Drafty windows are one of the most common complaints in Daly City, and there is a reason for it: this is one of the windiest, foggiest corners of the Bay Area, and a window that would feel fine in a sheltered inland town gets tested here every afternoon. When the wind comes off the ocean and up over the ridge, any gap around a window turns into a felt draft, a whistle, or a cold spot on the couch. The good news is that a draft is a symptom with a short list of causes, and not all of them mean new windows.
This is a guide to finding where the air is actually coming in, deciding whether a seal-up or a replacement is the right fix, and knowing what to look for on a new window's label if you do replace. Most of it you can check yourself in an afternoon.
The Quick Version
A draft is air leaking through gaps around or within the window, not heat passing through the glass, so the fix is different from an efficiency upgrade.
Worn weatherstripping, failed caulk at the trim, and gaps at a sliding or hung window's moving joint are the usual sources.
If the window is structurally sound, sealing and new weatherstripping often fix the draft for very little money.
If the frame is failed, warped or a single-pane aluminum unit with no thermal break, replacement is usually the honest answer.
On a new window, the NFRC Air Leakage rating tells you how tight it is, capped at 0.3 for a qualifying product, with lower being tighter.
Why Windows Get Drafty
A draft is moving air, not heat, and that distinction decides the fix. Heat loss happens slowly through the glass and frame, while a draft is air physically pushing through a gap you could often find with a wet finger. Most drafts come from three places: weatherstripping that has hardened or fallen off, caulk that has cracked where the frame meets the wall, and the moving joints of a window that slides or tilts.
Age makes all three worse. The rubber and foam seals in a window are wear parts that stiffen and shrink over years of sun and salt air, and older single-pane windows were never tightly sealed to begin with. A window can look intact and still leak badly once its seals have given up.
How to Find Where the Draft Is Coming From
You can locate a draft in a few minutes without tools. On a windy day, run the back of your hand slowly around the edge of the sash and the frame, and you will feel the cold ribbon where air enters. For a clearer picture, hold a lit incense stick or a thin candle flame near the edges and watch where the smoke bends. Daylight visible around a closed sash, a sash that rattles, or condensation only along one edge all point to the same thing.
Check the obvious suspects in order: the weatherstripping where the sash meets the frame, the caulk line where the window trim meets the siding or stucco, the meeting rail on a double-hung, and the track on a slider. A draft that eases when you push the sash tighter is a seal problem, while a draft that persists no matter how hard you close it is usually the frame or the wall around it.
It Is Not Always the Glass
The glass is rarely the source of a draft. A sealed insulated glass unit can fail and fog up, but that is a different problem from air leakage, and a fogged unit does not necessarily leak air. Chasing a draft by replacing only the glass usually leaves the draft exactly where it was.
The real leak is almost always at a joint: the perimeter where the frame meets the rough opening, the weatherstripping around an operable sash, or the seam where two sashes meet. On older Daly City homes the gap between the window frame and the stucco is a frequent culprit, because decades of wind and settling open up cracks the original caulk no longer bridges.
Weatherstrip and Seal, or Replace?
If the window is otherwise sound, seal it before you replace it. New weatherstripping on the sash and fresh, flexible caulk around the exterior trim will stop most drafts on a window whose frame is straight, whose hardware works and whose glass is intact, and it costs a fraction of a replacement. This is the right first move on a newer window that has simply worn its seals.
Replacement earns its place when the unit itself has failed: a warped or rotted frame, a single-pane aluminum window with no thermal break, sashes that no longer close square, or hardware that cannot pull the sash tight. The U.S. Department of Energy attributes 25 to 30 percent of a home's heating and cooling energy to heat moving through windows, so on an old, leaky, single-pane opening a replacement fixes the draft and the efficiency together in a way a bead of caulk cannot.
The Air Leakage Rating on a New Window
If you do replace, the number that measures draft resistance is Air Leakage, and it is printed on every certified window's NFRC label, capped at 0.3 for a qualifying product, where a lower number means less air passes through. It sits alongside the U-factor and solar heat gain coefficient, and for a wind-exposed house it is the rating worth reading first.
Operation type affects it too. A fixed picture window has no moving joint to leak, and hinged casement windows, which crank shut against a gasket, generally seal tighter than sliders and single-hung windows that close along a sliding track. On the windiest walls of a Daly City house, that difference is worth weighing when you choose the style.
Why Daly City Homes Feel Drafts More
Daly City earns its drafts. The city sits on ridges and hilltops that catch the wind coming straight off the Pacific, and the same marine air that brings the fog brings a steady pressure against west- and north-facing walls that inland homes never feel. A gap that would barely register elsewhere becomes a constant draft when the wind leans on it every afternoon.
The housing stock adds to it. Many of the city's post-war tract homes were built with single-pane aluminum windows that were never tight and have had decades to loosen, and the salt in the coastal air is hard on seals and hardware. If your windows are original to a mid-century Daly City home, worn seals plus relentless wind is the usual recipe behind the draft.
Before you spend anything, do the incense test on a windy afternoon and mark every spot where the smoke bends. Half the time the worst leak is a cracked caulk line you can fix for a few dollars, and knowing that keeps a genuine window problem from being masked by a cosmetic one, or the reverse.
How to Work Through It Without Overspending
Work from cheapest to most involved. Start by finding the leaks and sealing what you can, because a caulk gun and a roll of weatherstripping solve a surprising share of drafts on sound windows. If the draft survives that, or if the window is an old single-pane aluminum unit that fights you every time you close it, that is the point where replacement stops being optional and starts saving you money on both comfort and heating. Judge each opening on its own, because a house rarely needs everything done at once.
When a draft turns out to be the window itself rather than its seals, our energy-efficient window installation and full-frame window replacement work is built for exactly the wind-exposed, older openings common here. Daly City Window Replacement can tell you honestly which openings need replacing and which just need sealing.
Sources
Feeling a draft you cannot pin down? Describe where and when, and we will tell you whether it is a seal or the window.
(650) 278-4593 — ask an estimator