Fire In The Attic

I entered an attic of a 2000 sq. ft. property in Plano Texas last week and was confronted with a burnt area covering around a third of the attic. A disconnected flue that exhausts into the attic just below the roof decking caused the burning. I was amazed just how much damage the discharge of fumes into the attic had caused but found out later that the current roof had been installed 14 years ago and the flue may have been disconnected then. It is known that high temperatures have a dramatic effect on lumber’s load carrying capacity and increases the probability of brittle failure at the weakest link in the piece of lumber associated with a defect - notably, a "large" knot^{(Note 1)}. There was a failure present and visible in the attic as the following picture shows. This raised my concern in three areas. First there is a distinct possibility that the attic could catch fire, second that the structural integrity of the attic has been so compromised that it could collapse and last, but not least, the probability of carbon monoxide entering the living area.

In the picture below you can see some discoloration of the outer flue pipe. Steel changes color as its temperature rises, which may indicate that the pipe achieved a very high temperature at some point in the past. Since flue gases leaving a flue can reach over 500⁰F^{(Note 2)} it is possible that these very high temperatures were reached.

The temperature at which wood chars depends on multiple variables and I do not intend to discuss it here only to note that it is generally above 150°F^{(Note 1)}, which is the temperature that lumber’s load-bearing ability starts to drop dramatically. In addition 170ºF is the temperature cited in the 1959 UL as a safe maximum for lumber. It is also known that long-term exposure to hot pipes can cause lumber to burn³.

The following picture shows a tar deposit running down the surfaces of the decking and framing. The roof was covered with 20-year 3 tab shingles and this is evidence the heat may be melting the tar in the shingles and it is seeping into the attic.

Although a burnt attic is an unusual find I have found this type of issue in the past, which prompted me to write this short description of the problem. At the time of writing I have had no adverse feed back from the sellers regarding the issue other than the listing agent saying the attic had been inspected by two other inspectors in the last month and they had not mentioned the burn damage at all.

In my opinion this burnt attic represents a considerable risk to my clients and the current occupiers of the property and I would be interested to know how many times this has been found by other inspectors in the last few years. The following is the call out that went into the report.

Call Out

The right elevation of the attic has extensive burn damage. This burn damage will result in the weakening of the attics structure. The cause of the damage is the central heating furnace that vents into the attic just under the roof decking. In addition to structural damage caused by the missing flue to the furnace the heating of the decking will have caused the shingles to degenerate. Finally there is a possibility of Carbon Monoxide entering the living area. You should arrange for a structural expert to access the damage to the attic and what repairs need to be made. In addition you should

·      Obtain an assessment of the roof insurability from an insurance company

·      Enquire if the building is habitual under current City regulations

All this should be completed before escrow.

You can find out more information on

References.

1) Modeling the reliability of wood tension members exposed to elevated temperatures http://swst.metapress.com/content/h9h673482r173h6g/

2) Flue Gas Temperature and Heat in the Flue Gas Flow (Btu/hour) http://ackerandassociates.com/computer_program_examples/23_flue_gas_temperature_and_heat_in_flow/

3) ‘Pyrophoric Carbon’ and Long-term, Low-temperature Ignition of Wood  http://www.doctorfire.com/low_temp_wood1.pdf

https://drive.google.com/file/d/0ByvFfKK7TGciX3VMUDVlQ3NxbVU/view?usp=sharing