This really surprised me: Some builders in our area put R49 insulation in the attic but my builder only uses R38. I asked if I could upgrade and he said sure for $300 but it probably isn't worth it, he said. He also said he things some places just tell you it's R49 and hope you never bother to measure it. I'd believe it. I plan to live at this place forever, so naturally $300 bucks is pennies to me if it saves me money.

Here's the thing: According to my geothermal guy who says he used "elite software" to calculate heat loss, he's right. I'll save about $2 a year "upgrading." Our builder said you reach a point of diminishing returns with insulation. Anyone have this experience?

The problem with all this is that if the insulation under consideration is loose or batted fiberglass, it isn't delivering anywhere near R thirty whatever or R forty whatever, mostly because fiberglass lets air blow right through it, and it winds up getting compressed, wetted, moldy or pushed aside or whatnot over the years.

If, on the other hand, you are considering various thicknesses of either closed or open cell sprayfoam, then you are getting pretty close to rated performance and yes, upgrading from R38 to R49 might save 2 bucks per year.

Take for example the extreme case of the attic being 100 degrees hotter or colder than the conditioned space, and suppose the attic is atop 1000 square feet of ceiling. Insulated to R40 it loses 2500 btuh Insulated to R50 it loses 2000 btuh, a difference of 500 btuh. In very very round numbers, geo delivers heating or cooling for about a penny per 1000 btu so the insulation upgrade saves half a cent per hour during the 100 degree extreme weather event; proportionally less during milder weather. It would take 400 hours of extreme weather for the failure to upgrade to cost $2

For $50 you can get a 60 day license to use HVAC-CALC. Load your house and experiment with various r values and watch calculated load changes.

I happen to have the Elitesoft package, and it works well, but I can also say that HVAC Calc returned about the same loads for my house as Elite, and only HVAC-Calc has the cheap short term license

Engineer. I'm curious about insulation performance and you've mentioned it in threads before. Can you point me to some literature or studies on it? I found stuff on the fiberglass sites touting fiberglass, stuff on the cellulose sites touting cellulose, .... etc. but not an independent source testing them. It seems like an easy test, so I'm surprised that I can't find anything on Consumer Reports or elsewhere on it. I don't want to spend thousands of dollars more on insulation unless I'll get thousands of dollars returned.

Google Joe Lstiburek, also check out FineHomebuilding.

You need to think beyond the mere R-value per inch of insulation materials to the performance of the entire building envelope.

Installed R value differs from material R value.

I have a 3400 SF ICF house with sprayfoam, and it handles winter design of 30 and summer design of 95 with an 038 heat pump nearly always locked in low stage, in other words, an 026 might have been the better choice. We have plenty of windows and doors. That's proof to me that proper materials properly applied result in excellent performance.

Engineer. Thanks for the references. Any guess as to the price increase I'm looking at for a 28 by 36 two-story. R19 in basement ceiling. R21 in walls R38 in attic floor. I heard it's tons of money but I don't know for sure. This is new construction. I'm handy, too, but I hear that stuff is hard to DIY.

Hopefully, all the voids are going to be sealed with foam insulation and/or caulking. Wouldn't this air barrier from the outside eliminate the need for an additional air barrier? I'm just some dummy so I'm just guessing, but I would think there would be other ways of keeping a draft out of the home.

Perhaps this is a better way to spend the $300 than R38->R49.  As has been pointed out, cellulose and fiberglass aren't air barriers (whereas foam is).  If you seal up all the air leaks then I think you'll get about the advertised value from the loose fill.  If you have leaks, then I suspect that you'll loose a lot through infiltration.

Since foam is an expensive material and caulking/foaming all the leaks is labor intensive(expensive) one compromise I've seen is a thin layer of spray foam to seal the whole area and then loose fill on top of that.  Whether that's cost effective probably depends on the capabilities of the insulation installer.

If I may offer it, here are some quick words of advice.

1 - No one contracted to work on your new home has to pay YOUR energy bills for the next 50 years. No one cares as much about them as you do.
2 - Yes, there is a point of diminishing returns with regards to increasing R-value, however I would be amazed if you could reach such a point with fiberglass as it is both cheap and often ineffective.
3 - It is much more difficult to upgrade your insulation later. Do it now before walls are closed in.
4 - Depending on where you are in you project, investigate SIPs, and spray foam - please don't settle for fiberglass.

Good Luck,
Ed
www.GouinGreen.com

Egouin,
Thanks for the points. As for point 1, I agree with it mostly but think builders have some interest in your heating bill. Around here, all you have to do is ask a few HVAC or other people if Builder A builds a tight home or if Builder A builds a tighter home than Builder B. Many local builders are willing to sacrifice time and money making sure their reputation remains untarnished. Sure, they're all out to make a buck but some have been around for a long time and want to keep it that way.

As for SIPs being better insulated than a stick build home, that makes a lot of sense to me. Every stud is like R-8 so voids are everywhere on stick built. Our builder doesn't do many ICFs anymore, he says, and I don't know many around here (State College, PA) who do.

ICFs confer a couple advantages of SIPs - strength and thermal mass

R38 should be plenty. The R49 is mostly a marketing gimmick. Upgrading your windows (and any sliding glass doors) during construction gets you the most bang for your buck. Adding insulation to attics after the fact is fairly inexpensive. You can also look into a radiant barrier (cheap and easy to install during construction). .

Penn Lyon (the company that built my house) is in Selinsgrove, PA.  Not far from State College.  It might really be worth a call to them.  My transportation costs were in the neighborhood of $15,000 (not sure it was buried in the price).  Obviously, this would not apply to you.
Ed

ICF was my first choice.  It should be yours if you can afford it.  I could not.  Nor could I afford the quotes I got for site-built SIPs.  Modular/SIP it was.

I did get quotes for an ICF foundation - it was nearly 2x the cost of a standard foundation after adding a layer of 2" rigid foam to both sides.  I ended up with a modular foundation.

Ed

I think this forum might argue that the most bang for your buck would be geo.
Double pane windows for instance are only 5% more efficient than well glazed singles with well fitting storms. While it's all a piece of the puzzle, and insulation has 0 up-keep the most bang for the buck is always in the heat plant....especially with tax credits.
J

Cellulose is a pretty good air barrier, if its thick enough. Dense pack cellulose in wall cavities almost rivals foam as an infiltration barrier. The all borate stuff is actively mold and insect resistant, and cheap too. It can be heavy though, may require beefier ceiling drywall to support the weight.

You ought to look up Dana1 on the residential forum he/she is a real insulation guru.

We'll have to disagree on this one - but the reason is our basic assumption and locations.

You assume glazed, well fitted windows.  We don't see that here in Florida very often on standard builds.  Most windows are single pane unglazed.  Upgrading to glazed windows would certainly help a lot.

And we have more sliding glass doors which generally are poorly sealed.  How poorly I did not realize until one day I leaned my head against my glass doors and looked to the side.  I cold clearly see a gap between the doors - meaning I had a huge air leak! 

Also, windows lose far, far more heat than any other part of the house (you can see the impact by doubling the glass space in a Manual J calculation especially if you use single pane unglazed).

Come to think of it, the best bang for the buck is probably putting a film on your existing window (do it yourself - contractors are pricey for this).

gspike. you weren't kidding. Dana is an insulation god! Thanks for the referral.