# Reducing Skylight Heat Loss?



## longshanks (Jul 23, 2009)

Hi to all from the new guy.

We just bought a house that has some ice damming issues. I'm pretty sure the ice damming results from heat loss through our 2 skylights. We live in an area that gets deep winter snow (northern Canada). House was built in 1996, and skylights are good double pane Velux units, but there was a horrendous amount of ice below them last winter. We get deep snow here.

The skylights are situated above (1) the stairs, and (2) the bathroom. Both skylights are at the top of tunnels which extend from the ceiling about 7' up to our 5 12 pitch roof. Unfortunately, the bathroom skylight is only about 20" away from the top of a gable valley, where the major ice problems occurred.

I have heard that one way to reduce heat loss up these 'tunnels' is to frame in an acryllic 'window' at the bottom of the tunnel, to prevent heat/steam from escaping up the tunnel and melting snow on top of the glass skylight. Has anybody attempted this, and can you advise if it has been effective in minimizing winter-time heat loss?

Our roof also has very little exhaust venting, so I'm planning to have continuous ridge venting installed to allow any heat to escape. 

suggestions?

thanks!


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## Yoyizit (Jul 11, 2008)

My attic fan is wired so that I can override the fan 'stat and turn it on in the winter to prevent ice dams. Never had any more ice dam weather so never tested it.


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## Scuba_Dave (Jan 16, 2009)

Are they venting skylights?
If so you want the layer removeable

One apt I did install some heavy glass as a barrier
Anything that prevents heat from going up the trunnel will help 
Also check to make sure around the tunnel was insulated
And of course the attic...or is it a cathedral ceiling?

Any lights nearby? Incandescent? Change them to CFL


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## longshanks (Jul 23, 2009)

attic floors are very well insulated, and the skylight has wrap around silver stuff (fiberglass mats I think). In terms of 'venting' skylights, they don't open up, they are fixed. Is that what you mean?

6 pot lights in the opposite end of the house and we're changing them to CFLs. 

re: the fan, I can see how this would help, but I am going to go the non-powered route first, doing things such as insulating and ventilating, to see how far that takes us.

thanks for your feedback


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## Scuba_Dave (Jan 16, 2009)

If they are fixed then I would make a permanent lower glass block


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## longshanks (Jul 23, 2009)

thanks SD,

any reason you suggest glass instead of acryllic?


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## Scuba_Dave (Jan 16, 2009)

Acrylic will discolor over time
You can get some glass cut thicker


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## longshanks (Jul 23, 2009)

thanks SD.

sounds like a much more fun project than wrapping fiberglass insulation bats around the skylight tunnels up in the attic. I'm putting that one off until cooler fall weather.

I have some further questions about the most appropriate roof venting for this house, will post soon.

great forum, thanks for your help.

cheers


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## Gary in WA (Mar 11, 2009)

I would put up a plastic obscure panel before glass. I frame skylight trunks with maximum flare at both ends, some finish out at 2'x8'. That would be one big, heavy piece of glass, especially if safety glazed. I would be worried of the liability if it ever fell from an earthquake, poor installation, etc. 

Skylights may be tempered, heat-strengthened, laminated, wired, or approved rigid plastics- IRC 308.6.2 

After you close off the trunk at the ceiling level, you may still get condensation in the 7' high trunk. This will probably mildew or mold, so keep an eye on it. The sun is warming the whole trunk with a heating- cooling cycle, without the ventilation it had before the panel. The paint will start to peel and discolor, the curb frame start to cup or twist. Been there, done that, until I removed the whole thing. Once you close it off, it will get even hotter, putting even more heat into the attic, much worse than before. Be safe, G


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## Scuba_Dave (Jan 16, 2009)

Good point on the flared tunnel

Possibly remove the glass in warmer weather?
Or have it framed out/hinged so you can open it


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## longshanks (Jul 23, 2009)

Good point!

Our skylights are good double-paned Velux units, and I've never noticed condensation up there yet. As you mention, his could change if I close the unit off, but I don't have any other options at this point, other than improving ventilation and blocking off the tunnel at the ceiling.

The main problem is that in winter, when there is a 30 degree celsius (sorry for the Canadian units) difference between indoor and outdoor temps, the snow on top of and around the skylight glass melts away and turns to ice. 

If the skylight remains problematic in a year or two, would replacing this skylight with a solar tube beat my problems? How expensive are those things?


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## Leftyho (Apr 12, 2009)

Hi,

Has the ice caused a problem?


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## longshanks (Jul 23, 2009)

well, the ice damming in this location has worn out an area of 25-year shingle roof in 13 years, and last year water leaked under some shingles and resulted in an insurance claim for the previous owner. We are shelling out for a new roof, and I'd ideally like to prevent the skylights and associated heat loss from causing any more damage.

plus, as my wife would say, I'm anal retentive:laughing:


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## Ed the Roofer (Jan 27, 2007)

You will still have heat trapped in the rafter bays of the particular rafters that align with the skylights, IF this is a vaulted/cathedral ceiling that you are talking about.

