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Old 03-13-2013, 03:35 PM   #1
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Insulation in an old cape


I have an old cape code style house (1.5 story) and want to better insulate the attic to keep 2nd floor cooling costs down in the summer. Aside from increasing the amount if insulation in the attic, there are 2 other things I am thinking of doing but I'm not sure if its a good idea.
On the sides of the rooms upstairs, there is a knee wall, then the wall/roof line slopes up to the ceiling. There is insulation above the ceiling but none in the knee wall or in the rafter for about 5 feet between the knee wall and the ceiling. There's no way to get behind the knee wall without tearing down the plaster...so that is out.
What I'd like to do is install rigid foam insulation between the roof rafters in that 5 ft section of uninsulated wall. From the attic, it looks like I should be able to slide the foam down there.
Does that sound like a good idea? Also, Is there a certain type of rigid foam that I need to use or should I just go with the greatest R-value that is still thin enough to fit in the cavity while allowing air to vent through?

The other thing I was thinking of is adding a radiant barrier as well. The only concern I have is that the house doesn't have a ridge vent. Just gable vents as well as an attic fan that I installed last year. I'm not sure if the radiant barrier would be effective without a ridge vent.
Any help or suggestions would be appreciated.
Thanks!

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Old 03-13-2013, 10:58 PM   #2
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Insulation in an old cape


If it were me, I would just leave it alone and go with your current configuration of 2 gables and attic fan, with a programable thermostat for about 35 dollars. If it just an upstairs bedroom keep thermostat at 64 during day and 66 at night.

Use either 2 gables with attic fan like you have already or ridge vent. Do not use both, as they will work against each other.

Main thing is, you want air to get to the underside of your roof to prevent rot and mold.

Just a suggestion,-------------------------- This is mainly an hvac forum.


Last edited by Gary in WA; 03-16-2013 at 10:15 PM. Reason: removed non-applicable forum suggestion text.
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Old 03-13-2013, 11:05 PM   #3
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Insulation in an old cape


#1 Go back and add your location to your profile.
Just go to quick links.
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Old 03-14-2013, 08:48 AM   #4
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Insulation in an old cape


If you are going to insulate the underside of the roof, the reality is that you will be treating that kneewall area as conditioned space and in order to keep that air from stagnating, it should be circulated.

The other issue is that you will be keeping that framing much colder by thermally uncoupling it from the interior and if you have any open gaps in the foam or areas where moisture (vapor) can get through, the rafter will be so cold that they will foster condensation.

Can it be done, yes...just carefully.

You will probably want to dense pack and insulate the slopes at the same time and leave the last section of the upper attic as vented.

Location will help with the specifics as Joe mentioned too.
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Old 03-14-2013, 09:56 AM   #5
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Insulation in an old cape


if there is NO access to that kneewall, cut the access panel and insulate the kneewall itself and the flat. Why heat and cool the unused space. Also, airseal ALL penetrations in this area, including the bays that I assume travel underneath your floor. That is going to make a world of difference for you alone.
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Old 03-15-2013, 02:08 PM   #6
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Insulation in an old cape


Thanks for the replies! Just for clarification, my main concern is keeping the 2nd floor cool in the summer. I'll be a dad in a couple of weeks and the second floor is ridiculously hot in the summer. I have an attic vent fan that I installed on the roof 2 years ago. Motor keeps burning out. I guess I'm setting the thermostat too low (I think I had it set at around 110-115 degrees.
When the fan worked, it did help. On really hot days it would get well into the 90's upstairs. After installing the fan on the roof the upstairs temperature was noticeably reduced...so I need so swap out that fan motor and lower the thermostat while its still bearable in the attic
Getting behind the knee wall would require ALOT of work and with the baby coming I don't have the time nor do I want to make a mess and expose the kid to possibly harmful substances.
right now there is no insulation anywhere inside that cavity behind the knee wall on the south side of the house.
I renovated the entire first floor last year and removed the plaster and insulated all of the walls on the perimeter of the house as there was no insulation. While renovating I was able to get behind the knee wall on the north side of the house by going up through the 1st floor ceiling joists. I wasn't able to do that on the south side of the house...where the sun is beating on the roof all day.
I'm trying to do anything possible to keep the heat down aside from keeping the window AC units running all day long. Plus my wife doesn't want an AC in the babies room because she thinks it's not good for the baby. (not sure how true that is. I guess I need to research that next).

Last edited by frankdb; 03-15-2013 at 02:11 PM.
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Old 03-16-2013, 01:02 PM   #7
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Insulation in an old cape


Just a couple of links that might be helpful
http://blog.energysmartohio.com/blog/
https://www.google.ca/url?sa=t&rct=j...43828540,d.aWM
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Old 03-16-2013, 02:06 PM   #8
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Insulation in an old cape


Just realize that ANY insulation work you do is going to be compromised by having that open kneewall. You need to incapsulate the entire building envelope.

Just as an example, if you have a flat attic of 1000 ft, and the gaps and breaks in the fiberglass add up to only 50-100 ft, it kills about 30-40% of the effectiveness of the insulation.

So having that entire kneewall completely untouched is going to truly hurt the value of any other investment you might make in the area, whether it be an insulation upgrade, or the air conditioner.
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Old 03-18-2013, 08:43 AM   #9
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Insulation in an old cape


Thanks again for the replies. Unfortunately getting behind that kneewall will have to wait a while. The kneewalls are actually in closets that run along each side of the room. So to get back there, I would need to remove the closet shelving and make a hole in the kneewall and even then...I dont think any normal sized human would be able to fit back there...so I'd probably need to take the whole plaster wall down...
I also decided not to go with the rigid foam when I saw the prices at home depot. I'm going to try to figure out a way to slide some fiberglass insulation down there. I know it's not idea but its better than nothing.
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Old 03-18-2013, 10:49 PM   #10
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Insulation in an old cape


just my thoughts again, but don't waste the time or effort. I can tell you that you are going to see VERY minimal results from insulation that isn't properly installed. You would be better off to keep the extra money in your pocket for now, and possibly hire a pro when you can afford as cape cods are the most difficult houses to address properly with all the angles in your thermal boundary.

If you are in NY, and you have no insulation in that kneewall now, go look into the NYSERDA program. It will offer you rebates and interest free financing. You may even be able to get it done with no money down. PM me if you want to run the preapproval paperwork info.
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Old 03-19-2013, 10:32 AM   #11
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Insulation in an old cape


Quote:
Originally Posted by asinsulation View Post
just my thoughts again, but don't waste the time or effort. I can tell you that you are going to see VERY minimal results from insulation that isn't properly installed. You would be better off to keep the extra money in your pocket for now, and possibly hire a pro when you can afford as cape cods are the most difficult houses to address properly with all the angles in your thermal boundary.

If you are in NY, and you have no insulation in that kneewall now, go look into the NYSERDA program. It will offer you rebates and interest free financing. You may even be able to get it done with no money down. PM me if you want to run the preapproval paperwork info.

Thanks! I'm going to look into this.

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