Building Homes or Extensions/Wall cavity noises

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Question
We just had a two storey extension which has been finished 6 weeks. We can hear the sound of small masonry falling in the wall cavity in our new bedroom. We thought it would stop after a few weeks but still happening. Can't see any cracks or anything but starting to worry it's not structurally sound! We did have a few walls knocked out but the structural engineer advised it would be fine. Builder doesn't seem bothered and says it must be mice or a bird, but no signs of anything like that in the loft so seems unlikely. Any advice welcome. Thanks

Answer
Hi Amanda, that's a tough question to answer.  Depending on the method of construction it could be anything.  When you say you can hear the sound in the wall cavity can you tell if it is between your drywall and the masonry? Or does it sound like it is inside the masonry?  Is there any insulation in your wall cavities?  What kind of exterior do you have? Brick? Is there an air space between the brick and the masonry?  On the interior are there furring strips between your drywall and the masonry?  Or is it a full framed stud wall? If so are the studs/furring strips metal or wood? What kind of ventilation does your attic have? Are there eave vents, roof vents,  or both?  The reason I ask is that sometimes when you have a ventilated attic space, air flow can cause strange noises.  Air flowing through an eave vent over an open wall cavity can create a Venturi affect that may dislodge debris and you may be able to hear it rattle down the inside of the wall.   Sometimes little mortar "boogers"  on the face of masonry can pop loose and rattle down inside a wall cavity. Or as your contractor suggested there might be some kind of animal causing the noise..has anyone gone around the house looking for potential entry points for critters?  Try sealing up any potential places animals can crawl through and see if that puts a stop to it. Also are you sure it's coming from your house? I had a lady write me about what she thought was a building structure failing when every day she heard a booming noise that rattled her windows at work.  It turned out to be a jet crashing the sound barrier and creating a sonic boom..maybe there is an external cause and it just sounds like it is in your wall. .  One last thing.  Most bathrooms have exhaust fans which are ducted to the outside.  Inside the ductwork is a one way flap to keep outside air from entering the conditioned space.  These little buggers can make noise like Poes raven and keep tap tap tapping when the wind blows just right.  I hope this information helps, please feel free to write again regarding this or other matters, sincerely, Bruce Johnson, bejohnsonconsulting.com

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Bruce E. Johnson

Expertise

I can answer any construction related question in regards to carpentry, concrete, drywall, masonry, structural elements of any type of building, residential or commercial. Interior or exterior.

Experience

Custom Commercial and residential buildings. Churches, theaters, schools and auditoriums. Most recently I am working with the Catholic Church on several design build committees. I have a website related to scheduling and project supervision. Although my expertise is more related to multimillion dollar commercial, educational and theatrical projects my generous credentials in residential and remodelling construction make me a viable source of information regarding all forms of building questions.

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