Cost · Detail
How to compare dormer quotes side by side
Comparing on the total price at the bottom of a quote is how people end up disappointed. The interesting work is one level up: same scope, same materials, same finish — then look at the price.
7 min leestijd·Onafhankelijke informatie
Short answer
Ask three companies for itemised quotes for the exact same dormer. Compare them line by line — materials, glazing, insulation, frames, lead work, permit handling, transport — before you look at the bottom line. The spread you see is usually 20–30% and is almost always explained by a difference in scope, not in greed.
The principle: bring the scope onto one page first
The most common comparison mistake is reading three quotes for three slightly different dormers. One uses HR++, another triple glazing. One quotes 5.0 m of width, another 4.6 m. One includes the permit, another does not. Before you compare price, force the scope to be identical.
The axes that explain price differences
- Materials and brand. Generic PVC vs branded composite (Trespa, Keralit) can shift the price by 10–20%.
- Glazing. HR++ → triple is a noticeable jump, but worth it on a south-facing or noisy street.
- Insulation package. R 3.5 vs R 4.5+ shows up in comfort, not just in the energy bill.
- Frames. PVC, aluminium-clad timber, hardwood — different lifespans, different prices.
- Lead and flashing. Code 4 vs code 5 lead, lead replacement strips, corner detailing.
- Interior finish. Plasterboard only, plasterboard + paint, or full finish with mouldings.
- Permit handling. DIY, the company does it, or "we will advise" — three very different scopes.
- Crew. Own employed crew vs subcontracted — affects warranty and aftercare quality.
Example: three quotes for the same dormer
| Item | Quote A | Quote B | Quote C |
|---|---|---|---|
| Cladding | PVC | Keralit composite | Trespa HPL |
| Frames | PVC, white | Alu-clad timber | Alu-clad timber |
| Glazing | HR++ | HR++ | Triple |
| Insulation R-value | 3.5 | 4.5 | 5.0 |
| Lead | Standard | Code 5 | Code 5 + corners |
| Permit | Excluded | Included | Included |
| Crane | On application | Included | Included |
| Warranty | 5 years | 10 years | 10 years + trade body |
| Total (excl. VAT) | €8,200 | €11,400 | €13,700 |
Checklist before you decide
Checklist
Run every quote through these
- 01Same width and height in all three quotes.
- 02Same glazing type and frame material.
- 03Insulation R-value stated, not 'standard'.
- 04Lead work spelled out (grade and detailing).
- 05Permit handling explicit, with cost.
- 06Crane and transport included or named.
- 07Interior finish level described.
- 08Lead time and install duration stated.
- 09Warranty length and any trade body cover.
- 10Payment milestones (deposit, install, handover).
FAQ
FAQ
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01How many quotes should I get?
Three is the practical minimum. Two is not enough to see the spread, four or more makes comparison harder. Pick three companies that take dormers seriously, not three random builders.
02Is the lowest quote usually a bad sign?
Not always, but a quote that is 25–40% below the others is. It usually means a different scope: thinner insulation, lighter lead, simpler frames or excluded items. Read it line by line before deciding.
03What if two quotes look identical but the prices differ a lot?
Look beyond the totals: warranty length, lead time, install team (own crew vs subcontractor), aftercare promise and brand of the materials. The cheaper price often hides one of these.
Conclusie
A good comparison is a boring spreadsheet. Once every quote is on the same page, the right answer almost picks itself — and usually it is not the cheapest one or the most expensive one, but the one in the middle that explained itself best.