How to Vet a Window, Door, and Siding Installer

Last reviewed: 2026-08-08

Researched and written by one person, not an editorial team. I am an independent researcher, not a licensed contractor, and I do not install windows, doors, or siding — see the About page for exactly what I do and don't do. This page carries a lead-capture form at the foot; if you submit it, your contact information is routed to a disclosed set of installation companies and/or lead networks, and I am paid for that referral. That disclosure, and the current list of who sees your information, is shown next to the form itself, not buried here.

You're about to spend somewhere between roughly $5,000 and $15,000 (often more for a whole-house job), and the difference between a window that performs as advertised for 25 years and one that leaks, drafts, or rots the framing around it is, almost entirely, the installer. A well-made window installed badly is a bad window. The same window installed to the manufacturer's instructions, flashed and sealed correctly, and air-sealed to the wall assembly is the window you paid for.

This page is a deep-dive reference for the verification step: what credentials exist, what they actually mean, how to look up a contractor's license in your state, how insurance works (and what happens to you if an uninsured worker is hurt on your property), and what the EPA's lead-safe rule requires for homes built before 1978. It is the long version. For the quicker "five things to check before you call" checklist, see the companion vetting-overview page.

What this page is, and is not. We are not contractors, lawyers, or a contractor-licensing board. We have no trade experience and we don't rank or recommend individual installers. We compile public, sourced information so you can verify a contractor yourself before you sign. Every factual claim on this page links to a primary source — the state board, the EPA, the certifying body, the statute. If a link is broken or a fact is wrong, the source is named so you can check it directly. This page is not legal advice: we state what statutes and rules say; we do not interpret them or tell you what to do under them.

1. Contractor licensing: what it is, and how to look it up

Most states require a contractor to hold a state-issued license (or, in a handful of states, a registration) before bidding or performing residential window, door, or siding work above a modest dollar threshold. The point of the license is not that the state guarantees the contractor's workmanship — it does not. The point is that the state has verified the contractor met a minimum bar (experience, exam, bond, insurance), and that there is a public record you can check, and a board you can complain to, if the work goes wrong.

Three things matter about the license, in this order:

  1. Does one exist, and is it active today? A license number on a business card proves nothing. A license lapsed last Tuesday still prints on last year's business card. Look it up in the state's own database and confirm the status reads Active (or your state's equivalent) on the day you check.
  2. Is the license classification the right one for the work? Some states issue a single "general contractor" credential that covers residential window and siding work; others issue specialty classifications, and a contractor licensed only for, say, HVAC may not be licensed to replace your windows. Read the classification on the license record, not the one printed on the estimate.
  3. Does the entity on the license match the entity on the contract? A license issued to "Jane Doe, sole proprietor" does not cover work performed under "Jane Doe Windows LLC." If the legal names don't match, the license doesn't apply to your contract, the bond attached to that license doesn't cover you, and a complaint against that license won't reach the work done under the LLC name.

The state license-lookup table

Below are direct links to the official license-lookup or registration-lookup tool for 12 states, chosen to cover every U.S. region (Northeast, Mid-Atlantic, Southeast, Midwest, Southwest, Mountain West, Pacific). For each state, the table gives the name of the licensing body and the direct URL to that body's own public database. We went to each board's site and pulled the lookup URL — this is the part of the page a listicle cannot reproduce, because it requires going to each board and finding the actual portal, not a Google result.

A note on state variation: not every state licenses residential window/door/siding contractors at the state level. New York, Illinois, Ohio, and (for general contractors) Texas leave most residential contractor licensing to counties and cities. For those states we list the state-level trade board that does exist, and we say plainly that for window/door/siding work you will usually need to verify at the county or city level. That is the honest answer; a listicle that hands you one fake state-level lookup link for every state is lying to you.

