Does anyone know if this tubular skylight needs additional insulation around the tube in the attic?
Nope. Kind of like a big double-pane window.
And just how energy efficient is that big double-pane window? I would definately insulate around it in the attic as you suggested.
The skylight is closed at both ends. No conditioned air can get into the tube.
There is still heat loss into the chamber where its sealed or not. Why not insulate the outside of the tube that runs through the attic and reduce the heat loss from that large surface area. There will still be some loss through the dome but the less the better.
FWIW, the Solatube installation instructions make no mention of insulation:
You wouldn’t lose heat through convection, since there are no air currents in a sealed tube. You wouldn’t lose heat through radiation, because there’s so little thermal mass. The only way to lose heat would be through conduction, and the only surface exposed to the warm interior is the clear face. The sheetmetal sidewalls of the tube are thin enough that it’s hard to imagine much heat getting transfeerred from the clear face to the sidewalls and being conducted to the cold attic or exterior.
The only reason I can think of not to insulate is the possibility of condensation forming and becoming trapped.
I’m afraid I disagree with on this one. With the size of the tube, convection air currents most certianly would occur, even in a sealed unit.
With double-glazed windows, the air space between the panes of glass has a big effect on energy performance. A very thin air space does not insulate as well as a thicker air space because of the conductivity through that small space.
During the 1970’s a lot of window manufacturers increased the thickness of the air space in double-glazed windows from 1/4" to 1/2" or more. If the air space is too wide, however, convection loops between the layers of glazing occur.
The same principle applies to the tubular skylight.
It may not be required to insulate but the cost of insulation will easily be recovered by the savings in heat loss.
The only condensation (not roof leaks) problems I have every seen have been with regular skylights where the moisture entered in from the open bottom skylight well. This should not be a problem in tubular skylights. Moisture from the attic side is unlikely if the attic is properly vented and sealed from the conditioned space.
I just got off the phone with Solatube. They don’t recommend insulating the tube for condensation reasons.
Can you explain to me where and how this condensation occurs?
Paul, I just googled them and called customer service for contractors. The guy said something about energy star and heat loss being taken into account during design. The cell signal wasn’t that good and I didn’t really ask for details. I’m sure there’s some heat loss but I think it’s pretty minimal.
Grab a coffe guys and see if this helps.
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Manufacturer’s recommendations for the particular product prevail.
I would not recommend deviating from the installation guidelines and offering alternative installation (insulation) methodology.
The sola-tube installation is NOT air tight. Only water tight at the roof line, “Hopefully”. We all know what happens to dual glazed windows when they loose they’re air tight seal, hello condensation…
Here’s what I got back from solatube…
Solatube does not recommend insulating the tube in the majority of cases - unless dictated by local building codes (I believe there is a mandate in Oregon). Condensation inside the tube can occur if warm, moist air from the living space enters into the tube, rises to the top of the dome, and when the outside temperate is an extreme opposite, condensate can form in the dome. Our new design that was introduced in Dec. 2006 has an airtight ceil at the diffuser level to minimize air infiltration into the tube. If it were to occur, however, the Solatube dome is designed to whisk any condensation along the inside of the dome to the dome ring, which has a moisture relief channel to hold and relieve the water from the system. The moisture control system in the dome ring will relieve any condensation. When the system is installed per our instructions, you should not have condensation.
If there is condensation in the attic, it is most likely the result of the underside of the flashing being exposed in the attic (if the hole is oversized for any reason). If the flashing is cold, and there is warm air in the attic that rises and hits the flashing, condensation could form on the underside of the flashing and drip down into the attic (or along the outside surface of the tube). The way to prevent this is to use the Solatube Flashing Insulator.
As far as heat loss and Energy Star rating, (which is a concern for northern climates) we meet the standards set forth for how much heat is lost from the interior area through the system.