We’d also like to figure out why, so if you have a moment take our quick survey. Full disclosure: we are NOT affiliated in any way with any solar tube manufacturer. We just think this is a really cool technology that needs more exposure. Promoting energy efficient practices is one of our goals at Small House Building.
To start you off let’s look at one of the better videos out there on solar tube installation from the “Dummies” series. They use the term ‘tubular skylight’. There are others, but this is a great starter one to give you a good overview of the process.
In case the video becomes unavailable someday here’s a brief rundown of how to install a solar tube:
1) Many solar tube kits comes in a standard 4-foot length, although additional segments are available. First start in the attic. Find the approximate location of the top of the solar tube directly above where you’d like the interior to come out. On the underside of the roof mark that point with a small nail, tapped into the decking half way between rafters.
2) With a plumb line attached to that nail mark the opposing point in the drywall right below it.
3) From the attic side tap a nail into the ceiling at the mark you made. Drive the nail in all the way so it protrudes into the interior space.
4) From inside the house find the nail and mark a circle around it. Follow the manufacturer’s directions on how large the circle should be.
5) Cut out the circle with a drywall knife. Insert the ceiling ring that comes with the kit into the hole. Your kit may not say anything about caulking or air sealing, but it’s a good idea to caulk the underside of the ring. Use a type of caulk that stays very flexible with temperature and humidity changes.
6) Now that you know for sure where the solar tube will come out on the roof decking drive the roof nail completely through so it protrudes on the roof. Mark the circle on the roof deck, right on top of the shingles.
7) Cut the circle in the shingles and tar paper with a utility knife. The actual hole through the decking will likely be slightly smaller than the shingle hole — follow manufacturer directions. A Sawzall is your best tool for cutting through the decking.
8) Apply mastic under the shingles on the upward side of the hole, as well as the left and right.
9) Put the flange in place on top of the mastic and under the shingles on the upper, left, and right sides. The flange should be on top of the shingles on the downward side. Secure with screws provided (they are likely corrosion resistant, which standard construction screws are not). Replace roofing material around the flange.
10) Drop into the roof flange the interior upper elbow of the solar tube.
11) Back inside the attic attach the lower elbow to the interior collar ring. Determine the distance from the upper elbow to the lower elbow in the ceiling. Use the number of sections that are needed to reach from the upper to the lower without cutting any of them. If the total length of the tubes is a little long then nest the tubes further together instead of cutting them.
12) Remove any protective coating on the interior of the tubes. Add the sections one at a time and tape together with the provided tape. Don’t use your own tape! The tape that comes with the kit is designed for this application and will remain adhesive for a very long time, even through temperature extremes. Duct tape will not.
13) Secure the tunnel to the ceiling ring with the screws provided. Additional air sealing with caulk may be necessary around the lower elbow. Preventing air infiltration is very important here. Replace insulation around the tube.
14) Add the clear dome on the top and secure with screws provided.
15) Add the interior diffuser plate, rotating and locking into place. Most kits have an optional multi-layered diffuser plate which provides greater insulation for this surface. If you’re in a climate with cold winters these extra layers are advisable.
16) Add the trim ring on the interior. Rotate or snap into place.
Energy Efficiency of Solar Tubes
At first glance it seems like solar light tubes might be an area of heat and/or air leakage. And with air leakage comes a potential for moisture condensation. Not good. The manufacturer literature that I read seemed to talk about all the good points of energy efficiency with light tubes. But, I thought the best place to find out the truth of this was from a business that does energy audits on homes.
I talked with Josh Keeney of Dr. Energy Saver in Wisconsin and found out some interesting things. Josh and his team have experience installing solar tubes, and says that if they’re installed correctly they’re not a problem. “In fact they’re better than regular skylights,” he says. “Too many things can go wrong with regular skylights.”
There are 2 important factors to consider when installing light tubes correctly:
- Proper air sealing at the ceiling end.
- Thoroughly insulating the entire tube with spray foam.
Josh recommends a generous amount of silicone caulk inside the ceiling ring. The tape that comes with the typical light tube kit is usually not adequate to fill and seal that space for a long time frame. And if that tape looses its adhesiveness there’s not a way to tell as it’s out of site inside the ring. If room air can get through this space there’s potential for condensation on the cool surfaces inside the attic. Condensation is bad.Insulating the entire tube from ceiling to roof with spray foam is also highly recommended. This will help ensure that the entire length of the tube is insulated, but that it’s also air tight. Spray foal fills and covers every little gap and nook, unlike fiberglass insulation. The downside of spray foam insulation is that it requires professional installation. It’s very difficult, and even dangerous, to work with and is best left to the professionals. (If you’ve every worked with spray foam in a can and had it get onto your clothes or skin you’ll know what I mean! It’s very difficult to get off your skin, and impossible to get out of fabric. I shudder to think what would happen if caught in hair!)
If the multi-layered diffuser plate is used then the heat loss through this surface is minimal. Unfortunately, it’s not standard on solar tube kits.
