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Can a slab-on-grade be salvaged after a burn-out?

The heat from a fire can result in the breakdown of the chemical composition of concrete. Other effects include spalling of the concrete which is seen as large pits. The concrete may have protected substrates below, but further investigation is probably required. Water used on the fire can also adversely affect the soils below. I have inspected damaged footings following a fire. Have an engineer familiar with concrete test for strength. Sometimes it may look like the concrete is ok, but then later it begins to crumble.

I have also set up structures for training fires and then assisted in the removal of debris. I found the heat does wonders to breakdown the mortar which makes it easier to remove brick.
 
Jobsaver,

IMO, most of the intense heat went up and not downward. Also, how thick do you believe the slab area to be?

Again, IMO, a typical 3.5 inch thick slab would not be affected enough to be detrimental to reframing upon it.

In this area, we have had houses burn down to the ground, that were originally constructed on a "slab on grade"

foundation. The DWV system was in tact except for some charring, slight damage at the surface.

The "new" house was rebuilt right on top of the existing slab. "New" anchoring bolts were installed and away

they went.

.
 
Heat is transferred by convection, radiation and direct flame contact. Convected heat tends to move upward. Radiant heat travels in all directions. Flame contact will travel with building materials that are capable of heat transmission, (i.e. pipe, rebar, etc.). Smoldering debris can cause significant damage to localized materials due to direct flame contact.

Radiant heat will transmit energy to "black body" materials. The energy will be absorbed based upon the materials properties.
 
Thanks for the responses.

In this case, the insurance company apparently is going to make a determination on the salvage value of the slab . . . and subsequent loss from the fire, by contacting the ahj, (me).

Historically, we have allowed rebuilds after burn-outs, but only on portions of structures and in older neighborhoods. It probably shouldn't matter, but the idea of building an entirely new home in a new neighborhood on a burn-out slab is causing me to question the integrity of it a bit more.
 
Jobsaver,

FWIW, if this particular foundation is in an older area ( i.e. - poorer neighborhood ), will

an engineering analysis be a burden / additional cost added by your office, vs. the Fire

Dept. or the insurance company requing one? If you say "In your opinion, no not

required", will your Fire Dept. or the insurance co. still require it?

.
 
Before I built something on it I would do a core test and see if the concrete still met code. I guess that would be rational for the AHJ as a condition for a permit.
 
I have a Q.

Will the house need to meet new code requirements like the: 2009IRC P2719.1 floor drain can no longer be under the furnace? Also plumbing stacks through the floor would give you some insight on PVC plumbing that may have melted due to the fire, if no issue at the base of the stack, plumbing could be ok? IMO

pc1
 
I vote no.. prove that everything in the slab still works (and a core sample isn't the right solution.. quick way to destroy the vapor barrier - if there was ever one installed).
 
Interesting post, we had a house fire a couple years ago to an architects dads house, and he wanted to rebuild on same foundation, we had them engineer foundation and results came back ok to re-build. I am not sure extent of fire to foundation walls though, I dont think the walls were affected that bad in this case.
 
I decided the issue sufficiently cloudy as to punt! I assume the insurance company will replace the slab. Will post on this thread and let all know what happened. Thanks for all of the comments.

March 15, 2010

Mr. Greeson:

Pursuant to your inquiry, the following items will be required by the City of Sherwood before a rebuild permit will be issued for constructing a new home on the existing slab on grade foundation located at 9508 Westlake Circle.

An affidavit from a registered design professional certifying that the effects of the fire have not significantly lowered the structural bearing capacity or water vapor retardation of the slab, including a minimum of two concrete core strength tests.

An affidavit from a licensed plumber intending to plumb the new home, including accepting legal responsibility for all of the plumbing systems, including a camera tape on existing DWV lines located within and under the slab.

If you have any additional questions, please call the Permits and Planning Department.

Sincerely,

W.A. Wilson - Building Inspector
 
Jobsaver said:
Pursuant to your inquiry, the following items will be required by the City of Sherwood before a rebuild permit will be issued for constructing a new home on the existing slab on grade foundation located at 9508 Westlake Circle.

An affidavit from a registered design professional certifying that the effects of the fire have not significantly lowered the structural bearing capacity or water vapor retardation of the slab, including a minimum of two concrete core strength tests.

An affidavit from a licensed plumber intending to plumb the new home, including accepting legal responsibility for all of the plumbing systems, including a camera tape on existing DWV lines located within and under the slab.

If you have any additional questions, please call the Permits and Planning Department.

Sincerely,

W.A. Wilson - Building Inspector
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A question: Have you ever required an affidavit from any design professional attesting that the materials are installed properly?
 
Jobsaver said:
Yes. And, have never received an affidavit. I can think of a number of examples, but none of which when an affidavit was ultimately substituted for jobsite corrections.
Click to expand...
I asked because I think you are asking for something completely outrageous. (I like the contradiction of you wanting a core sample and peach saying a core sample will destroy the vapor barrier. I accept different opinions, but I would be more comfortable if those asking for "proof" had a good engineering background.)
 
"I accept different opinions, but I would be more comfortable if those asking for "proof" had a good engineering background.)"

Hence, we ask for an "engineers" opinion, because us common folk don't have an "engineering background" and as we are repeatedly told, can not "practice" engineering..........
 
Taking core samples, or poking other holes, through the vapor barrier will affect the integrity of the vapor barrier. However, the integrity of the vapor barrier can be largely restored through the core sample opening left in the slab, before patching the concrete. Work an oversized piece of 6 mil into the opening under the edges of the hole.
 
And to that question.........living and working in the great American desert, we don't even do the vapor barrier around here......so non-issue. But yes, I think you could figure out a way to reseal the barrier, where it is required.
 
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