I live in SE New Mexico 88210.  It's very hot here in the summer and most of the year but can and does get cold in the winter.  I have a 2 story wood-frame home with hipped roof - no gables.  There is blown in insulation above the ceiling of the top floor, but I have always felt it was too little, and our summer heating bills would support this idea.  We have 2 heat pump units, one for the ground floor and one for the 2nd story which has the blower and ducting in the attic space.  This space is extremely HOT during the summer and the 2ns floor is always much warmer than downstairs despite the AC coming on all the time just to keep it comfortable.  My family and I have decided on becoming greener and one of the steps toward that is reducing our energy usage.  I have to believe that if I can better insulate the attic space then we will reduce our usage.  I'm just not sure what method is best. 

I've read many posts by some of you very knowledgeable people who seem to favor spray foam under the roof decking and seal the vents.  We have very little humidity here - it's a desert after all.  So it seems that leaving the blown in stuff on the floor and adding foam would help greatly.  Problem:  I have searched and cannot find any contractors in my area who do the spray foam.  Secondly, the DIY options seem to be very costly for the size of the space I need to cover. 

I'm just a homeowner, pretty handy, and trying to do more with less.  Any help would be appreciated.

A sealing coat of half pound foam would be great, but it's not a DIY project by any means. But you can still make great strides by air-sealing between the attic & top floor and insulating over it.

If they're not already, seal all the duct joints & seems with duct mastic (available in box stores.) It's a miserable job to do mid-summer in the middle of the day- might want to get up before dawn for this one. Also seal all the seams on the air handler with FSK tape (2" wide aluminum tape.)

Then, seal as much/many of the plumbing & electrical penetrations between the upper floor and attic as you can find. Sometimes this may take some sheets of corregated cardboard trimmed stapled in place, with some spray foam to make it air tight around the edges. Next to chimneys & flues you'll need to use steel and heat-rated caulking, and something to keep a 3" clearance from any insulation later. If you have any recessed lighting fixtures sticking up there, replace then with gasketed air-tight insulation-contact versions (or build an air tight box out of 1/2" sheet rock over them with 3" of clearance, sealed at the ceiling interface with foam.) Depending on the complexity of the ducting, plumbing & flue work this could take better than a whole weekend, but sealing it before insulating is important.

If the building is balloon-framed without full top plates on the walls, you may be able to find out whether the wall cavities are insulated while you're up there. Poke around with a flashlight at the soffits, see what you find. In some older homes it's possible to blow cellulose down the wall cavites from the attic. It'll be blocked by headers over windows & doors, but you can still typically get more than 50% of the wall area insulated without drilling if the tops are open. I won't go into detail about how to install the wall insultion unless it proves to be the case that it's open, but that too should be done before insulating the attic floor if you can. (You can always have pros come and side-drill it for blown insulation later if it's closed at the top.)

Then, (and this may seem strange at first) do the same thing to your basement ceiling, taking care to foam-seal the foundation seal & rim joist as well. This can be treated as a separate project, but when you seal both the attic & basement, convection flows drop dramatically, no matter how leaky the floors in-between are.

Is there a full floor in the attic, or just plank-walks? If it's mostly open, dry-blowing cellulose over open joists is a reasonable DIY project. Most box-stores who sell cellulose have free blower rentals if you buy more than some minimum. If the ducts all hug the floor, just heaping cellulose over them at the same time you do the floor works. If not, you need to give them at least an R8-R11 fiberglass batting insulation.

If your exterior walls aren't air tight to the interior you may run into wintertime frost issues at the soffits if you don't provide a purpose-made vent chute to keep the insulation from blocking ventilation air from entering the attic there. They can be corrugated or foam (also available at box stores.) Get that all set up before you buy the insulation & rent a blower.

The Oak Ridge Nat'l Labs cost-effectiveness model indicates R38 attics are cost effective for you:

http://www.ornl.gov/~roofs/Zip/tmp/results17941.html

http://www.ornl.gov/~roofs/Zip/ZipHome.html

In cellulose that'll be ~10-11" deep, and about 1.4-1.5lbs of material per square foot at that coverage. Most box stores sell it in 25lb bags @ ~$10-11/bag, so you can do the math on what it'll set you back. (If you have a building supply house see if they can't get you "borate only" ore "suflate free" cellulose, which is more benign to metals should it get wet, and is a better insect-deterrent.) Buy at least 20% more than the standard coverage charts from the manufacturer- they tend to represent results from perfectly maintained blowers & experienced installers in laboratories, not DIY hacks using abused gear rented/borrowed from a box store, eh? ;-) The R-value per inch of depth is about the same independent of density, and odds are yours will be lumpier than in the lab- you need the inches. Odds are pretty good that this will cover the tops of the joists completely. If you want to be able to lay down planking or flooring later it may be worth installing some 2x lumber on edge 24" o.c. lateral to your joists for that purpose. If your indended final depth works out to be close to the combined existing joist + 2xX so much the better- you'll have a well distributed depth-gauge to work with.

