What's the R-Value of OSB?

Reply

  #1  
Old 12-05-08, 09:23 AM
Member
Thread Starter
Join Date: Feb 2008
Location: Southern Illinois
Posts: 281
What's the R-Value of OSB?

Sometime within the next couple of weeks, I'm going to replace my old attic insulation with blown-in cellulose. (I'm also going to do something in my crawlspace, but that's another question which I haven't quite formulated yet)

Using the available calculators, I can't get to the required depth for the recommended values, if I keep the cellulose between the joists. I'm also planning to put at least a crawl-line of OSB down the middle and maybe floor a bit for storage, but if it'll give me significant insulating gain at a cost-effective price, I could floor more, rather than less of the space?

And if so, if I use 1/2" OSB (sheathing/waferboard) could someone give me the expected R-Value and I assume that if I half the number again, it'll tell me the benefit, if I go with 3/4"?

Thanks in Advance
 
Sponsored Links
  #2  
Old 12-05-08, 09:28 AM
Gunguy45's Avatar
Super Moderator
Join Date: Dec 2007
Location: USA
Posts: 20,977
Well, heres some common values for many materials. Don't see OSB, but I'd suspect that it would be a bit less than plywood. Don't ask me why I think that...just do...lol

E-Star: Energy Saving Calculations - R-Values of Materials
 
  #3  
Old 12-05-08, 09:28 AM
dhamblet's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Oct 2008
Location: PAcific Northwest
Posts: 264
Your best value on insulation is not to replace old insulation but to add more over it. OSB will add negligible R value to the package and aside from having a walkway (assuming you need one) is a waste of money.
 
  #4  
Old 12-05-08, 10:05 AM
Member
Thread Starter
Join Date: Feb 2008
Location: Southern Illinois
Posts: 281
I have to say that this definitely set a record for quick responses -- Thanks!

After looking at the link, I'm guessing that OSB might also be called "fiberboard", but I'm not sure and because it's not all that more than plywood, as both helpful respondents have indicated, the dollars to thickness ratio makes it not worth the expense.


As for the ripping-out of the old: Whatever is up there could be more than 50 years old, if they made insulation back then and though it was obviously never very thick to start, the years has pressed it down to maybe half an inch, if that.

There's also been a few leaks over the years and though I doubt mold is any kind of problem (I live in the desert), whatever's there is significantly discolored in spots and in some places, there's leaves and/or debris from a wicked bad hailstorm. My plan before starting is to simply take out the old, Shop-Vac up the accumulated dust, nails, whatever and then blow all new stuff in, as I go. Of course, once I start, I may just take out only the clearly "bad", but that's something I figured I'd address, once I go.


Thanks again for the quick responses and based on your advice, plus that very informative chart, I'll stick with my original plan of just flooring a crawl-line down the middle for access.

Though, I might also consider putting a few sheets of styrofoam over the unfloored parts (or maybe even sandwiched along the crawlline), since it looks like that might help. It'd actually be a little more expensive than straight OSB and it'd have to have holes for the conduit to run through, but it would have an established R-Value and could be worth the expense.

Any thoughts?


Thanks again and thanks in advance.
I couldn't do this fixer-upper, if it weren't for these forums and this site's helpful members.
 
  #5  
Old 12-05-08, 10:34 AM
Gunguy45's Avatar
Super Moderator
Join Date: Dec 2007
Location: USA
Posts: 20,977
I think fiberboard is more of the "brownboard" type sheathing that used to be around...not sure.
 
  #6  
Old 12-05-08, 12:17 PM
Member
Join Date: Oct 2008
Location: New England
Posts: 9,990
While you have everything exposed, before you add the cellulose, try to seal as many air leaks as you can. I recently built a commercial building and didn't want to compromise the R-value where I wanted a crawl-line (in my case it was 9' high) so I added 2X6 on edge along the walking path, filled below with 12" of insulation and covered with OSB. A couple of 2X4's down each side of your crawl-line, fill with cellulose and cap with OSB. Might be cheaper than the rigid.
Bud
 
  #7  
Old 12-05-08, 01:08 PM
Member
Thread Starter
Join Date: Feb 2008
Location: Southern Illinois
Posts: 281
Bud - I wondered about the idea of just piling-on more cellulose that the joists (rafters?) would hold. Basically filling the part between the boards and then blanketing everything with more blow-in, burying the wood. It sounds like that's what you did, with just your crawl-line elevated. Am I reading you right?

