Why Windows Get So Much Attention During Inspections
Windows do more than let light in. They're complex assemblies that have to manage thermal transfer, water intrusion, air sealing, structural loads, and daily mechanical operation. That's a lot to ask of a hole in your wall covered by glass and some hardware.
The average home has 10-15 windows. In my experience, homes over 20 years old almost always have at least one window issue worth noting. That's not a criticism of older homes. It's just reality. Moving parts wear out. Seals fail. Caulking dries and cracks.
According to the Department of Energy, heat gain and loss through windows accounts for 25-30% of residential heating and cooling energy use. That statistic alone explains why window condition matters so much during a sale.
The Big Four Window Components
Every window inspection focuses on four main areas: the glass assembly (including seals), the frame and sash, the hardware and operation, and the interface with the wall. I check all four on every window, every time. Miss one and you might miss the real problem.
Inspecting the Glass Assembly and Seals
Modern double-pane and triple-pane windows have an insulated glass unit, or IGU. Two or three panes of glass with a gas-filled space between them. That space is sealed at the edges. When those seals fail, the gas escapes and moisture gets in. That's how you get foggy windows.
I check every IGU for condensation, fogging, or a hazy appearance between the panes. Failed seals are incredibly common. In homes with windows 15-20 years old, I find at least one failed seal about 40% of the time.
How to Spot Failed Seals
The telltale sign is fogging or condensation between the panes that doesn't wipe away. On sunny days, the fog might temporarily disappear as the window heats up, then return when it cools. That's thermal pumping, and it confirms seal failure.
I also look for mineral deposits. After months or years of moisture cycling in and out, minerals accumulate on the interior glass surfaces. These show up as white or hazy streaks that can't be cleaned because they're inside the sealed unit.
What Failed Seals Actually Mean
Here's the thing most buyers worry about unnecessarily: failed window seals are primarily an aesthetic and efficiency issue, not a structural problem. The window still works. It still keeps rain out. You just lose some insulating value and get a foggy view.
Replacement costs run $150-400 per window for just the glass unit. Full window replacement runs $300-800 per window depending on size and type. I always recommend getting quotes because prices vary wildly by region.
Cracks, Chips, and Glass Damage
Any crack in glass weakens it. Small chips at the edge might not spread, but stress cracks usually do. I note all glass damage, but I'm particularly concerned about cracks that extend more than a few inches. Temperature changes make them grow.
Impact damage is obvious. Stress cracks are sneaky. Look for cracks that start at the edge and run at an angle. These often develop from frame settling or improper installation. They'll keep growing until the window eventually breaks.
Frame and Sash Evaluation
The frame holds everything together. The sash is the movable part that holds the glass. Both take abuse over time from sun exposure, moisture, temperature swings, and mechanical stress from opening and closing.
Wood Frame Issues
Wood windows look beautiful but require maintenance. The bottom corners of wood sashes are ground zero for rot. Water pools there. Paint fails there first. And once rot starts, it spreads fast.
I use a probe tool on every wood window sill and bottom sash rail. Soft wood means moisture damage. Paint bubbling on the exterior often signals rot underneath. The worst cases I've seen had completely deteriorated sashes held together mostly by paint and hope.
My colleague Dave Walsh found a situation last year where the homeowner had been repainting wood windows for a decade without realizing the lower rails were 50% rotted. The paint was literally the only thing holding them together.
Vinyl Frame Problems
Vinyl doesn't rot, but it has its own issues. Heat warping is the most common. South-facing and west-facing vinyl windows take tremendous sun exposure. Over time, darker-colored vinyl can warp enough to affect operation or seal integrity.
I also look for vinyl that's become brittle. Old vinyl, particularly from the 1990s, sometimes cracks at the corners. Once the frame is compromised, water gets into places it shouldn't.
Aluminum Frame Concerns
Aluminum was popular in the 1960s through 1980s. These windows are tough but terrible insulators. The main issues I find are corrosion (especially near coastal areas), failed weather stripping, and worn hardware that makes operation difficult.
The biggest concern with aluminum is the thermal bridging. Metal conducts heat right through the frame, bypassing whatever insulation the glass provides. Many older aluminum windows also have single-pane glass, doubling the efficiency problem.
Hardware and Operation Testing
Every window needs to open. That's an egress requirement for bedrooms and just good sense everywhere else. I test the operation of every operable window in the house. Not just 'does it open,' but 'how hard is it' and 'does it stay where you put it.'
