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Old 10-03-2011, 11:31 AM   #1
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no venting in a Cape


I need some advice from the roofing side of things...

I have a 1.5 story Cape, no dormers. I have knee wall "attics" that run the entire length of the house on the front and back. I also have an "upper attic" above the second floor.

I've got 5~6' long sloped portions of my ceiling that connect the knee wall and the upper attics. The rafters are 2x6. In the back half there is a wide open space (above the second floor stair case) that acts as a man-sized chase from the back knee wall attic to the upper attic (this is how you'd crawl up to the upper attic).

I have no soffit vents in either knee wall attic, I do have a ridge vent.

We have a bump out vestibule (like an entry way air lock) with a roof that runs perpendicular to the main roof, it's only one story, so it forms a gable about 4-5' out from the main front exterior wall of the house. There is a gable vent in that, and that space is connected to the front attic.

There is no insulation in the knee wall attics, and very little in the upper attic (R15 at best I'd say). So, I'm having insulation done, I've had two professional contractors in, both are very highly rated in the area. Both suggested that I would be better off filling the sloped portion ceiling w/ cellulose up to ~R-19 vs. adding vent chutes, losing 1-2" of depth and then only being able to achieve ~R-13 in the sloped portion.

What is your opinion of filling in those sloped areas? From the back knee wall attic to the front there will still be good general air movement between the two because of the man-sized chase--however there are no intake vents in the knee wall attic back there. From the front there will now be no open channel from the front knee wall to the upper attic if the sloped ceilings are filled.

I will be having a new roof installed within 5 years, the current roof is 20 years old. The front (south facing) is in good shape, but the back has some growth on it, we also had a problem with an ice dam forming back there last year and leaking around a vent stack (which runs up the back exterior wall of the house, so it exits the roof only about ~12" in from the gutters. When the new roof is put in I'm open to some new/alternative venting options (above the sheathing deck perhaps?). I am also open to using those fascia boards that are "hollow" and form soffit vents.

Thanks in advance for any advice

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Old 10-03-2011, 01:38 PM   #2
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no venting in a Cape


Without ventilation in your sloped ceiling section you'll cook your shingles and reduce their lifespan. Also, ventilation only works if you have a top and a bottom (aka soffits in the knee wall space, ridge vent in the main attic, and vent bafles in between). Be sure not to use the styrofoam ones as they will just be crushed by the cellulose.

As for the future roof replacement, they have things called 'ventilated nail base' which is insulation and a vent space screwed directly over the existing sheathing. That is a whole other kettle of fish though...

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Old 10-03-2011, 01:52 PM   #3
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no venting in a Cape


ventilated nail base panels are the best option for capes to get roof ventilation and good insulation without a huge effort.
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Old 10-03-2011, 01:53 PM   #4
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Quote:
Originally Posted by shazapple View Post
Without ventilation in your sloped ceiling section you'll cook your shingles and reduce their lifespan. Also, ventilation only works if you have a top and a bottom (aka soffits in the knee wall space, ridge vent in the main attic, and vent bafles in between). Be sure not to use the styrofoam ones as they will just be crushed by the cellulose.
The roof is nearly 20 years old now and except for the north face side (which has some sort of a fungus growing on it) it doesn't look bad at all. No curling, the shingles are not very brittle either. I've been in both knee wall attics during rain storms, no leaks that I can see (except ice dam ones around that one vent stack).

The south facing side of the house is heavily shaded by large 200 year old trees, and the other side is north facing, so doesn't get much sun at all.

Because of the lack of soffits there is no venting on the back side (north face) and the venting on the front side (with the gable) is inadequate at best.

The insulation contract includes installation of the vent chutes. I am planning to supply the chutes for them to use, they are the thin plastic type found at Home Depot, I was thinking ~5 chutes per slope--two sets of two doubled up and set so they are butted against each other and one to overlap that seam--I want to prevent doing just what you said, which is collapsing them with the dense cellulose.

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Originally Posted by shazapple View Post
As for the future roof replacement, they have things called 'ventilated nail base' which is insulation and a vent space screwed directly over the existing sheathing. That is a whole other kettle of fish though...
So this ventilated nail base... does it make up for having a filled slope section of the ceiling? If it does, then I'd be willing to consider them filling the space now (to get the max. insulation value there and then getting a roofer in 3~5 years who can handle installing the vented nail base.
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Old 10-03-2011, 02:02 PM   #5
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no venting in a Cape


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So this ventilated nail base... does it make up for having a filled slope section of the ceiling?
I assume you mean does it make up for the insulation in the filled slope section? I could...depending on what R-value you choose to go with. You could put anywhere from an R-6+ (1" insulation) to more than you'll want to afford. Below I put a bulletin about the process and a list of 3 products. Even if the "vent board" only reaches a certain R-value you could always add flat foam-only insulation boards below it to reach the desired R-value.

Bulletin: http://www.polyiso.org/BulletinFiles/tb114.pdf

Products:
1) http://www.hpanels.com/images/storie.../Cool-Vent.pdf

2) http://products.construction.com/Man...tion-NST8455-P

3) http://www.atlasroofing.com/tabbed.php?section_url=51
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Old 10-03-2011, 02:49 PM   #6
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Basically you remove your existing shingles, screw down rigid insulation (whatever thickness you want), screw down strapping, screw down new sheathing, install new roof. The strapping gives you an airspace which will lead to new soffits and ridge vent.
The downside is that is makes your fascia very thick looking. Also foam board is fairly expensive.

If you did the above, you could fill in the sloped ceiling section, as well as inbetween the rafters in your knee wall section. This would give you an R value of R19 + the rigid board (usually R5 per inch)

Alternatively, to save money, you could not install the rigid board and just the strapping/sheathing/new roof.
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Old 10-03-2011, 03:12 PM   #7
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no venting in a Cape


Thank you Shazapple and AGW.

I guess what it boils down to is: I am planning to insulate my 1.5 story Cape so that the skin of the interior becomes the thermal envelope (knee-wall attics are to become unconditioned space). I'm currently debating about whether to fill the sloped portion of the ceiling w/ cellulose or not. The advantage of filling it is that I can achieve close to R-19 in that area, the disadvantage is I block venting between the knee wall and upper attics through those channels which will also eliminate air flow on the underside of the roof sheathing.

What I'm hearing is that if I were to replace the roof: have the roof stripped to the sheathing, have some add'l insulation added in the form of a foam board, followed by this vented nail base, then underlayment and finally shingles, I'd achieve venting for the entire roof while also adding some add'l insulation, so having my sloped ceiling area filled with cellulose would no longer be a problem when it comes to venting the roof assembly. Is that right?

If I were planning to do vented nail base within 5 years, would that change your opinion of my insulation plans (putting thermal skin at the interior walls/ceilings--keeping the knee wall attics as unconditioned space, vs. putting the thermal skin at the rafters--keeping the knee walls as conditioned space). One advantage to the thermal skin following the interior walls/ceiling is that I can insulate to at least R-30 on the floor of the knee wall, where-is if I kept it at the rafters the best I could do is R-19 unless I planned to build out the 2x6's to additional depth.

It seems like the vented nail base will also help to prevent ice dams from forming... I'm planning to install close to 400' of de-icing cable within the next month or so, my house is 36' long, I have gutters and four down spouts. Last year we had horrible ice dams that would have ruined our kitchen had the walls not been removed for renovation. In an effort to prevent that from happening again I am planning to install and run the de-icing cables (which nearly ALL my neighbors with similar style homes have). When done I will have close to 2000W of cables running, I figure the costs will be about $250-500/season depending on how often I need to run them. Assuming my current insulation plan does not solve the ice dam formation issues (because I still will have inadequate venting) this vented nail base probably will...
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Old 10-03-2011, 04:28 PM   #8
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no venting in a Cape


Quote:
Originally Posted by bubbler View Post
What I'm hearing is that if I were to replace the roof: have the roof stripped to the sheathing, have some add'l insulation added in the form of a foam board, followed by this vented nail base, then underlayment and finally shingles, I'd achieve venting for the entire roof while also adding some add'l insulation, so having my sloped ceiling area filled with cellulose would no longer be a problem when it comes to venting the roof assembly. Is that right?
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Old 10-05-2011, 10:59 PM   #9
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no venting in a Cape


bubbler, do you have mold in the attic anywhere?

Where are the ice dams located on the roof?
The ice dams are from warm air leaking through the ceiling below. Ventilation will help but air sealing will mostly stop them. http://www.greenbuildingadvisor.com/...stop-air-leaks

http://www.finehomebuilding.com/PDF/Free/021105092.pdf

Many coastal areas may not need venting; http://www.fpl.fs.fed.us/documnts/pdf1999/tenwo99a.pdf

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Old 10-06-2011, 07:19 AM   #10
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bubbler, do you have mold in the attic anywhere?
I haven't seen anything specific, but it smells very musty. This Nov. will be our first year in the house, so I'm not sure if it always smells musty or it's new this year--there was definitely water in the attic as a result of the ice dam over this past winter.

