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Old 03-05-2014, 05:36 PM   #1
dvcochran
 
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insulating a steep pitch roof upstairs


Thanks to everyone who submits advise. We live in middle TN in a cape cod style house with a 10/12 pitch roof. Originally the upstairs was unfinished so the floor was insulated. Several years ago I finished the upstairs. The rafters are 2x6 so the highest R value roll insulation that seemed to fit without being smashed down considerably was R13 with I ran from the ridge down to the soffit. It has knee walls on both sides, each about 5' tall then transitioning to the roof line then transitioning to a ceiling that is around 8' across. The small ceiling area has about 12" of insulation, it is as thick as I could go and not be higher than the ridge vents on each end of the house. The 2x4 knee walls are R13. Again, the rafters are insulated all the way. All the walls are sheetrock. The house has three dormers on the front and a salt box addition out the back roof so neither knee wall is "straight". Where I was able, I made storage areas and/or closets on the front side. The salt boxed area is a large bathroom and walk-in closet that extends to about 2' from the back wall of the house. Also on the back wall is a pull out book shelf and directly behind it sets the hvac air handler. As best I can, I have went in and added another layer of R-13 (with the kraft face pointing toward the outside of the house) but there are some areas I just cannot get to because of the duct work. The house sets facing east so particularly the back of the house really gets hammered by the sun in the afternoon.
My problem:
There is about 900 sq/ft upstairs and originally there was a 2-ton split unit heat pump installed. It was an R-22 system and in the summer was never able to keep up with the rise in temperature in the afternoon. Often the unit would run continuous from around noon to 7or 8pm. There would be a 6-10 degree rise in temperature above the setpoint which I set at 72 degrees so sometimes the upstairs would get up to 82 degrees making it uncomfortable, I think partly because of temperature but also because of humidity.
Last winter the original unit failed. I replaced it with a 16 SEER 2.5 ton compressor with a 3 ton air handler. The hvac contractor said this is the max the ductwork can handle. It moves a LOT more air out the registers. This considerably helped the problem with afternoon temperature rise but not completely. Some days the new unit will run from around 1-2pm to 5-6pm however the rise in temperature over the setpoint doesn't exceed 5 degrees. I even tried a 1500 cfm attic fan (which is noisy) but it made zero difference making me think the heat is not coming from the roof area but instead the knee wall/rafter area. Is there anything I can do insulation-wise or other to remedy this problem or is this just life in the south?
Thanks for the help.

David Cochran

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Old 03-06-2014, 06:38 AM   #2
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insulating a steep pitch roof upstairs


David there is a bunch you can do but Capes are tough to insulated well.

What is the condition of the roof? The reason that I ask is that the easiest want to insulated the slopes is from the top down.

Back the kneewalls and get them insulated and that should go a long way.

Don't start cranking on the attic fan unless you have proper intake and make up air.

How is the venting on the roof?

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Old 03-06-2014, 07:04 AM   #3
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insulating a steep pitch roof upstairs


An interesting problem to say the least since my 2.5 ton AC does a reasonable job with a 1,700 sq. ft. ranch with less insulation than your cape. What is the orientation and size of the windows, the sq. ft. area and is the stairwell open or closed.

Last edited by Fairview; 03-06-2014 at 07:07 AM.
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Old 03-06-2014, 07:17 AM   #4
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insulating a steep pitch roof upstairs


Adding you location to your profile will be a big help with questions like this.
Go to quick links to edit.
Unless you went with spray foam in those rafters you should have built them down enough to fit the proper amount of insulation and baffles against the sheathing for air flow from the soffits to the peak of the roof.
http://www.energystar.gov/index.cfm?...sulation_table
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Old 03-06-2014, 07:54 PM   #5
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insulating a steep pitch roof upstairs


Thanks for the responses. I will try to answer the questions. The shingle roof is in very good condition only 5 years old. The roof has a full ridge vent and large louvers on each end so I feel ventilation is good. I also added a static vent out the wall in the largest area behind the knee wall. Also the soffit lets those areas breathe. As I said, it is impossible to get behind some of the knee wall. What I can get to I already added an extra layer of R-13. Doesn't sound very practical to insulate from the outside in.
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Old 03-06-2014, 07:55 PM   #6
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insulating a steep pitch roof upstairs


I already mentioned that I am in middle TN.
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Old 03-07-2014, 11:09 PM   #7
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insulating a steep pitch roof upstairs


Joe reads too fast... lol. "ridge vents on each end of the house"---- so, R-13 instead of R-38 per code (minimum)....http://energycode.pnl.gov/EnergyCode...tate=Tennessee

That could have something to do with it. Do you mean gable vents in the gable end walls or ridge vents on the peak of the roof?

The second layer shouldn't have a vapor retarder (asphalt paper) but not a biggie- pull it off if you can.
Does the HVAC have an outside air supply or drawing from hot attic?

Gary
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Old 03-10-2014, 07:58 AM   #8
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insulating a steep pitch roof upstairs


The roof has a continuous ridge vent (runs the full length of the ridge?). On each end of the house is a large gable vent. I don't know how to say this any different. The R-13 runs the full length of the 2x6 rafters. There is no way I could fit R-38 on the rafters without cramming it in which would defeat the purpose. Above the ceiling is over 12" of insulation which I am sure is more than R-38.
The HVAC return comes from the conditioned air inside the living space.

Thanks,
David Cochran
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Old 03-13-2014, 09:47 PM   #9
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insulating a steep pitch roof upstairs


Yes, the sloped ceiling requires more than R-13, even it means furring down with new rafters/plywood gussets to stop your heat/cold extremes. As Joe said earlier. You could also add rigid foam board to the attic side of knee walls and cover if required by local AHJ.

Gary

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