Insulating attic space behind bedrooms and hall


  #1  
Old 01-13-09, 01:46 PM
S
Member
Thread Starter
Join Date: May 2006
Location: Vancouver, BC, Canada
Posts: 178
Received 0 Votes on 0 Posts
Insulating attic space behind bedrooms and hall

It is tough to explain, but we have an attic space that runs the length of our house, behind our bedrooms and hallway. We have an access door to this space in our hallway which we use to throw some storage stuff in. I was in there the other day and I noticed that there is no vapour barrier and hardly insulation on the backside of the interior wall as it is completely open to see. Our bedrooms are quite cold, so I am hoping to add some safe and sound insulation all on this wall and also a vapour barrier to help insulate it better.

My question is, how do I install the vapour barrier? I know it should be on the warm side, but given I only have access to the backside of the wall, how do I do this? Or is it ok to add the insulation first and then the vapour barrier over it from the backside?
 
  #2  
Old 01-13-09, 02:35 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,524
Received 37 Votes on 34 Posts
Hi snaffoo, To answer your questions, the vapor barrier, if you add one would go on the inside. It cannot go on the cold side as that would definitely cause a moisture problem. Your options are: to go without and just add insulation; to remove the insulation that is there, add a VB and then add all of your insulation; add vinyl wall paper to the inside for a VB; then a variety of rigid or spray foam options.

How far north are you and what is in the walls now, 6 or 3 ? Are there sloping ceilings up to the flat ceiling as those spaces will need to be addressed as well.
Here is some reading to get you started:
Welcome To Home Energy Magazine Online

Ill check back
Bud
 
  #3  
Old 01-13-09, 03:46 PM
S
Member
Thread Starter
Join Date: May 2006
Location: Vancouver, BC, Canada
Posts: 178
Received 0 Votes on 0 Posts
Not sure what you mean about what's in the walls now. It's just a 2x4 interior wall that has very thin insulation. The ceiling in the attic space is sloped so when you walk in it's wider at the bottom and then goes to the top of the wall in question, ie. the cavity is triangle shaped. There is another attic above our bedrooms and hall that is separated from this attic space.

So my best approach I think would be to remove the old insulation, wrap a vapour barrier around the studs and backside of the drywall, and then insert the new insulation. Can I add another vapour barrier with holes cut out in it over the new insulation so it hold the insulation in place and also keeps it from getting all over me everytime I go in there?
 
  #4  
Old 01-13-09, 04:16 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 27,333
Received 989 Votes on 900 Posts
One way to add a VB to your wall would be to add a layer of 1/2" XPS foam. You'd want to rip pieces on a table saw so that they fit nice and snug into your stud bays, then seal the edges with foam adhesive or spray foam. Then install unfaced insulation over that, which would need to be held in place by straps or wire/staples. The XPS foam would also add R-3 or so.

You could staple a VB around the studs like you suggest, but if you have any wires in your walls, and end up making a bunch of seams in the VB, it will be a real waste of time.
 
  #5  
Old 01-13-09, 04:18 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,524
Received 37 Votes on 34 Posts
With 2x4 walls, you can't get a lot of r-value in there. You say thin, so maybe you have 2 1/2", but that doesn't allow for much extra and you can't compress it much without loosing its effectiveness. You didn't say how far north you are, but you need at least r-20 and many would say r-38. If you fill the 2x4 space you will have about r-13. To get additional r-value and a place to hang the extra, you can pad out the existing 2x4's with another 2x4 or run them horizontally. Yes, you can cut up the kraft and use it to hang the fiberglass.

I said before there were some rigid foam options, one of which is to add two inches of pink, blue, or foil faced over the studs filled with fiberglass. Now, even though it would be considered a vb, if it is thick enough it will work. It's expensive and needs a fire protective covering like sheetrock, but good r-value. Did you check out the link, it has some issues that you might as well take care of at the same time.

Bud
 
  #6  
Old 01-14-09, 07:57 AM
S
Banned. Rule And/Or Policy Violation
Join Date: Jul 2008
Posts: 9
Received 0 Votes on 0 Posts
Seal Up the Chaseway

In the South we call this a "hot wall" I guess you would call it a "cold wall" but the fix is the same. Fill the stud cavities with good insulation and get full contact with the five sides. Then cover with EPS foam board. This will eliminate the thermal bypass and minimize the convective looping within the insulation. The foam board will give full contact with the sixth side.

THEN, check this. Do you have floor joists running perpendicular to the wall? If so you probably have what's called an "open chaseway" Fixing the wall is great, but if hot/cold attic air can enter BETWEEN the floor of the second floor and the ceiling of the first floor the the the floor (and whole room) will be cold. You can cut foam board and "block" between each joist/truss and then foam/caulk. OR the best way is to have a spray foam company come in and spray it shut. They can do it quickly and perfectly. And, you could have them spray the wall to while they are there INSTEAD of putting in batts and covering with foam board as described above.

This will fix your problem.
 
  #7  
Old 01-21-09, 05:36 PM
F
Member
Join Date: Jan 2009
Location: New England
Posts: 2
Received 0 Votes on 0 Posts
spray foam insulation

If you are looking for a spray foam company, we recently had our attic done and have been very pleased. It was a MA-based company called Greenstar.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: