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Old 06-11-2009, 08:17 PM   #16
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Quote:
Originally Posted by Ron6519 View Post
The smaller areas will undoubledly benefit from continuous ventilation to the ridge through a linear vent system in the soffit.
Ron

Ron,
If you mean take out the individual vents and put in a continuous one, I'm not even sure I could do that at this point unless I was to remove and replace the whole soffit face, since the holes I cut were 8" for the large vents. I think the strip vent is half that. I may add more individual vents depending on what sort of benefit I see from the insulation.

I'll take a look up top this weekend and see what how continuous the eave looks.

Thanks
Eric
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Old 06-12-2009, 08:08 AM   #17
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I have a program that can tell what you should save by insulating. If you want me to run your numbers I'd need to know:

1.) What's the closest major city near you that has similar weather to yours (they will likely record the heating & cooling degree days which I need)

2.) What's the Sq. Ft of the roof

3.) What do you pay per kW for electricity
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Old 06-12-2009, 08:22 AM   #18
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Everyman, one thing you may want to consider: It seems you are pretty set on using blown insulation to achieve a certain height of insulation in your attic and that's not a bad idea. BUT- I had our local GA. Power Energy Audit team come to my house a few years back, as they do a free Energy Audit to help you, and they gave me some recommendations I had never thought of. Included in this was that addition of adding attic insulation when I thought I had plenty. They recommended though, that I add batts or rolls perpendicular to the run of the ceiling joist and leave the air space between the old insulation and the new as it was created. They had all these fancy charts which showed that the air trapped between the old and new insulation would act as extra insulation at no cost. I admit I had more room to work than it sounds as you may have but it was still a PITA, but worth it. Just a thought, David
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Old 06-12-2009, 10:31 AM   #19
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Even when properly secured, the weight limit for unsupported insulation over regular 1/2" USG drywall on 24" joists is only 1.3 lbs/sq. ft. So check out the weight of what you are wanting to add and try to estimate the weight of what is there. If the total exceeds 1.3 lbs/sq ft then you will need to find a way to support the additional weight of the insulation on the joists instead of on the drywall.

Some guys don't even think about what weight their drywall can support, add a bunch of insulation and have problems. It's good you're checking into it before adding more insulation.
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Old 06-12-2009, 04:41 PM   #20
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Quote:
Originally Posted by Piedmont View Post
I have a program that can tell what you should save by insulating. If you want me to run your numbers I'd need to know:

1.) What's the closest major city near you that has similar weather to yours (they will likely record the heating & cooling degree days which I need)

2.) What's the Sq. Ft of the roof

3.) What do you pay per kW for electricity
Wow sounds cool, I live in Austin, hopefully that shows up. If not SA would be the next closest and then Dallas.

The house proper has a 2000 Sqft footprint. I'm not sure about the roof. It has the lowest pitch without being flat. I pay .10678 flat per kW all day.

Curious to hear what this is going to amount to.

Thanks
Eric
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Old 06-12-2009, 04:47 PM   #21
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Originally Posted by Thurman View Post
They recommended though, that I add batts or rolls perpendicular to the run of the ceiling joist
David,
I'll give this some thought. For the most part I doubt I'd get very much air space because even with the compression it's no more than an inch below the height of the rafters and even then only in spots. The other problem is due to the low pitch and goofy angles there seem to be trusses fanning out every which way. It would definately be a chore to run it as they are suggesting. However this way would offer the not inconsiderable benefit of not putting any extra weight or very very little onto the drywall as it would mostly be supported by the rafters. I could also I think could totally skip having to crawl around stapling up all of the rafter guards. This idea does merit some consideration.

Thanks,
Eric

Last edited by everyman; 06-12-2009 at 04:54 PM.
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Old 06-12-2009, 04:54 PM   #22
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Quote:
Originally Posted by jogr View Post

Some guys don't even think about what weight their drywall can support, add a bunch of insulation and have problems. It's good you're checking into it before adding more insulation.
Thanks, I try to think ahead as much as possible. There's little I hate more than spending a bunch of time and money doing a job only to find it's created another job for me to have to deal with. I can easily weigh what's up there; I'll have to find a way to get some stats on the weight of the new AttiCat stuff.

