The answer
A cheaper alternative to VELUX can be found among other makers, such as Fakro, Keylite and Roto, which sell roof windows for pitched roofs. Compare them on how well the window fits your rafter spacing, which flashing kit is made for your roof covering, the glazing and U-value, and whether spares and replacement glass stay available.
Where other makers compare
VELUX is a well-known roof window brand, and other makers fit the same openings. Fakro, Keylite and Roto are among those that sell roof windows in the UK. We fit VELUX and other makes, so the choice rests on the roof and the room.
The comparison that matters is made on four points, and the window needs to do well on all of them:
- the size range, so the window suits the gap between your rafters
- the flashing kits made for your covering
- the glazing, and its U-value against the Part L limit
- spares, including glass and seals, years from now
Fit and flashings on a slate or tile roof
Watertightness in a roof window comes from the flashing, and each maker supplies kits for particular coverings. Slate, stone slate and tile roofs all want their own, and a profile cut for plain tiles can be wrong for a slate. Check that the maker lists a kit for your covering before you compare anything else. The guide to flashing kits for slate and tile roofs shows what a kit contains.
Size codes also differ from maker to maker. In VELUX codes the letter stands for width and the digits for height. Another maker uses its own system, so compare sizes by their dimensions, since the codes do not translate. A window that is a few centimetres out can mean cutting a rafter that did not need cutting, which adds cost back.
Glazing, U-value and the Part L limit
Part L allows a new or replacement roof window in an existing house a U-value of 1.4 W/m²K at most, or Window Energy Rating band B. A cheaper window passes if its figures do. Look for the maker's stated U-value and the glass specification: double or triple glazing, the gas fill and any low-emissivity or solar-control coating. The lower a U-value, the less heat escapes, and the difference between two windows shows up in the heating bill over the years.
Opening type matters too. A centre-pivot sash rotates on a central axis, while a top-hung sash is hinged at the top and opens outward. Check that the model you are pricing opens the way the room needs.
Questions to put to any supplier
Whatever make you pick, a few plain questions separate a window that suits your roof from one that merely costs less on the day:
- Which flashing kit is supplied for my roof covering, and is it in the price?
- What is the window's U-value, and is it within the Part L limit for a roof window?
- Is the window sold in the size that fits between my rafters, or does it need a larger opening?
- If the glass fails in future, can the glazed unit be replaced on its own?
The answers to the last two matter more than they look. A window that needs a rafter cut costs structural work, and a sealed unit that cannot be bought separately turns a small job into a full replacement. A maker that gives clear answers to all four is worth considering, and a fitter who works with several makes can tell you which has them.
Our overview of roof window installation in Leeds describes how a window is chosen for a room and roof, and who can install a VELUX covers the fitting side.
Spares, guarantees and the long run
A window can last for decades, and a sealed glazed unit can fail in that time. A maker with a long-running range may still supply a matching replacement unit, flashing or blind years later. Ask each maker how long it keeps parts, and read its warranty for what the product covers. Our own 10-year workmanship guarantee covers the fitting, as the guarantee page describes.
The price of the window itself is only part of the total. The flashing, the access and the plastered reveal inside are the same whichever make goes in, and the roof window installation cost breakdown goes through each. Our written quote is fixed and records which window goes in which room, and at what size.