For a builder, windows are a deceptively high-stakes scope. The product cost is significant, the schedule sits on the critical path (no windows, no insulation, no drywall), and installation defects surface as warranty callbacks — water intrusion, drafts, operation failures — long after the sub has been paid.
Having worked as a window and door subcontractor for general contractors across the Twin Cities, here's the vetting checklist we'd use on ourselves.
Schedule reliability is the whole ballgame
A window sub who slips three days cascades into your insulation, drywall, and closing dates. Ask specifically: How many crews do you run? How do you handle weather days? What's your communication protocol when a date moves? The right answer involves proactive notice measured in days, not a truck that just doesn't show. References from other builders answer this question better than any promise — ask for two GCs the sub currently works with.
Installation standards you can audit
Good crews install to the manufacturer's instructions and the details in your plans — flashing integration with the WRB, sill pans where specified, proper shimming at hinge and lock points, low-expansion foam or specified insulation at perimeters, and fastener schedules that don't void product warranties. Walk a sub's active job before you hire them: consistent flashing laps, clean foam work, and level/plumb/square units tell you everything. Manufacturer certifications matter, but a tidy opening tells you more.
Full-service vs. labor-only: pick the model that fits your workflow
Some builders want a sub who takes the whole scope — measuring, ordering, receiving, installing, and warranty service — with one accountable throat to choke. Others buy product direct and want a skilled labor crew on their schedule. A flexible window sub offers both and is honest about which fits your project. Full-service shifts ordering-error risk to the sub; labor-only maximizes your margin control. Either way, get who's responsible for a mis-measure in writing.
The paperwork that protects you
Before the first opening, a professional sub provides:
- Current MN contractor license number and certificates of liability and workers' comp insurance.
- A written scope with unit counts, install details, and exclusions — no 'per plans' hand-waving.
- Lien waiver process aligned to your draw schedule.
- A punch and warranty commitment: who answers homeowner calls in year one, and how fast.
We're built to be that sub
JMB Builders installs windows and doors for builders and GCs across the Twin Cities metro — full-service or installation-only, with clean sites, honest schedules, and installers your super won't need to babysit. Call 763-204-2099 to talk through your next project or set up a standing crew arrangement.
