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Venting Cathedral Cieling W/ Skylights

 
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Old 12-06-2009, 03:34 PM   #1
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Venting Cathedral Cieling W/ Skylights


I'm a newbie to this site. I'm 34 years old and have been on my own doing (mostly) remodels, additions and alot of flooring for about 3 years now. I've been in construction (doing mostly remodels) for about 7 years. The question I have is actually about my own house. I bought our (wife and 4 kids) house 4 years ago and last winter I had a huge ice dam on the sunroom that is on the front of the house (ranch house w/ 5- 12 pitch roof. The house has a basic attic and dont have an ice problem on the rest of the house but every winter I have an ice dam on the sunroom (the room is about 8 feet deep and 13 feet wide and was an addition to the front of the ranch). It's kind of a unique room that is right off the living room and sits about 2 feet below the rest of the house w/ steps going down and a 6' wide by 7' high opening. It has cathedral ceilings w/ 3 skylights that are only about 2' from the drip edge on the front of the sunroom.
When I had the ice dam last winter water came in all over on the front of the sunroom- mostly ran down the drywall and came in through the casing on the top of the 10' wide window in the front of the room and I also know the skylights were flashed wrong and the new roof (it was replaced right before I bought the house) was installed w/ the shingles not over hanging the drip edge!
I thought what caused the ice dam was the lack of venting in the soffit on the front of the sunroom. When I tore all the drywall out they did put in vent baffles before they insulated but never vented the soffit so I assumed this was the problem until we just got pounded this last weekend w/ snow.
When I redid the inside of the sunroom before I drywalled I installed the styrene baffles then put in R22 insulation. I couldnt put in R38 because the joists arent big enough. I then vented the soffit w/ those 3 1/2" round vents (one every foot, 12 total). I also had my roofer put ice and water shield over the hole sunroom roof (and actually a couple feet above it) and got the correct flashing kit for the lights.
Here we are in the snow season again and I have ice cycles all over the front of my sunroom and an ice dam forming ! The thing that really gets me is that I'm a builder and I consulted 2 of my friends who are good builders (one of them actually said I'm prolly screwed and stuck w/ just using heat tape) and thought I had it done right, guess I was wrong.
If any one has a suggestion I really appretiate it. I dont have water coming in (praying!) and I'm glad it's my own house and not a customers, at least I can figure it out at my expense instead of at my company names!! Thanx again for any suggestions...
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Old 12-06-2009, 04:14 PM   #2
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Re: Venting Cathedral Cieling W/ Skylights


What directional side of the house is it on?

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Old 12-06-2009, 04:16 PM   #3
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Re: Venting Cathedral Cieling W/ Skylights


In some circumstances, ice dams are impossible to prevent. Low pitch roofs, improper venting at eaves and ridge, heat escaping through light fixtures and heat runs, etc. Last year we had our harshest winter in 20 years. We looked at a few jobs with ice damming and learned a lot. The cathedral ceilings are also a factor, but there is nothing that you can do about that. Heating cables can be installed and possible even a power vent system. Some of the roofers around here were out breaking up ice dams last winter as a form of maintenance.
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Old 12-06-2009, 08:29 PM   #4
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Re: Venting Cathedral Cieling W/ Skylights


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Heating cables can be installed and possible even a power vent system..
How do the power vent systems work?? The house does have a ridge vent and the pitch of the roof is fairly common, it's a 5/12. There's no heat runs in it and I know it's vented (however, I'm concidering getting rid of the 3 1/2" vents and replacing all the soffit w/ vented aluminum on the sunroom). I also know the vent baffles go from the overhang into the attic w/ no obstructions. I did install 3 can lights but I looked for "hot spots" above those on the roof (melted snow) and there arent any. The odd thing is that there are 2 hot spots just above the sunroom roof that are actually over the living room (in the same bay as the skylights, maybe a coincidense?). I think I'll also go in the attic w/ a bag of insulation and put it over in this area.
Twill59- the sunroom (and the front of the house) faces straight south.
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Old 12-06-2009, 09:19 PM   #5
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Re: Venting Cathedral Cieling W/ Skylights


This is more of a remodeling question for the DIY forums, isn't it?

Facing south is most of your problem besides the lack of insulation. A Contractor would have pointed that out for you. If you could post a pic, it would be helpful.
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Old 12-06-2009, 10:45 PM   #6
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Re: Venting Cathedral Cieling W/ Skylights


even the building science guys don't all agree on roof venting details
thing you have to remember is that soffit vents can bring in huge amounts of moisture laden air that can and will condense on insulation and roof sheathing if conditions are right
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Old 12-06-2009, 10:58 PM   #7
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Re: Venting Cathedral Cieling W/ Skylights


I have seen several cathedral ceilings framed with 2x6's, stuffed with insulation, ganged skylights, and no vetilation.

All in the same addition, all without a problem.
It is like black magic sometimes.
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Old 12-06-2009, 11:37 PM   #8
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Re: Venting Cathedral Cieling W/ Skylights


Hello,

When you redid the insulation and venting did you cross vent below and above the skylights? If not, no matter how much soffit or ridge vent you put in, the bays below and above the skylights are not venting. This could very well be your problem.


