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Question DetailsAsked on 2/16/2015

InsulSafe SP blown in insulation added to existing attic insulation worth almost twice the cost of Johns Manville?

House is 23 years old, in Florida with original R19 insulation. Colder in house than outside lately and somewhat drafty in spots. One quote for 2400 sq ft house was $1700.00 to bring to R38 using InsulSafe SP and other was $800.00 using Johns Manville to bring to R30.

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Interesting question, the way it is phrased - I am going to keep this one as a teaching example for energy conservation and insulating classes. Note that you are not only comparing R30 to R38 - you are comparing (assuming original R19 is actually R-19, which is more likely about R16-R18 now, and actaully about R13-R14 including the intervening joists or trusses. You are, dollar for dollar up front, comparing ADDING R-19 blown-in InsulSafe versus R-11 JM. So, nominally 73% more insulation value being ADDED for 125% more cost - so that does not sound like a deal.


If you look at it from the standpoint of what TOTAL insulation you are getting, which is what controls your energy costs so the proper way to compare them to figure energy effectiveness, which is your end result - then comparing $1700 for R-38 end result versus $800 for R-30, or 125% more cost for 27% more total insulation value - so this way the InsulSafe does not sound like a deal at all. This example also demonstrates the flaw of over-insulating - except in very cold areas or areas with extreme energy costs (or shortage of fuel availability like remote sites), once you get beyond about R-24 to R-30 the incremental effectiveness of adding insulation drops off sharply.


As you can see above, which way you look at it can make quite a difference - especially when looking at increasing already nominally adequate insulation, because for every added inch of insulation your relative gain is less - which is where the government recommendation of R60 in all attics falls apart from the practicality standpoint. The other risk with thicker insulation is, especially in cold climates, the freezing front drops will into the insulation because ofthe reduced heat flow, so you can get ice layers forming in the insulation if you have any mosture coming up from below. I have seen attics with a solid inch or so layer of hoarfrost in insulation because of that, where with say R-19 that moisture would have normally either vented through the attic vents, or ended up as frost on the underside of the sheathing, where it commonly evaporates in the spring without causing significant damage.


You do not say what the JM product is - blown-in fiberglass or cellulose, or batt ? (You can respond backk using the Answer This Question link below your question).


If you are talking blown-in fiberglass in each case, then the InsulSafe is no bargain because it is at best a comparable product. If the JM is R-11 fiberglass batt, then you are comparing a blown-in product that can be expected to lose 15-25% of its R value over time due to settlement/mating, versus 5-15% for batt typically so that makes the JM look even better if it is batt. If cellulose (which I hate because vermin love it and it absorbs moisture, and also retains moisture and causes rot in the event of a roof leak) then it can lose up to 50% of its insulating value over time from packing, which would make the InsulSafe look better over the long run.


To really make a fair comparison you should be comparing R-19 in both products - and preferably be looking at the long-term R values, not the as-installed values. However, in Florida I am not convinced that R-38 is a good deal anyway - winter areas are where it really becomes worth it, assuming your attic is properly ventilated so it is not an oven.


One more factor between batt and blown-in - if you have trusses or a lot of cross-bracing in the attic, then blown-in generally does a better job of filling in tight around the bracing unless the contractor is very careful to cut-in the battaround the bracing. On open-bay attics batt works well and can actually go in quite a bit faster - be sure it goes in at least with joints staggered with the existing insulation - in most cases it is best to install it perpendicular to the existing insulation.


Also, you say your house is cooler than outside and drafty right now - of course, if actually colder inside at night then your A/C is working overtime or someone is doing serious raiding of the reefer at night. If you mean cooler in the daytime, then assuming your A/C is not providing cooling (which you should check on), attic insulation is likely not your issue because that situation says the overnight cooling of the house is being retained and the house is not closely "following" the outside temperature rise in the daytime - a good thing.


Sounds to me, just based on what you have said, like your money might be much better spent (and generally much more cost effectively than insulation if house is noticeably drafty) on sealing up air gaps and draft sources. This needs to be done to at least the ceiling and top of the walls before insulating the attic anyway, so you are not losing household air through the insulation and adding moisture to the attic which can get trapped in the thicker insulation and cause attic structural rot issues.


Remember also you are seeing record-breaking cold conditions this year, which may not be at all the norm - so insulating against cold might not be at all cost effective in your area. If you do not feel the heat radiating down into the rooms from the ceiling in the summer, your attic may be fine. You have not said WHY you are looking at attic insulation - did someone come to you suggesting it, neighbors have done it, had energy audit done, or what ?


