Why Windows Rattle and Whistle When the Santa Ana Wind Blows
The first hard Santa Ana wind of the autumn usually arrives with a sound. A low hum starts at one window, a rattle joins it from the next room, and by midnight the whole house seems to be talking. In Riverside the wind comes down through the passes and across the valley, and it finds every gap in a window that has been quietly wearing out. The noise is useful information, because each kind of sound points to a different fault.
Why do windows rattle when the Santa Ana wind blows?
A window rattles when something in it is free to move. Wind pushes on the glass and the sash with steady pressure and sudden gusts, and any part that is loose will shake against its neighbour. In an older double hung window the usual cause is a worn balance system. The sash no longer sits snug against the frame, so it taps against the stops each time a gust arrives. In a slider the rollers wear flat and the sash shifts sideways in its track.
The frame itself can be the culprit. Wood windows in houses around the Mission Inn and the older streets near downtown have been through a century of seasons. Wood swells in damp winters and shrinks in the dry heat, and each cycle leaves the joints a little looser. Aluminum frames from the middle of the last century have thin walls that flex in a gust, and the glass inside hums against the glazing tape that has long since hardened.
What does a whistle mean, compared with a rattle?
A rattle is a loose part. A whistle is air moving through a small opening at speed, and it tells you where the gap is. The pitch rises as the gap gets narrower and the wind gets stronger. Common whistle points are the meeting rail of a double hung window, where the two sashes should lock together, the corner of a casement where the weatherstripping has flattened, and the bottom edge of a slider where the pile strip has worn away.
A quick test is to hold a lit stick of incense near the frame on a windy day. The smoke bends toward the gap and shows the exact line the air follows. Many people are surprised to find that the leak is at the lock or the corner, and not along the glass. That finding matters when deciding whether new weatherstripping will solve the problem or the whole unit has to be replaced.
How much noise is the glass itself responsible for?
Single pane glass transmits sound almost directly. A freeway, a leaf blower or a neighbour's dog comes through with very little loss. Two panes with a sealed gap between them reduce that noticeably, and the width of the gap and the thickness of each pane both matter. Two panes of different thickness work better than two identical ones, because each thickness resonates at a different pitch and the pair does not amplify one tone.
Laminated glass has a thin plastic layer bonded between two sheets and damps vibration well. It is used on rooms facing a busy road, such as a bedroom on a street that runs toward the University of California Riverside, where traffic noise carries into the evening. For most rooms in the valley a standard double pane with a good frame seal is enough, and laminated glass is saved for the one or two walls that need it.
Which parts of a window let dust in during wind?
Santa Ana days carry fine dust from the dry washes and from the slopes of the Box Springs Mountains. The dust enters the same way the sound does, through gaps. The most common entry points are:
- the meeting rail of a double hung window, where a worn seal leaves a thin slot along its length
- the track of a slider, where dust piles up on the sill after each windy week
- the joint between the frame and the stucco, where old caulk has dried and pulled away
- weep holes that were plugged with paint or sealant, which trap water and dust together
- the head of the window, where a missing flashing detail lets air in behind the trim
A film of dust on the inside sill after a windy night is a reliable sign that the exterior joint has failed. It is cheaper to find that out with a flashlight and a strip of paper than after the stucco stains show up below the window.
What stops the wind from getting in?
Three layers do the work, and a weakness in any one of them lets wind through. The first is the weatherstripping on the sash, a compression bulb or a fin strip that closes the gap when the window is locked. The second is the seal between the frame and the wall, which is a sealant joint with a backer rod behind it on a properly installed unit. The third is the flashing inside the wall, which keeps wind driven air from slipping behind the nailing fin.
When a window is replaced, the choice of operating style affects how well it holds up against the wind. Casement and awning windows close by pressing the sash against a seal all the way around, so wind pressure pushes them tighter. A slider and a double hung window close by sliding past a seal, so wind can bypass it. A picture window has no moving sash at all, which makes it the quietest and tightest option where the view allows.
Frame choice and wind
A vinyl window with foam filled chambers is stiff and quiet, and it resists humming. A fiberglass window is stiffer still and stays stable through the heat of an Inland Empire afternoon. Thin, hollow vinyl can flex a little in a hard gust, and a lightweight aluminum window can pick up the vibration and pass it to the glass. The frame should feel solid in the hand, and the corners should be welded or fused, not held together with screws alone.
Does the installation matter for noise?
It matters a great deal. A good window installed badly is louder and leakier than an average window installed well. The gap between the frame and the rough opening is usually filled with low expansion foam or packed with insulation, and the amount of fill makes a difference to both sound and air. Too little leaves a hollow that rings. Too much foam can bow the frame inward and bind the sash, which causes new gaps along the closing edge.
The shims that hold the frame in place need to sit at the right points, behind the hinge or lock locations, so the frame cannot move when the sash is slammed or the wind leans on it. Fasteners go through the nailing fin or the frame at the intervals the manufacturer specifies. A crew that skips those details leaves a window that passes a quick look and starts to talk on the first windy night.
Can a loose window be fixed without replacing it?
Often it can. A rattling double hung sash may only need a new set of balances and a fresh pair of weatherstripping strips. A slider that wobbles may need new rollers and a cleaned track. Cracked or dried out glazing tape on an old aluminum frame can be replaced, and loose lock keepers can be moved a quarter inch to pull the sash tighter against the seal.
Repairs stop making sense when the frame is the problem. A wood frame with soft spots at the sill, an aluminum frame that has bent out of square, or a unit whose sealed glass has fogged between the panes is at the end of its life. At that point the repair buys a year or two at most, and the same labour goes into a new unit that will last.
A short checklist for a windy night
- Walk the house during a gust and note which windows make noise and what kind.
- Test each one with a strip of paper closed in the sash. It should resist being pulled out.
- Look at the stucco joint outside for gaps, cracks or dried caulk.
- Check the weep holes and tracks for blockage and dust.
- Decide per window whether a repair covers it or the unit has reached the end.
The wind will not go away, but a window that is sealed, shimmed and flashed properly turns a loud night into a quiet one.