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Old 12-07-2009, 12:08 AM   #9
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Re: Venting Cathedral Cieling W/ Skylights


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Originally Posted by Roofboy View Post
Hello,

When you redid the insulation and venting did you cross vent below and above the skylights? If not, no matter how much soffit or ridge vent you put in, the bays below and above the skylights are not venting. This could very well be your problem. Keith
No- I dont know how to do this as the skylights are 2' wide so they completely fill the void between the joists. I just put a baffle in front of the skylights (toward the soffit) and insulated right to the sheathing behind them because no matter what I did venting behind the skylights would've been useless. Also, I tried to put pics of it up but cant figure out how and I cant find good words to narrow a search on how to do it (searching "post pictures" comes up w/ alot of results!). Thanks again for the help.
Also, I thought about putting this in the remodeling part but it was kind of questionable.
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Old 12-07-2009, 01:45 AM   #10
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Re: Venting Cathedral Cieling W/ Skylights


Hello,

What you do to cross vent is (if from the roof top) use a skil saw and cut out a 5" to 6" section of both rafters on either side if the skylight about 1 1/2" deep. Do this in the front and the rear of the skylights. This allows air flow to enter the bay and go around the skylight. If the roof top option is out and you can get at the rafters from the inside use a 1" to 1 1/2" paddle bit and drill several holes close to the sheeting( at least 5 to 6 holes) in front of and behind the skylight. Again this allows air flow.

Hope this helps.

Keith

Last edited by Roofboy; 12-07-2009 at 02:05 AM.
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Old 12-07-2009, 12:54 PM   #11
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Re: Venting Cathedral Cieling W/ Skylights


I guess you need to have fifteen posts before you can post a pic, this is #13
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Old 12-07-2009, 12:54 PM   #12
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Re: Venting Cathedral Cieling W/ Skylights


This would be #14
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Old 12-07-2009, 12:55 PM   #13
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Re: Venting Cathedral Cieling W/ Skylights


Now I should be able to put up a couple pics of it....
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Old 12-07-2009, 12:59 PM   #14
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Re: Venting Cathedral Cieling W/ Skylights


I didn't read all the replies, not even all of the topic but here goes my answer based stricly on your title for this thread.

When venting a athedral ceiling, the most common problem is the insulation restricting the air flow. Therefore often the roof deck needs to be removed and rafter baffles installed to create a positive gap betwen the insulation and roof sheathing. It's a shame, because the insulation contractors went cheap and didn't buy the baffles... most consumers have no idea and in the end get what they paid for.

So let's assume the insulation was properly done, or you are correcting it, the best way to ventilate around skylights is to drill a series of holes no larger than 1" in diamater spaced at the exact center of the rafter. You may need to futher compress in the insulation in these areas to allow air flow. The key is to drill the several holes on the rafters on both sides of the skylight both above and below the skylight. In doing this you create a horizontal air flow around the skylight.

Some of you may be thinking that doing this will weaken the rafter, and you are partially correct. IF the holes are not palced in the exact center (between sheathing and ceiling) then yes the rafter will be comprimised. However if the holes are exact center and properly spaced (if drilling 1" holes leave 2" between each hole) the rafter will not be weakened in any way.
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Old 12-07-2009, 02:26 PM   #15
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Re: Venting Cathedral Cieling W/ Skylights


I just tried to attach files, see if it worked??
Attached Thumbnails
Venting cathedral cieling w/ skylights-dsc03999.jpg   Venting cathedral cieling w/ skylights-dsc04000.jpg   Venting cathedral cieling w/ skylights-dsc03935.jpg  
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Old 12-07-2009, 03:09 PM   #16
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Re: Venting Cathedral Cieling W/ Skylights


I'm going to hazard a guess and say where the sunroom ties into the main roof, the ventilation stops there.

There is probably a lintel beam or headers galore at that tie-in, with no way for the attic air from the sunroom to escape into the attic of the main house, creating an ice dam on the sunroom and not the main building. If this is the case I would say the best thing to do is drill some holes to allow ventilation (more recommended, however probably not legal!), or install a shingle over vent spanning the entire width of the room (not recommended). .

Just a guess.
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Old 12-07-2009, 03:49 PM   #17
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Re: Venting Cathedral Cieling W/ Skylights


Too bad you probably can't reach the old eave in the orginal attic. You could bore some holes in that to let the sun room vent into the main attic of the house.

It might just be chocked off by those skylights and nothing you can do now.
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Old 12-07-2009, 09:45 PM   #18
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Re: Venting Cathedral Cieling W/ Skylights


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Too bad you probably can't reach the old eave in the orginal attic. You could bore some holes in that to let the sun room vent into the main attic of the house.

It might just be chocked off by those skylights and nothing you can do now.
The room is vented from the soffit on the front to the original attic w/ the end caps on the ends of the bays that go below the vent baffles to keep the insulation in, I installed the insulation and the baffles- basicly did everything except the final roof and the drywall. The skylight bays however are not vented behind them. It (to me) is just a flat out weird deal. I've seen alot of skylights that didnt have the cross venting (didn't even know you could drill holes legaly in the top of a joist) that didn't have a problem like this. The real weird thing is that the room is lower than the rest of the house so because heat rises you would think it would be less of a problem than the rest of the house. I hate crap like this. I still say I'm glad it's mine and not a customers. I would have gotten cocky and said "I can fix that no problem" and would be ripping it all apart this winter for free. Could it be something w/ air flow cuz the rest of the house is not cathedral and only this small room is?? Maybe it does need some form of forced airflow installed??
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Old 12-07-2009, 10:03 PM   #19
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Re: Venting Cathedral Cieling W/ Skylights


power venting in the winter could make things worse,they can actually pull conditioned air from the living areas up into the attic
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Old 12-07-2009, 10:16 PM   #20
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Re: Venting Cathedral Cieling W/ Skylights


I still don't see how that vents from the soffit up to the ridge vent......There should be full venting from the soffit up, including chutes in every rafter all the way through that vaulted ceiling.

It appears the ridge vent is letting a ton of heat out also.

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