COMPARISON

New Windows or New Siding First? A Contractor's Honest Take

By AJ Roofing | April 2, 2026 | Southwest Suburbs of Chicago

This question comes up constantly when homeowners are planning a full exterior renovation: "We want new windows and new siding — which do we do first?" The short answer is that it depends on the installation method — but if you're getting both done, there's a strong argument for doing them at the same time. Here's why, and what goes wrong when the order is reversed.

Why Installation Order Matters

The relationship between windows and siding is physical. Siding wraps around window frames, and proper installation of each affects the other. New replacement windows — the most common type, where the new window inserts into the existing frame opening — typically leave the existing exterior casing (the trim around the window) in place. New siding then installs up to and around that existing casing.

Full-frame window replacement, where the entire window including frame and casing is removed and replaced, integrates differently — the new window is installed into the rough opening, and siding is then installed over and around the new window frame directly. In this case, siding absolutely comes after windows, and any siding installed before the windows are in place will need to be modified or partially removed.

The standard sequence when doing both: windows first, then siding. The siding contractor installs J-channel around window openings to create a clean transition, and the result is a weathertight assembly. If siding goes in first and windows come later, the siding contractor has to cut around existing windows and the window installer has to work around finished siding — creating more opportunities for flashing gaps and water infiltration.

When Doing Both at Once Saves Money

When both windows and siding are done in the same project, the efficiency gains are real. A single mobilization cost covers both crews. Scaffolding or lift equipment, if needed, serves both trades. Flashing and weatherproofing at window-siding interfaces is done by one coordinated team rather than two separate contractors hoping the other person did their part correctly.

The waterproofing at window-siding interfaces is particularly important. The gap between a window frame and the surrounding siding is a primary entry point for water infiltration in older Illinois homes. When one contractor installs both, accountability is clear and integrated flashing tape and housewrap details are executed as a system rather than improvised by a second contractor working around someone else's work.

The Storm Claim Scenario

In our area, many full exterior renovations are triggered by a significant hail or wind event. When an insurance claim covers roof, siding, and windows simultaneously, doing all the work under one contract is clearly the right approach. A single project scope, one adjuster meeting, and one contractor responsible for the complete exterior restoration is simpler, faster, and less prone to gaps in coverage between trades.

AJ Exteriors — AJ Roofing's parent company — is set up precisely for this scenario. We handle roofing, siding, gutters, and windows under one contract, meaning storm-damaged homeowners deal with one team, one schedule, and one point of accountability from start to finish.

What Happens When the Order Gets Wrong

We've seen homes where a window contractor installed new windows against existing siding that was then damaged by hail two years later. The siding contractor doing the replacement had to work carefully around relatively new window casing, cutting and fitting siding around finished exterior trim rather than integrating cleanly. The result was a patchwork that required extra flashing work to waterproof properly — and added cost.

More common is the reverse: new siding installed when the windows were already old and due for replacement. A year or two later, the homeowner wants new windows, and now the window contractor is removing and cutting into finished siding. It's not impossible, but it's messier and more expensive than doing it in sequence the first time.

Our Recommendation

If both windows and siding are in your five-year plan, do them together in the same project. The savings and coordination benefits are significant, the waterproofing is better, and you're not paying two separate mobilization costs. If you must do them separately, always do windows first, then siding. And if a storm claim is covering both, let AJ Exteriors handle the full exterior scope as one coordinated project from inspection through completion.