You'd be surprised how many windows I find painted shut. Or nailed shut. Or so stuck from years of neglect that opening them requires a pry bar. None of that is acceptable.
Double-Hung Window Issues
Double-hung windows have two sashes that move up and down. The balance mechanisms (springs, spiral balances, or weight-and-pulley systems) wear out over time. When they do, the sash won't stay up on its own.
Broken balances are the most common hardware issue I find. The repair usually costs $20-50 per sash in parts, more if you pay someone. Old houses with rope-and-weight balances sometimes have broken ropes or missing weights, but those are actually easier to fix than modern spiral balances.
Casement Window Problems
Casement windows crank open and closed. The operator mechanism wears out, especially in humid environments. I check that the crank operates smoothly and that the window closes tightly and locks.
Stripped gears are common. If the crank spins without the window moving, the gears are done. Replacement operators run $30-100 depending on the brand. Some older casement operators are hard to find replacements for.
Slider Window Maintenance
Horizontal sliders ride on tracks that collect dirt, debris, and dead bugs. Dirty tracks make sliding difficult. I check track condition and verify the window moves freely and locks properly.
The rollers or guides on slider sashes wear out. When they do, the window binds, drags, or derails completely. This is usually a $30-50 fix, but finding matching parts for older windows can be challenging.
Water Management and Flashing
This is where window inspections get serious. A foggy seal costs a few hundred to fix. A flashing failure that's been dumping water into your wall cavity for years can cost thousands. I've seen $15,000 repair bills from failed window flashing on houses that looked fine from the inside.
Exterior Evaluation
Outside, I look at how water moves around the window. The sill should slope away from the glass. Caulking should be intact where the window meets the siding. Flashing (the metal or membrane designed to redirect water) should be visible and properly lapped.
Missing or improper flashing is disturbingly common. Especially on windows installed during renovations or additions. The original builder might have done everything right, then someone added a window without understanding how water moves on a wall.
Interior Warning Signs
Inside, I look for evidence of water intrusion. Staining on the drywall or paint below the window is an immediate red flag. So is bubbling paint, soft spots in the wall, or musty odors near windows.
I use a moisture meter on the wall below suspect windows. Elevated moisture readings mean water is getting in somewhere. Sometimes the source is obvious. Sometimes it requires removing trim or even cutting into the wall to find.
The 'Looks Fine' Problem
Water damage can be completely hidden. The window looks fine from inside. No staining visible. But behind the drywall, water has been wicking down into the wall, rotting the studs and growing mold. I've pulled back trim expecting to find dry wood and found black mold colonies instead.
This is why I never just do visual inspection on windows with any warning signs. If the exterior flashing looks wrong, or if there's any hint of water staining, I want to investigate further. Sometimes that means recommending a more invasive inspection.
Energy Efficiency Assessment
Window energy performance matters for comfort and utility bills. Old single-pane windows in a climate with cold winters can cost the homeowner serious money every year. The Department of Energy estimates that upgrading from single-pane to double-pane windows can reduce heating and cooling bills by 10-25% in most climates.
Identifying Window Types
Single pane is easy to identify. Look at the glass edge on or hold something up to the glass. One reflection means single pane. Multiple reflections mean multi-pane IGU.
I document window types in my reports because it affects the home's energy profile. A house full of 1970s single-pane aluminum windows is going to perform very differently than one with modern low-E double-pane windows.
Low-E and Coatings
Low-E coatings reflect infrared light while letting visible light through. They're invisible but make a real difference in energy performance. Some windows have a visible tint from low-E coatings, but many look clear.
I can't always tell if windows have low-E coatings just by looking. Sometimes the window label is still visible and shows the specifications. Otherwise, buyers should assume windows over 20 years old probably don't have advanced coatings.
Draft Testing
I check for drafts around window perimeters. Obvious gaps where daylight shows through are a problem. Less obvious drafts can be felt on windy days or detected with a smoke pencil.
Air leakage around windows often points to failed weather stripping, which is cheap to replace. But it can also indicate frame settling or improper installation that's harder to fix. I note both the symptom and the likely cause.
Common Window Issues by Age
Window problems are predictable based on age. After thousands of inspections, I can walk into a house and have a pretty good guess what I'm going to find based on when it was built.
