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I have an old house with exterior walls about 4 1/2″ thick. If I compressed and fitted 5 1/2″ fiberglass bats in the walls would I loose much R value. I don’t have much to insulate so blown in is not practical.
Thank you,
Dave
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Danny,
Compressing FG actually increases the r-value per inch, but since you are decreasing the number of inches, you will be decreasing the total r-value.
If normal R-19 FG has an R-value of about 3.45 per inch, compressing it may up that to say 3.75 per inch (I don't know what the actual number is), but you've only got 4 1/2 inches of it for a total r-value of 16.8.
ORNL testing has shown that an R-21 5 1/2" batt compressed to 3 1/2" yields R-15.
Steve Zerby
(Got this info out of Gene Leger's book)
*In the Feb JLC they published a chart from certainteed but also summarized it as for each one percent you compress, you loose 1/2 of 1 percent of R value.
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I just gotta disagree with the statement that compressing FG actually increases R value. The whole purpose of it is to be fluffy to hold air, to warm it, to create a time-lag buffer between warm areas and cold. Although, if the other guy is right that compressing 1% reduces it by R -.5, means that you are compressing it by 18% which would mean you loose R-9. Ouch ! Save me, this has gotta be wrong. Logically though, if the cavity is filled with FG with compressed versus purely fluffy FG, you are probably trapping just about the same amount of air. The time it takes this air to flow and move about and lose heat will also be similar. It will definitely not impede heat loss as well as properly fluffed-up fiberglass though. So, I will guess that R-19 gets reduced to R-14 or 12 or so. Hey, all of this is a bit general when you're talking about a house where lots of variables exist. You should consider: A-not worrying about it; B-using two layers of thinner FG; or C-switch to some layers of custom cut rigid board. You can even work in a nice 3/4" dead air space that way.
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Not to duck the question, but based on my recent experience a blown in cellulose will suit your purposes better. Unless you are committed to tearing out every single wall, you will get a much better fit more quickly than with batts and will reduce air in/exfiltration too.
Gary, my understanding too was that compressing the fg was not an improvement becuase it is the air, not the glass, that provides the insulation value (glass is not a good heat insulator, just touch a window to check). Cynically, I bet if there were an advantage to compression, Certainteed & Owens-Corning would promote the heck out of it, all the better to sell more fiberglass to the energy purists.
*I don't know if the 1% 1/2% rule is right or wrong - it's what's published by a manufacturer - something I always am skeptical of - but its not .5 r - its .5% of the R. So - a 5.5 r19 bat in 4.5" is approx 18% less thick so 9% less r or R 17.2. Thats the manufacturer's claim not mine.
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Hey, I'll buy that ! That follows what I said about how you are still holding the air within a filled cavity. But Hey again, all you guys (gals) out there that talk about cellulose. I used to be a retrofitter during the energy crisis and have "blown" many a house (excuse the expression). I love the stuff but don't overlook how you have to have the right amount of pressure when you deliver it. You need to periodically check the pressure on your machine. People tend to crank the pressure up to get the job done quicker and what you get is a lot of settling. Whamo, now you have big gaps at the top of your wall cavity. This can negate the whole effort of insulating. The pressure should be just enough to deliver the material (to be non-technical about it). The only other issue is that you have to be permanently diligent about preventing leaks in any of these areas or else you get a big puddle of recycled paper poo poo at the bottom of your stud cavity. (looks a lot like a cow patty, if you know what I mean.) Good luck to all.
*Since you don't have much to do, I would suggest either going with 3 1/2" batts and letting it expand a little (it will) or doing the same with the addition of a 1" version of rigid foam giving you a R value about equal to the 5 1/2" batts.RandyR
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What kind of insulation were you blowing? I shut the gate almost all the way off so it blows lean product to air mix to get the dry cells to pack.
*These numbers also bear out the fact that compressing the FG gives you a higher r-value per inch, though less total r-value. R-19 at 5.5 inches = 3.45 per inchR-17.2 at 4.5 inches = 3.82 per inchSteve
*Oh, Bill!You ruined eveything! We almost solved this country's dependency on foreign oil....Back to the previous argument--if you lose .5R for each 1% the fg is compressed, here's what we do:*Go back to 2x4 construction*Stuff two 3.5" batts into each cavity, thus compressing the batts 50%.*50% compression equals a loss of R25.*With no compression, two 3.5" batts equals R22.*Due to the compression, the R22 is reduced by R25, for a net of minus R3!*The insulation is now acting like a heat pump, sucking heat into the house from the outside!*Now, we mandate all future housing to be timber frame-style with removable insulated panels built with compressed fiberglass.*All we have to do is pull out and reverse the panels in the summer and they will suck the heat out of the house and send it outside. Free airconditioning!To think my engineering degree almost went to waste. Time for a Guiness to celebrate my upcoming Nobel Prize.For our humor-impaired participants, uuhhhhh, this is a joke. Except for the part about getting a Guiness.Mongo
*Pretty good sound proofing too!