State Licensing body (official name) What it covers Direct lookup tool
California Contractors State License Board (CSLB), under the Dept. of Consumer Affairs All residential & commercial contractors (statewide). Window/door/siding falls under Class B (General Building) and specialty Class C classifications (e.g., C-17 Glazing, C-39 Roofing, C-61 Limited Specialty subclasses). CSLB "Check a License or HIS Registration" — search by license number, business name, or personnel name; returns status, classifications, bond, workers' comp status, and disciplinary history. (CSLB home)
Florida Dept. of Business and Professional Regulation (DBPR), Construction Industry Licensing Board (CILB) Statewide licensed general, residential, building, roofing, sheet metal, and other contractors. DBPR Online Services — Verify a Licensee — search by name or license number across all DBPR-issued licenses. (DBPR online services home)
Virginia Dept. of Professional and Occupational Regulation (DPOR), Board for Contractors Statewide contractor licensing (Class A/B/C by project value, with classification/specialty). DPOR License Lookup — select "Contractor" from the profession dropdown; search by name, license number, or business. (Board for Contractors)
Maryland Maryland Home Improvement Commission (MHIC), under the Dept. of Labor Statewide home-improvement contractor license (required for any home-improvement work on residential property); MHIC also administers a Guaranty Fund for unpaid judgments against licensed contractors. MHIC License Search — search by contractor name, trade name, location, or MHIC license number.
Georgia Georgia State Licensing Board for Residential and Commercial General Contractors, under the Secretary of State's Professional Licensing Boards Statewide residential and general contractor licensing for projects above $2,500 (combined labor and materials). GA Secretary of State license verification — choose "Residential and General Contractors"; search by name, license number, or business. (Board page)
Arizona Arizona Registrar of Contractors (ROC) Statewide contractor licensing; ROC regulates any construction work valued above $1,000 in labor and materials (ARS §32-1121). ROC Contractor Search — search by license number, business name, or qualifying party; returns license class, status, bond, and complaint history. (Use the "Search for a Contractor" tool on the ROC site.)
Washington Washington State Dept. of Labor & Industries (L&I) Statewide contractor registration under the Contractor Registration Act (RCW 18.27) — Washington registers contractors rather than issuing trade licenses per se; electricians, plumbers, and elevator mechanics carry separate specialty licenses. L&I Verify a Contractor — search by business name, UBI number, or contractor registration number; returns registration status, bond, and insurance info on file with L&I.
New Jersey NJ Division of Consumer Affairs (DCA), under the Contractors' Registration Act (N.J.S.A. 56:8-136 et seq.) Statewide registration (not a trade license) for any home-improvement contractor doing work valued at $500 or more; specialty trades (electrical, plumbing, HVAC) are separately licensed. NJ DCA License Verification System — select "Home Improvement Contractor"; search by business/individual name or registration number. (DCA HIC program)
Pennsylvania PA Office of Attorney General, Home Improvement Contractor Registration (under the Home Improvement Consumer Protection Act, HICPA) Statewide registration of home-improvement contractors (with two narrow exemptions: small contractors doing under $5,000/yr, and large retailers with net worth ≥ $50M). PA OAG Home Improvement Contractor Search — search by registration number, business name, owner name, or county.
Massachusetts MA Office of Consumer Affairs & Business Regulation (OCABR), Home Improvement Contractor (HIC) Program Statewide registration of home-improvement contractors on existing 1–4-unit owner-occupied dwellings; administers a Guaranty Fund (up to $25,000 per eligible homeowner for unpaid judgments) and arbitration. Mass.gov HIC Program — "Check a Contractor" — use the "Check a Home Improvement Contractor" lookup on the OCABR page (search by name/registration number).
New York No statewide residential home-improvement contractor license. Licensing is at the city/county level (NYC issues the Home Improvement Contractor license; Nassau, Suffolk, Westchester each run their own). The NYS Dept. of Labor licenses a few trades (elevator, asbestos, crane) but not windows/doors/siding. For window/door/siding work, verify at the county or city level, not the state. NYC: Home Improvement Contractor License (NYC Dept. of Buildings / DCWP). For Nassau/Suffolk/Westchester, contact the county Office of Consumer Affairs or Dept. of Consumer Protection directly.
Illinois No statewide general contractor license. The IL Dept. of Financial and Professional Regulation (IDFPR) licenses only specific trades (roofing contractors, architects, engineers, home inspectors); electricians, plumbers, HVAC, and general contractors are licensed at the city/county level. For window/door/siding work, verify at the city or county level unless the job includes roofing, in which case the IDFPR roofing license applies. IDFPR (for roofing): IDFPR Roofing Contractor — License Look Up. For window/door/siding specifically, contact your city or county building department.

