Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Insulation

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 01-16-2013, 03:27 PM   #1
Newbie
 
Join Date: Jan 2013
Location: NH
Posts: 3
Share |
Question

Blow insulation OVER attic floor?


I have a simple rectangular attic, about 1,100 sq ft. Construction is 2 x 8 floor joists, 16" o.c. The house was built in 1977 and the existing floor insulation is about 6 inches of either rock wool or cellulose (gray dusty stuff) blown or poured in. The entire attic is floored with 3/8" plywood, mostly just lying there loose and bouncy. Access is by a pull-down stair. This space will never be used for storage or other access, so the floor really is unnecessary.

I figure the existing insulation is roughly R-20, which was state-of-the-art in 1977. Now the recommendation for my location in New Hampshire is R-50 to R-60. The easiest and probably cheapest way for me to upgrade would be to blow in cellulose. Although I could pull up the plywood sheets and blow in, the level would rise considerably above the joist tops, and then, what to do with the plywood? I'm getting old and can't do a lot of heavy work, and really don't want to drag all that plywood out of the attic.

So my big question is, is there anything wrong with simply blowing the cellulose over the top of the plywood floor? It seems like a good method to me, but I seek your advice if there is a problem with doing this. As I said, this attic probably will never be used for anything. Thanks for any tips!

Garblefarf is offline   Reply With Quote
Old 01-16-2013, 03:52 PM   #2
Retired from the grind
 
gregzoll's Avatar
 
Join Date: Dec 2006
Location: Midwest - Central Illinois
Posts: 14,021
Default

Blow insulation OVER attic floor?


You are going to have to rip up all of that flooring, then figure out how to re-frame, so that you have the space for R-50 or R-60. Basically means that to do it correct, you can no longer use that as a storage space in order to get the proper fill levels for insulation.

__________________
Ren: Now listen, Cadet. I've got a job for you. See this button? Ren: Don't touch it! It's the History Eraser button, you fool! Stimpy: So what'll happen? Ren: That's just it. We don't know. Maybe something bad, maybe something good. I guess we'll never know, 'cause you're going to guard it. You won't touch it, will you?
gregzoll is offline   Reply With Quote
Old 01-16-2013, 09:35 PM   #3
Member
 
Join Date: Mar 2012
Location: far sw sub chicago
Posts: 3,649
Default

Blow insulation OVER attic floor?


Quote:
Originally Posted by gregzoll View Post
re-frame, so that you have the space for R-50 or R-60.
re frame what ?
Fix'n it is offline   Reply With Quote
Old 01-16-2013, 09:43 PM   #4
Member
 
Join Date: Nov 2011
Location: Hartfield VA
Posts: 26,246
Default

Blow insulation OVER attic floor?


Plywood has to go, I agree, what framing?
Before doing it air seal everything that comes through the tops of the walls and the ceiling with expanding foam.
Add foam or plastic baffles so the soffit vents do not get blocked with insulation.
joecaption is offline   Reply With Quote
Old 01-17-2013, 09:58 AM   #5
Retired from the grind
 
gregzoll's Avatar
 
Join Date: Dec 2006
Location: Midwest - Central Illinois
Posts: 14,021
Default

Blow insulation OVER attic floor?


Quote:
Originally Posted by Fix'n it

re frame what ?
Reframe if they wish to use as storage.
__________________
Ren: Now listen, Cadet. I've got a job for you. See this button? Ren: Don't touch it! It's the History Eraser button, you fool! Stimpy: So what'll happen? Ren: That's just it. We don't know. Maybe something bad, maybe something good. I guess we'll never know, 'cause you're going to guard it. You won't touch it, will you?
gregzoll is offline   Reply With Quote
Old 01-17-2013, 10:18 AM   #6
Newbie
 
Join Date: Jan 2013
Location: NH
Posts: 3
Default

Blow insulation OVER attic floor?


Once again, it will not be used for storage. My main question is, what harm is there in leaving the plywood there?
Garblefarf is offline   Reply With Quote
Old 01-17-2013, 10:27 AM   #7
Member
 
Join Date: Nov 2011
Location: Hartfield VA
Posts: 26,246
Default

Blow insulation OVER attic floor?


It may act as a vaper barrier and cause mold to form.
joecaption is offline   Reply With Quote
Old 01-17-2013, 10:38 AM   #8
Home Performance
 
HomeSealed's Avatar
 
Join Date: Jan 2008
Location: Milwaukee,WI
Posts: 1,430
Default

Blow insulation OVER attic floor?


The only way that it would make any sense to leave the plywood would be if it was secured already. You'd then dense pack underneath and blow over it. If it is loose, hire some kid to come pull it all out so that you can add insulation effectively. As Joe mentioned, this would also be the time for proper air sealing up there. Also as mentioned, you'll want to add baffles down to the soffit vents and install dams to prevent wind-wash and/or all of your loose-fill insulation from falling down into the soffit.
__________________
Replacement Windows, doors, siding, roofing, insulation, and certified energy consulting.
www.HomeSealed.com
HomeSealed is offline   Reply With Quote
Old 01-17-2013, 01:20 PM   #9
Member
 
Join Date: Nov 2007
Location: Nashua, NH, USA
Posts: 6,932
Default

Blow insulation OVER attic floor?


Somehow I do not think that leaving the plywood there would cause a vapor barrier or moisture problem. Just do not add an additional moisture barrier.

Do not stuff more insulation under the plywood so as to compress either the new insulation or existing insulation significantly. That will actually reduce the R value a tad.
__________________
Stop wasting time re-adjusting the pattern. Have several lawn sprinklers, one for each pattern.
AllanJ is offline   Reply With Quote
Old 01-17-2013, 01:23 PM   #10
Member
 
Join Date: Nov 2011
Location: Hartfield VA
Posts: 26,246
Default

Blow insulation OVER attic floor?


Also if it really is only 3/8 I sure would not be doing any walking on it. It's to thin for that.
joecaption is offline   Reply With Quote
Old 01-17-2013, 04:14 PM   #11
Home Performance
 
HomeSealed's Avatar
 
Join Date: Jan 2008
Location: Milwaukee,WI
Posts: 1,430
Default

Blow insulation OVER attic floor?


Quote:
Originally Posted by AllanJ View Post

Do not stuff more insulation under the plywood so as to compress either the new insulation or existing insulation significantly. That will actually reduce the R value a tad.
That statement requires some extra clarification. Dense packing cellulose will not reduce R-value of the space, nor will it for blown fiberglass that is designed for dense packing. It will increase the R value and slow airflow as well... That said, you don't want to crush batts of fiberglass or regular loose fill.

__________________
Replacement Windows, doors, siding, roofing, insulation, and certified energy consulting.
www.HomeSealed.com
HomeSealed is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Attic insulation in MA - Strange problem Squished Insulation 37 10-03-2012 03:59 AM
Southern PA/DE - Attic Insulation LifeIsGood169 Insulation 4 06-23-2012 09:52 PM
AC Flex Duct - Suspend above attic insulation or lay it on top? fritzycat1 HVAC 13 08-17-2011 10:19 PM
Fiberglass Insulation: How Do I Cover the Attic? chueh Building & Construction 3 11-08-2010 02:33 PM
Insulation over Attic Walkway BigJimmy Building & Construction 4 06-23-2008 02:13 AM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.