*I built 2 test walls. The first one was 2X4 24" o.c. with R11 faced, R13 faced, compressed R19 faced, compressed R19 unfaced and cellulose in each succesive bay. Thermal imaging showed cellulose as best, unfaced R19 next, faced R19 equal to the unfaced in the center but worse near the studs, R13 next and R11 dead last. I did another wall with 2X6 24" o.c. With R19 unfaced, R22 faced, 8" unfaced batts and cellulose. Thermal imaging showed cels best, 8" batts next and the R22 faced with the poorer fit tied for last place with the R19 unfaced. In both walls the compressed FG was harder to put the vapour barrier over and to drywall. Drilling a 1/2" hole in the drywall 6" from the bottom of each bay and 3" from the top of each bay, for the next test, affected the heat loss of the fiberglass bays much worse than the cellulose bays. After the test I took out the insulation straped the 2X4 wall with 2X4s and straped the 2X6 wall with 2X2s and blew in cellulose. Now I usually build with 9 1/2" or 11 7/8" TJIs as wall studs and blow in cellulose.Over 30 (R30 that is) and loving it.
*Ron,Terrific testing. Do you still have the walls? Is there anyway to quantify the results rather than just thermal imaging?Steve
*GuiNNess, Mongo, didn't they teach you anything in the military? Or were you with the Miller Lite crowd?Guinness is worth finding on draught -- a hundred times better than the boiled bottled stuff. And let it warm a bit. Then solve the world's energy problems. I suspect the insulation loss factor is some sort of logorythmic (sp?) curve.
*Are you blowing dry cells? After the sheathing and drywall are in place?
*Ron,I hereby crown you b King Guru andb God of the Insulation World!Really glad to here someone's actual test findings verses all the armchair theory though the wrangling is fun to watch.Please become a regular poster!Now I have to get that walk in the "Park" started as the sun shines brightly....Jack : )
*I've got it on tap!I have had the cans, with the CO2 cartridges in the bottom, not bad. You're right, the bottles are inferior. I'll have to go punish myself for my poor spelling by hanging out in the tap room and studying a bit more...By the way, I'd think cells first, compressed FG second.
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Mongo;
Pour a Black & Tan for me.
Cheers; JE
*Mongo,Just to keep the record straight, the little widget (cartridge) in the bottom of the Guinness can contains a mix of CO2 and nitrogen. Nitrogen is a big part of the creamy head and is used with the draught version also.Cheers,Steve
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So, uh, Mongo, do you live nearby? Maybe we should get together sometime.
Did you know the Guinness in Europe is stronger than in the States? About as alcoholic as wine, a bit of a surprise to an innocent American in the Netherlands.
Um, what was the question?
*This is turning into the best thread we have ever had on this board. Only when we discuss having beers at a topless bar will this forum be like a true breaktime. Cheers.
*Hi folks, The walls are still up but all bays now have the cels. I had no way to measure the actual R value, but which insulation type that was better was what I was looking for. I had to have wet blown cells because the horizontal straping probably would have prevented a void free fill otherwise. That is why I now mostly build with TJIs as wall studs, very little thermal bridging and VERY straight walls. I usually blow in the cels thru holes in the top plate which is built up of 2x3s and a 9 1/2" or 11 7/8" strip of OSB after the sealed vapour retarder and drywall is installed. I will use compressed FG only for very small spaces that are hard to get to later such as under windows which can't be blown in from the top. I sometimes also build with SIPs. I will sometimes use Icynene in a retrofit if there is no vapour retarder
*Slide up to Canada some time and have a taste of what all those 'supposed' import beers you're ingesting really taste like. It was in the Carribbean that I discovered that 'import' beer bottled in the U.S. was actually just "yankee swill" as we call it with foreign labels attached. . . what a joke!!! Only in America.
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I have an old house with exterior walls about 4 1/2" thick. If I compressed and fitted 5 1/2" fiberglass bats in the walls would I loose much R value. I don't have much to insulate so blown in is not practical.
Thank you,
Dave