Go Back  DoItYourself.com Community Forums > Interior Improvement Center > Insulation, Radiant and Vapor Barriers
Reload this Page >

Options for insulating exterior wall with work I have planned

Options for insulating exterior wall with work I have planned


  #1  
Old 08-16-11, 06:34 PM
M
Member
Thread Starter
Join Date: Jun 2008
Location: Co
Posts: 76
Upvotes: 0
Received 0 Upvotes on 0 Posts
Options for insulating exterior wall with work I have planned

I’m trying to complete a few projects on one side of my house in the coming weeks. I’m hiring a contractor to convert the rough openings for a door and window into a rough opening for a French door and to install the French door. I’m residing the wall and installing a few new windows in the process. The week before I install the siding, I’m having new hardwood floors put down.

So that’s the background. Behind my current siding I have ½” rigid foam board with a foil face. My walls are 2x4 and have fiberglass mat insulation. I’d like to improve my energy efficiency and certainly don’t want to decrease it. That means that I’ll either have to improve the insulation in my walls or keep/replace my current rigid foam board.

I guess my first question is, is blowing in cellulose and discarding the foam board a viable option? I’m not sure if blowing around fiberglass is feasible or if it will even make much of a difference.

Due to timing constraints, my plan is to have the doors installed ahead of tearing off the old siding. If I go the foam board route, am I pretty much stuck using my existing foam? My understanding is that doors and windows have to be installed on top of foam.
 
  #2  
Old 08-16-11, 07:07 PM
D
Member
Join Date: Aug 2009
Location: USA
Posts: 4,344
Upvotes: 0
Received 1 Upvote on 1 Post
Why do you want to get rid of the existing foam board? Why can't it stay in place?

Cellulose isn't going to give you much more R-value than fiberglass. If you want to increase the R-value in the wall cavity, remove the fiberglass and spray 3 inches of closed cell spray foam. That will create an air seal, vapor barrier, and give you about an R-20.
 
  #3  
Old 08-16-11, 07:57 PM
M
Member
Thread Starter
Join Date: Jun 2008
Location: Co
Posts: 76
Upvotes: 0
Received 0 Upvotes on 0 Posts
I just pulled a plank outside and what's installed is .5" TUFF-R (R-3.3). I guess one additional question is, if I keep the foam is it a good idea to use house wrap over it? Even from looking under just one plank I saw spots where the foil was torn and folded over.
 
  #4  
Old 08-17-11, 02:49 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 9,460
Received 47 Upvotes on 43 Posts
What's left of the foam board will be less than its rating, holes, tears, as you observed.

Here's my approach. Order windows and doors for a 6" wall. Add 1 1/2" rigid foam over the 1/2" that is there. Removing the siding and installing the extra foam board is less than half a day and after they tape the seams if will weather for a bit while you wait to do the siding, a week or so. Then add new siding over the foam and you have a much better wall.

An old fiberglass install is usually poor at best. 3.5" walls are way below what today's energy costs require. While you are installing new windows, doors, siding is absolutely the perfect time to upgrade the wall insulation. Going from 2x4 to 2x6 dimensions is a standard step all contractors should be aware of. I'm adding 3.5" of rigid to my outside and have to re-trim and improvise at every step and it is still worth it. Don't miss this opportunity.

Bud
 
  #5  
Old 08-17-11, 06:41 PM
M
Member
Thread Starter
Join Date: Jun 2008
Location: Co
Posts: 76
Upvotes: 0
Received 0 Upvotes on 0 Posts
Unfortunately, doors and windows are already ordered and paid for. Any value in in blowing in cellulose around existing fiberglass and hanging new 1/2" TUFF-R?
 
  #6  
Old 08-18-11, 03:00 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 9,460
Received 47 Upvotes on 43 Posts
I doubt you would gain much with cellulose over the fiberglass and unless the foil faces rigid foam board is 50% of your wall R-value, it runs the risk of causing condensation. It ends up being a vapor barrier on the outside. You could remove the 1/2" foil faced stuff and replace it with 1/2" pink and tape it well to form a good air barrier with the same thickness as before.

Bud
 
  #7  
Old 08-20-11, 09:38 AM
P
Member
Join Date: Feb 2008
Location: Lake Wales, FL
Posts: 424
Upvotes: 0
Received 0 Upvotes on 0 Posts
Adding windows will result in greater heat loss unless you install treble glazed or two lots of double glazed windows, making quad glazing.

You intend to fit hard wood floors, are you fitting floating floors with at least two inches of polystyrene under?

Keeping in mind that you are trying to keep warmer at lower heating cost?

The way to go, is to install at least three inches of polystyrene sheet insulation on the inside of the frame, that means walls and ceilings then cover with drywall.

With your existing insulation, the 1/2 inch board does little to insulate and the fiberglass is useless. The only benefit is that the foam board helps slow the escape of your warm air.

To get the best result throw the fiberglass and carefully fit foam boards inside the framing, then cover the frame with another three inches of polystyrene board.

One eighth of your floors walls and ceilings are solid wood, wood is not a good insulation at the moment you are throwing money away on wasted heat that is lost by conduction through the wood frame.
 
 

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