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Where are the ice dams located on the roof?
The ice dams are from warm air leaking through the ceiling below. Ventilation will help but air sealing will mostly stop them.
The ice dam seemed to be located right at the edge of the roof where it meets the gutters. My "overhang" is only ~6", the dams seemed to be situated right above that. The leaking was located at the vent stack which is located in the exterior wall and projects up through the roof.

This picture might give you a better idea:


This is after I had raked this area (all the cleared area is from my raking, there was no obvious melting in any one area, it was fairly uniform. I had chipped away at the ice dam to let the moisture run off. Ultimately I raked the entire roof of all snow. There was nearly 12" I'd say, which is crazy considering the relatively steep pitch of the roof. This is the north-facing side of my house, so the roof is growing little... things... not sure what they are. They seem dead to me, and they come off easily enough.

But anyway, the vent stack is only about 2 shingle's depth from the edge of the roof, that gives you a rough idea of the depths of my overhang. I am green when it comes the idea of ice dams, so I had no idea about the need to rake roofs, etc, the snow built up, then before I knew I had 6" tall walls of ice just before my gutters front & back.

This back area is the only one that leaked into the attic, and as I said, I'm fairly sure it leaked around that vent stack, otherwise it was an amazing coincidence. You can see that there is a slight depression around the stack as well, the sheathing is 1x12s and in that spot it's unsupported and a bit wonky--I didn't want to start re-enforcing or doing anything to change the shingles because is presently does not leak even in the heaviest rain, so I don't want to mess with it too much. But, it's basically the worst possible location for a roof penetration when an ice dam forms. At the time I asked a plumber about relocating it by cutting it off in the attic, going to PVC which would be angled and run along the rafters, then exit the roof maybe 4' higher, but his price to do so was nearly $1000 and he said he wouldn't have been able to do it until warmer weather anyway, plus I'd need a roofer to patch the old location.

The plumber had said if he relocated the vent he would use a "Kozy Kollar".

The fact that it's a metal pipe probably doesn't help with the melting situation, because it will conduct heat.

...for this winter I do plan to rake the snow after every storm, which I didn't start doing until after the leaking started this past year... I am also thinking of adding the heat wires to the edge of the roof and gutters to try to keep them clear of ice.

We're ~10 miles from the coast, so I don't think the coastal considerations will apply to me.



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Old 10-06-2011, 08:52 AM   #11
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Air Seal and insulate that attic.

That will go a long way to controlling the heat loss and melting on the roof.
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Old 10-06-2011, 11:13 PM   #12
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From my library:
http://www.homeenergy.org/show/artic...rmation/id/824

http://bct.eco.umass.edu/publication...ting-ice-dams/

http://www.extension.umn.edu/distrib...ng/dk1068.html

Replace the first 2’ of batt insulation shown here with rigid foam board, taped together shoved tight to the roof deck over the exterior wall outside edge; http://www.buildingscience.com/docum...d-135-ice-dams
Install some more in between the rafters over the wall plate, cover with 2” of fiberglass batt insulation for a ignition break.

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Old 10-07-2011, 11:11 PM   #13
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That kozy kollar is a piece of kozy krap. It is an unfortunate spot but that is usually where you find venstacks. A shingle roof is not meant to be waterproof, just water shedding, so i think you are getting a bit sidetracked on minor things. Heat wires are a bandaid solution. Air sealing, insulation, and ventilation will solve your problems.

GBR, what do you mean by the 2" fiberglass acting as an "ignition break"?
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Old 10-08-2011, 05:43 PM   #14
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Quote:
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That kozy kollar is a piece of kozy krap. It is an unfortunate spot but that is usually where you find venstacks. A shingle roof is not meant to be waterproof, just water shedding, so i think you are getting a bit sidetracked on minor things. Heat wires are a bandaid solution. Air sealing, insulation, and ventilation will solve your problems.

GBR, what do you mean by the 2" fiberglass acting as an "ignition break"?
Most code requires an ignition or thermal barrier over exposed foam depending on the location and accessibility.

http://www.foam-tech.com/theory/firebarriers.htm
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Old 10-09-2011, 12:32 AM   #15
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Whoops, I stand corrected- 1-1/2" fiberglass: http://publicecodes.citation.com/ico...016_par007.htm Thanks, WW.

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