ᐅ Change in the size of roof windows after building permit approval
Created on: 27 Mar 2019 10:20
C
chrisw81
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!
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!
chrisw81 schrieb:
From which rafter spacing is the 94 cm (37 inches) derived? I have to admit I’m not sure about that specifically, as I wasn’t involved in the roof window area. If the nominal size refers to the rough opening between the rafters, it would be around 110 cm (43 inches). In general, rafter spacing has increased over time because rafters’ cross sections have also changed in relation to insulation thickness. Forty years ago, 80 cm (31 inches) spacing was still common and, except for very narrow double casement windows, it was almost standard to require reinforcements.
chrisw81 schrieb:
Could you maybe remove a rafter and flange it on, Flange it? To what and how?
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11ant schrieb:
Flange on? ? ? – what, onto what? This means you remove a section of the rafter and place a slightly longer one next to the resulting gap. This way, you gain the width of the rafter (about 6cm (2.4 inches) in my case). See the image "Rafter spacing slightly too narrow"
M
Mottenhausen4 Apr 2019 21:09I would have seen it as a kind of "change" as well, but the sketch is quite informative about the different types.
Without battens to clamp this auxiliary rafter in place, it seems like a poor construction to me. Torsion is practically inevitable. This might still work with laminated veneer lumber, but with solid wood, it’s a joke.
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11ant schrieb:
Without a counter batten to secure this auxiliary rafter, it seems like a botched construction to me. Warping is practically inevitable. This might be acceptable with laminated veneer lumber, but with solid wood, it’s a joke. You’re probably right. I think there are only two options: either a proper beam transfer or trying to space the rafters a few centimeters further apart—if the structural engineer and the carpenter allow it.
chrisw81 schrieb:
You’re probably right. And if not, I still firmly believe it anyway ,-)
chrisw81 schrieb:
I think there are only two options: either replace properly or try to space the rafters a few centimeters further apart Forget it, it’s not necessary. I just checked in https://www.hausbau-forum.de/threads/grundrissplanung-Einfamilienhaus-mit-rund-150-m.26772/page-46#post-260043. There’s no need for wider spacing; all the double casement windows are purely secondary, and even at the staircase it’s sufficient. If anything, only install a wider* one there—but so that it can be cleaned from the gallery. In the floor plan, the double casement windows appear to fit in width between two rafters, but their spacing doesn’t align rhythmically between rafters. So, I expect some adjustment will be needed; then shift them to the next field toward the interior.
*) Or taller: it’s enough for the top to exactly reach the 2m (6 ft 7 in) line.
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