And if so, did you bury the wiring?


Thanks
 

Last edited by TryAgain; 12-05-08 at 01:23 PM.
  #8  
Old 12-05-08, 03:25 PM
Member
Join Date: Oct 2008
Location: New England
Posts: 9,990
We could jump over and ask the electricians, but my take on it, is you can't bury electrical boxes in a wall where you can't get to them. Burying them under insulation makes them hard to find, but you can get to them. I see it done all the time. As long as your ceiling can hold it, you can add insulation. But cellulose is heavy so let's see if someone will jump in and tell us how much is max. Certainly a few inches over your joists should be fine. In my example, I was using batts.

I also want to mention, when you blow that insulation in, make sure you protect the soffit ends so 1. you don't fill the soffits, and 2. so you leave a space above the insulation so air can vent up from the soffits. They have baffels if you can get down there to put them in.

If you do anything with batts, I made up an 8' pole with a fourteen inch "T" on the end with nails protruding like a devils pitch fork. I could spear the end of an eight foot batt of insulation and guide it right into place. Actually, my son did all of the spearing and I did my best to keep up feeding him insulation. 4,000 sq. ft. two layers of 6" and done in 4 hours. And they wanted $2,000.Beer 4U2

The advantage of using some cellulose and then covering with fiberglass batts for more insulation, is the cellulose acts as an air block, reducing any air leakage.

Am I making any sense?
Bud
 
  #9  
Old 12-12-08, 07:38 PM
Member
Thread Starter
Join Date: Feb 2008
Location: Southern Illinois
Posts: 281
Bud - You made perfect sense and I apologize for the delay in replying, but I wanted to get an accurate measurement (which until I install the attic access, it means going through a hole in my roof) and I've got several balls in the air because I'm trying to finish this fixer-upper within the next couple of months.


Right now, all of my wiring is in EMT. I'm hoping to do/get an electrical upgrade and at least a partial rewire within the next few weeks and because it will have to be inspected, I ordered enough cellulose to stay within the rafters (joists?) and I'm going to install your raised walkway, while I still have a hole cut in my roof and can easily get it into place.

I'm figuring that once the inspection is finished, I'll either order more cellulose and blow it in or I'll lay batts of fiberglass perpendicular to the joists. The cellulose manufacturer gives depths to achieve different R-values and they include on their <A HREF="http://www.greenfiber.com/_assets/PDFs/PM-6.3-19.pdf">chart</A>, a calc using 2"x6" joists, so I assume that burying is okay and I think the EMT is adequate fire protection, but my local inspector is kind of persnickety and depending on how much rewiring we do, I might just raise up the wiring to be above the insulation, anyway.

Right now, I don't know. I ordered enough to get me to an R-27, which is much better than the half-inch of old fiberglass that's up there. And, because I'm more than a hundred miles from any of the box stores, I ordered from DoItBest through my local building supply house. (The thru-store price was less than the online ship-to-store price, but it's still 52&cent; higher than the box stores and I'll still need to rent the blower from them ($28/day), but once you calculate delivery, multiple trips or the price of a truck rental, it was still cheaper for me to go the local route.)

As for the weight, I forget the exact number that my local supplier and I arrived at, but we took the product's shipping weight and divided it by installed square feet, then based on nothing but our own conjecture and his experience, we decided that my locally-milled, Douglas Fir 2"x8"s (16oc) would most likely be able to support the cellulose and a double layer of sheetrock.

Though, I guess I won't know until I try.


Anyway, thanks to you, GunGuy, dhamblet and anyone else who'd like to jump-in for all of the help. Of course, if I have any problems when I start blowing the stuff around in about a week, you'll know to which forum, I'll turn.

(Now, if I could just get an answer to my register placement <A HREF="http://forum.doityourself.com/ducting-systems-air-ventilation/370860-new-ceiling-registers-inside-wall-outside-wall-windows.html">question</A> and if my helper-wife could take her vacation early, I'd be good to go.)

Thanks
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes