Expert: Dan Griffin - 4/11/2008

Question
3 years ago we had a small addition added on to our 1968 single story ranch home in Northern CALIF., stucco, with pitched roof and walking atticspace, 8ft ceilings and crawlspace.  Addition was added same level, but poured a raised slab to meet the height of the crawl, the addition has cathedral ceiling and attaches with valleys to older part of home.  Here is the problem:  since addition was built, soon as Spring hits and temps warm an exterior wall in the older part of the home that attaches to the new addition makes LOUD POPPING noises at very specific times of the day (the warmest part of the day at 4-6pm and then softer popping noises again during the coolest time of night at3-4am).  I'm guessing because this does not happen in winter and only happens at the hottest and coolest times of day/night during the warmer seasons that it is thermal expansion and contraction.  But why???  and what can we do???  I am having my husband add additional intake/soffit venting to our attic as we speak (we had venting at every soffit but it was only slits-husband is cutting out slits to open intakes with 4x16vents, however we always had adequate venting prior to the addition, maybe after the addition it wasn't considered adequate?  We have plenty of outtake venting RIDGE/2GABLES/ADD'L EYBROWS. Or are we on the wrong track and could it be a lack of expansion joint somewhere in wall or roof?  Then what can be done?  What else might it be?  It sounds like gun shots and if we have to get an expert to come hear it, it WILL happen at those times of days and it WILL be heard.  Very annoying (especially at night when sleeping-although much less pops and lower volume at night).  Frustrated with my gorgeous addition.

Answer
Roxy, that has to be a disturbing sound.  I agree that it sure sounds related to thermal expansion/contraction.  Here are some additional thoughts, though none are solutions.

Is one roof system trusses and the other cut rafters?
Are some of the roof sheets common to both roofs?
You mentioned a cathedral - is there good venting from eve to ridge?
Could there be anything about the crawl space creating a major temperature difference in the walls?

Increasing the venting sure can't hurt.  YOu might even consider a power vent or wind turbine in the vicinity of the problem.  Is there a way to begin to isolate the sound to a specific source?  Is there a way to contact the original contractor in a very non adversarial role seeking advice and opinions?

I sure wish I could be of more help.