Other states

If your state isn't listed above, the same pattern applies: search for your state's "Contractors' Board," "Department of Consumer Affairs," or "Professional Licensing" agency, and look for that agency's license lookup page — nearly every state that licenses contractors runs a free, public, searchable database. Be skeptical of a search result titled "Verify a [State] contractor license" on a commercial (non-government) site; many such pages are built by marketers to capture your click, and the data behind them is often scraped and stale. The official lookup is the one linked from the licensing agency's own website — which is usually on a .gov domain, but not always: some states run their official license database on a contracted platform that does not end in .gov (New Jersey's official portal, for example, is at newjersey.mylicense.com). The test is whether the licensing agency's own site links to that portal — start at the agency's .gov home page and follow its link, rather than trusting a domain suffix by itself.

2. What installer certifications actually mean

A license is what the state requires; a certification is a separate, voluntary credential issued by a trade association, the EPA, or a specific window manufacturer. A certified installer is not automatically a better installer. Certification tells you the installer sat through a class, passed a test, and agreed to submit to the program's rules. It is a risk-lowering signal, not a risk-elimination signal — and that distinction is the whole point of this section. A genuinely excellent installer with no certifications exists; an installer with a wall full of certificates who skips the flashing step also exists. Use certifications as one filter, not a verdict.

Here is what the four most-cited certifications actually certify — and, just as important, what each one does not certify.

Comparison table: window/door/siding installer certifications

Program Issuing body What it requires (training, exam, experience) What it certifies What it does NOT certify Recertification / validity Primary source
InstallationMasters™ (Combined, Replacement, and New Construction segments) Fenestration & Glazing Industry Alliance (FGIA) Combined segment: 2-day class + written exam (installers); 5-day class + exam (instructors). Replacement segment: 1-day class + exam. Minimum 1 year documented field experience to register. That the installer has been trained in industry-accepted window & exterior glass door installation practices for residential/light commercial new construction and/or replacement. Does not guarantee any specific installer will follow the practices on your job. Does not audit individual jobs. Does not warranty the work; the cert is credentials, not a bond. Installer and professional (instructor) certifications are each valid for 4 years. Recertification is an open-book online test that extends the credential another 4 years. Certification is per-segment (Combined, Replacement, or New Construction); program materials were republished in 2026. FGIA — InstallationMasters · program handbook (PDF) · self-study info
AWDI Installation Certification (American Window and Door Institute) American Window and Door Institute (AWDI, LLC) — a private industry body, not a government agency AWDI describes a 5-part program (regulated training and/or demonstrable field experience with verified references; a written standard now at "Version 1.3.2"; a "Certified Installation Mark"). Advertised Level II Replacement cert fee is $149 at time of writing. AWDI's own installation standard for vinyl replacement windows (creating a "consistent opening," removing opportunities for error). Does not constitute a government credential. Does not guarantee job-site quality. AWDI itself notes the certification is "training and/or demonstrable field experience," not an exam of every installer's work. AWDI does not publish a recertification cadence on its public pages; confirm with AWDI directly. AWDI home · AWDI Certification Program
EPA Lead-Safe Certification (RRP Rule) U.S. Environmental Protection Agency (or an EPA-authorized state/tribal program, e.g., Oregon CCB/OHA) Firm certification: $300 fee, valid 5 years. Renovator certification: 8-hour training course from an EPA-accredited training provider, plus a refresher every 5 years. At least one certified renovator must be assigned to each job, and all workers must be trained either as a certified renovator or on-the-job by one. The firm is authorized to perform renovation, repair, and painting work that disturbs painted surfaces in pre-1978 housing and child-occupied facilities using EPA-defined lead-safe work practices. The renovator is trained in those practices. Does not certify quality of window/door/siding installation. Applies ONLY to pre-1978 target housing and child-occupied facilities — it is irrelevant for post-1978 homes. Does not certify the firm for any non-RRP trade. A certified firm can still cut corners; the rule sets the lead-safe floor, not the workmanship ceiling. Firm: 5 years. Renovator: 5 years (with refresher). EPA — Lead Renovation, Repair and Painting Program
Manufacturer-certified / authorized installer programs (Andersen, Marvin, Pella) Each window manufacturer Varies by manufacturer. Generally: the contractor business must be an authorized dealer/seller of the brand, meet minimum business, licensing, and insurance requirements, and complete the manufacturer's installation training (and often an annual refresher or audit). The contracting business (and usually a qualifying party/owner, not automatically every crew member who arrives on site) is trained on the specific manufacturer's installation instructions and is authorized by the manufacturer — which often matters for warranty coverage, because many manufacturer warranties are conditioned on (or voided by) installation that does not follow the manufacturer's instructions. Does not certify the installer's work on any other brand's product. Does not guarantee the manufacturer's warranty will cover every issue (warranties have specific exclusions — improper installation, aftermarket films, modifications, etc.). A "certified" or "authorized" dealer is an independent business, not the manufacturer's employee or agent. Crucially, the program credentials the business, not the person on your job — Pella's program, for example, is explicitly for "owners/operators of residential remodeling (R&R) businesses only" and is "not for individuals seeking window installer positions," so a certified company may still send employees or subcontractors to your house, and that program credential does not by itself prove the person on site was trained. Each program differs: Pella Certified Contractors, e.g., must pass an annual certification training and local installation training/audit; ask specifically which individual on the crew holds the manufacturer training credential. Andersen Certified Contractor Program · Marvin — find a Certified Installing Retailer (Marvin Limited Warranty PDF) · Pella Certified Contractor / loyalty program, Pella warranties

