bad idea for anything this brittle and heavy. It is also sited in an area with plastic clay soils so differential pier movement may also be an issue.

Thanks in advance for your input.
 
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XR250, this sounds like a coordination issue, which I don't think you can be held accountable for. Whoever decided to install 2k of masonry should have made you (or the project manager, or GC) aware of it. I don't think it is reasonable to expect you to be familiar with all types of fireplace inserts. Should we all also start keeping up to date on new tubs, kitchen appliances, etc... just in case someone decides to install a new 5,000 lbs freezer that no one knew existed?

If the architect specified this fireplace than he/she is responsible to communicate that, obviously. But, the architect could have been just as unaware of this as you were.

Depending on your relationship with the client/contractor, you might give him a break on the fees to design a fix. But based on the info you provided, I wouldn't accept any responsibility for the problem.

Out of curiosity, what design load did you consider when designing the framing below the fireplace?
 
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Thanks CANPRO.
I actually did not so any calcs under the fireplace. I had to install a pier under each side of the firebox opening to cary a ridge load split by the header. The fireplace sits on the main girder with flanking 2x10 x 9'-6" 2x10's on each side. Seemed like it shoulda be plenty stout for something that wasn't as brittle as glass.
 
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It sounds like the framing should have been able to handle the 2k load fairly easily as well. This might be straying from "Business Practices and Issues" and more into "Structural Engineering and Other Topics"....but I wonder if maybe the 2x10 shrunk a bit vertically and the beam did not (I'm assuming the beam is steel or engineered wood). I can't imagine the 2x10 deflected enough that close to its support to have caused issues. I have seen 2x10 shrink significantly enough to cause a noticeable hump in the floor at the beam location. I don't know all the details of your framing, but my gut says this is probably more likely of a scenario than the 2x10 deflecting excessively under load.
 
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CANPRO,

The 2x10's and girder were 1950's existing so that may not be the case. Their is def. a hump in the floor due to them being installed slightly low on the beam back in the day.
He is a good client so I will probably not charge for this. I believe the best I can do is have them construct two additional piers at the rear corners of the fireplace and connect all of them with (4) light I-beams and then block solid between the joists with some LVL (for low shrinkage). I am not sure if the installer did anything to mitigate bending of the materials over the hump.

Thanks for your thoughts.
 
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