I wonder how crazy it would be to lay and even staple plastic sheet over the rafters and then blow the glass on top of that? That way much like running batt perpendicular to the rafters, the weight would be distributed over the them rather than the drywall? I'm not sure what the effect would be of putting a hard moisture barrier like that up there though.
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Old 06-12-2009, 05:36 PM   #23
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Great, living in the major city sure makes things a lot more accurate! The heating degree days for Austin is 1,920 and cooling is 2,628. 2000 sq ft ceiling is being used, and with the 3" insulation you have now if it is blown cellulose is currently R10.5 and you pay 0.10678/kW (I'm a little curious if you included all the additional fees as I pay $0.23/kW when's all said and done).

Increasing the attic insulation to R18 total (I recommend blown) would save you 5,120,000 btu's of heating and 7,008,000 btu's of cooling which amounts to
$219.26/year in electricity for cooling
And for heat savings
$160.19 if you use electricity for heating ($379.44/year total)
$95.54 if you heat with oil (@ 2.09/gallon) ($314.80/year total)
$99.65 with pellets (@ $225/ton) ($318.91/year total)
$50.12 with wood (@ $185/cord) ($269.37/year total)

Increasing it to R30 in total would save you 7,168,000 btu's heating and 9,811,200 btu's cooling which amounts to
$306 for cooling
and for heating (using prices already stated)
$224.26 for electricity (for $531.22/year total)
$133.76 for oil (for $440.72/year total)
$139.52 for pellets (for $446.47/year total)
$70.16 for cord wood (for $377.12/year total)


Increasing it to R40 total would save you 7,936,000 btu's heating and 10,862,400 btu's cooling which amounts to
$339.85 for cooling
and for heating (using prices already stated)
$248.29 for electricity ($588.14/year total)
$148.09 for oil ($487.94/year total)
$154.46 for pellets ($494.41/year total)
$77.68 for cord wood ($417.53/year total)

As you can see, you have to determine if it's worth paying the extra money to go from R30 to R40 there isn't that big a difference so... if it's cheap to do or you plan on staying there a while it will be likely worth it. Also, expect slightly more savings than stated because you'll be covering the tops of the ceiling joists so they will no longer short circuit heat/cold to the ceiling below. My program can't account for the additional savings that will incure.

Last edited by Piedmont; 06-12-2009 at 05:49 PM.
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Old 06-12-2009, 07:32 PM   #24
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Very nice. That's great to hear, because it looks like I could get ROI on this in just a few years. Currently I only live in half of it and rent the other out. Depending on my financial situation I might move to something bigger in a few years and then both units would be rented. Even though I wouldn't be profiting from the insulation directly at that point, it will still be a major benefit in trying to keep it rented. Tenants like cheap bills.

The only thing not included in my energy rate is a $20/month access fee, which currently adds about 15-20% to my total bill which varies from $85 to about $175 next month.

I think what you stated about covering the tops of the walls is important because I've felt since moving in here that the wall mounted thermos are giving me erroneously high readings which unfortunately tenants see and assume something is broken. My last tenant was calling me every day and telling me the AC was broken, because it wouldn't go below 76 in the summer, but every time I'd go over there, it was like an ice box all through the place, but of course the walls were sightly warm because they were wicking heat, so the thermo said it was hot. She wasn't the sharpest tool in the shed and couldn't get was I was saying and kept trying to force the system down to 70. Then she complained that it would never shut off.

It sounds like r30 is definately the sweet spot.

I do have one other question although it's slightly off the topic of the thread. I've been told that it's not wise to allow the ducts to be covered by insulation as this can act like a warm blanket. The ducts are the newer style silver insulated flex lines I think R6. The problem is the company that the PO hired to install both systems cut corners and didn't really allow enough slack to hang most of them so they are off the ground. Also I've already spent a full day up there mastic'ing all of them onto the vents so I'm less than keen on the idea of trying to extend or replace them. How much will I be shooting myself in the foot to blow insulation around the sides of them? I have to wonder whether the "energy audit" company that told me this even knew what they were talking about as they are now apparently out of business. The guy's theory was that insulation just slows heat transference down but that it still retains the heat that it absorbs, so whatever heat it took in would eventually soak into the duct work. If this was an issue why would they insulate ducts? I don't follow the logic, however I've seen plenty of photos of ducts hanging in the air so someone must believe it.

Regards,

Eric
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