The honest read on certifications

The pattern across all four is the same: each one certifies that the installer was exposed to a standard, agreed to follow it, and can be audited against it. None of them sends an inspector to your job. None guarantees the installer will do the work correctly on the day your windows go in. A certification is worth one thing and one thing only in your decision: it raises the probability the installer knows the right practice, because someone taught it to them and tested them on it, and it gives you a body to complain to if they don't. Use it that way and stop.

The manufacturer-authorization point is the one most homeowners underweight. If you buy Marvin windows, your warranty depends on installation done per Marvin's instructions; an installer Marvin has trained and authorized is the one most likely to keep that warranty intact, and Marvin's published Limited Warranty explicitly excludes "improper installation." That's a financial argument for a manufacturer-authorized installer when the brand matters to you, separate from any quality argument.

3. Insurance: general liability vs. workers' comp, and what a certificate of insurance is

This is the section where "vetting" most often turns into "finding out, too late, that you're holding the risk." Insurance is the part you cannot skip.

The two policies, in plain terms

  • General Liability (GL) insurance covers damage to your property caused by the contractor's work. A dropped window shatters your tile floor; a ladder gouges your siding; a mis-cut flashing lets water into your wall six months later and rots the sheathing. Those are GL claims. GL does not cover injury to the contractor or the contractor's employees.

  • Workers' Compensation (WC) insurance covers injury to the contractor's employees while working on your job. A installer falls off a ladder and breaks an ankle; an employee cuts themselves on broken glass. Those are WC claims. In most states, a sole proprietor with no employees is not required to carry WC for themselves and often does not — they carry GL and assume personal liability for their own injuries. That is legal and common, and it is exactly the situation where the question below (what happens if they get hurt on your property) becomes your problem.

What a "Certificate of Insurance" is, and is not

A Certificate of Insurance (a "COI," often on an industry-standard Acord 25 form) is a one-page summary of a policy — not the policy itself. It lists the insurance company (the issuer), the named insured (the contractor's business), the policy numbers, the coverage types (GL and/or WC), the policy effective and expiration dates, and the coverage limits. It is proof that a policy existed on the date the certificate was issued.

A COI is not proof the policy is still in force today. Policies lapse for non-payment all the time. A contractor can hand you a real-looking COI from six months ago for a policy that was cancelled last month. This is why the single most important sentence in this section is:

Verify the certificate with the insurance company that issued it — not with the contractor who handed it to you.

This is a phone call, not a website visit, in most cases, and that's fine. The COI has the insurer's name and a policy number. Call the insurer's claims or policy-verification line and ask: "Does this certificate reflect an active policy for [contractor name], policy number [X], with the coverages and limits shown, on today's date?" A legitimate contractor expects this question and will not be offended by it. A contractor who gets defensive when you say you'll verify with their insurer is, itself, the answer to the question.

Also check: does the COI list you as a "certificate holder" or, better, an "additional insured"? The distinction matters more than the form suggests. The industry-standard COI form (the Acord 25) expressly states that it confers no rights — it is a summary of the policy, not the policy itself. So:

  • Being listed as a certificate holder does not, by itself, guarantee you will be notified if the policy is cancelled; whether you receive cancellation notice depends on the policy's provisions and any separate notice endorsement, not on the COI line. Do not treat "certificate holder" as proof of anything other than a record that you received a copy of the COI.
  • Being named as an additional insured on the COI alone is also not enough by itself — the actual coverage extension is a policy endorsement (a formal amendment to the policy), and the COI is merely evidence that the endorsement exists. Request that the additional-insured endorsement be issued, and that the insurer confirm it.

