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Old 05-26-2017, 07:52 AM   #1
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Recommendations for insulation on new construction in SC


Good morning-

We live in upstate SC and are building a new home. We are going with 2x6 exterior walls and will have vinyl siding with a wrap on the outside of the house under the vinyl. The house is a total of 2600 SQFT with the majority downstairs and a small bonus room over the garage. We are planning to live here for the next 50-60 years.

I want to do at least R-19 in the walls but was looking at R-21. The contractor is quoting an increase of 100% in cost to go from R-19 to R-21 in the walls and about $1600 to go from R-13 to R-19. In the attic we are currently spec'd at R-30 and R-19 in the crawl space.

What would be the recommendation for the insulation? Would I be good going with R-19 in the walls and R-30 in the attic or should I move to a higher R in the attic and leave the walls R-19? Also the increase from R-19 to R-21 was much more than I expected. Is that typical? If so I don't imagine I'd recover the costs in energy savings until 20 years or so from now.

I will be using a heat pump that's dual fuel.

Thanks!
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Old 05-26-2017, 09:48 AM   #2
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Re: Recommendations for insulation on new construction in SC


First question is, is the ac unit in the attic? Very common but the worst place to put it.

Quote "The contractor is quoting an increase of 100% in cost to go from R-19 to R-21 in the walls and about $1600 to go from R-13 to R-19."
That doesn't seem correct. It says he wants $1600 to go from R-13 to R-19 and then he wants to double that to go up to R-21.

First, he should never have quoted R13 to be used in a 6" wall, very poor option.
Second, the material costs difference between R-13 and R-19 don't justify $1600, since the labor is the same. Then, going to R-21 might justify doubling the material costs (materials would be about 65% more) but not the labor.

Add in a comprehensive air sealing effort and either R-19 or R-21 is good in your climate zone.

If there will be an ac unit in the attic it needs to be air sealed before it is wrapped in insulation. I believe code now requires that.

Bud
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Old 05-26-2017, 10:43 AM   #3
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Re: Recommendations for insulation on new construction in SC


Hi Bud- Thanks for the response.

The AC unit will be under the house -- this is a crawl space with vents in the crawl space.

That is what I was thinking and from comparing prices on Lowes and Home Depot it seemed way off. I'll have to talk to him again about it. I was suprised about the R-13 and assumed he just missed updating it from the standard used for 2x4 exteriors but didn't expect that big of an increase to set it to what it needs to be for 2x6s.

Basically it sounds like going from R-19 to R-21 for my zone in SC wouldn't warrant the extra cost even keeping the home as long as we are. I see other houses are at R-30 in the attic and that likely would be good as well as I could always increase that later on more easily.
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Old 05-26-2017, 11:09 AM   #4
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Re: Recommendations for insulation on new construction in SC


Give me your nearest big city and with the 2,600 ft² I can estimate your energy costs with R-19 and then R-21. I'm a retired energy auditor and now do consulting. My handicap is I'm do predominantly heating costs so will enjoy playing wit cooling costs.

With this being a forever home it does justify going the extra mile on insulation. One of the points not emphasized is code minimums are just that "minimums". The upper limit is as you said. If you include air sealing that will reduce your home energy costs by about 25% and at a cost that will be recovered much more quickly. Energy star has a web site for guidance.
https://www.energystar.gov/ia/partne...ide_062507.pdf

Although you should be able to do some of the air sealing your builder can do more, more easily and he SHOULD be familiar with the process as it is becoming a requirement. I don't know where NC stands on their energy codes but a quick calll to your local code office would tell you. Even if they aren't mandating some of the newer standards they will before you sell and difficult to retrofit, not that you would need to.

Bud
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Old 05-26-2017, 01:56 PM   #5
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Re: Recommendations for insulation on new construction in SC


Thanks Bud. I'm near Greenville, SC 29615
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Old 05-26-2017, 02:12 PM   #6
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Re: Recommendations for insulation on new construction in SC


Don't know why I was thinking NC, I am getting old. I have a good friend over in Easley maybe some day .

I'll work on the numbers,
Bud
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Old 05-26-2017, 02:34 PM   #7
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Re: Recommendations for insulation on new construction in SC


really rough estimate, but the question is, will it save $50 per year or $500 per year. The answer was close to $50 when comparing R-30 vs R-40 in the ceiling.

I would much rather see the additional $1,000 or $2,000 whatever it would cost put into that air sealing effort, both for the house and the ac unit in the unconditioned crawl space.

Hope that helps,
Bud
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