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Old 10-10-2011, 10:00 AM   #1
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Another cape insulation question


I've read every thread here and in other places on cape insulation, but I've got a question I can't figure out.

What we have:
An unventilated 1955 cape cod style w/ no soffits - just three 12"x12" gable vents. House is in Southern Maine. The upstairs insulation currently looks like this:
- r32 in the 1st floor joists (layers of r13 and r19)
- r13 on knee wall
- r13 in sloped ceiling section (2x6 rafters)
- unknown r-value in upper attic space

Our problem:
Ice dams. I realize there's a ton of heat loss, particularly in the sloped ceiling section, causing the ice dams. I'd like to do something to address this, but we will also be re-roofing within the next few years (possibly even next summer if we add a shed dormer) so I don't want to spend too much now.

My question:
I was considering adding r30 over the joists behind the knee wall and 2" rigid (r10) board against the knee wall and sealing the joist bays. Would this help much with heat loss and, most importantly, ice damming? Would this reduce the heat enough to make any difference or would that r13 sloped section still cook my roof just as much and melt the snow?

Thanks!

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Old 10-10-2011, 11:52 AM   #2
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Another cape insulation question


Don't know what your budget looks like, but if you're doing a new roof next year, then I'd suggest investigating rigid insulation on the roof surface. You can get ventilated rigid insulation panels that can be ordered with varying thickness and R-values. It would be cheaper to add batt. insulation, but I don't think you will reach the goals you are looking for. Also, since you're in Maine, when you do your roof you may want to consider the metal roofing at the eaves (http://www.buildingscience.com/docum...oto_02_web.jpg) to help guard against ice dam formation and leakage.

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Old 10-10-2011, 12:00 PM   #3
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Another cape insulation question


Thanks, AG.

When we re-roof, I am leaning towards closed cell foam and have been considering some rigid on the roof as well. Our budget is likely too limited for the metal eaves...

I'm really sort of curious if insulating behind the knee walls like I described above would be any sort of help for this winter, or am I pretty much screwed if I can't address the r13 in the sloped section?

If I am screwed with out addressing that, Is there any sort of short term (1-3 year) fix that wouldn't involve peeling off roofing or sheetrock?
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Old 10-10-2011, 02:32 PM   #4
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Another cape insulation question


Adding the insulation certainly can't hurt. The sloped section will likely continue to be a source of burden as far as ice dams go. If you've had recurring ice dam issues over the past few years and want a "quick & easy" fix, I suggest the heat trace cables along the gutter lines.
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Old 10-10-2011, 03:04 PM   #5
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Another cape insulation question


Quote:
Originally Posted by exiledgator View Post
My question:
I was considering adding r30 over the joists behind the knee wall and 2" rigid (r10) board against the knee wall and sealing the joist bays. Would this help much with heat loss and, most importantly, ice damming? Would this reduce the heat enough to make any difference or would that r13 sloped section still cook my roof just as much and melt the snow?

Thanks!
I'm going through similar thought efforts, but with less insulation to start with. Some thoughts I have, unfortunately they raise more questions then provide answers--

- Reducing the temps in the knee wall attics will help, last year that was the source of most of my hassles, I had ice climbing up beyond the overhang. I think if I had less heat leaving the knee wall attics I would have had less melting snow/ice building up the ice dams

- Do you have any venting in the slopped area yet? You said you have R13 in there with 2x6 rafters, if you currently don't have good venting there, then improving that might help? My thought is that to prevent any ice dams you don't necessarily have to stop the heat from transmitting (with higher R values) you just have to keep the sheathing for the roof cold. By getting more ventilation through the sloped portions you may reduce the melting there (but won't save any money on heating for sure). Keeping the knee wall attics colder may also help there because the air moving from knee wall attic to upper attic may be colder

- Depending on where your ice dams are forming, have you considered the electric roof heating wires? I know ppl here do not like them, but I think they can be a very good bandaid for people in your (our) situation--you don't want to invest thousands in insulation if you're planning to expand to a shed dormer within 5 years or so, those wires will cost you money to run each season, but they may prevent ice dams from forming, so they would be worth it. As I mentioned in a thread in the roofing forum, I see that many of my neighbors here have them and last year they did not have ice dams while I and several neighbors w/o the wires did.
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Old 10-10-2011, 03:34 PM   #6
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Another cape insulation question