Draft control, on the other hand, might be energy and cost effective - both because it takes a lot of insulation to equal the energy savings of a few hundred dollars of weatherstripping and airflow blocking outlets and so forth, plus buildings with noticeable drafts "feel" typically about 5-10 degrees colder than stagnant ambient air at the same true temperature due to windchill effects, so cutting drafts can save not only save the energy cost of setting the furnace 5-10 degrees warmer, but also reduces the often quite substantial loss from the house of the heated air you spent money heating (or cooling). I have seen (in a generally cold area with little air conditioning season) far more buildings where $1000-2000 in weatherstripping and localized insulation gap repair provided dramatic returns than ones where reasonable insulation (short of total gutting to reinsulate from scratch) could. I do not have specific numbers to back this up, but my feeling (and that of other energy experts and several energy efficient building instructors I have talked with in the US and Canada) is that for the first $500-1000 you commonly get maybe 5-10 times as much energy savings per dollar as with adding insulation or increasing heating system efficiency, dropping off to probably about equal by the time you have spent around $2000 because by that time you have pretty well solved the air leakage issues, so all you have left is optimizing fuel use or adding insulation to gradually reduce the overall heat transfer. The reason for this is pretty obvious - with drafts, you have effectively largely negative insulation at the leak points because you not only have essentially zero R value airgaps but are also actively transferring quantities of undesireable air, so a bit of air blockage and localized insulation (like around door/window frames) has FAR more effect than maybe bumping the wall or ceiling insulation up by 25-100%. The same applies to door and window changeouts - while improving insulation around the window frame and weatherstripping effectiveness can stop a substantial amount of undesired airflow and heat loss, even the most efficient window changeout for normal (as opposed to ultra-efficiency) triple pane gas-filled windows rarely changes the R value by more than a few points. The most efficient normal construction windows have an effective R of around 5 - about equal to an uninsulated wall, so replacing them for improved R value for many hundreds of $ for a few square feet of slightly improved R value makes absolutely no sense in many cases, especially in houses with poor or even no wall insulation. Even the highest efficiency ones are only about R-20 - about the same as a standard insulated 2x4 wall. That is one reason why under-siding insulation is gaining in popularity - because for about $1-2/SF ballpark you can get a significant improvement in heatflow through whatis typically the largest heat transfer surface in the house.



Personally - if you are committed to insulating the attic, make sure the R-19 is peeled back and the airflow sources from the house (penetrations in ceiling and walls) are sealed as part of the job, and I would only go with the R-30 unless you are trying to achieve a specific energy star rating for resale purposes. Florida building code requires R-19 minimum in attics. EnergyStar recommends R-38 nationwide, and the DOE goes whole hog (without economic justification backup) with R-60 recommended nationwide - course, they also recommend R-40 in walls - good luck getting that in all but special (and expensive) new construction.



My experience is that people spend a LOT of money the wrong place. If youy have not had one done, if you get an energy audit for about $250-400, a proper one will show how much energy you are gaining/losing through windows, doors, air infiltration, walls, floors, and ceilings. In many cases, people jump on increasing existing moderate insulation (like in attics) or new windows to replace existing double ro triple pane older ones, where in terms of savings per $ the best-spent money is in infiltration control and (where opened up for remodel or residing) the area where you have the most exposure - your walls and floors open to outside temperatures (over unheated crawlspace or basement), and uninsulated slabs on grade. For instance, lets say high-efficiency doors or windows cost about $50-100/SF installed for maximum R4 increase with the best ordinary multipane windows. That is equal R value to about 1 inch of foamboard insulation on the wall - so if installed when remodeling or residing you are getting 100 times more for your money (ballpark) with the wall insulation. The same kind of numbers can be run for foam insulation board under new floor slabs in ground contact (though the temperature difference across the slab is less, so the energy savings drop by half or so in most cases).


Granted, with the super or ultra-efficient windows the R value can get up to around 20 or about the same as a 2x4well- insulated wall, but still at around $100-200+/SF - there are an awful LOT of places in the normal house that you can get more bank for your buck.


If not inclined to go for the energy audit, I would go with the R-30 option at most and spend the other money on infiltration control. One other thing - with only two bids you don't know if the bidder differences in price are due to materials or bidder pricing range - you really need 3-4 bids to start to get an idea of who is high and who is low. Also, one of those bidders may be looking at ceiling infiltration control measures in the attic - whereas the $0.33/SF guy is almost certainly not, at that price.

Answered 5 years ago by LCD




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