Insulation, Cost and Effectiveness
I am starting to do research on building a SF spec house and have always done batt insulation, but am looking to upgrade on this current green project. In my area, the requirement is R25 in the walls and R38 in the lid.
The problem is cost. Some of these kinds of insulation are a multiple of regular batt insulation.
I am wondering if anyone has put in a $/sf cost for the different kinds of insulation available, or, better yet a multiplier. It would be nice to know that batt insulation is X, blown in fiberglass is 3X (that is the bid I just received) and on down the line through the different spray in type foams. Do any of these pencil out if you don’t live in the house for 50 years?
Also, does anyone have an opinion on what is the most cost-effective type of insulation where there is the most bang for the buck. For instance, a friend here in Seattle insists the most cost effective strategy is blown-in fiberglass insulation in the walls and doubled up 12 inch batts (at 90 degree angles) in the lid. Your thoughts?
Replies
My memory is a bit fuzzy, but my recollection was that fg batts were about $1 / sf, cellulose about $3 / sf, and icynene was about $6-7 / sf. I'm sure it varies a lot by region, but that might get you close as to the relative costs.
Everybody wants to be green and reduce energy costs, but for some of these products it's really tough to justify the added cost. I really wanted to put icynene in, but I just couldn't see it ever paying off in my lifetime in the house. Even if the better stuff is 10-20% more efficient, fuel bills just aren't that high to justify the added expense, IMHO, unless you really think you'll live in the house for 30 years.
I went with blown in cellulose, and then 1" of solid foam insulation (for a thermal break). That seemed to be a good mid-range option.
Thanks. That is along the lines of what I am hearing here too. On my last project, we ran all the hydronic heating and the hot water off a 60 gallon fast response gas water heater. Plenty of heat and hot water for both in a 3500 sf house-- worked great. But the best insulation dollars spent by far was triple insulating the water heater (so it did not heat the garage where it was located) and insulating the hot water lines and heating lines to the point where you wanted the hot water. Also running a well insulated continuous loop in the hot water system was very efficient, saving gas and water.I am of the belief that real green building also saves you green-- in your wallet.
If you're really an energy nerd then look into spray foam insulation. For Corbond you can roughly figure 3x the cost of a garden-variety fiberglass batt job.
Thanks. I have used Corbond before in limited areas where I had a waterproof deck over heated space. Three times would not be so bad at all. I seem to recall 6 times and 7 times the cost of regular batt insulation on a $/sf basis.
I think it depends on whether its closed cell foam or open cell foam. Open cell foam has a similar R-value/inch as cellulose, and costs around 20% more (I believe). This is probably a little more than 3X fiberglass.
Closed cell foam has an R-value/inch that is about 2X cellulous, and also costs about twice as much as cellulose (and around 2X as much as open cell foam), and around 6-7 times fiberglass.
I think you get what you pay for- isocyenene spray application is like having a SIP manufacturer coming to your site to manufacture SIPs for you. The sealing characteristics don't compare to other insulations available.
The other advantage to help you justify the cost is the stability of the structure. Here in the Pacific NW we have a lot of earthquakes. A 2x4 structure full of closed cell foam has the same stability as a 2x6 structure.I guess it adds substantially to soundproofing as well.
>>A 2x4 structure full of closed cell foam has the same stability as a 2x6 structure.
Who has done the testing that supports this?
I am not sure. I heard from my inspector that there were houses still being built with 2x4 walls that passed seismic/structural review because of blown in rigid foam insulation. I guess I can see it. The whole thing would be like a reinforced Igloo cooler. But in an earthquake, I am a big believer in California code, lots of wood, hold-downs, etc. The Kobe earthquake proved that. But, if cost is no object, you can always do both. Go with 2x6 wall construction sprayed full of closed cell foam. You will always be warm and you will worry less about earthquakes too.
Consider BIB system and wet applied cellulose. Should not increase significantly your cost and provide better cavity coverage. I did my HD fiberglass a couple years ago in Hood River for about $1 a sqft installed (about what I would pay to buy materials only!). Seems like the installer told me it wouldn't cost me 20-30% more for the wet applied cellulose ... I've seen this and am impressed ... messy, but effective.
You could set up a spreadsheet as you get bids and compare on a cost per R-value basis. That might help put it in perspective. Generally I think you tend to get what you pay for.
Also consider the absolute cost in perspective to the entire project. Spend and extra $1,000 or 2 on insulation ... it's not much if the house is $300K and it provides long term performance.
Attics - if you have a traditional open attic, I would encourage cellulose for better coverage and good density to resist air flow ... don't forget to seal all ceiling penetrations!