If access decking/planking isn't an issue and you want to minimize thermal bridging from lumber (which WILL enhance performance), make yourself up a set of cardboard depth gauges with clear contrasting marker on it at your controlled depth, and staple them to joist liberally so you'll always know when you've filled in the area sufficiently. Start at the edges and work backward, taking breaks to rake it level and fill in holes as you go, and take care to not fill up those soffit chutes you spent time stapling in place, eh? You'll need a pretty-good dust-mask & goggles- it's a dusty operation. The fire-retardents are about 15% of it, and are in powdered form. They're non-toxic to humans (the borates are hell on ants & termites though), but choking down dust of any type all day isn't good for you. If you have a few bags left over at the end you can either add them to the top or take 'em back to the store for refund. (If you end up with R50 instead of R38 it's not exactly a disaster, eh?)

Attics are one thing, walls are another. If you can, peek around electrical boxes on exterior walls to see if there's anything there. If not, hiring a pro to do exterior walls at some point will be well worthwhile. If you have it quoted both as "dense packed" and "2-hole method". You can do either, but the more expensive dense-packing makes the place measurably tighter, reducing air infiltration losses significantly. It takes about 1.5x as much material as 2-hole, and a similar labor-factor, so it'll be more expensive, but well worth it IMHO. (If you're really up for it, dense-packing can also be a DIY project, but it helps if you own or have unlimited access to the blower and a heavy duty drill like a Milwaukee Hole Hawg or similar. It can run into man-week or more if you're doing it alone, less as a 2 or 3 person job, one driller, 1 or 2 people on blower-duty.)

Last, not least, if you have any live knob & tube wiring, you're required by code to decommission it and install code-approved wiring before insulating those areas. SFAIK there has yet to be a case where knob & tube wiring ACTUALLY caused a house fire when insulated-over with cellulose or foam, but the theoretical basis was that a faulty twist-splice could generate enough heat to eventually ignite insulation in direct contact with it. IIRC Ohio was considering repealing that a few years ago due to the absence of relevant case history. Don't know if they did or didn't, but most states have it on the building code books. BX, Romex, etc, not a problem...

If you decide to pursue DIY celluose beyond open-blow attics, a guy named Rick Karg has a huge amount of well illustrated & explained web-published tips, tricks of trade, and good advice in general. Google [karg cellulose ]- it's out there!

Dana1:

Wow! Thanks for all the info. It gives me a lot to consider. The house is only 8 years old and I had it built. I had all penetrations into the attic sealed with foam before the insulation was blown in. All of the outside walls are insulated with wet spray recycled material. My main concern is the temps in the attic space. On a day like today, I can put my had to the ceiling in the 2nd floor and it is hot. Would more blown in cellulose and adding a radiant barrier be an improvement? These are both things I could do myself.

If I were to find a contractor who could do the job and not gouge me, would the spray foam on the underside of the roof decking be a good move?

I think I have more questions now than when I started...

Ok, so if it's fairly tight new construction... (I probably went way too verbose-mode on attic insulation with the picture I had in my mind at the time, eh? :-) )

What IS the R-value of your existing attic insulation?   If the ceiling feels hot to the touch, it can't be TOO much.  How deep, and what material?

If it's over R35 radiant barrier isn't going to buy you much.  At R19 it'll be significant (25-30% reduction in heat transfer on killer-hot days), but not as much as doubling your insulation depth.  But at any insulation level radiant barrier won't lower the air temp in the attic.  Radiant barrier lowers the temperature of the upper layer of the insulation, which is higher than attic ambient since it is absorbing/re-radiating heat that radiates from the hot roof deck, not absorbing heat from the air.  With a radiant barrier in place the top of the insulation runs at the the attic air temp, which will still be hot, but the thermal transfer to the conditioned space will be reduced because the top of the insulation is now cooler.  (The bigger the R value of the insulation, the less difference it makes.) If you can blow over the joist-tops to form a thermal break it'll be be a bigger difference, since the thermal short circuit of the joists is about a quarter of the heat gain at insulation depths of 9.5" (2x10 joists filled to the top, ~R35, if cellulose), despite the joist-tops being less than 10% of the surface area.  6" of cellulose over the the top of a 2x10 doubles the R-value at those critical stripes, while only increasing the R value of the space between the joists by ~60%.

