How to Compare Secondary Glazing Quotes

Is the system named?

The quote should say what it is: two panel horizontal slider, three panel slider, balanced vertical slider, side hung hinged unit, or lift out panel. If it just says secondary glazing unit, ask. The difference between a lift out and a balanced vertical slider is the difference between a panel you take down twice a year and a window you open every morning, and their prices reflect that.

Is the glass specified in millimetres?

Acoustic glazing lives or dies on the glass. The quote should state 4mm toughened, 6.4mm acoustic laminated, 6.8mm acoustic laminated, a Low E soft coat, or a sealed unit thickness for heavy duty hinged systems. It should also, on an acoustic job, be a different thickness from your existing glass, because two identical panes share the same coincidence dip and lose performance at the same frequencies.

Is the cavity depth stated?

Cavity is the biggest single acoustic variable and it costs nothing except reveal depth and planning. A quote that promises a large noise reduction while installing 30mm from the existing glass is promising something the physics will not deliver. Anything from 100mm upwards is doing real work. If your reveal is shallow, the quote should say how the installer intends to get the depth, usually with a subframe.

• Under 50mm: draught and condensation benefit only
• 50mm to 100mm: solid thermal, moderate acoustic
• 100mm to 200mm: the acoustic sweet spot

How is the frame sealed to the reveal?

A continuous compressed seal or bead of low modulus sealant around the full perimeter is what turns two panes of glass into a working system. Foam tape stuck to a dusty reveal is not the same thing. Ask what the perimeter detail is, especially on stone or uneven plaster where a packing and sealing strategy is needed rather than a straight push fit.

Made to measure, or nearest standard size?

Openings in period property are rarely square. A made to measure frame is manufactured to the surveyed dimensions of that specific opening, including any taper. A standard size frame packed out with trim will look approximate and will leak air at the packing. If a quote arrives without anyone having measured the windows, treat the figure as an estimate rather than a price.

Who fits it?

Ask whether the fitters are employed by the company or subcontracted, and whether the person who surveyed will be involved in the installation. Secondary glazing is a fitting led product: the same panel installed carefully or carelessly performs very differently. Ask how many fitters attend, how long they expect to be on site, and what happens to the room while they work.

Guarantee, aftercare and the small print

Check the guarantee length, whether it covers hardware and glass as well as frames, whether it is transferable if you sell, and what the callout policy is for adjustments in the first year. Balances and rollers occasionally need a tweak after the building has moved through a season, and a good installer treats that as normal rather than a chargeable visit.

• Guarantee length and what it covers
• Adjustment visits in year one
• Deposit terms and payment stages
• Lead time in writing

The two questions that settle it

If you only ask two things, ask these. What cavity depth am I getting, and what is the glass specification in millimetres? Those two answers predict how the finished job will perform better than any brochure, and any installer who cannot answer them immediately has not designed your job yet.