# Should I add more insulation to the tunnel of a skylight?



## nrwilson (Jan 2, 2015)

My skylight is forming condensation on the glass and it is dripping to the lowest corner and then making streaks on the drywall. I had the glass replaced since a carpenter said that was the problem. There is still condensation on the window that drips down and drips in my room. The roof ceiling around that lowest skylight side is all frosty and looks as if water iced it. If I put more insulation around the tunnel after the new glass was cauked and sealed in will this fix the problem? Do I need to insulate the roof ceiling around the skylight? I am hoping for any help, since it cost $500 just to replace the glass, which now apparently was not the problem.


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## oh'mike (Sep 18, 2009)

Yes,Insulate it well---

I had a tall tunnel in a bathroom once---and installed an exhaust fan into it--that was severe--dumb design---

Sometimes--a sheet of clear plexiglass is installed to a tunnel ,at the ceiling--that acts like a storm window---and ends the condensation.


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## nrwilson (Jan 2, 2015)

Yes I had a piece of plexiglass there before the carpenter came and decided that I needed new glass and took it out. It still streaked down the drywall with it in then too. It was not sealed in there completely though because they just pulled it out easily. If I put it back in does it need to be sealed with caulk or what?


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## ddawg16 (Aug 15, 2011)

The warm air rises. Any moisture in it will condense on the glass. It takes a really well insulated glass skylight to not have condensation.

What is the RH% in the house? 

Insulation is always good. But, if you have a lot of moisture, creating layers is about the only way to fix it.

I've heard of some people have an exterior 'dome' they put over the skylight in the winter to create another layer so as to not have to deal with the plexiglass inside.


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## nrwilson (Jan 2, 2015)

So, how do I determine the relative humidity of the house, to see if it is a problem? The furnace has an aprilair and I run a dehumidifier in the basement during the fall to winter months. The tunnel is right in front of the main entrance that has a vented overhang that allows outside air to come in and hit the tunnel directly behind it. Does this have anything to do with increasing the condensation possibility?


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## Gary in WA (Mar 11, 2009)

Welcome to the forum!

Cold chute walls + warm house air = condensation. Either dehumidify or insulate the chute's walls/add house wrap, after air sealing in the attic.http://www.buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion

Gary
PS. Yes, the lower glazing needs to be air-tight to work.


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## nrwilson (Jan 2, 2015)

If I put the plexiglass back how far away from the skylight is the best distance to try to stop the condensation? Does it need to be caulked or sealed somehow to make it air tight?
Also do I need any insulation on the roof around the tunnel or something else? It is icing up there on the roof coming off the lowest side from the skylight. Is this because of or from the condensation?


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## nrwilson (Jan 2, 2015)

Thanks for taking time to help a novice at attic repairs! Thanks for your input!


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## Gary in WA (Mar 11, 2009)

I'd add the p-glass at ceiling level BUT the chase will still be cold- even with tons of insulation without heat from the room. With the heat is moisture, from people, pets, cooking, showers, washer/dryers, etc. that has to go somewhere. Any pinhole (1/32") is enough to give moisture there. Rigid foam board makes a good air seal for the attic side, if accessible; http://www.finehomebuilding.com/des...y-smart-details/insulated-skylight-shaft.aspx May also need to be covered with ignition barrier...

No added insulation ON the roof. Gary


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## nrwilson (Jan 2, 2015)

Wow what an education you just gave me with the two links you provided Gary! Thank you! Thank You!! 2 inch Rigid foam around the shaft since I am in zone 6 and the plexiglass on inside. Does anyone know of any qualified and reasonably priced people in Rock County in WI to complete this work?


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## oh'mike (Sep 18, 2009)

You want an insulation contractor--


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## Gary in WA (Mar 11, 2009)

You're welcome! 98% of the time, I get no response..... glad we could help.

Gary


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## nrwilson (Jan 2, 2015)

Thanks again for all the pointers from everyone! I really appreciate them! It gave me a solid starting point and direction to go! Thank you!


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