If so, then read this and get the brochure from the link.

Pay attention to the very last page.

Download a brochure from the Air Vent website, entitled, "Venting Hip Roofs" and on the last page of the brochure, it shows a method to ventilate the rafters below and above the Skylight that is installed in the path of air flow, which impedes the direct eave intake to roof top exhaust pathway.

Forget it. Here is the link:

http://www.airvent.com/pdf/literatur...s_HipRoofs.pdf

Ed


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## Leftyho (Apr 12, 2009)

Hi,

There is a 7' tunnel. It is not a cathedral ceiling.


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## Ed the Roofer (Jan 27, 2007)

Thanks Lefty,

I missed that because of the lateness of the hour when I went through this thread.

Ed


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## longshanks (Jul 23, 2009)

thanks everybody for your input on my question. I've spoken to some knowledgeable roofers in our area, and we have a game plan.

Our existing skylights are Velux 'guardian' units. We've had no problems with them, other than the fact that they melt snow (as most skylights would do), and they're no 13 years old. In light of the fact that we're looking at putting on a 30-year roof, our roofer suggested replacing these units with new models, which are considerably more efficient. Considering the cost of doing this while the roof is being done, vs. doing it a few years down the road, I think this is the time to do it.

With proper ice and water shield downslope of the skylights, and with laminate shingles, he felt that we will have no further problems with roof leaks.


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## longshanks (Jul 23, 2009)

hi again.

checking back in here. Unfortunately, I was unable to have our roof or skylights replaced this year. This is now planned for spring. I was looking at our problem areas yesterday, and noticed that 1/2" of ice has formed already under the 5" snow load on our roof. This ice is showing in the valley under our skylights

While I made some improvements to the soffit ventilation in this area last summer, this ice tells me that I still have some more work to do. I know that there is some heat escaping through the glass panes in the skylight, but the areas of ice damming are probably resulting from heat loss into the attic as well. I've inspected the entire attic, and the obvious culprit is the 7' long skylight tunnels. Right now they have only a thin reflective blanket, yellow with shiny silver coating on it. 

Can anybody advise what the best way would be to insulate these tunnels properly to reduce heat loss? Do I insulate all the way up to the roof sheathing? There is at least 2' of blown in insulation all over the ceiling. Do I insulate all the way down to the ceiling? Where does the vapour barrier go? Are there any potential downsides with putting more insulation around these tunnels?

I'd like to do whatever I can to reduce this heat loss this winter, and then tackle the roof and skylight replacement in the spring. Not sure about putting panels across the bottom of the skylight tunnels yet. I'll save that as a last resort.

thanks for your help


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## MisterPG (Nov 25, 2009)

Hey Longshanks - Did you get my reply to your other post? ( http://www.diychatroom.com/f17/need-dry-out-my-garage-57304/#post353807 ). My skylights are fully backframed and insulated with fiberglass batten. It's also vapour barriered from the rest of the house, just like the ceiling and walls. I have pictures of the construction, framing and insulating process if you're interested. - Also, as noted in my other reply, A Q&A might be easier in person if you're interested... I'd just have to work around my work schedule and my kids' activities schedules.... Let me know.


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## longshanks (Jul 23, 2009)

Thanks for your generous offer MisterPG. I'll try to send you a private message.


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## MisterPG (Nov 25, 2009)

Sounds good - I tried to figure out how to do the same, but all I can find is my inbox message location.... If you can't do it, let me know and I'll temporarily put my email address up here this afternoon...


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## Gary in WA (Mar 11, 2009)

This for anyone else that may want to know: http://books.google.com/books?id=jT...onepage&q=insulating a skylight shaft&f=false

Leave the rafter space two inches for air travel from the soffits to the ridge. From: http://books.google.com/books?ei=3Z...ng+a+skylight+shaft&lr=&as_brr=3&sa=N&start=0

Be safe, Gary


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## Scuba_Dave (Jan 16, 2009)

MisterPG said:


> Sounds good - I tried to figure out how to do the same, but all I can find is my inbox message location.... If you can't do it, let me know and I'll temporarily put my email address up here this afternoon...


You need 10 posts before PM's become active
This is to prevent spammers uisng PM's right away


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## longshanks (Jul 23, 2009)

hi

for some reason I've been unable to send a pm or email to you MisterPG. I think maybe you have disabled this function? Are you able to send me a pm? Would like to pick your brain regarding skylights!

cheers


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## MisterPG (Nov 25, 2009)

Scuba_Dave said:


> You need 10 posts before PM's become active
> This is to prevent spammers uisng PM's right away


Ahh - Thanks, Dave


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## MisterPG (Nov 25, 2009)

LS - Wanna send me an email for now? EDIT:Got your email - I'll get back to you ASAP.. Cheers!~m


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## AaronB (Jan 29, 2005)

Ice does not wear shingles out. Many times homeowners will chip ice away, which will damage the roofing. Ice on a roof is not a bad thing. It can have an insulating effect. If youre getting a new roof, make sure to address this situation with your roofer. Any good roofer can keep water out IF he gets properly paid for his work.


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