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Roof poping noise

Roof poping noise

Roof poping noise

(OP)
Would like to know the mechanism, that causes on occasion, considerable popping and snapping in a 6 year old truss roof. The roof is fairly complex with 4 different length trusses, the longest about 56' and shortest about 36', all on the same axis but with staggered ridges. The primary pitch is 6-12 with a 3-12 pitch over a 8' wide porch that wraps around 3 sides of the house.
Yesterday late afternoon and evening the there was considerable popping every 15 to 30 minutes. A couple days before we had had 5-6" of snow over <1/8" of ice. The day following the snow was sunny and 40 degrees, after which about 1/3 of the roof near the ridge was free of snow, then some visible ice going to several inches of snow at the eve. The next day was sunny with slowly dropping temperatures going well below freezing after sun down to near zero at midnight. The popping started just before sun down and continued to 9 or 10 PM. Sometimes there were a series of pops in a second or so that chased across portions of the upper roof. At times it sounds like someone gave a truss or something, a really good smack with a hammer. We had heard this popping before but only a few a day. The attic has eve and ridge vents with about 18" of blown fiberglass above the ceiling.
What mechanism would cause this noise, ice interacting with the 45 year asphalt shingles, chip board decking and or trusses shifting due to thermal affects? Any explanation of this noise, and potential consequences of this audio activity would be appreciated.

RE: Roof poping noise

Tricky.....
Would I be right in understanding that the structure is 6 years old, and the 45 simply a reference to the warrantee for ths shingles?
By chip board decking, would I be right in understanding that the sheathing over the trusses and below the shingles is wood?
Are the trusses wood or steel?

RE: Roof poping noise

Would I be correct in understanding from your post that the popping is observed while everything is cooling, but not while everything is warming?

RE: Roof poping noise

Could the presence of ice at a "joint", or place of expansion/contraction, be inhibiting movement until the ice crushes when cooling is experienced, causing the sudden popping? This phenomenon would not happen when warming.

Mike McCann
MMC Engineering

RE: Roof poping noise

(OP)
Triangled, You are correct on all counts. The trusses are wood.

We have had another sub zero cold cycle after a 5-6" snow with no melting or ice before hand, and only a pop or two It appears the ice is interacting with the roof in a noisy and hopefully nondestructive way. Could it be the ice is trying to restrain the roof structure as it tries to contract?

RE: Roof poping noise

Think Mike above has it. Likely not a structural item at all.

This from my roofing consultant....
" I have had some experience in investigating the mystery of creaking and popping of roof framing although most of my work involved residential wood-frame construction. It seems that all such occurrences are thermally induced which appears to be the case in the situation you have described.

In wood frame cases, the sounds are typically due to friction release of the fasteners joining the framing members as the system expands and contracts due to extreme temperature transitions. Most of my experience is right here in So Cal where very hot days are followed by significant nighttime cooling which is typically when the popping occurs. I have never seen a situation where any structural damage resulted from this movement.

Thermal cycling would appear to be the culprit in your case as well and I would suspect that most, if not all of the noise takes place during the cooling cycle as it usually occurs more abruptly than the warming cycle.

You had mentioned that you didn't know if the trusses were constructed of wood or metal and this is indeed a key element in determining potential structural risks. Whereas wood framing is usually connected with smooth nails that will move into and out of position without jeopardizing the integrity of the fastener, metal framing is typically connected with screws or pins that can easily shear with forced movement. Metal has a much higher expansion coefficient and will experience much greater actual movement than wood. While I have very little experience with metal framing, I have seen sheet metal roofing fail due to expansion and contraction, usually due to the elongation of the the fastener holes through the material. Most systems now incorporate side clips that allow expansion and contraction without penetration into the actual panels.

In short, if you determine that you have a metal framing system, I would initiate an inspection of the system to see if the sounds are indications of fastener failure which would require immediate remedial attention.

For whatever my meager experience means, I hope it helps you out. "

RE: Roof poping noise

Could the humidity have dropped due to cold and you may be experiencing 'truss uplift' and the sound of fasteners attached to the ceiling and/or walls?

Dik

RE: Roof poping noise

I would add to the previous comments a new culprit based on the sounds heard;
If you hear a pop sound followed by a string of multiple pops all sequential,
like a machine gun but not as fast, it is likely the boundry nails (along the
edge of plywood sheathing) is failing in either the roof or wall sheathing.

RE: Roof poping noise

I agree with Dik. When a pitched truss in an attic has it's bottom chord buried in insulation, the bottom of the truss remains relatively warm and dry. The top chord however is exposed to the attic relative humidity, and will be colder and wetter than the bottom chord in winter months. The top chord will expand relative to the bottom chord, causing the truss to bow upward. If interior partition walls are firmly fastened to the bottom of the trusses, fasteners can pop. The partitions, in some cases, can actually be lifted.

RE: Roof poping noise

Is the roof still standing? <G>

Dik

RE: Roof poping noise

Yes, but the sound is the rats popping popcorn on the rat runs.

Mike McCann
MMC Engineering

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