Solar Tubes vs. Skylights
It seems like sooner or later traditional skylights leak. Especially in northern climates where the snow will sit on and around a skylight for many months at a time, going through freeze-thaw cycles. And skylights that can open seem especially prone to leakage. (Just do a search for “leaking skylight” images and it’ll be quite scary what can happen!)
Traditional skylights, if improperly installed, may also be more prone to condensation problems. If the framing around the window isn’t insulated and sealed adequately the slightly cooler surfaces will condense any moisture in the air. Condensation that sits on painted drywall will eventually soak in.
The framing that’s required in a traditional skylight is also an issue. Because a skylight is usually larger than standard rafter spacing special framing has to be created, which means more time and skill, and more expense. If there’s a distance between the roof deck and the interior ceiling the entire column has to be framed and insulated. Not easy.
Solar tubes require no special framing, or rearranging of framing if installed later. Even the large size (about 14″ in diameter) fits adequately between rafters. And because the tubing can be slightly bent that means that the hole in the roof doesn’t have to be exactly plumb over the interior end of things.
The flashing materials that come with a solar tube kit are wide enough to fit a good distance under adjoining shingles (and on top of the downward side shingles). This single unit makes it far less likely that a leak will develop. Just make sure that any exposed screws are generously covered with waterproof caulk or mastic (whichever the manufacturer recommends).
And because the roof flange is round there’s no place for snow or water to site and pool, unlike a rectilinear skylight.
Even though the amount of light coming through a solar tube might be slightly less than a skylight the difference is not significant. The main aim of using a solar tube is to gain generous ambient light, whereas a skylight will let in direct sunlight. Is direct sunlight from the roof really necessary? Some people might feel this is actually a drawback as direct sunlight can heat up interior space when it’s most unwanted — summer.
Solar Tube Costs
As with any building materials or project the cost can vary widely in different States and countries. The ‘Dummies’ installation video quotes about $450 (USD) for a typical 4-foot kit, uninstalled. With each additional foot costing about $35. In the moderately-populated upper Midwest (where I live) I’ve seen Velux kits starting at $149 for the 10″ diameter model, with approximately 3.5 feet of tube, at my local big box store. The next size up, about a 14″ diameter, is twice the price.
Which size you go with largely depends on how much light you’d like coming in. Also on the amount of light available on a particular spot of roof. Placing the exterior dome on a north-facing part of the roof, as well as being shaded by trees or buildings, will affect how much light it can gather. If you can place your tube with the exterior landing in a place of continuous, direct sunlight you’ll probably want to go with the smaller diameter.
The size of the room that you want to illuminate will also affect which tube size to go with. Generally the 10″ size is for small rooms of up to 200 square feet. Hallways come to mind for the best application here. The 14″ size seems appropriate for about 300-350 square feet. Multiple smaller ones in a larger room could also work nicely, giving the effect of multiple “can lights” in the ceiling.
Be aware that these kit prices are just the beginning. If you have significant home building experience you can probably get away with just purchasing the kit, any extensions or accessories, and installing it yourself. Hiring a pro to install a sun tube is preferable! Getting the flashing, sealing, and insulating right so as to prevent heat loss and condensation is very important. After speaking with a home energy auditor it sounds like proper sealing is more critical than I would’ve imagined at first glance.
The benefit of hiring a pro (that’s installed solar tubes before) is that you know the job will be done right, especially if their company specialized in Energy Star construction and energy auditing. Looking up reviews on websites such as Angie’s List will help give you an idea of their skill and professionalism. After finding out more details about what can go wrong with solar tubes this is one job I’d definitely hire out.
Flexible vs. Rigid Tube
Which kind of solar light tube you go with depends on a couple factors:
- How straight or twisted the route from ceiling to roof is.
- The intensity of light you want on the interior.
If going from the interior exit point to the roof is a straight shot then rigid tubing is probably your best bet. Even if the exit through the roof isn’t exactly plumb vertical over the interior outlet — and there’s no cross members in the way — you can use the rigid tube system. There IS a little wiggle room in using the rigid light tubes. But, if the route is a little “wanky”, having to go around framing members, ductwork, wiring, etc. to get to where you need to then the flexible tubing is going to be your only option.
The amount of light you get on the interior will also depend on which tube style you use. Not only is the rigid tubing straight — allowing light rays to come through with minimal bouncing around — but the straight tubes will usually have a mirrored interior surface. Both of these factors allow more sunlight to get from the roof to the interior. Sometimes too much, in some people’s opinion.
The flexible tubing has a lot more interior texture that light can get “caught” on (this is just an analogy). Even though the material in the flexible tubing is metallized and shiny, there’s lots of very small surfaces that end up reflecting the light every which way but down into the interior space. So the flexible tube system is best if you actually prefer a more diffuse light coming in. However, the interior covering can always be changed later to something more translucent and “frosty” if the amount of light is too intense.
Solar light tubes are a great way to get daytime lighting into interior spaces within a home. And once you’ve paid for the initial installation you’ll get free lighting while the sun shines! The downsides are few, and the benefits are many. After researching this article I will definitely prioritize solar tubes over skylights on my next home building project.
Have you had experience with solar light tubes? Let us know in the comments!