Here’s an odd one. Just got a call to install some soffit vents. House is about 15 yr old colonial in southern NH and was recently re-roofed (~ 8 pitch roof with architectural ashphalt shingles). The original roof included typical ridge vents but the intake was done by simply keeping the upper edge of the facia board about an inch below the underside of the roof deck. The air gap was maintained by keeping the drip edge about a half inch out from the facia. The attic has cellulose with proper vent down near the tails so the system seems like it should have worked, however, the reason he had the house re-roofed is because of all the shingle damage that occurred over the years from ice dams (mostly from him chipping away at the ice with an ax!). Other than looking to improve his intakes by adding soffit vents, he mentioned that since having the house re-roofed, he hears a very low humming sound throughout the house just about sunrise. He says that it lasts for an hour or two then it stops. He described it as sounding like a refridgerator fan on its last leg. He thought it was something mechanical so he shut off all the power to the house trying to pinpoint the source, but no luck, the sound was still there. He said it seems louder on the south corner of the house, but it can be heard throughout the building, including over an attached garage. He thinks that roofer may have installed the drip edge to tight to the facia, restricting the air flow in, creating a possible venturi effect. Maybe, maybe not. Anyone ever have a house go into harmonic oscillation before?
Thanks,
Red Hen
Replies
Hmmmm, the house must not comply with Fung Sheui and has bad karma.
Ok, just kidding. No frigging idea, bizarre.
I jokingly asked if there were any indian burial grounds nearby and he looked at me like I was serious. The only reason I'm going to take this job is because I need an excuse to buy a new four inch hole saw (and a new half-inch drill motor to go with it).
The only reason I'm going to take this job is because I need an excuse to buy a new four inch hole saw (and a new half-inch drill motor to go with it).
Hmmmm, if you plan to use it at his house as it seems you are going to do, then let him know that when you're there the humming noise is you happily using your new power tools and accessories so that he won't think it's more of the same. <grin>If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
Before I finished reading I thought the humm maybe from his well (you can here mine as a slight humm at the corner of the house at my bathrooms when it kicks on) but a roof problem causing that doesnt sound right, even if the vents are covered up it isnt a totally airtight attic.
I am surprised that no one has given you the answer yet.
The house hums, because it does not know the words !
Actually early morining makes sense. That is when the sun is hitting the roof and air is starting to move.
I am wondering about what kind of baffeling there might be in the ridge vent.
I wonder if there was some mistake in the installtion so that the air is only going through one small piece and that there might be a loose baffel.
Or what if the hole ridge had been pappered over and there is one small place where there is a lap joint that acts as a reed when air is pushed past it.
What key is it in? If it's in the key of E flat, I know some killer harmonies.
I had a college professor tell me with all seriousness that the Earth is tuned in the key of F. I was so startled that I couldn't even think of a comeback, even though it cries out for one.
There was a new residential apt. bldg. built in NYC in the 90's (like 50+ stories), with decorative louvers on the roof top concealing the mech. equipment. At certain times the wind going through the louvers created a sound described as similar to blowing on the top of a coke bottle (albeit a very tall one) and could be heard clear across town. Needless to say the louvers had to be altered.
Is there a turbine vent? Is there a static vent?
worse comes to worse call in the FD, they will chop a hole in the roof right quick..I bet it stops.
Spheramid Enterprises Architectural Woodworks
Maybe the house has been infested with toadfish. Had a lot of trouble with humming noises in Sausalito that has been attributed to them:
http://www.sfgate.com/cgi-bin/article.cgi?f=/chronicle/archive/2003/12/18/MNG0K3PPQ71.DTL&type=science
That's it..they ate the crickets too. I hate when that happens. Spheramid Enterprises Architectural Woodworks
I think that soffit vent makes a really big whistle, you couldn't duplicate it if you tried to though, .... on the harmonic vibration, we had to relocate our furnace exhaust because it set the neighbours aluminum soffit vibrating ...
In my house when the wind blew from a certain direction hard enough I'd get a humming from a down spout off the gutter. I finally wedged some Styrofoam between it and the siding to stop it. But at sunrise, sounds like the air is heating up and moving through the vents. I guess I'd make sure there are no restriction on the vents and that everything is tight. I wonder if you went up on the roof at sunrise you'd hear it if you were near the ridge.
There was a statue of a god in ancient times that freaked everyone out because it was designed to whistl or hum when the sun rose--for the same reasons you are suspecting here, that the warmed air rushed out.
Thanks all for your thoughts. Assuming the sound is being caused by air movement through the vent system (which I am leaning towards) why do you suppose it isn't heard during the hottest part of the day when you'd figure the most amount of air was moving through the roof? I'll be checking all the things that were suggested and will let you know what I learn.
Thanks,
Red Hen
Just a guess, but I'm thinking it occurs when there is the greatest differential between outside air and inside. Sun heats up the roof and heats tha air in the "attic" in the morning while the outside air is still cool? How early in the morning does this happen? Maybe I'm wrong in that the sun wouldn't have had enough time to heat the roof.
Sometimes vibrations need the air movement to be of a specific speed. Perhaps at that time the speed is optimal.
Don't rule out that the recent work has made it possible to hear something that has always gone unheard, but was always there.
If you haven't drawn blood today, you haven't done anything.
Hmmm. Interesting.
Not saying this is the case but I once saw a attic fan that got whacked where the housing was interfering with the fan. The thermostat would kick on when the temperature in the attic rose past the set point. The fan would grind along the housing and stop. The motor humming loudly. Of course the humming would stop when the attic temperature dropped and the thermostatic switch stopped calling.
Bad thing about this was that the motor was getting quite hot. It had a thermal overload that cut the power when it got dangerously hot but these units can fail. Something that could have caused a fire.
Look around for power vents. Perhaps one the roofers removed the shroud from, so you may only be able to find it from inside the attic space, but left the motor and power supply connected. it is a long shot but I have seen far stranger things.
How difficult would it be to get up to the ridge with some tarps? If it's not too much work, you might want to get there in the AM when it's humming, and see if throwing tarps over the ridge vents stops or alters the sound.
Another thing to try would be a microphone on the end of a long paint roller pole. Run the cable to a recorder with monitoring earphones, and see if you can find the source.
Go ahead and buy the hole saw, but make sure that the venting setup is the real culprit before you start making holes. ;-)
-- J.S.
"He thinks that roofer may have installed the drip edge to tight to the facia, restricting the air flow in, creating a possible venturi effect."
If it's a hummer, it's actually called the "Lewinski" effect. ;)
The Breaktimer formerly known as "Steve-O"
"Preach the Gospel at all times; if necessary, use words." - St. Francis of Assisi