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dderolph 10-24-2007 11:27 AM

attic insulation question
 
I'm going to be helping my son insulate an attic in a house in Columbus, Ohio, that now has no insulation. I've seen tables in home improvement supply stores saying the recommended R-value for attic insulation is R-38. But, based on the insulation products sold in the stores, I don't see how an R-38 value is accomplished, since the highest value faced insulation sold seems to be R-19.

Does achieving R-38 require two layers of insulation, one layer installed between the ceiling joists and then another layer of insulation (unfaced) laid across/perpendicular to the faced insulation?

Having to add a second layer across the joists seems like it will be a major inconvenience anytime someone needs to go into the attic for some reason. The joists will be hidden by the insulation, making stepping around in the attic a precarious exercise. It would also mash down the insulation where stepped on.

Am I missing something here?

ratherbefishin' 10-24-2007 11:49 AM

You can buy it all the way up to R-38, faced or unfaced. You just won't find it in the big box stores. If you go with two layers of R-19, be sure you use faced for the first layer, with the kraft facing down, then use unfaced for the second layer, so you don't create a moisture trap that will cause mold problems later. Also, be sure not to block any soffit vents.

Walking around in an attic is always an adventure, you just have to be careful. How often do you have to go up there, anyway? :huh:

dderolph 10-24-2007 12:04 PM

Thanks for the quick reply. I'll check with some local building material suppliers who cater more to contractors than to home owners. Maybe they have the R-38 insulation you say exists. If not, I guess we'll have to go with the two layers.

You ask, "How often do you have to go up there, anyway?" Well, hopefully, very seldom now. The house is about 80 years old. Since my son bought it about 2 years ago, the attic has been accessed to install some electrical wiring and to remove the top of an unused chimney and close the hole in the roof left by that removal. But, now that those things are done, the need to go up there should rarely occur.

Edit: I imagine two layers of R-19 would be a little more effective than single layer of R-39 because of the criss-cross pattern which would completely cover the joists.

ratherbefishin' 10-24-2007 12:26 PM

You're welcome, and you're correct about covering the joists. The wood has no insulating value.

concretemasonry 10-24-2007 12:56 PM

How about blowing in cellulose?

It is far superior to fiberglass in every way. Many big box stores or others that sell it have blowers available.

Don't forget to use "chutes" (cardboard or foam) between the rafters at the outer walls to keep the ventilation from your soffit vents open to the roof vents. If you do not have ventilation, you run the risk of ice dams and moisture.

joasis 10-24-2007 06:15 PM

Time will prove that all the hype about R value and fiberglass is just that, hype. The facing on the fiberglass has as much to do with it's insulating value as the thickness. You can rent a blower and add 12 inches of cellulose and get what you want, plus, get the added benefit fire retardant, insect resistance....mice don't like it either.

moneymgmt 10-25-2007 11:20 AM

Quote:

Originally Posted by ratherbefishin' (Post 69716)
You can buy it all the way up to R-38, faced or unfaced. You just won't find it in the big box stores. If you go with two layers of R-19, be sure you use faced for the first layer, with the kraft facing down, then use unfaced for the second layer, so you don't create a moisture trap that will cause mold problems later.

Ok I'm overthinking again. I too am insulating my 2x6 attic roof, but mine is going to be drywalled over and finished. I know I need to get the carton looking inserts to vent along the actual roof before insulating (help me out... can't think of what they're called...) but would I put the insulation face on the roof side or the drywall side? I was planning on using r-19 do you think that is sufficient? I think too much and confuse myself.....:thumbup:

IckesTheSane 11-02-2007 11:30 PM

Quote:

Originally Posted by dderolph (Post 69712)
Having to add a second layer across the joists seems like it will be a major inconvenience anytime someone needs to go into the attic for some reason. The joists will be hidden by the insulation, making stepping around in the attic a precarious exercise. It would also mash down the insulation where stepped on.

I was thinking about adding some additional insulation to my attic, but had this exact worry. The solution I've thought of (but haven't tried yet!) it to nail down wood sheets over the fist layer of insulation and joists, then put the next layer of insulation on top of that. That way, at least you know you won't put a foot through the ceiling, or worse.

As for mashing down the insulation, I though maybe cellulose would be a good choice, as you could shuffle your feet around and kind of plow through the insulation, instead of walking on top of it.

Only issue I've though of is if the wood sheets would act as a vapor barrier. I don't know if it would or not, but it crossed my mind. If it did, you could always leave a small gape between the boards; enough for some air to move, but not enough to step through.

Since I'm thinking of doing this also, does anyone with actual knowledge in this sort of thing think this is a decent idea, or am I missing something critical?

AtlanticWBConst. 11-03-2007 08:04 AM

To achieve an R-38 Value using traditional fiberglass Batt type insulation:

Use R30 unfaced insulation and one layer of "Reflectix"(which is rated as R-8).

We have used it on Attic Remodels and have had no problems passing insulation inspection requiring R-38 ratings. Just make sure that you install strapping over the reflectix - to attach your sheetrock onto.


Reflectix: http://www.reflectixinc.com/diy/defa...?pageIndex=530

tyler101 11-03-2007 03:44 PM

OP, You may be better off having someone come and do the insulation for you. I've heard that NCI of Ohio does very good work. I believe they have an office down that way.

beExperienced 11-03-2007 05:21 PM

No one has mentioned that any attic / ceiling should be airsealed before an ounce of insulation is installed. Uncontrolled air leakage can be responsible for up to 40% of house heat loss......insulation will only slow it down, not stop it.

Also: The uncontrolled air loss from the house below will contain moisture from your house activities that will condense on the now cold roof sheathing leading you to believe that you need more ventilation....NO! NO! NO!

STOP THE MOIST HOUSE AIR FROM GETTING TO THE ATTIC. It will reduce your need for more attic ventilation and reduce your energy bills more than the insulation by itself.

See: http://www.cmhc-schl.gc.ca/en/co/mah...gemare_001.cfm For newer info about attic venting.

Oh! Forgot to mention: after airsealing, if you're doing it yourself, blow the attic to R50 with cellulose. It'll be worth it in a couple of years.


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