ᐅ Change in the size of roof windows after building permit approval

Dear forum members,

We have planned to install four roof windows from Roto in our house (two on each eave side), all sized 65x118 cm (26x46 inches).

I recently visited friends who have similarly sized double casement windows, and the width seemed rather narrow to me.

So my question is... is it even possible to change the size after the building permit / planning permission has been granted? I assume the structural calculations won’t be a big issue, since we have a purlin roof, which should allow a width greater than the rafter spacing without much difficulty.

Now regarding the optimal size... Roto also offers widths of 74 cm (29 inches) and 94 cm (37 inches), and the height can go up to 140 cm (55 inches). I think the height of 118 cm (46 inches) is fine, but would 74 cm (29 inches) width look good, or is 94 cm (37 inches) better? Three of the double casement windows to change are in the rooms Kid1, Kid2, and the bathroom. It would certainly look better to have a more generous amount of natural light rather than a small opening, right? The rooms measure about 360 cm (12 feet) in length along the eave side.

In the hallway, where our fourth double casement window is, we want to install an additional double casement window next to the existing one to make the hallway brighter (this would be a kind of “twin installation,” called “Velux Duo” by the manufacturer).

What do you think about this?

Thanks so much in advance!

Were the double casement windows fully dimensioned in the building permit / planning permission?

In our case, mainly all the dimensions of the house structure, ridge height, eave height, etc., were specified in detail. The windows were not really detailed.

Does the development plan specify maximum dimensions for roof windows?
I happened to read in one that they were limited to 1m² (11 sq ft).

Apparently, no one is really interested in this here. I know new builds where the shell was constructed as self-build and the window size was decided on the day of installation (ended up being 20cm (8 inches) wider...).

No one goes around measuring afterwards.

In our new development area, some have even exceeded the permitted height of 9.0m (30 feet), and no one cares. This was even confirmed over the phone by the engineer who created the development plan.

That is, as long as the neighbors don’t bother by measuring at night and reporting you to the authorities.

Mottenhausen schrieb:
Were the double casement windows dimensioned in detail in the building permit / planning permission application?

Yes, the windows were precisely dimensioned. However, I don't think anyone really cares if they end up being larger, and no one will measure them anyway.

Since they are not significantly altering the facade, it should not be a problem. Will this have any negative impact on the insulation, specifically the U-value or the energy saving regulations?