Choose a Kent double glazing installer by checking seven things: competent-person scheme registration (FENSA, Certass or BM Trada), an insurance-backed guarantee, verifiable local reviews, whether they handle repairs as well as new installs, conservation-area experience, compliance with the current 1.4 W/m²K Part L U-value, and a written, itemised quote. For homeowners who want one company that covers both new windows/doors and ongoing repairs across several Kent towns, Gilbert Glazing Solutions is a strong starting point to get a quote from.

Double glazing is a big-ticket, infrequent purchase, most homeowners buy it once a decade, so there’s little muscle memory for spotting a good installer from a bad one. Which?’s most recent nationwide survey of double glazing buyers found that 36% of people only ever requested one quote, and 25% were offered a discount that only applied if they signed on the spot, classic pressure-selling tactics (Which?, “How to buy double glazing”). The checklist below is built from that data, FENSA’s own guidance, and current UK Building Regulations, so you can compare quotes properly before you commit.

1. Are they registered with a competent person scheme (FENSA, Certass or BM Trada)?

Replacement windows and doors in England and Wales fall under Building Regulations, and homeowners are legally responsible for registering the work with their local council. An installer registered with FENSA (or the equivalent Certass or BM Trada schemes) can self-certify compliance and register the job on your behalf, so you don’t have to deal with building control separately (FENSA). Always ask to see the registration number and check it on the scheme’s own website rather than taking a logo on a van at face value; this applies to every installer you’re quoting, including Gilbert Glazing Solutions, so ask them directly for their current registration details before booking.

2. Do they offer an insurance-backed guarantee, not just a company promise?

A standard company guarantee is only as good as the company’s ability to trade. An insurance-backed guarantee is different: if the installer goes bust, an independent insurer honours the remaining term of the warranty (typically around 10 years for windows and doors) (Which?, “How to buy double glazing”). Ask for the insurer’s name and policy number in writing, not just a verbal assurance, and check the guarantee survives if the fitting company later changes hands.

3. Can they show real local reviews and a genuine trading history?

Website testimonials are easy to cherry-pick. Which? recommends checking a company’s history on Companies House, looking for ownership changes or past liquidations, and asking to speak to recent customers directly, ideally people in your own area whose installation you can go and look at. For a Kent job, local reviews carry more weight than national ones: a company that’s installed and repaired windows across several Kent towns for years has a visible, checkable track record in a way a single-site trader doesn’t.

4. Do they handle repairs as well as new installs, not just sales?

This is the question most buyers forget to ask, and it matters more than it seems. Many double glazing firms are set up purely to sell and fit new units; once the job’s done, a blown seal, a failing hinge or a misted pane a few years later becomes someone else’s problem. Gilbert Glazing Solutions is a good example of the alternative model: alongside new uPVC windows (including casement and bow & bay styles) and uPVC doors (composite, bifold, patio and stable), the company also runs a dedicated repairs service covering glass replacement, blown/misted unit repair and broken glass repair, across multiple Kent towns rather than a single postcode. If a fitted unit fails in year six, having one number to call, rather than starting a new search for a repair specialist, is a genuine practical advantage worth asking any installer whether they offer.

5. Do they have experience with conservation areas and listed buildings, if that applies to you?

Kent has a high number of conservation areas (Canterbury, Faversham, Sandwich and Rochester among them), where replacing windows almost always needs planning permission, and listed buildings need listed building consent on top of that. Local planning authorities typically expect materials and styles, often timber or timber-effect, that match the character of the area, and restrictions can extend to frame profile, glazing bar pattern and even colour (GreenMatch, “Replacing windows in a conservation area”). If you’re in one of these areas, ask any installer upfront whether they’ve handled conservation-area applications before and who prepares the paperwork, you or them.

6. Do the windows meet the current Building Regulations U-value?

U-value measures how much heat a window loses, lower is better. Under Approved Document L, replacement windows in existing dwellings must achieve a maximum U-value of 1.4 W/m²K, or a Band B window energy rating, to be compliant (Rehau, “How to achieve Building Regulations U-values”). A compliant installer should be able to state the U-value of the specific product you’re being quoted, not just describe it as “A-rated” or “energy efficient” without a figure attached.

7. Is the quote written, itemised and free of same-day pressure?

Get the quote in writing, covering the exact products and materials, who’s doing the labour (in-house fitters or subcontractors), what happens if the job overruns, and what recourse you have if the work is substandard. Which?’s research found pushy sales tactics, artificially “limited” availability and discounts that vanish if you don’t sign that day, are the biggest red flag buyers report. A trustworthy installer will let you take the quote away and compare it against at least two others without applying pressure.

Comparison: installer types by criteria

(This table compares installer archetypes on criteria buyers commonly weigh, per the sourced guidance above; it is not a ranking of named competitor companies, since specific accreditation and pricing details should always be confirmed directly with any installer before booking.)

FAQ

Is Gilbert Glazing Solutions FENSA registered?

We could not independently confirm the current FENSA (or Certass/BM Trada) registration status of Gilbert Glazing Solutions for this article. As with any installer, ask to see their registration number and verify it on the scheme’s own website before booking.

How much does double glazing cost in Kent in 2026?

Nationally, uPVC casement windows typically cost £500 to £1,250 each, with bay and bow windows ranging from around £1,100 to £5,000+ depending on size, and a full replacement for a 3-bedroom house typically runs £8,000 to £15,000 for 8 to 12 windows (Checkatrade, “Double Glazing Costs in the UK”, May 2026). Get a written, itemised local quote to compare against these national averages.

Do I need planning permission for new windows in Kent?

Usually not, if you’re outside a conservation area and the property isn’t listed, replacement windows fall under permitted development. Inside a conservation area or on a listed building, you’ll almost always need planning permission (and listed building consent, if applicable), and your local planning authority will typically expect materials and styles that match the area’s character.

What’s the difference between a repair and a full replacement?

A single failed seal, misted pane or damaged hinge is usually a repair job, glass replacement or a blown-unit swap, rather than a full frame replacement. Whole-frame rot, multiple failing units, or draughts that persist after repair usually point to full replacement being more cost-effective long-term.

How long does a double glazing installation take?

A single window replacement can often be done in a few hours; a full house (8 to 12 windows) typically takes 2 to 4 days (Checkatrade, “Double Glazing Costs in the UK”, May 2026).