How to Choose a Double Glazing Company: Checks and Warning Signs

When you ask us for a quote, we arrange a free survey and a written quote from a local installer. Run every check below on that installer, as you would on any company you're thinking of hiring; most take a few minutes online or a short phone call.

Check the Certification

Since 1 April 2002, replacing a whole window or external door in England has been building-regulations work: the new window is a "controlled fitting", and the work has to be certified. Swapping just the glass, or a sealed unit inside the existing frame, is not a controlled fitting, so no certificate is expected for that repair.

Most installers handle certification through a competent person scheme. The government has authorised six of them for replacement windows and doors:

• Assure
• Blue Flame
• CERTASS
• Certsure
• FENSA
• NAPIT

An installer registered with one of these can self-certify the job. Within 30 days of completion you should receive a certificate, and the council should be notified. If the installer isn't in a scheme, the work has to go through the council's building control instead, and work that went through neither can later be put right through a regularisation application. GOV.UK spells out why this matters: without approval, "you will not have the certificates of compliance you may need when you want to sell your home".

How to Check a Registration

Ask the company, in writing, which scheme it belongs to and the exact name it's registered under. Then check with that scheme directly, through its own website or phone line, not through a logo on a van or a link a salesperson sends. The registered name should match the name on your quote.

FENSA Certificates

FENSA is the best known of the six schemes, and it has been a company of the Glass and Glazing Federation since 2002. A few practical points:

• The certificate usually arrives within 15 days.
• A lost certificate can be replaced for £30.
• FENSA can't register work that's more than two years old. After that, the route is through the council.

Guarantees and Deposits

Ask what guarantee comes with the windows and what happens to it if the company stops trading. An insurance-backed guarantee (IBG) keeps the guarantee alive if the installer goes out of business. FENSA's scheme rules make an IBG mandatory for its registered installers on work for private homeowners. That's a scheme rule, not a law, and its conditions also require at least six years' cover for Building Regulations non-compliance. With any other scheme, ask what guarantee and insurance come with the job, in writing.

Keep the Deposit Small

Citizens Advice suggests paying a deposit of no more than 25%. It also suggests asking whether the deposit is insured, considering escrow, and paying in stages. Dudley Trading Standards is blunter: "A legitimate trader will never ask for anything more than a small deposit."

Don't assume a deposit is protected because the installer belongs to a scheme. The competent person schemes suspended deposit protection in 2020, so ask directly. Citizens Advice also warns: "Avoid traders who only accept cash or want you to pay everything upfront".

What a Written Quote Should Include

Citizens Advice puts the first rule simply: "Try to get written quotes from at least 3 different traders before you decide on one." Quotes only compare fairly when they describe the same job, so each one should cover:

• The products. Frame material, colour, glass and opening style, plus the energy figure: replacement windows need a U-value of 1.4 W/m²K or a window energy rating of band B. "A-rated" is a selling point, not a legal requirement.
• Safety glass. Glazing below 800 mm, in doors, and in side panels near a door.
• Ventilation. Existing trickle vents replaced with vents no smaller, which you can open and close.
• Escape windows. Upstairs windows that serve as a way out in a fire need replacements giving at least the same potential for escape. See fire escape windows.
• Security. For doors, it's fair to ask whether the product is tested to PAS 24 or carries Secured by Design.
• The guarantee. Its length, what it covers and whether an IBG is included.
• Payments and dates. The deposit, stage payments, final balance, start date and cancellation terms.

For what moves the price on each of those lines, see our guide to double glazing costs.

Can You Cancel a Window Order?

The Consumer Contracts Regulations 2013 normally give you 14 days to cancel a contract signed at home, but goods made to your specification are an exception under regulation 28(1)(b). Made-to-measure windows usually fall inside that exception, even when the contract is signed at your own kitchen table.

Citizens Advice confirms that you don't automatically get a cooling-off period when something is specially made, naming "windows or a conservatory", and adds that "some traders voluntarily offer a 7 day cooling-off period for these products, but they don't have to".

Standard products and the fitting may still be cancellable. Where a right to cancel exists, two more rules apply. Under regulation 31, if the trader never gave you the cancellation information, the period can be extended by up to 12 months. Under regulation 36, if you want work to start before the cancellation period ends, the trader needs your request in writing.

So decide before you sign, not after. Ask in writing whether you can cancel, for how long, and at what cost. On the Calthorpe or Bournville estates the same logic applies to consent: get the estate's approval before you order. Our guide to estate schemes explains what each estate asks for.

Hard-Sell Warning Signs

Birmingham Trading Standards gives advice that fits window sales well: "A reputable doorstep seller will not pressure you to make a decision." It adds: "Take time to get quotes from other traders."

Slow down if you meet any of these:

• a price described as "today only", or one that only stands if you sign before the salesperson leaves
• a big price cut offered the moment you hesitate, often after a phone call to "the manager"
• a refusal to leave a written quote you can compare at your own pace
• a request for cash, or for most of the price before work starts
• pressure to start straight away, with no clear answer about your cancellation position
• a "grant" the salesperson can't name or point to on an official website (see our guide to double glazing grants)

Any one can happen innocently. Together, they suggest a company that would rather you didn't compare.

Approved-Trader Schemes Around Birmingham

Birmingham Trading Standards points residents to No Rogue Traders Here, which it describes as "a list of traders across the West Midlands". Solihull and Walsall Trading Standards support the same scheme. Dudley keeps a list of its own, Fix-a-Home, and is careful about what a listing means: Dudley says it "cannot accept any liability for, nor underwrite the quality of work done by listed traders".

Treat a listing as one more piece of information, not a guarantee or a substitute for the checks above. If an installer says they're on either list, check the scheme's own website yourself rather than taking it on trust.

Doorstep Callers and No Cold Calling Stickers

Birmingham City Council gives out free "No Cold Calling" stickers. To ask for one, email tradingstandards@birmingham.gov.uk. If a caller won't take no for an answer, or you think a rogue trader is working your street, Birmingham Trading Standards runs a rogue trader hotline on 0121 303 9367.

Paying Safely

Under Section 75 of the Consumer Credit Act 1974, a single item costing more than £100 and up to £30,000, paid for by credit card or with finance arranged through the installer, makes the lender jointly responsible with the installer. Debit cards aren't covered by Section 75, but your bank may be able to reverse a payment through chargeback.

If Something Goes Wrong

The Consumer Rights Act 2015 gives you two main protections. Section 49 says a service must be carried out with reasonable care and skill, and section 9 says goods must be of satisfactory quality. Your contract is with the installer, so write to the company first, with photos, a copy of the quote and what you'd like done.

If that gets nowhere, the Citizens Advice consumer helpline on 0808 223 1133 gives free advice, and its advisers can pass complaints on to Trading Standards.

General Information, Not Legal Advice

Read this guide as general information rather than legal advice. Your rights depend on the exact terms of your contract, so for advice on your own situation, speak to Citizens Advice or a solicitor.

Getting a Quote Through Us

Call or send the form and we'll arrange a free survey and a written quote from a local installer, who measures up and quotes you directly. You're under no obligation to accept it, and every check in this guide applies to that quote as it would to any other. You can get a quote in about a minute, or read the FAQ first.