Install Windows and Exterior Doors
Windows and doors are the eyes of your addition—get them wrong, and the whole project looks off. Matching your existing window style, grille pattern, and proportions is critical for seamless integration.
Quick Summary
Time needed
1-3 days
Cost per window
$400-$1,200
Professional help
Recommended
Why This Step Matters
Nothing makes an addition look "tacked on" faster than mismatched windows. Different grille patterns, proportions, or frame colors create visual discord that screams "addition!" to anyone looking at your home. The good news: most window styles are still available, and custom matching is more affordable than you might think.
Lead Time Alert
Custom windows can take 4-8 weeks to manufacture. Order windows at the start of framing—not when you're ready to install them. Standard sizes from stock may be available in days.
What You Need to Match
To make your addition's windows look like they belong, match these key elements:
Grille Pattern
Colonial (6-over-6), prairie, craftsman, or no grilles at all. This is the most noticeable element. Count the panes on your existing windows and match exactly.
Frame Color
White, almond, bronze, black, or custom colors. Take a photo of your existing windows in natural light and bring it to the showroom. Consider both interior and exterior frame colors.
Operation Style
Double-hung, casement, sliding, or fixed. Your addition can use different operation styles if needed (e.g., casement in a bathroom), but visible proportions should match.
Proportions
The width-to-height ratio matters. If your existing windows are tall and narrow, don't install short and wide windows in the addition. Measure your existing windows and maintain similar proportions.
Trim Style
Window trim (casing) around the exterior matters as much as the window itself. Match the width and profile of your existing window trim exactly.
Window Cost Guide
Window prices vary widely based on size, quality, and customization:
| Window Type | Price Range | Best For |
|---|---|---|
| Builder-grade vinyl | $200-$400 | Budget projects, rentals |
| Mid-range vinyl | $400-$700 | Most home additions |
| Premium vinyl | $700-$1,000 | Energy efficiency focus |
| Fiberglass | $800-$1,200 | Durability, aesthetics |
| Wood-clad | $1,000-$1,500 | Historic homes, high-end |
| Custom/specialty | $1,200-$2,500+ | Unusual shapes, sizes |
Prices are per window and do not include installation ($100-$300 per window).
Installation Process
Verify Rough Opening Sizes
Before windows arrive, verify that your framed rough openings match the window specifications. The rough opening should be 1/2 inch larger than the window on each side and top.
Common issue: Rough openings that are too small require re-framing. Too large is easier to fix with shims. Double-check measurements before windows are ordered.
Install Waterproofing
Proper flashing and weatherproofing prevents water intrusion—the leading cause of window failure and wall damage.
- Apply sill pan or flexible flashing at bottom of opening
- Install flexible flashing tape on sides (over house wrap)
- Top flashing installed after window is set
Set and Level the Window
Position the window in the opening, checking for level, plumb, and square. Shim as needed until the window operates smoothly and is properly aligned.
Test operation: Open and close the window multiple times before final fastening. A window that sticks or won't latch properly isn't level or square—keep adjusting.
Secure and Seal
Fasten the window through the nailing fin or frame (following manufacturer instructions), then seal around the entire perimeter.
- Use screws through nailing fin, not just nails
- Apply low-expansion foam in gaps (don't overfill)
- Caulk exterior perimeter with quality sealant
Install Exterior Trim
Apply exterior trim (casing) to match your existing windows. This is where matching details really matter.
Matching tip: Bring a piece of your existing window trim to the lumber yard. Many historic profiles are still available, or can be custom milled for a reasonable cost.
Exterior Door Considerations
If your addition includes an exterior door, matching requires similar attention:
Entry Doors
- - Match panel style (6-panel, craftsman, etc.)
- - Match glass pattern if present
- - Coordinate hardware finish house-wide
- - Consider same manufacturer for consistency
Cost: $800-$3,000 installed
French/Patio Doors
- - Match grille pattern to windows
- - Consider sight lines when open
- - Sliding vs. hinged based on space
- - Frame color must match windows
Cost: $1,500-$5,000 installed
Common Window Selection Mistakes
Choosing cheaper windows to save money
Mismatched windows scream "cheap addition" and hurt resale value more than the savings. Match quality, not just appearance.
Ignoring grille pattern details
The difference between grilles-between-glass and simulated divided lites is noticeable. Match not just the pattern, but how the grilles are constructed.
Ordering standard sizes that don't match
Standard sizes are cheaper, but if your existing windows are custom dimensions, the addition windows should match. Pay for custom sizing.
Forgetting about energy codes
Your addition may require windows that meet current energy codes, even if your existing windows don't. Factor this into your matching strategy.
Frequently Asked Questions
My existing windows are 20+ years old. Should I replace them all?
Consider it. New energy-efficient windows will save on heating/cooling costs, and having all new matching windows eliminates the integration challenge entirely. Get quotes for both matching and full replacement.
Can I install windows myself?
Technically yes, but improper installation voids warranties and causes leaks. Most window manufacturers require professional installation for warranty coverage. If budget is tight, handle interior trim yourself but hire out the window setting.
How do I find the manufacturer of my existing windows?
Check between the panes of glass (etched logo), on the frame corners, or on the hardware. Original home builders sometimes keep records. Bring photos to window showrooms—experienced salespeople can often identify brands by sight.
What if I want bigger windows in the addition?
You can use different sizes, but maintain proportions. If your existing windows have a 1:2 ratio (width to height), keep that ratio in larger sizes. Group multiple windows together rather than using single oversized units.
Ready for the Next Step?
With windows and doors installed, it's time to address one of the most common integration challenges: matching interior floor heights between your existing home and the new addition.