Average Labour Cost/Price to Build/Construct a Dormer Window (including video introduction)

Job 1
To fit a small, felted flat roofed dormer, with slated / tiled cheeks and an off the shelf PVCu window, in the middle of a roof pitch. This will be plastered and finished inside and will take two men 10 days.
Labour…….£2500, scaffolding…….£250, materials……..£600

Job 2 With a pitched roof add…………£700.00

A Guide and Information Sheet to the Cost of Building a Dormer Window

I’m assuming that you already have a loft conversion, presumably an oldish one, which you now want to enlarge with said dormer window. There’s not much point in fitting one if the loft is simply that…a loft and if you are considering a new loft conversion, get the builder to include the window in his quote!

Right then, it will probably need planning permission, it certainly will need supervising by a building inspector and depending on the configuration of the roof and how picky the inspector is, it may need to be specified by a structural engineer, all of which will cost you money. All three could set you back around £650.00. There will be scaffolding needed and the roof will have to be opened up and there will be a lot of mess, so ask the builder to seal the room off and do all his coming and going via his scaffolding and “the hole”.

The structural work won’t be decided by you, in fact there is a short treatise on trimming joists in our article on velux windows, but unless you are a bus spotter, you probably won’t find it all that interesting! We do however, let you have some say in your dormer design i.e. It’s width, will it be a pitched or flat roof, the window type and the cheek coverings.

If you choose a pitched roof , give it a central ridge and cover it in the same tiles / slates as the rest of the roof. In fact they can use the very same tiles they just removed to make “the hole”. If you have a flat roof and it’s a small dormer, you might consider lead, then you can forget all about it for ever. Most of the time though, flat roofs are felted.

I suggest you fit a PVCu window, because a wooden one will need painting every 3 years and that will need scaffolding each time.

Cheeks are what we call the sides of a dormer and like a pitched roof they look best if they match the main roof.

Simple, this building lark, isn’t it!