I’m reinsulating my attic space and not sure if I need insulation on the attic’s exterior walls? I figured I can leave them bare because the attic is vented, so why try to insulate it, right?
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Treat the walls like your roof deck... it just gets less sun and rain on the outside.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Tu stultus es
I think maybe he's talking about the gable end walls.View Image
Yup .... that's what he thought.
Right. Gable end walls and any other walls that are above the attic floor insulation do not need to be insulated, in a standard ventilated attic.
Yea, it is the gable end wall that I'm wondering about. I wanted to be sure I was doing the right thing before I close it up. Thanks for the info.
Right on ..... the thermal envelope is not always the same shape as the weather envelope. If you have a cooling issue w/ an extreme western exposure, one MIGHT consider insulating that end wall. But normally .... no.
While we're talking about insulating an attic... here's my dilemma. I own a Cape Cod that has sizable attic floor space on either side of a kneewall. I've insulated the kneewalls with fiberglass topped with 1 1/2" styrofoam. Nice a cozy. However, under the attic floor boards, I have 50 year old fiberglass...probably 3"-ish in a 7" X 16" OC joist bay. Not good. The floor boards are shiplap and obviously run perpendicular to the floor joists. What's the best way to add insulation?? Drill holes in flooring and blow insulation in each joist bay or remove 2-3 floor boards (oh boy) and try to pull fiberglass batts through each bay? I may have obstructions to deal with for sure. On one side of the house I have 8' wide section, the rest are typically 5'-6' wide sections. Who's had experience with this?
Thanks.
Blow. Can you get to the joist spaces behind the knewwalls?http://www.quittintime.com/ View Image
Yep. Every one of them. Where can a DIY guy rent an insulation blowing machine and what's the cost?
Most big boxes (Home Depot, Lowes. etc) have machines. When I added cellulose to my attic (5-6 years ago), if one spent $200 on insulation, the blower rental was free.http://www.quittintime.com/ View Image
Okay, so let's say I rent a blower. How much insulation will I need and how to figure it? Also, do I raise up a few floor boards, or drill circular holes at each end? How do I guarantee that I'm filling the cavity and not just throwing a thin layer of insulation down? Most of us have never used an insulation blower. How tricky are they to handle? I'm also guessing I'll need to do some blocking to prevent insulation from being blown into joist cavities between 2 heated areas, ie. the 2nd floor of the 'Cape'. That shouldn't be too tough.
Has anyone done this type of project before? What are some pitfalls to avoid? Any good tips?
Thanks.
How much insulation will I need and how to figure it?
It's sold by the cubic foot. Figure how many square feet you need to cover and multiply by how deep (the joist ht).
do I raise up a few floor boards, or drill circular holes at each end?
I'd raise a few boards.
How do I guarantee that I'm filling the cavity and not just throwing a thin layer of insulation down?
If you lift a board every 5' or so, you can pretty much see what you're doing.
How tricky are they to handle?
Pretty simple. 2 person job - one loading and one pointing the hose. It's either on or off. You get the feel of it quickly.http://www.quittintime.com/ View Image
Okay, so it sounds like the way to go is raise floor boards enough to be able to fill the joist cavities. What will my R-value be when I'm all done with cellulose in a 7" cavity? Seems to me I'm not going to get a whole heck of a lot of R value for the floor. Should I look at styrofoam board instead? Sure would be more work, but mucho more R value. Also, if I use cellulose, how do you fill the joist cavity so it's full but not too full, and keep it from blowing all over the attic?
What will my R-value be when I'm all done with cellulose in a 7" cavity?
http://www.coloradoenergy.org/procorner/stuff/r-values.htm
You'll get about R3 per inch. But more importantly, you'll be reducing infiltration.
how do you fill the joist cavity so it's full but not too full, and keep it from blowing all over the attic?
That's like trying to answer "how do I ride a bicycle?" You'll get the feel for it quickly.
Should I look at styrofoam board instead? Sure would be more work, but mucho more R value.
Unless you foam each piece in, you won't reduce infiltration. Cellulose will give the most bang per buck.http://www.quittintime.com/ View Image
Check out this explanation. I started to add a couple of points to SeeYou's comments, then thought that an explanation with photo's might be more meaningful to someone who's never seen it done.
http://www.diynetwork.com/diy/he_home_insulation/article/0,,DIY_13895_2274825,00.htm
Hey thanks to all for the advice, suggestions, links. I need to round up some mat'ls and a buddy and cut the shiplap flooring to gain access... and enjoy the warmth and savings.