The stronger protection you want on a job this size is the additional-insured endorsement (the policy amendment, not just the COI line item) — that is what actually extends the contractor's GL coverage to you for claims arising from their work on your property. Ask for it by name, and then verify with the insurer (per above) that the policy is in force and that the endorsement is attached. (Acord 25 form — "THIS CERTIFICATE IS ISSUED AS A MATTER OF INFORMATION ONLY AND CONFERS NO RIGHTS")

What happens if an uninsured worker is injured on your property

This is where it gets uncomfortable, and we state what the statutes and boards say without telling you what to do about it.

  • In most states, if an uninsured worker is injured on your property while performing work you hired them to do, you — the property owner — can be exposed to liability for that worker's injuries. The legal theories vary by state (premises liability, the "peculiar risk" doctrine in some jurisdictions, statutory liability for hiring unlicensed contractors in others), but the practical outcome is the same: an injured worker who has no workers' comp coverage may pursue the homeowner's liability coverage, and if that coverage is insufficient or excludes the claim, may sue the homeowner directly.

  • The California Contractors State License Board — the licensing board itself, in its published consumer guidance on owner-builder risks — states plainly: "If your workers are injured, or your subcontractors are not licensed or do not carry liability insurance or workers' compensation insurance and they are injured, you could be asked to pay for injuries and rehabilitation through your homeowner's insurance policy or face lawsuits." (CSLB — "The Downside of Being an Owner-Builder")

  • Homeowners insurance policies commonly exclude claims arising from work performed by contractors you hired, and may exclude injuries to employees of such contractors. The practical consequence, as multiple consumer-protection and construction-law sources note, is that a homeowner who hires an uninsured contractor can end up paying medical and rehabilitation costs out of pocket, or facing a personal lawsuit, even with a homeowners policy in place. This is the gap that verifying WC insurance up front is designed to close.

We are not interpreting these statutes for your state or advising you on your liability. We are stating what a state licensing board and the published record say. If you want to know exactly how this works in your state, the state's insurance commissioner and the state contractors' board publish consumer guides; the links in §1 take you to the board for your state, and from there to its consumer-information pages.

4. The EPA Lead-Safe (RRP) rule, stated precisely

If your home was built before 1978, there is a federal rule in play that has nothing to do with state contractor licensing and everything to do with whether your installer is allowed to disturb the paint on your house. It applies independent of, and in addition to, any state license.

What the rule is

The EPA's Renovation, Repair, and Painting (RRP) Rule requires that anyone paid to perform renovation, repair, or painting work that disturbs painted surfaces in target housing (housing built before 1978) and child-occupied facilities (such as daycares and preschools built before 1978) must be certified and must follow EPA-defined lead-safe work practices that minimize occupants' exposure to lead dust. (EPA — Lead Renovation, Repair and Painting Program)

Window and door replacement on a pre-1978 home is squarely within the rule's scope, because removing an old window or door almost always disturbs painted surfaces (the painted frame, the painted trim, the painted sash). Siding replacement is the same. If your home was built in 1978 or later, the RRP rule does not apply to it.

What the rule requires of the firm and the renovator

  • The firm must be EPA-certified (or certified by an EPA-authorized state/tribal program). Firm certification costs $300 and is valid for 5 years. (EPA program page)
  • At least one certified renovator must be assigned to the job and must be physically present while signs are posted, while containment is established, and while cleaning is performed; at other times the certified renovator may be off site if available by telephone and regularly directing the work. All other workers on the job must be trained either as a certified renovator themselves or on-the-job by a certified renovator. Renovator certification requires an 8-hour training course from an EPA-accredited provider; the initial certification is valid for 5 years. To renew, the renovator takes a refresher course — a refresher that includes hands-on training renews the credential for 5 years, while a refresher without hands-on training (including an online-only refresher) renews it for only 3 years. When you verify a renovator's credential, ask which type of refresher they last took, because a current-looking card may be 3-year (not 5-year) refreshed. (40 CFR 745.90; EPA RRP program page)
  • The firm must follow the EPA's lead-safe work practices (containment of the work area, minimization of dust, clean-up, and post-renovation cleaning verification — a specific DIY cleaning-verification procedure using disposable cleaning cloths and a cleaning-verification card; this is not a lead-dust "clearance examination," which is a separate, stricter requirement that applies to abatement work, not ordinary RRP renovation) and must give the owner/occupant the EPA's "Renovate Right" lead hazard information pamphlet before work begins. (40 CFR 745.85; EPA RRP program page)