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Originally Posted by bubbler View Post
I'm going through similar thought efforts, but with less insulation to start with. Some thoughts I have, unfortunately they raise more questions then provide answers--

- Reducing the temps in the knee wall attics will help, last year that was the source of most of my hassles, I had ice climbing up beyond the overhang. I think if I had less heat leaving the knee wall attics I would have had less melting snow/ice building up the ice dams

- Do you have any venting in the slopped area yet? You said you have R13 in there with 2x6 rafters, if you currently don't have good venting there, then improving that might help? My thought is that to prevent any ice dams you don't necessarily have to stop the heat from transmitting (with higher R values) you just have to keep the sheathing for the roof cold. By getting more ventilation through the sloped portions you may reduce the melting there (but won't save any money on heating for sure). Keeping the knee wall attics colder may also help there because the air moving from knee wall attic to upper attic may be colder

- Depending on where your ice dams are forming, have you considered the electric roof heating wires? I know ppl here do not like them, but I think they can be a very good bandaid for people in your (our) situation--you don't want to invest thousands in insulation if you're planning to expand to a shed dormer within 5 years or so, those wires will cost you money to run each season, but they may prevent ice dams from forming, so they would be worth it. As I mentioned in a thread in the roofing forum, I see that many of my neighbors here have them and last year they did not have ice dams while I and several neighbors w/o the wires did.
The only ventilation is a single 12"x12" gable vent in each section (one in each lower attic and one in the upper). I have considered installing another vent in the upper attic in hopes of getting some cross flow and getting some heat out the gables rather than through the roof, but I'm not sure how effective that would really be.

I too am hoping that further insulation of the lower attics would reduce the heat flow across that sloped section, but it's only a theory. After all, R13 for that 5' of roof is a little shy of the R-49 suggested for my zone.

I've estimated I can roll out R-30 faceless rolls and add rigid 2" in the lowers for ~$350 and a nasty day of my time. Perhaps it's worth the experiment?

And what about taking the opposite approach? Would I be foolish to seal off the rafters heading up from the lower attic spaces in an effort to keep even less heat from rising into that space? Just run the bathroom fan more?

It's interesting that you and AG have suggested those wires. I've been told that they're pretty ineffective here. I also just found this while pricing them out a minute ago, this guy's in NH: http://www.amazon.com/review/R3TC0BI...videoPreplay=1

Thanks for your input, guys.
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Old 10-10-2011, 04:07 PM   #7
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Another cape insulation question


I'd add heating cable to the roof line, in the gutters and down the leaders.
This would be in addition to the insulation changes. It will eliminate the ice dams and the associated leaks.
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Old 10-10-2011, 04:29 PM   #8
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Another cape insulation question


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Originally Posted by exiledgator View Post
I've been told that they're pretty ineffective here.
I wouldn't consider the heat trace cables to be the sole saviour. But I do believe that if they are properly installed they can serve to be a helpful piece when the worst case scenarios arise. In light of that video, I would certainly read up on the cables and their effective ranges before shelling out the $.
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Old 10-10-2011, 04:43 PM   #9
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Another cape insulation question


Quote:
Originally Posted by exiledgator View Post
And what about taking the opposite approach? Would I be foolish to seal off the rafters heading up from the lower attic spaces in an effort to keep even less heat from rising into that space? Just run the bathroom fan more?
I have two pro insulation recommendations where they both said that I'd be better off putting dense-fill cellulose into that space to create an R15-19 barrier than going with vent chutes and dropping myself to R13 or so. They both stated the venting the space is less of a concern for "climates like ours", in fact one of the specifically said that "they don't even use venting chutes like that in Maine". I have no idea if they are correct or not, it gives me pause for thought, especially since I plan to replace the roof within 5 years, so I will probably go with a vented nail bed for the shingles to move the venting to the "outside" of the current sheathing. Of course that doesn't help with moving moisture/air around inside the attic spaces.