1960s-1970s Windows
Expect aluminum frames, single-pane glass, failing glazing putty, and hardware that barely works anymore. These windows are usually candidates for full replacement, though they can be refurbished if they're in a historic home where preservation matters.
1980s-1990s Windows
The early vinyl and wood-clad era. Vinyl from this period can be brittle. Wood-clad windows often have failed cladding or rot beneath the aluminum covering. Double-pane IGUs from this era are past their expected lifespan and many have failed seals.
2000s-2010s Windows
Better manufacturing quality, but some seal failures showing up now on windows from the early 2000s. Hardware problems are more common than glass problems in this age range. Most of these windows have another 10-15 years of useful life with minor maintenance.
2010s-Present Windows
Usually in good shape. Main issues are installation-related (improper flashing, inadequate foam sealing) rather than product failures. These should be operating well with no moisture intrusion. If they're not, installation is the likely culprit.
What Buyers Should Prioritize
Not all window issues are equal. Some are cosmetic. Some are expensive but not urgent. And some need immediate attention.
Deal-Breakers and Red Flags
Water intrusion evidence demands attention. If I find water staining, elevated moisture readings, or visible rot around windows, that goes at the top of the repair list. Hidden water damage gets worse, not better.
Missing or improperly installed flashing also qualifies as a serious issue. Every heavy rain could be causing more damage. I've seen walls that looked fine from inside but were full of mold because the window flashing was never installed properly.
Negotiate-Worthy Items
Failed IGU seals on multiple windows add up. If a house has eight windows with failed seals, that's $1,200-3,200 to repair or more to replace. Worth negotiating on price or requesting repairs.
Inoperable bedroom windows are safety issues. They're supposed to be usable as emergency exits. Painted-shut or mechanically failed windows in bedrooms should be fixed before closing.
Maintenance Items
One or two failed seals on a 20-year-old house is normal wear and tear. Sticky hardware that needs lubrication is minor. Weather stripping that needs replacement is a Saturday afternoon project. These are things to be aware of but not reasons to panic.
The Inspection Process
Every inspector has their own approach. Here's mine, refined over 16 years.
I start outside, checking each window's installation, flashing visible, caulking, and overall condition. I note any visible water staining on siding below windows. Then I move inside and check each window's operation, glass condition, and any evidence of moisture problems.
For each window, I'm asking: does it open, close, and lock properly? Is the glass intact and the seal good? Is there any sign of water intrusion? Does the frame show damage or deterioration?
Problem windows get extra scrutiny. I'll use a moisture meter on the wall. I might pull back accessible trim to look at the rough opening. On really concerning cases, I recommend further investigation by someone who can do more invasive testing.
What Gets Documented
My reports include photos of any window issues found. I try to photograph both the problem and its location so buyers understand exactly what they're looking at. Failed seals, damaged frames, water staining, inoperable hardware. It all gets documented.
I also note the general window type and age when known. That context helps buyers understand whether they're looking at normal wear for 25-year-old windows or premature failure on 10-year-old ones.
Getting Quotes and Making Decisions
When the inspection finds window issues, the next step is getting repair or replacement quotes. This is where many buyers get confused by wildly varying numbers.
Repair vs Replace
For failed seals, glass-only replacement is usually possible and costs less than full window replacement. But if the frames are damaged or the windows are ancient, replacement makes more sense.
My general rule: if the windows are less than 20 years old and the frames are solid, repair. If they're older or showing frame problems, replace. But always get quotes for both options.
Getting Good Quotes
Get at least three quotes. Ask specifically what's included. Some quotes cover just the window, others include trim work, paint touch-up, and haul-away. Make sure you're comparing the same scope of work.
Watch out for replacement window companies that push full-house replacement when only a few windows need attention. I've seen buyers convinced they need $30,000 in new windows when $1,500 in repairs would have solved the actual problems.
Final Thoughts on Window Inspections
Windows age. They wear out. Finding issues during an inspection doesn't mean the house is bad or the seller is hiding something. It means you're buying a home that's been lived in.
The key is understanding which issues matter. Water intrusion is serious. Everything else is mostly just money. Some of that money is modest, like new weather stripping. Some is significant, like full window replacement. But almost nothing I find with windows is unfixable.
What I want buyers to take from their inspection is a clear picture of window condition and realistic expectations about costs. That foggy bathroom window isn't an emergency. That water stain under the living room window might be. Know the difference and you can make smart decisions about what to negotiate, what to fix, and what to simply live with.