What the rule does NOT do

  • It does not require lead testing of every surface; it assumes painted surfaces in pre-1978 housing contain lead unless a certified lead inspector or risk assessor determines otherwise.
  • It does not require abatement (permanent removal of lead-based paint hazards). Abatement is a separate, stricter process governed by different rules. RRP work is renovation, not abatement.
  • It does not certify the contractor's window/door/siding installation skill in any way. The RRP certification is exclusively about lead-safe work practices.
  • It does not apply to certain "minor repair or maintenance" activities that disturb 6 sq ft or less of painted surface per room for interior work, or 20 sq ft or less of exterior painted surface. However, the EPA rule expressly excludes window replacement from that minor-repair exemption regardless of the square footage disturbed — window replacement is a covered renovation under RRP no matter how small the window. The same categorical exclusion applies to building demolition and several other activities listed in the rule. So the minor-repair exemption is not a path around RRP for a window or door job; treat any window/door/siding replacement on a pre-1978 home as in scope. (40 CFR 745.83 — definition of "minor repair or maintenance activity"; EPA RRP program page)

How to verify a firm's RRP certification

The EPA publishes a searchable database of certified renovation firms. You can search by firm name, certification number, or location (city/ZIP). If a contractor claims "lead-safe certified," this is where you confirm it.

Verify: EPA — How can I find a certified renovation firm in my area? — links to the EPA's searchable firm locator. You can also call the National Lead Information Center at 1-800-424-LEAD (5323).

A handful of states (Oregon, Wisconsin, Iowa, and several others at time of writing) are EPA-authorized to administer their own RRP programs in place of the federal EPA. In an authorized state, the firm is certified by the state agency, not the EPA, and you verify through that state agency's database. Oregon, for example, administers RRP through the Oregon Construction Contractors Board and the Oregon Health Authority (Oregon RRP program page); the firm's RRP credentialis a state "Lead-Based Paint Renovation" license, not an EPA certificate. If your state is EPA-authorized, the EPA locator will tell you, and you verify through the state.

5. Red flags — what to look for, and what disqualifies

Vetting gets a lot faster once you know the failure modes. These are the ones that should stop the conversation, in roughly the order they appear:

  • No license where one is required, or a license that doesn't verify. First confirm whether your jurisdiction actually requires a contractor license or registration for window/door/siding work (see §1 — a few states, such as New York and Illinois, do not license general residential contractors at the state level and leave it to localities). Where a license or registration is required: if the contractor won't give you the number, or the number doesn't come back Active in the issuing board's own database (see §1), do not hire them. Most jurisdictions that require a license set a dollar threshold (commonly $500–$2,500 depending on the jurisdiction) below which no license is needed; a full window/door/siding replacement exceeds those thresholds wherever they exist. Where the jurisdiction has no license requirement for this work, this red flag does not apply — but the insurance, RRP, and proposal-checklist items below still do, and you should verify any local (city/county) requirement that applies instead.
  • License classification that doesn't match the work. A contractor licensed for HVAC is not licensed to replace your windows. Read the classification on the license record.
  • Pre-1978 home and no RRP firm certification (EPA or EPA-authorized state). If your home was built before 1978, the firm performing the work must be RRP-certified. In most of the country that means an EPA firm certificate (verifiable in the EPA locator in §4). In EPA-authorized states (see §4 — Oregon, Wisconsin, Iowa, and others administer their own RRP programs), the firm holds the state's own lead-safe license instead of an EPA certificate and may not appear as a "firm" in the EPA's federal locator — verify through the authorized state agency instead. Either way, a current EPA or state-authorized RRP firm credential is required; its absence is a hard disqualifier, not a negotiation point. One carve-out: if a certified lead inspector or risk assessor has made a written lead-free determination for the components the renovation will disturb (see §4), that specific renovation falls outside RRP's scope — if the contractor is relying on that, ask to see the written determination.
  • Refusal to provide a Certificate of Insurance, or resistance to your verifying it with their insurer. A legitimate contractor gets a COI in your name from their agent in minutes; pushback here is a flag, not a quirk.
  • No WC coverage while using employees on your job. A sole proprietor working alone may legitimately not carry WC; a contractor with a crew and no WC policy is your liability exposure (see §3). Ask specifically.
  • Repeated or unresolved complaints on the licensing board's record. The state board's license lookup usually surfaces disciplinary history and complaints. One old resolved complaint is one thing; a pattern is another.
  • Pressure to pay in full up front, or in cash. State consumer-protection offices (e.g., MHIC in Maryland) commonly advise paying no more than roughly a third of the total as a down payment and never paying in cash. A contractor who demands full payment before any work has happened is not a contractor you should sign with.
  • No written proposal with the NFRC data, the installation method, the timeline, and both the manufacturer's and installer's warranty terms. See the proposal-checklist companion page; the absence of any of these in your written proposal is a flag.
  • Bid far below the others, with no explanation for the gap. A bid 30–40% below comparable contractors usually omits something — permits, flashing detail, proper disposal of the old windows, insurance. The omitted thing is almost always converts to your cost later.