I'm not sure what you mean by running the bathroom fan more? though I do think that an effective fan, which is run before/during/at least 10 mins after a shower is a good thing I installed a Panasonic fan 80CFM fan in my 8x5 bathroom, it's a bit oversized for the room, but I'm more concerned w/ reduced moisture (and smells) then with attaining best energy efficiency. My bathroom door is also cut a tad high which lets it pull air from the hallway easier (rather then thru every other crack/opening). I have the fan on a Leviton occupancy sensor I bought at Home Depot, the fan will start when you enter the room fan and will turn off 10 minutes after you exit, works like a charm and also ensures that guests don't use the shower w/o running the fan. If you have significant moisture on your mirror/walls then you have an issue... everything outside the shower/tub area itself in my bathroom is bone dry after even the hottest showers.

Quote:
Originally Posted by exiledgator View Post
It's interesting that you and AG have suggested those wires. I've been told that they're pretty ineffective here. I also just found this while pricing them out a minute ago, this guy's in NH: http://www.amazon.com/review/R3TC0BI...videoPreplay=1

Thanks for your input, guys.
I think their effectiveness really drops with the temperature, then again do you really need them if the temp is that low? Even if you don't install them on the roof edge itself installing them in the gutters and downspouts will help to keep them flowing. My guess is that a double loop of 6W wire in the gutters will keep them free enough.

Raking the roof after snow storms is also really important--helps take away the most important component of the ice dam which is the snow/water/ice!
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Old 10-10-2011, 04:53 PM   #10
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Another cape insulation question


Another thought on these cables--I didn't watch the video, but was this guy running the cables all the time, or just on a timer? If he had them on some sort of a moisture sensor it's possible they might have started too late after too much snow had built up.

They do make different wattage cable, these are only 5W cables, I have seen higher wattage available, and you can also choose to increase/decrease the size of the triangle pattern, decreasing the top angle (making the triangles more "narrow") will increase the density of the heat. He may also have not doubled up the cable in the gutter.

Lastly, I'd say it also looks like maybe this guy wasn't raking his roof on a regular basis. We went through a pretty bad winter last year, lots of storms dumped a foot+, spending 20-30 mins raking your roof can go a long way. If you don't have a snow blower to cut paths around your house it is much for a pain though
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Old 10-10-2011, 05:00 PM   #11
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Another cape insulation question


Quote:
Originally Posted by bubbler View Post
I have two pro insulation recommendations where they both said that I'd be better off putting dense-fill cellulose into that space to create an R15-19 barrier than going with vent chutes and dropping myself to R13 or so. They both stated the venting the space is less of a concern for "climates like ours", in fact one of the specifically said that "they don't even use venting chutes like that in Maine". I have no idea if they are correct or not, it gives me pause for thought, especially since I plan to replace the roof within 5 years, so I will probably go with a vented nail bed for the shingles to move the venting to the "outside" of the current sheathing. Of course that doesn't help with moving moisture/air around inside the attic spaces.
That's great to hear. While it'd be hard for me to blow anything in w/o pulling something down or making holes, I think I might just go with sealing off those rafter bays. Thanks for sharing those pros recommendations.

Quote:
I'm not sure what you mean by running the bathroom fan more?
I was just referring to getting moisture out of the house if I do reduce my already limited ventilation.

Quote:

Raking the roof after snow storms is also really important--helps take away the most important component of the ice dam which is the snow/water/ice!
I raked the lower ~5' after every storm (that's all I can reach) last year and still lost the battle. I think I just had so much snow melt coming off the sloped ceiling section there was nothing I could do. Plus, I can't reach the back eave as it's 2 stories high in the back yard...

My last ditch thought was to just pay someone to beat the crap out of my roof a couple times this winter to keep the ice dams off...

