We would like to have several "tubular skylights" in the construction we are planning. These are skylights consisting of a circular opening in the roof with attached dome-shaped or circular window, attached to a cylindrical duct with a reflective material on the inside, which eventually reaches the interior through the ceiling, terminating at some kind of window. These skylights not only deliver the light from outside, but they also "disperse" the light (using the tube's inner material) so that upon exit at the ceiling the light is spread out over a larger area and not as concentrated as it would be otherwise.
As far as I can tell, 10" diameter is the smallest size offered among today's tubular skylight products.
We are going to be using a concrete roof technology that has a fixed spacing between its concrete beams. I currently understand it to be the case that 10" would not pose structural problems in the roof, and it may not necessarily interrupt one of the beams, but we would prefer to opt for more numerous openings of a smaller size given that strength and storm resistance is a priority for the building.
I suppose that the "volume of light" that is delivered, both physically and with regards to our perception of it, diminishes exponentially as the diameter of the skylight decreases. This may be one justification for the minimum of 10" among the available products. Aside from that, it is not clear to me whether there would be a big issue with hitting some kind of other physical diameter threshold, smaller than which we would be severely limiting the function (light delivered and/or proper dispersion of the light) of the skylight.
There are two particularities to our situation that make me think a smaller diameter would be OK. (1) There will be no bends in our skylight tubing, whereas generally the commercially available skylights are designed to accommodate bends in the tubing (and the eventual decrease in delivered light); (2) Our tube will be short, maybe 4 feet from exterior to interior, whereas existing products are designed to accommodate longer lengths. So we already have two factors which appear to boost the effectiveness / functionality in our case.
Other possible benefits of producing our own skylights: We can adapt it to our specific use, and specifically we can make it more storm resistant or adapt it to the particularities of our roof (which is more-or-less flat and will be topped with a concrete slab, which is different from the average roof with shingles etc). Another is that existing skylights seem to be expensive, though I haven't researched prices much.
I wonder what people think about that reasoning so far. I am thinking of having openings that are as small as 4".
Now, aside from whether it is a good idea or not, I am looking for advice on constructing the skylights. It seems straightforward to create a cylindrical tube, and apply a reflective material to the inside. However I am not sure about:
- what to use for the exterior light collecting window / dome, which are usually designed to collect light from all angles. We do not need to take into account storm resistance necessarily, because we can install separately some kind of shutter that encloses the dome. I am thinking that we may be able to just install a 10" dome even though the opening that it will sit over will be smaller.
- How best to connect the tube to the dome, in a way that minimizes leaks into the roof opening/canal; or if they are not connected, how to best secure the dome to the roof to minimize leaks.
- What to use for the interior circular window.
- General construction advice for assembling these items.
I apologize if this question is very long. Thank you.
Best Answer
Your question is very complete. But, for a flat concrete roof? Yes, I know, it won't truly be flat and it better not be. Either way is No Way...you'll be re-caulking every year and it'll take all year long with that Swiss Cheese.
Please have the mason customize the roof for these. I'd like to see a 2" to 3" (twice that if you regularly get snow and ice) ramped cone poured for each location that's part of the initial monolithic pour...not some add-on guaranteed failure afterthought nonsense that actually collects and retains water.
Also, please don't run short-lived Romex under the slab for the night and cloudy lighting. Use the aluminum armored cable, unless it's attacked by the concrete. Then you might need the PVC or epoxy coated armoring.
I'd actually suggest a sidewall stovepipe looking singular tube that feeds a fiber optic lighting box. Of course, it could be a nice feature like a faux gable or corner turret. But, this would allow for experimentation and scalability. Maybe 4-inches is too bright in a fiber optic setup and you just need a 2" periscope that operates as a flagpole.