You are not going to believe this one

[BrotherBart]

The problem with the code is it makes no allowance for distance from the clay liner to the outer masonry, or mortar mass between the liner and the masonry.

You could have a 6 foot wide chimney with one clay liner down the middle, like mine, but if the sides of the masonry touch the house (like mine) it's not code. That just does not make sense to me.

Covered by one of the three exceptions contained in IRC R1001.15.

"3. Exposed combustible trim and the edges of sheathing materials, such as wood siding, shall be permitted to abut the masonry chimney side walls, in accordance with FIGURE R1001.15, provided such combustible trim or sheathing is a minimum of 12 inches (306 mm) from the inside surface of the nearest flue lining. Combustible material and trim shall not overlap the corners of the chimney by more than 1 inch (25 mm)"

 

[fire_man]

I was referring to the actual building, not just the trim work. If you had a 6x6 foot square chimney running through the center of your house with one flue running down the center, and 4" of masonry outside the clay liner, code says you STILL have to have 2" of clearance from the structure of the house to the masonry surface. - or tell me if I am interpreting this incorrectly.

But at least the code does allow, as BB points out, trim to be in contact.

 

[bholler]

yes bart there are exceptions but not as far as the main body of the chimney in reference to the main body of the house there you still need the 1" for ext. and 2" for int. unless I am missing it. I am looking at my copy of irc now and not finding anything about an exception for that.

 

[BrotherBart]

Heck wood mantels are attached directly to the masonry with no air space. What about dem apples?

 

[fire_man]

The code should be written to somehow specify an "R" value requirement, with the provision that the flue gases must pass through a secure lining.

The lining would have to be separated from combustibles by a certain R value equivalent, which would be some combination of masonry and/or air space.

 

[BrotherBart]

Arguments that have been going on since the building boom after WWII. What about the wooden trim at the ceiling on my brick fireplace?

 

[BrotherBart]

The lining would have to be separated from combustibles by a certain R value equivalent, which would be some combination of masonry and/or air space.

One of the problems is that in testing masonry has no outer limit of heat transmission. It takes a long time to heat up but will just keep getting hotter and hotter since it has zip for insulation value but is an excellent transmission medium for heat.

 

[begreen]

I agree with most everything but note that common brick has an R value of .8 for 4". It has to have some insulation value or it wouldn't be allowed for use in getting the 33% clearance reduction as an NFPA 211 wall shield.

 

[fire_man]

Wouldn't there be a certain thickness of masonry which would have the same "R" value as a 1/2" ceramic blanket insulation wrap?

Or a combination of air distance from the clay liner and total masonry thickness?

 

[BrotherBart]

The code should be written to somehow specify an "R" value requirement, with the provision that the flue gases must pass through a secure lining.

The lining would have to be separated from combustibles by a certain R value equivalent, which would be some combination of masonry and/or air space.

Pretty much handled by exception one.

"1. Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777, and installed in accordance with the manufacturer's installation instructions, are permitted to have combustible material in contact with their exterior surfaces."

 

[fire_man]

Yup, I get that. It's saying you can have a lousy masonry chimney touching your house, but it's ok if you install a lining system listed and labeled for use IAW UL 1777.

I'm saying I think there should be allowance for a properly built pure masonry chimney, and it would be acceptable for it to be in complete contact with the house - the way most chimneys are actually built, nearly touching the house.

 

[bholler]

but it's ok if you install a lining system listed and labeled for use IAW UL 1777

yes that is true if it is installed according to the instructions including proper insulation.

I agree that the code has problems but it is the code and mantles are covered under exemption 4. I agree that it doesn't make sense that a mantle is ok but that is what we have to work with.

Many chimneys do have more masonry but there are also allot that only have the 4" nominal that absolutely can have enough heat transfer through to eventually cause combustion.

 

[fire_man]

Are you saying 4" of masonry, and a secure liner, without the presence of a chimney fire can cause combustion?

 

[bholler]

Yes over time it can not often but it can. What usually happens though is that the wood gets dried out and the kindling point gets lower and lower through the years then there is a chimney fire and it ignites.

 

[BrotherBart]

Are you saying 4" of masonry, and a secure liner, without the presence of a chimney fire can cause combustion?

Irrelevant. Code and specs are so the place will still be there after a chimney fire.

But yes, over time exposure to heat lowers the combustion point of wood. Read up on pyrolysis.

 

[smokedragon]

I wonder how many chimneys really are built to code

Very few........

And I know code is there to protect us, but sometimes it is just asinine.

 

[Soundchasm]

Begreen, glad their precious cargo is intact. They are lucky that with you on the job THIS will NEVER happen again.

 

[Motor7]

Very few........

And I know code is there to protect us, but sometimes it is just asinine.

I really think the asinine one's are codes that codes that were put in place to make someone money and they are more prolific than we think.

Begreen, keep us posted on the "fix" and if it's not a tear out I am curious as to the solution.

 

[fire_man]

I really think the asinine one's are codes that codes that were put in place to make someone money and they are more prolific than we think.

I think of this every time I see one of those large plastic shield covers that are required on outdoor electrical outlets - which break the first year and get ripped off anyway. They are now code and replace the simple metal gasketed covers that lasted 20 years.

 

[begreen]

I really think the asinine one's are codes that codes that were put in place to make someone money and they are more prolific than we think.

Begreen, keep us posted on the "fix" and if it's not a tear out I am curious as to the solution.

Will do. I think it will be a complete teardown and rebuild. I suggested they consider a pair of metal chimneys in a chase.

 

[stoveguy2esw]

one for the fireplace that the stove was connected to. The exposed flue was for the fireplace!!

WOW! the flue was for an open fireplace? didnt look big enough to support one in the picture. scary thougt there

 

[begreen]

Correct. Very scary indeed.

 

[Seasoned Oak]

What is going on above the roof-line? I mean how did they cover their tracks when the chimney tile hit the roof-line? brick on top of 2x4 rafters?

THats what it looks like in the pic.

 

[begreen]

This is the only picture I have but yes, that sounds like a correct assessment.