I have R19 fiberglass in the attic already, and we all know that isn't going to cut it. I'm looking to blow in cellulose. I'd prefer the spray foam, but doubt I could afford it. This will be a DIY adventure.

How much blown in cellulose should I add? Reading online, it looks like I need to be in the R40 - R50 range for TN, does that sound correct?

Thanks

I'd just put more bats in.  Lay them in at a 90 degree angle to the R19's and call it good.  Blown in insulation is a pain in the ass.  At least you can move bats around if you need to.

bats suck and the gaps=poor thermal protection





OP I would add 12" over the top



ETA make sure you dont blow it in any vents/air passages

Are you hiding $10,000?

This information is correct.

Cellulose is heavy. It will compact the batts, and as it settles it will compact onto itself as well.

You would get a better R-value, that lasts, if you blow in fiberglass insulation. It sounds horrid, but it does not make you itch like you think it might. It does not compact down or form a crust. It is not dusty as you blow it in, like cellulose is. It is much easier to work with.

The only drawback is, since it does not crust over, aggressive air movement in the attic can push it around. That is not a problem, normally. Make sure you do not block soffit vents or blow it tight to the underside of the roof.

You would use the same machine to blow in fiberglass as you would use to blow in cellulose. You will find blow-in fiberglass at the same place you buy blow-in cellulose.

I just bumped mine from 10 to 35, and it's made a substantial improvement in comfort and energy consumption.

Generally you'll find recommendations from 38 to 60.  Best thing you can do is seal up all air penetrations prior to adding more R value.  EPA actually puts out a pretty decent document here: http://www.energystar.gov/ia/partners/publications/pubdocs/DIY_Guide_May_2008.pdf?1443-f242

Since you're set on cellulose I'll assume you have a continuous vapor retarder in the ceiling plane.  If this is not the case, then you'll want to switch to fiberglass.  Either way you should still seal up all ceiling penetrations.  Make sure you have plenty of high and low roof ventilation, and don't block it.  You might need to retrofit baffles to your roof structure to contain the blown insulation.

Energystar.gov recommends you add R-38 on top of what you already have.  I think that's overkill for your climate, but if the cost difference is marginal then go for it.  I'd say blow in 10" of fiberglass (or 7" of cellulose) and call it good--should put you into the low 40s overall.

Is the roof vented to current code?  

If you want to make a HUGE difference, rip off the composite roof and install a white metal roof.  Will drop attic temps 40 degrees in full sun and your current insulation will be plenty.

Adding more insulation under a black composite roof with poor venting is a waste of money.

This AttiCat machine is great to blow in fiberglass you can blow in over your existing. Its free rental if you purchase the fiberglass from homedepot. The new fiberglass is not itchy at all like the old stuff.  I did an entire 1600sqft of attic in under an hour with someone feeding the machine.
http://www.youtube.com/watch?v=2a8DTuUYHNA
If you have any recessed lights make sure they are (IC - Insulation Contact Rated).



I would also install rafter baffles even if you don't have a vented soffit yet, you can install the baffles now and cut soffit vents in the future. Its cheap and easy to install them now, it will be harder to install them once all the insulation is blown in in the future.


 

Just switching from dark to white colored shingles makes a huge difference and could greatly extend the life of your roof.

I've never heard of blown fiberglass. How does the price of that stack up against cellulose? I'm not sold on any particular method, I'm just trying to plan what I'm going to do. The current insulation is insufficient and I'm tired of sweating during the day.

Cellulose will breakdown and settle over time, fiberglass will never breakdown. How many sqft is your attic area?  If you already have R19, you will want to add R30 on top.





This will tell you how many bags you need per 1000sqft: http://insulation.owenscorning.com/assets/0/428/429/431/af2a2cae-f7c3-43bd-8e88-9313ed87dd2d.pdf