My local HD only has 4x8 sheathing which I probably can't get to work. Lowe's has Reflectix with R19/R21 rating. I've also seen Atticfoil which has no R-rating but seems to have good reviews and has been around for a while.

"However, is there any benefit to adding faced insulation batting to the rafters in addition to increasing the insulation on the attic floor?"

No. Insulation needs to be placed at the home's thermal boundary-- which in your case is the attic floor. If you want to move the thermal boundary to the roof in order to create an unvented, conditioned attic, you would insulate under the roof decking and not the attic floor.

My electric bill is not high. Even in August, it may run $150. I'm not adding more insulation for cost savings, but for comfort. The second the AC turns off, there is a dramatic drop in temperature. You know during summers when you are on long road trips and have the car AC on max and your nose gets cold? And you turn it off but within about 3 minutes the vehicle is unbearably hot? That's basically my house.

There's a number of problems doing what you suggest, in the way you are suggesting that you are going to do it... listed this problem in HVAC, Old House, DIY. You say Texas, but not where exactly. It's important because some areas of Texas are considerably drier while others like my area in Katy, Texas is much more humid than some.

Humidity might be your problem. If it is, doing what you suggest will make this situation worse. Because? Putting in a bunch of insulation will decrease the load, which in turn will decrease the run time of the system, could cause short cycling of the equipment because after the insulation is complete the system is now "over sized" for the structure. So whether humidity is your problem or not it could become your problem with an over sized AC system due to insulation being increased. To often people get fixated on one thing, without considering the effects of doing such. HVAC is a big picture problem especially in an older home. How old? The older, the more problems. Was the house designed for AC when built? The questions only get longer from there.

Typically most of Texas is R30-R38 in newer builds. Older homes could be anywhere from R11-R19, typically. You would also have the walls of the home to worry about too. Doing all that without considering the ramifications to AC sizing via heat loads it's more likely not to work like you think it might -- by simply adding insulation to the attic floor.

AC System short cycles... an over abundance of them causes more problems than just comfort issues.

You don't say what you consider "hot"... lots of people moving to Texas from other places and comfort means different things to different people... especially those that haven't lived in Texas all that long. Maybe this is you... maybe this is someone who reads this post weeks, months, years later. (This post isn't just for the OP)

I service the Katy, Texas area.

"No. Insulation needs to be placed at the home's thermal boundary-- which in your case is the attic floor. If you want to move the thermal boundary to the roof in order to create an unvented, conditioned attic, you would insulate under the roof decking and not the attic floor."

Spray foaming the decking is out. There are very few people that do it within a 50 mile area and it is cost prohibitive. if batting between rafters/under the decking is out and spray foam is out, what about a radiant barrier like was suggested by Raye?

We put spray foam in our current house but used radiant barrior foil to the deck in a previous house and it definitely helps. we have used both the bubble wrap and the regular foil and they both work but since you are insulated bottom chord i would just use the attic foil.

"We put spray foam in our current house but used radiant barrior foil to the deck in a previous house and it definitely helps. we have used both the bubble wrap and the regular foil and they both work but since you are insulated bottom chord i would just use the attic foil."

How long ago did you install the atticfoil? Do you have any issues with cell signal/wifi signal? My house has minimal signal with AT&T as is. A block to the right and I have full service. A block to the left and I have no service.

Hi, Luna,

Radiant barrier sheathing is a proven method for reducing radiant heat transfer in attics. Short of removing your existing roof to install it, it's not an option for you. That leaves you with the option of installing a radiant barrier film between rafters. Be sure to leave an air space between the radiant barrier and the underside of the roof sheathing to allow moisture to be ventilated. I don't recommend installing radiant barriers on attic floors because of the potential to trap moisture in the insulation between it and the ceiling of the living area below.

If you're interested in preserving the warranty on your roof shingles (and it's pretty rare for anyone to successfully collect on a warranty claim in my experience,) you should check to see if the manufacturer has any restrictions or special instructions.

Charles -

My roof was recently replaced in 2019. However, there are too many loopholes on the manufacturers warranty for shingles that I do not anticipate it ever being covered. I did not think about replacing the decking with sheating. Just like I did not think about having the roofers rebuild my dormer windows. Lessons learned for a first time home owner.

While I am sure the sheathing is a superior option, does the radiant barrier film also work? It'll be a fairly cost effective upgrade, but if it doesn't do much, then I'd rather put the money in extra blown-in insulation.

Hi, Luna,

Here's a link to some information from DOE. It includes a pretty color photograph showing the installation of a radiant barrier film between the rafters, too.

https://www.energy.gov/energysaver/radiant-barriers

I hear you about att, we have them also. We had the foil in the house for ten years before we sold it. Didn't have any issues with the roofing but must admit to sometimes taking the cell phone to the front porch for better reception. That said, radiant sheathing has been code here for many years with a lot of houses built since then so maybe not a big issue?

Radiant barriers should have no effect on cell or wi-fi service.