6. After they leave: verifying the work was done

Hiring vetting ends when the contract is signed, but the verification of the job itself happens when the crew loads up the truck. A few concrete checks:

  • Get the written closeout. Before the crew leaves, get a signed write-up listing exactly what was done: each window/door by location, the NFRC label data for each unit (U-factor, SHGC, VT, Air Leakage — these are the performance numbers; see the NFRC label page for what each means), the installation date, the installation method used (insert vs. full-frame, the flashing detail followed), and the warranty terms — both the manufacturer's product warranty and the installer's labor warranty, which is a separate, shorter, contractor-specific instrument.
  • Register the product and read the actual warranty terms. Manufacturers differ on whether registration is required for coverage or merely expedites a future claim. Andersen's published warranty, for example, states that product registration is not a condition of warranty coverage — it helps speed up service; Marvin's current Limited Warranty likewise does not impose a blanket registration deadline. Other manufacturers may require registration within a stated window — so read your specific manufacturer's warranty document (linked in §2) rather than assuming a uniform rule. What uniformly matters: keep the serial numbers and the original purchase/install documentation with the warranty paperwork, and confirm whether the warranty is conditioned on installation per the manufacturer's instructions (many are) — another reason §2's manufacturer-authorization point matters. File the registration the manufacturer asks for, on the schedule it specifies.
  • Ask whether they performed (or will perform) an air-sealing verification. The industry-standard diagnostic for air infiltration is a blower-door test. Most window installers do not perform one — it is not standard for a window replacement job — but the IECC and ENERGY STAR reference it as the way to verify the as-installed infiltration rate. If the installer doesn't perform one, you can hire a home energy auditor to run a blower-door test. A note on what that can and cannot tell you: a blower-door test measures aggregate whole-building air leakage (reported as an ACH50 number), not the infiltration of any individual window. A test run only after install can report the current leakage rate, but it cannot, by itself, prove your envelope improved or attribute any change to the window work — establishing that requires a pre-install baseline test before the old windows come out, then a post-install test, with the difference compared. If you want the verification to actually mean "the windows reduced my air leakage," schedule both tests with the same auditor around the install date. That is an out-of-pocket cost you can elect; for a whole-house window job, it's the verification that earns the word. See the blower-door / air-sealing companion page for the IECC infiltration limits and what the numbers mean.
  • Inspect the obvious things yourself. Operate every window/door: do the latches engage, do the sashes slide smoothly, are the weep holes (on a window with a sloped sill / weep system) clear of debris and caulk? Look at the exterior: is the flashing lapped shingle-style (over, not under, the course below it), is the sealant continuous and tooled, is there any exposed un-caulked gap at the frame-to-wall transition? Water intrusion at these joints is the most common failure mode of a window replacement, and it is almost always an installation-method failure, not a product failure.
  • Keep everything. The contract, the proposal with the NFRC data, the COI, the warranty paperwork, and photos of the install in progress. If anything fails inside the warranty term, you will need these to establish (a) what was installed, (b) who installed it, and (c) that the failure is within the scope of the manufacturer's product warranty or the installer's labor warranty. The split is: manufacturer covers defects in the product, installer covers defects in the installation. Know which one you're claiming against before you make the call.

Sources

All retrieved 2026-08-08. Primary sources cited inline and consolidated here: