Banging noise from thermal expansion/contraction
My dwelling has cathedral ceilings and we have a problem with thermal expansion/contraction causing a “banging” noise after sunrise and at sunset. I have a high moisture reading in the morning and but the attic temperature is close to the outside temperature and by mid-day, the spread between the attic and outside increases to around 20 degrees and the moisture reading will goes from wet to dry. At the recommendation of 3 roofers, I had ridge vents added. The overhang is only about 10 inches but has vinyl venting all the way across. There is no venting on the side eves. There are baffles but some are laying on top of the insulation, others were nailed to bottom on the decking.. The shingles are white and the roof is 15 years old. I was in the attic one time and the noise see to have occurred in the cdx decking. Is the root cause of thermal expansion/contraction the result of heat and moisture? Would it be advisable to have Thermal Imagining done? Any recommendations would be appreciated.
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Replies
David,
I'm used to the creaks and pops from metal roofing expanding and contracting, but your phenomenon -- a "banging noise" -- is a new one.
Readers?
The "banging" noise sounds like someone breaking wood. It's sounds more like a snapping sound.
Do you have an HVAC refrigerant line? Is the noise coming from its general direction?
The timing -- near sunrise and sunset -- is the key.
It's not the HVAC system. It's some type of thermal expansion and contraction.
Thanks Martin and you are correct. I assume it's the result of moisture and heat. In the mornings, I usually have a high moisture reading but the outside and and inside temperatures are the same or close to being the same. As the day goes on, the attic temperatures rises about the outside temperatures (as much as 20 degrees) but the moisture lowers and I have a dry reading. The popping noise occurs within 2 hours of sunrise and at sunset to one hour after sunset.
I really want to hear what this sounds like.
I'm wondering if the cause is similar to the 'banging bolts' that happens rarely in steel buildings.
Truss movement? Just spitballing here, don't know the construction of your cathedral ceiling. We had a house that occasionally experienced a very loud boom noise. I suspect that it had to do with relative movement (stiction) of the truss, especially the bottom chord with respect to walls. Either it was attached and not floating (interior wall?), or something. Someone else at the time mentioned truss uplift, which is different but also involves the movement of trusses. Remember that the bottom truss in most systems is buried in insulation, while the top of the truss assembly is in the exposed attic, so there could be differences in thermal expansion of various truss components.
This may not be your situation, but perhaps it points in the right direction?
Thanks Andrew. The drywall ceiling for the cathedral ceiling is attached to the Engineered trusses with rolled insulation between the trusses. If there were movement, wouldn't there be cracks in the ceiling?
David,
In the summer, when the sun has been on my south facing wall for several hours, I quite regularly hear a similar snap somewhere close to the header or rim joist above. I've had that wall open and there is no moisture or anything else odd about it. In the absence of any other symptom I wouldn't worry about it.
We're getting 10-12 pops a day (morning then evening). I would think it would have to be the result of a combination of heat and moisture. As I previous stated, the mornings the attic and outside temperatures are almost the same but the moisture reading is high in the early morning as as the day warms up, the difference between attic and outside rises to about 20 degrees and as the temperatures rises, the moisture reading moves from wet to dry. Is there any fix for thermal expansions with rafters?
David,
It sounds like you have scissor trusses. Unlike typical trusses where the bottom cord can move vertically with temperature changes, scissor trusses also move horizontally (you can see the allowable movement on the engineering specs that came with the roof if you still have them). If that's what is causing the popping I don't think there is much you can do about it.
Thanks Malcolm. It's Half Scissor for the Cathedral Ceiling and full Scissor for the front half of the house. Shouldn't there be signs of movement with cracks in the cathedral ceiling?
David,
It may move like a hinge, and at the peak it's perhaps not enough to crack the mud. If the boarders were diligent in keeping fasteners away from the intersection of the wall and ceiling, or used clips, it should be able to tolerate a bit of movement there too.
When I replace the roof, would you recommend anything to replace or check on? They did use clips on the decking. Also, would improving the air flow help?
David,
No sorry, I don't know anything helpful to suggest. Perhaps the truss manufacturer's engineer might have some ideas?
Thanks for your help Malcolm. I located an engineer with a background working with Trusses. Two previous engineers had no clue as to what to do.
Please see my reply to the thread! I am hoping to have you read my situation and update yours to help me. I am going nuts over this problem! Thanks David.
David I see you posted this 4 yrs ago But I bought a 1967 block home in SW FL and have the same problem in the summer/hot months Only (whenever temps are over 85 and then drop off sunset/sunrise there are loud noises like wood splitting but also abrupt pops/booms that can wake you in the night! I have pinpointed it to the ceiling/attic (Not sure if it is trusses or wallframe header?) I know it is not animals or HVAC or pipes Etc). It is wood/expansion and contraction for sure. Can you update me as to if the engineer you found gave you all possibilities and then if they determined your cause & solution. Cost? I was told it COULD be a Previous roofing repair issue but it does not sound like it comes from roof planks that may be expanding/contracting from not being staggered (I have planks not plywood). I will be re-roofing soon and want to try to pinpoint this issue ad it sounds more like my ceiling or trusses (there is a crack in drywall). The sellers did not disclose a lot of the details that may tell me more so I am exploring everything! I am not builder savvy so I am not sure what I trusses I have or anything). Thank you!