If you are following the 10,20,40,60 rule, stud walls with foam sheathing will not get you there, unless of course you are planning on using 4" of XPS exterior foam sheathing. Even then, as Springtime notes, thermal bridging plays into the assembly and reduces the total r value. If you want to hit r40 walls, the cheapest way to do so is with double stud wall construction. Also if you want to hit r60 with spray foam on the roof....get ready to pay dearly. And then pay some more! I prefer to detail the air barrier at the sheathing plain, and the go to product is Huber ZIP sheathing. It creates a good air barrier and eliminates the need for wraps and products such as Tyvek. Caulking is critical at plates, headers, sills, heads, etc to continue the air barrier. Once the house is tight (first priority) then you can insulate. It is next to useless to insulate a loose house. As Worthy states, houses dont breath, at least by means of leaking through the walls. Give it mechanical lungs that allows you to control when it breaths (ERV/HRV for your climate). While spray foam is a good product, its also a very expensive product. Even though open cell is getting more affordable, its still a lot more expensive then caulk and blown fiberglass/cellulose. It also air seals the stud bays, but fails to address leak prone areas such as top and bototm plate connections. Spray foams place the air barrier at the inside of the sheathing plane. The advantage to placing it on the exterior plane is the sheathing can extend down past the sills, rim joist area, top plates, etc to help prevent leaking in those areas. You also do not want to use exterior foam AND spay foam on the inside. This creates a moisture trap and prevents drying of your assembly to either direction. However after you get to around r30, your walls stop controling your biggest loss. your windows and doors will limit the total performance of your assembly. You can have r100 walls surrounding a large expanse simply dual pane glass and it would be all for nothing. Triple glazing windows helps, but sometimes do not always pay off. My go to wall assembly for most climates is a 2x6 framed wall, blown/dense packed fiberglass or cellulose insulation, air sealing/caulking, Huber zip sheathing, 1-3" of XPS exterior foam (depends on zone), vertical strapping for a drainage plane.

"Get references for an energy rater and make sure that they are trained." ditto I am reading in other forums of 'free' or minimal cost energy audits. if the sole purpose of the audit is to sell the fix up package and leakage is defined simply as equivelent to 3x5 hole in wall it isn't showing you where the leakage is located. Ideally have the audit done by an independent company that tests before and shows you leakage sites with recomendations as to how to seal them..and tests once sealing has been completed. This way the auditors loyality is to the consumer..not the company doing the repairs. caulking seals a lot of leakage and is flexible enough to provide a long lasting seal. mastics for ductwork and hvac related leakage will provide a long lasting seal for hvac. knowing where the leaks are and how to seal them is the true goal of an energy audit..imo & experience. foam insulation provides air sealing and insulation in one. sealing the leakage and conventional insulation is the equal if enough of the air sealing is done. this takes time and materials.. first you want an air barrier..then insulation. recessed lights that are not ICAT (insulation contact air tight) oversized cuts at bath fans, stove vents are large leakage sites. cuts in ceiling where supply boxes are installed should be mastic sealed as should return air and all duct connections,and plenum connections. sealing these (and other leakage sites) will improve your air barrier to the attic.. if you install cellulose keep in mind that the 'dust' from the newspaper & borates is very fine and can enter the living space and duct system. this is recirculated throughour the house. any gap from attic to living space will allow these particles to enter the house, as will leaks at supply boxes, r/a and plenums. one place to find energy rates is natresnet.org best of luck.

I have a recommendation for whole-house fans, and that is to go with the ones made by Triangle Engineering of Arkansas (made in the USA!). These things move more air than any other brand. As an example: the 36" belt-drive model sold at Lowes & Home Depot moves 6,900 CFM on its highest speed. The 36" one that Triangle makes moves 10,600 CFM. I just put one of these in last week and am so taken with it that I'm evangelizing for Triangle now. These things are much higher quality than the other brands too -- these are made with very heavy-gauge solid welded steel (as opposed to the thin, flimsy metal - often aluminum - that other brands use). They use a very solid motor made by Emerson, the best of the top three motor-making companies (the other two being Fasco and A.O. Smith). They come pre-framed on a wood frame for installation, AND they have sponge-rubber noise-dampening material between the fan and the frame, so they are much quieter than the other brands. Also, Triangle holds a patent on an automatic belt-tensioning system these things use, so you don't have to worry about getting the tension right when you install the fan (or in the years thereafter as the belt loosens up). Also, they come in more sizes than the other companies -- from 24" all the way up to 48" blade diameter (which moves a ridiculously whopping amount of air; no one else makes one that big). They're sold online at Southern Tool amongst other places that ship nationwide, so they're available wherever you live. Also, Triangle re-brands some of these as a private label for Dayton, which is the "store brand" of Grainger - so if you have a Grainger store near you (check your phone book or their website), you can buy one there. I will say this, though - Grainger/Dayton makes their own shutters, and those shutters are much better than the one Triangle makes. Triangle makes great fans, but crappy shutters. Luckily, they're sold separately -- so buy a Triangle fan and Dayton shutters; money can't buy better products. They also re-brand some for a company out in San Francisco called "Fanman" (a/k/a "Delta Breeze"). A word to the wise -- these fans move a lot of air, so make sure to install at least the recommended minimum amount of attic exhaust space (gable vents, soffit vents, roof vents, some combination thereof, whatever works for you) - if you don't have enough, the fan will operate at reduced capacity, and there will be a backpressure which will cause the shutters to rattle when the fan is in operation (any time you hear whole-house fan shutters rattling, you know there isn't enough exhaust space). Oh, and one other thing -- only buy a belt-drive whole-house fan, don't EVER buy a direct-drive model...the direct-drive models are at least five times louder, they sound like standing on an airport runway next to an old prop plane getting ready to take off. Several of the dedicated whole-house fan installing companies have chosen to use Triangle fans; that should tell you something. These companies want satisfied customers, so they use Triangle and only Triangle. Refer to http://www.trianglefans.com/wholehouse.html for more info Here is a link that might be useful: Triangle whole-house fans

Can I just put unfaced roll on "E. woodboard" noted in the picture? there will be a gap/void in the insulation under the woodboard (walkway?). this air space needs to be eliminated, as it lessens the value of the R-19. wood is R-1 per inch. I'd build up joists under walkways & insulate before covering walkways with insulation. how much walkway do you have? heating system & ducts in attic? air sealing the attic floor/ceiling of the rooms below will really benefit you. do this prior to adding insulation. recessed lights, oversized cuts in sheetrock ceilings for the can lights, each hvac supply box & around bath vent fans & stove vents need to be sealed. insulation slows air movement. as the attic air is drawn into the house below through the insulation, it leaves a trail of dirt deposited through the insulation. look for dirty insulation, move it, and there is the air leak. same with ductwork, pull the insulation back at the supply plenum...dirt trails will show you where the leaks are. mastic seal duct leakage sites. I use Hardcast brand 1402 tape, seals plenum/duct take offs, supply boxes/ bath fans/stove vents to sheetrock ceiling. as air moves through the insulation it also devalues the R-value of the insulation. best of luck