I know that fiberglass insulation is not supposed to be compressed — have 2×8 ceiling that I need to put insulation in – 400sf. It is attic space but need to put the floor back down for storage.
2 options – Option 1: put the 6.25″ down for a R-factor of 19 or go with Option 2: put 10″ down and have an R-Factor of 30 (if it was not packed in the joist bay? I will put the facing towards the heated room beneath – don’t worry. I am stuck on Fiber Glass and do not want to consider blown in due to the mess and need for a second hand.
I know we should not put the thicker insulation down but I know it settles over time and runs counter to my thinking that more may be better – just this once — Any thoughts? — Tks — and all the best – Dudley
Replies
Dudley,
Compressing the R-30 to 6 inches will give you a higher R per inch than using 6 inch thick batts. It will not be R30 but will be more than R19. Someone else may know just how much more. I think there is a table somewhere that shows what your effective R per inch will be. This has been discussed a lot here. Try a search.
Steve
Option 2 is Bo-o-o-o-gus!
You won't get R-30 if you pack fg into 7-1/2". Maybe R-20. It's the depth of the space that is most important, not how much fg you can cram in. In fact, extra glass may actually reduce the R value.
BTW, blown-in, if done properly, is no more of a mess than fg. Heck, it's in the attic, after all! And, done properly, you CAN do it one-handed! ;-) 400 sq ft is about 15 minutes work.
Mike Hennessy
Pittsburgh, PA
Tks Mike and Steve - see I can agree on the loss of R value if it is packed but I want a R-Factor of 22-23 if I can get it. Becaseeu the 19 will compress by gravity and evntually become 15.
On blowing it in -- doesn't it take 2 oen to manage the hose and the other to dump the bag in the machine? I cant be two places at one time - Tks Dudley
No, the reduction in R-value is not that bad.One of the manufactures, OC I think, has a Q&A about this..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Someone here posted a table of how R-value changes when it's compressed but I can't find it now. According to that table the R-30 would be more than R-19 but less than R-30 if compressed. Go ahead and try it, then let us know how it works ;-)
Why don't you run 2x4's across the 2x8 joists to give yourself more space for insulation?
Mike -- that is a great idea and I am going to do it -- with heating bills being what they are going to be this winter I'm seeking all the R-Value I can find as my house is a double masonry wall furred out and plastered -- 1953 era.
I modified the bedroom ceiling to a 5x5 tray ceiling with the ceiling fan tucked up there and almost fell over when I noticed there was no insulation in the bedroom/den ceiling - no wonder is has been 5 degrees colder than the rest of the house -- it is ok for sleeping but tough getting up -- when we finish, I'll post some pictures in the Photo Gallery -- all the best Dudley
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Here's a link that might help:<!----><!---->
http://www.owenscorning.com/around/insulation/CompressionChart.xls<!----><!---->
It shows R30 compressed in a 2x8 as yielding R25.<!----><!---->
I'm doing something similar to what someone else suggested. I have mostly 2x6 attic joists (interior load bearing walls, short spans). I'm adding 2x8 on top, filling new cavity with FG batt, then plywood on top. I agree that blowing in would require a second person. Not that anyone suggested it but blown FG has a lower R than FG batts. Most here would suggest blown cellulose.
Nov -- tks the chart - confirms my gut feeling - as I want as much insulation as possible to get me through the winter -- all the best Dudley
Glad to help. You will also be able to cross layers of insulation, which will minimize thermal bridging. We look forward to seeing pictures--
My 2 cents. First of all 6 1/2 inches of insulation is/should be more than R-19 ... You get R-19 and R-21 out of 5 1/2 inches.
10 inches compressed to 7.5 should give you maybe R-25+ ... just guessing.
Fiberglass simply does not 'settle'.
Option 3 ... increase depth w/ e.g. 2x2s nailed/screwed to ceiling joists ... gives you more space ... problem?? It's cheap and easy.
I think you are taking a reasonable approach considering your situation/personal feelings.
Don't forget .... seal penetrations of the ceiling while you have the chance ... it's not fun, but it's more fun now then later.
Clew -- I am going to add a layer of 2x4's to raise the floor an additional 1.5" and to nail the floor to.
I would never have thought about adding the additional layer of 2x4s' without the feedback I received here -- had a mindset of keeping things the way they were - the additional 1.5" will give me 8.75" to lay the FG in and place the floor on top - tks to all and all the best Dudley
Like I always say to myself ... brainstorm, searh and explore all your options ... THEN you are in a better position to make the most informed decision yourself. One of the good things about BT is that you literally get total strangers points of view to brainstorm for you ... at little or no effort on either's part. We help keep you/each other out of a mindset that may be blocking creative solutions or learning new things you didn't even know about.
I would use the 6" and buy some extra so I could peel 1-1/2" strips from the and lay it on top of the 6" to make it 7-1/2". Optimal R value and no compression.
EDIT: All the other responses were not showing when I posted, so I guess you should disregard my suggestion. Of course building up the joists is the best way to go for optimal r value.
See my work at TedsCarpentry.com
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Edited 9/11/2008 9:43 am by Ted W.
Should have posted under "energy ... etc." not general discussion.