attic cracking sounds

[Randy West]

I received an email from someone who had 'cracking' sounds in her attic (I have not inspected this house). It is a new home, and her contractor stated it is from the attic lumber drying and could go on for 5 years. News to me! I asked her the following questions (her responses follow each question).

Anyone run into something like this before? Seems like something to do with hvac ductwork. But "automatic weapons" and noise when opening exterior doors is weird. We are a dry climate, 30's at night, 60's at day.


Yes, the sounds are at their worst whenever the heat is running; however, do occur all the time with or without the heat but much less in the afternoon and evening. Interestingly, but maybe not significant, is the loudest sound occurs near a vent in the livingroom which is in line with two other vents in an adjoining room which are closed. The sound also occurs with multiple snaps/pops when the heat is on and one of the exterior doors opens.


How loud are the sounds, eg like twigs snapping, would you hear them over a television on normal listening volume?


In some locations, the sound is a very slight popping sound but in other locations, it sounds like wood splitting. All sounds can be heard over the TV. We have 10’ ceilings so the sound seems to reverberate. The sounds can occur in multiple locations in rapid succession like an automatic weapon across the house.


The sounds are more noticeable when the furnace is operating- but they are also noticeable when the furnace is not operating? And just as loud but less frequent, or not quite as loud?


Yes, they occur when the heat is not on, but not at the same frequency but the loudness of the sounds is the same.


Have you noticed any correlation with time of day (morning or evening) or outside temperature?


Yes, it is worse in the morning which is why we blame the heater although it could be the sun heating the attic. The HVAC dude told us that the attic is very cold right now, and he said we have no heat loss from the vents. He said it could be framing but he wanted to discuss his findings with his boss so he may have found something else he doesn’t want to reveal to us with the installation of the vent system, I don’t know. He said someone would get back to us.​

[Ian Page]

Could be attributable to lumber drying but sounds more like rigid ductwork flexing through heat/cold cycles. Possibly combination of both. Nothing much you can do about the lumber but the ducting could be braced or stiffened to some extent. I'd have an HVAC guy look at the possibility.

[Vern Heiler]

I had a home where the PVC piping rubbed the framing and made similar sounds as discribed.

[Jerry Peck]

Almost sounds like metal ductwork (which is rare in residential construction) expanding and contracting, and no provisions were allowed for that expansion and contraction when the ductwork straps and supports were installed.I would think that ductboard would not make those noises because it is not rigid like metal ductwork.And flex duct shouldn't have any of those issues.

[JeffGHooper]

I had that every year when I was in Minnesota. The heat on the bottom chord of the truss and cold on the top chord sometimes makes a cracking sound and loud cracks. But I am betting it is a vent stack or ducts. Just throwing in another option.

[Ian Page]

As Jerry said, rigid ducting would be unusual in residential construction. The plenum would be rigid sheet metal and could flex but any sounds isolated to its specific location and not transferred throughout the attic. If the duct is all rigid, highly unlikely and unusual, then that's a different story. It's all guesswork until someone is actually in the attic when the noises occur.

[Lon Henderson]

That much popping seems excessive. If it's a tract home, she should ask her neighbors. Occasional popping is common when cold metal ducts heat up, but not continuous.

[Trent Tarter]

Is the HVAC system located in attic, if so it be an electronic air cleaner popping.

[John Kogel]

Rigid metal ductwork is standard here, so don't discount the obvious.
We are waiting now to hear what the HVAC guy comes up with.

Wood drying out for 5 years in Arizona? That's a laugh.

[Randy West]

Rigid metal ductwork is standard here, so don't discount the obvious.
We are waiting now to hear what the HVAC guy comes up with.

Wood drying out for 5 years in Arizona? That's a laugh.


Thanks all. She gave me more info. Popping starts a lot when an ext door is opened. And last summer the master bedroom was 8 degrees warmer than the rest of the home, so the hvac contractor completely closed half the supply vents (this was a few months ago). The hvac contractor was there yesterday, in the attic when the noise was happening, but all he said was he had to confer with his boss/owner.

After hearing the latest from her, I sent her a loonngg email. I told her she has a real problem with the hvac. She should not have to close supply vents, no room should be 8 degrees warmer. I told her to check for airflow at all supply vents (good), and for undercut doors (needed- they blow closed). I told her to mention Manual J and D to the general and/or hvac. Her one year is up next month. I may go out there, since I think this is a contractor screw-up. And she says if she waits until 8:00 to turn on the furnace she can guarantee some attic cracking for me.

[Lon Henderson]

And she says if she waits until 8:00 to turn on the furnace she can guarantee some attic cracking for me.
And who doesn't like some attic crack?

Let us know what the conclusion and/or fix is.

[Jerry Peck]

... undercut doors (needed- they blow closed).


Doesn't need undercut doors, needs jumper vents or transfer vents installed instead ... that is, unless you don't mind the doors being cut 6" high above the floor ... :) ... but that would look a little bit weird to most people, and all the sounds in the bedroom would be open to outside the bedroom ... and vice versa.