I love snow so much, but ice damming is challenging that love affair!
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Old 10-10-2011, 05:06 PM   #12
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Another cape insulation question


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They do make different wattage cable, these are only 5W cables, I have seen higher wattage available...
7W cables ... these are available at Home Depot as well.
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Old 10-10-2011, 05:16 PM   #13
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Another cape insulation question


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I raked the lower ~5' after every storm (that's all I can reach) last year and still lost the battle. I think I just had so much snow melt coming off the sloped ceiling section there was nothing I could do. Plus, I can't reach the back eave as it's 2 stories high in the back yard...
I'm fortunate, my roof is a steep pitch so I have access to the entire thing from below. From the front yard it's only about 10' to my gutters from the ground. From the back it's more like 17', and it IS a chore though to get the entire roof. I have a 24' long snow rake, for the backyard I had to setup a 6' A-frame ladder, that gave me the height I needed... it was a little nerve wracking to stand on the last step while having snow rushing down and piling up against the ladder feet, but I figured worst case I fall from 4~5' into a 3' deep pile of snow

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My last ditch thought was to just pay someone to beat the crap out of my roof a couple times this winter to keep the ice dams off...
The friend I mentioned who is getting the new roof did that... first, he paid what I would consider to be an outrageous sum for the effort ($700 for 4 hours of labor) and last the person doing it did a HORRIBLE job--he used metal shovels (like you'd see used for cement), a pick axe and the claw end of hammers... the got the dams down, but they trashed the roof in the process in several places. Since they are "in and out, where's the cash?" type of people you can forget about holding them liable for any damage.

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I love snow so much, but ice damming is challenging that love affair!
This is how I feel about it after buying a Cape too... Growing up we lived in a Colonial, my grandparents in a split level, when I got older we moved to a 3-story townhouse, our apartments have been in triple deckers and victorian's... this is my first experience with a Cape and last year happened to be brutal. We have completely gutted and redone our kitchen, it was a on shoe string budget and we did much of the labor, but came out very nicely we think. Jan. of last year when the walls were down I had water literally pouring down the stud bays from the ice dam... I am absolutely petrified of a repeat this year and scrambling to do insulation and air sealing, as well as get the heat cables up before winter. I also have two snow rakes I bought last year, and will add a third with the little wheels this year to hopefully minimize any interactions with the heat cables.

FWIW, my plans for the heat cables are to separate them into two 20A circuits, one for the roof line and one for the gutters. The 100' cables are 700W each, I'll need four total, so each circuit would have 1400W, I think the power consumption rises with lower temps, but with 20A circuits I should be OK. I will end up with two outlets (one for each circuit) front and back which is a pain. The outlets will be wired to two switches in the basement near the panel, this will give me the option of turning the cables on/off from inside the house. I am anticipating wanting the gutters running more often then the roof line as the snow really packs into the gutter when raked from the roof which is why I want to break them apart. In the non-winter months I'll just unplug the cables have the exterior of my house wired like mad for whatever I need...

Heh, I was just thinking maybe I could buy some old 10W C9 christmas lights instead and string them up everywhere... maybe kill two birds with one stone...

Last edited by bubbler; 10-10-2011 at 05:27 PM.
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Old 10-11-2011, 12:22 AM   #14
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Another cape insulation question


With the minimal R-value in the attic, have you at least sealed any air leaks (source of heat for ice dams) in the exterior top plates? Or thought about adding 4” rigid foam board, taped and air-sealed over the plates and 1’ inbound?

Adding better venting at the slope between two attics could add heat from first attic to the roof deck on the slope. Have you thought about sealing the sloped section from the lower attic? Keep the lower attic colder by adding more insulation there and on the knee walls with a housewrap included or foam board on the attic side studs to prevent wind-washing, air blocking under/over the knee wall. Treat the sloped ceiling as a non-vented one adding local R-value insulation to the inside- stopping air movement, pp.9: http://www.buildingscience.com/docum...d-roof-systems
Keep the attics separate, no need for an ignition barrier on the foam board.


Have you gone in the crawl/basement to air-seal the wires/pipes in all floor holes above and air-seal the rim joists with foam board? This will help stop the “stack effect”: http://www.wag-aic.org/1999/WAG_99_baker.pdf , that drives the heat to the attic warming the roof sheathing.

I’d do all/some of that before installing cables.

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Old 10-11-2011, 10:24 AM   #15
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Another cape insulation question


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no need for an ignition barrier on the foam board.
You sure? Is this a local exception to the code?

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