It isn't.
That's the short answer. Double glazing, doors, conservatories, and other home improvement products are not inherently expensive to manufacture or install. The materials have improved dramatically over the past 20 years. Supply chains are efficient. Installation teams are experienced and fast.
So why do the quotes always seem so eye-wateringly high?
The 40-Year-Old Business Model
80% of the UK double glazing industry — including the biggest household-name brands — has operated on the same direct sales, commission-based model for over 40 years. It has not changed because it works. For them.
Here is how it works. A company employs self-employed salespeople on a commission-only basis. The salesperson earns nothing unless they sell. And the more they sell a job for, the higher the percentage commission they receive.
This creates a structural incentive to charge as much as the customer will accept — not as much as the job is actually worth.
The Maths
| Scenario | Price Paid | Salesperson Earns | Customer Saves |
|---|---|---|---|
| Book price accepted | £12,000 | £1,500 (15%) | — |
| Mid-range negotiated | £8,000 | £640 (8%) | £4,000 |
| Floor price | £4,800 | £50 flat | £7,200 |
The product did not change. The installation did not change. Only the price changed — and the only thing that determined the price was how much the salesperson thought they could get away with charging.
The Fix
Knowing this, the question is not "why is double glazing so expensive?" The question is "what is the real price for my job?"
That is exactly what our free Quote Checker tells you. Use it before you sign anything.