Retrofitting a skylight

Hello.

Hoping that I have come to the right forum here, I have a question about retrofitting a skylight in a flat roof.

We have bought a house that dates back to 1934 and was extended 10 years ago by an annex. This annex partly – especially in the area of the staircase – has a flat roof. It is insulated and the ceiling under the vapor barrier foil is paneled. The flat roof has a slope of 1% over a length of 11 m and is about 1.70 m wide. The hallway with the staircase is a bit dark and we don’t want to have to switch on the light even during the day. So we now want to have a skylight installed. It should be quite large, preferably 120x240.

We have already had 3 roofers come who want to make an offer. However, each sees a different problem that the others don’t see:

1) The first roofer/carpenter thinks 1% slope is too little, especially since water would then also stand in front of the skylight. He suggests tearing up the entire flat roof and installing a steeper slope. Elsewhere I hear that 2% would actually be DIN-compliant, but less is also possible if high-quality bitumen membranes are applied and checked more often. Against water behind the dome, one could possibly install a kind of wedge.

2) The second roofer thinks that bridging more than one rafter with spacing joists is not allowed. The others are just nice experts that don’t know that. Since the rafters (8x16) are about 75 cm apart, a skylight can be at most 150 cm long.

3) The third roofer thinks the entire ceiling paneling must be removed in order to open the roof in the right place. One must work from the bottom upwards. He has also discussed this with a drywaller and he sees no other option. Whether the existing panels can be reused is uncertain. Other roofers suggest working from the top down, first making a smaller opening and drilling a hole through the ceiling paneling. Then one knows where one is and can proceed accordingly. Sounds plausible.

As laymen, we are now accordingly unsettled. Can you help?

Regards,
heiteck.

Hi,

so 1% slope is also really little. The first roofer is right about that. How to do the replacement, I would discuss with a structural engineer. If I were you, I would definitely get advice from a professional on site anyway (architect, civil engineer).

Regards

Hello,

The hallway with stairs is a bit dark and we don't want to have to keep the lights on even during the day. So we now want to install a skylight. It should be quite large, preferably 120x240.

The 1% is indeed a bit too little, as E.Curb has already confirmed .... if you don't want to have the flat roof's slope changed, there are cheaper ways to bring daylight into the dark hallway. These spots are now sold nationwide by the major suppliers in the industry; in my opinion, it should be no problem for you to get a quote for installation through one of the roofers.

Kind regards

Hello E.,

thanks for your reply. So, what I left out: We initially asked the architect of the extension about the project. He then drew us a nice pyramid (140x200), on which the first offer is also based. The slope was no problem for him; the suggestion with the wedge comes from him. The question about the headers only came up later when, for cost reasons (the glass of the pyramid alone is supposed to cost 2000 EUR), we had already decided on a plain Licktkuppel. Yes, we can ask him about the headers, even though he is not a structural engineer. Hopefully, he will still talk to us when he finds out that we are rejecting the pyramid.

Regards, heiteck

Thank you, construction expert, for the tip. I once showed my wife these light spots in a living magazine. She didn't seem very enthusiastic. I think she wants to see the sky. Did I understand that correctly?: The spots let more light through a smaller hole, therefore the barrier for the flowing water is smaller ... also because they are round. Can you say which spot size corresponds to which light dome area? Regards, heiteck.

Hello,

I once showed my wife these light spots in a living magazine. She didn’t seem very enthusiastic. I think she wants to see the sky.

Personal taste/preferences cannot be disputed ; I was more focused on the costs. By the way, besides the use of considerable financial resources, cleaning light domes can be quite a hassle .... your wife might not have considered this or did you volunteer for regular cleaning?

Did I understand that correctly?: The spots let more light through a smaller hole, therefore the barrier for draining water is smaller ... also because they are round.

There are different systems and variants of the spots; some "align" almost flush with the roof surface, some look like a ventilation pipe of a toilet or bathroom to the untrained eye. For flat roofs, however, all providers offer special spots; the existing slope is always taken into account.

Can one say which spot size corresponds to which light dome area?

Feed Aunt Google with Velux + daylight spot; Velux is one of the better-known providers of such spots. There is a tab called "light calculator" where you can enter the data for your extension and after completing the entries, you will see under which lighting conditions you would save which output - in lux or 60 W incandescent bulbs - by installing a daylight spot.

For various reasons, I am not a fan of double-wing windows/light domes; therefore, where they seem sensible to me, I gladly offer these spots to my customers.

Kind regards