If you can find somebody to spray half-pound foam between the rafters for under/around 45 cents/board-foot (square feet of coverage x depth in inches) and seal the vents the same time, that WILL lower the attic temp, but if you already have R38+ and sealed/insulated air handler & ducts it won't lower the AC & heating bills enough to be cost-effective.  But if you only have ~R19 on the attic floor, by all means, foam the rafters with half-pound stuff to 6" or more.  (Adding 6" of cellulose DIY style would be about as effective for signficanly lower cost though.)  It'll add 10F or so to the peak temp of the south-facing shingles, reducing their lifespan 5-10%, (but I'd take 23 years of energy savings from the foam over another 2 years of shingle life for a 25-year shingle, eh?)

With R-value more is always better, but where that additional R has the best return will vary. If you have a gaping hole in the thermal boundary it doesn't matter if you raise the R value of the rest to R200, the heat loss through the hole is dominating.  Having the air handler & ducts outside of the thermal boundary represents the biggest discernable thermal-hole in your description so far.  Foaming the rafters would put it somewhere in the middle of the thermal boundary, so the AC system would still benefit greatly from sealing & insulation.

No matter what else you do, seam/joint sealing & insulating the AC ducts will be significant boost to cooling system performance.  If they're not sealed & insulated to at least R8 this is an absolute must-do.  It's OK for the attic to run hot- it's on the outside of the thermal boundary, you have to expect it. But any duct-air communication with that space from duct leakage is an efficiency-killer, as it the conducted heat gain through the ducts surrounded with 120-140F air.  If you had a foam contractor in the area 3-4" of half-pound foam over the ducts would both seal & insulate.  But mastic sealing and a heaping cellulose overblow can be as-good for less money as a DIY project.  If the air handler is basically a flat-sided box with R-4 or less of internal insulation (most are- many have NO insulation), FSK-taping the seams and putting 1" of ISO board (with FSK taped edges) is reasonable, and still allows reasonable service access when needed.

When it's time to re-roof, using high solar reflectivity moderate emmisivity "cool roof" materials will actually reduce the air temperature in the attic.  RB on the underside of the rafters only keeps the hot roof decking from radiating heat directly to the joist-tops, ducts and insulation, but the thermal transfer to the air stays about the same. With  high reflectance & IR-emmissive exterior roofing materials the interior of the roof deck itself runs cooler. The effect is more dramatic with flat roofs, but I'm assuming your hipped roof has at least a 5/12 pitch(?),  above which convection cools from the outside far better than flat roofs.  Under California Title 24 a "cool roof" (defined as 70% minimum solar reflectivity, 75% minimum emissivity) or radiant-barrier or addtional insulation is required in hotter regions of the state, when re-roofing,  unless the pitch is over 2/12.  There are models out there that can tell you with some precision how well your roof sheds heat via convection based on it's pitch and orientation, etc, but you're probably already into the "good" zone, where cool roof & radiant barriers could improve it somewhat but not in a major fashion.  But when the costs of a cool roof and other are similar, "some" still beats "nothing".

So in order:

*Seal & insulate ducts & air handler

**Measure your existing insulation level- if under R38, either add more to the rafters (sealing the attic), or blow cellulose over the floor to depth of at least 10", and if you can cover the joist tops by 3" or more by going a bit deeper it'll worth it (way more than a radiant barrier would be.)

***Then look at other primary solar gain issues:  If you don't have low-E low-gain windows on the E,S, & W sides, low-E window film will make a difference.  If you don't have awnings/overhangs over your S windows, they too will make a difference.  Shutters or exterior (and to a much lower degree, interior) Venetian-blinds ore exterior rollup sun shades (eg:  http://www.builditsolar.com/Projects/Cooling/RollupSunShades.htm ) can cut solar gain on the E S & W windows.  Treating N side windows isn't as important unless you have highly reflective buildings or ground on that side.  If it's white sand or whitewashed adobe, the gain is still large, and low-E windows/films and blinds/exterior shades will cut it by way more than half.

As it is very dry there, what about using an evaporative cooler to ventilate and cool your attic space?