If the exterior cladding isn't on already, you can use XPS sheathing which will give you the nominal R value you're looking for. And effectively much more than a nominally similar standard 2x4 wall. It's my favourite effective and economical system.

If not, you have several possibilities, as you already know.

Sprayed fiberglass and flash and batt are the leading candidates in my mind.

For the attic, consider a non-vented attic. They can be especially effective in a windy area. But doing this now may require some framing modifications. Otherwise, if there's room, I'd go with blown cellulose. But it's critical in a vented system that you have a clear airflow from the soffits. Can you do that with the required cellulose? Not trying to rub it in. But it's best to think out your specs before you start building.

Consider dense-pack cellulose wall insulation combined with rigid insulation on the exterior or furring on the interior.

In our area there are "energy specialists" who perform energy audits, certify homes as "Energy Star" and who can be paid to consult on jobs to recommend insulation and sealing specifications. We are meeting with a fellow this week to make recs for our house on what type of insulation will be best, given our already purchased and installed HVAC system. I found him through the energy star.gov website. Our consult is $160, will be more if we decide to get Energy Star certified. Good luck.

you are gettin excellent info.
adding 1" closed cell foam sheathing boards to the exterior..your choice of insulation in walls and ADA to interior.
pay to have a load calculation performed based on the specifics of your home (SHGC's for windows..R-value of
insulation..spec'd air infiltration rate..to determine size
of central sytem your home requires. Bigger central systems are not better..Manual J will give size of unit based on your needs. get several bids..R-8 ductwork..mastic seal of ducts and return air chases.

by minimizing air infiltration in to your home, the payback is smaller tonnage of central unit. less
to heat and cool as house is not communicating with the
great outdoors..or attic and basement.

check out www.buildingscience.com for specific to your location information.

best of luck.

I think down the road you'll be glad you did not do the spray foam in the attic. No one else seems to see the problem I envision down the road when the roof leaks over the foam insulation. You will never know.... The water will do it's mischief undetected for years until some structural failure occurs.

Gary

open cell foam will allow water to exit through the insulation. that it does not is a misconception like
'benefits' of pav's and radiant barrier voiding shingle warrenties.

If you are concerned about roof structure damage from leaks, you should install Ice & Water Shield over the entire roof. An ounce of prevention ....

If you're expecting to find your roof failures by watching for water dripping through your insulation you're heading for a disaster anyhow. Water has an uncanny ability to leak in and travel to some place not obvious.

You'll still know it leaks...I've seen many roofs over the years that look good but leaked. Seeing discoloration of the ceiling is how 99% of bad roofs get detected. As for open cell foam...show me a sample that water will pass through. Open cell DOES NOT mean open like a sponge. Mightyanvil is right about the ice dam but that will raise your roofing cost.

"Mightyanvil is right about the ice dam but that will raise your roofing cost."

Well worth the cost. Because we have many roof lines and is cut up, the majority of our underlayment is w.r.grace ice and water shield. Why i didn't have the roofers just do the entire roof is something that I'll always regret. Live and learn!

We did the spray foam on the underside of a flat roof. Of course the roof developed a leak. The foam held the water against the plywood and we had a bit of a mess when pulling all the sopping wet foam out of the ceiling. It did leak eventually, but with the foam in place, far from where the hole was.
I'm pretty sure I'd do it again with that particular roof, but the newest roof won't have foam, since we had other choices.
The more I know the more I don't know.

It is wiser to put most or all of the roof insulation above the roof deck of a low-sloped ("flat")roof. Other solutions can lead to condensation problems.

Air tight drywall is the way for you to go. Its easy, simple, and cheap.

Add in air tight electrical boxes, and youre good to go.

I'm in NW Iowa

Thanks to all those that responded. I am meeting with an insulation sub today and have been getting several bids. The price for foam is coming down (from other bids).

One question, one insulator ran a quote for blown-in fiberglass in the flat attic space. Our attic is vented. What would be the pros/cons of putting fiberglass in the attic vs. foam. This same guy is suggesting putting foam everywhere else.

Rollie, I have looked into the air tight drywall approach. My builder has never done it before. If I go with foam, would I need to do the air tight drywall?

My main concern with blown-in fiberglass or cellulose is settling.

In cold climates, where there are big variations between the temperature in the attic and the conditioned space, the R value of the fg is reduced by 50%. (You can make up for this by adding more fg.) Wherever space is limited, blown in fg is not a great choice vs. blown in cellulose. The settled R value of cellulose is 2.1-2.7 vs. settled fg R value of 3.0.

"The settled R value of cellulose is 2.1-2.7 vs. settled fg R value of 3.0."

Worthy, is this correct or a misprint? It reads contrary to what you were saying in the rest of your post.

HH, It all boils down to how much foam you install in the stud cavity, so as to not have a condensing surface. Yes, the foam is airtight, so it would also be your air barrier, but technically, in a heating climate, you would want your air barrier on the warm side of the insulation.

Thats why the ADA works so well in climates such as our, with extremely cold temps and wind.

You would not need foam over the whole attic. Simply foaming the partition walls from the top side to seal them up would do wonders and not cost an arm and a leg. Heck, you could get a couple froth packs and do them yourself, if youre at all handy. Air tight recessed cans are a must and even then, they are not anywhere near airtight but lots better than their predecessors.

My choice for the attic would be cellulose and make sure it is applied to the desired bags per sq foot, and not simply how thick it is. They can cheat the depth by adding more air.(fluffing), They cannot cheat the bags per sq foot ratio. Cellulose will settle,(and should somewhat) but as long as the required B/SFT is installed, then you will get the rated R factor. I would not recommend any batts of any kind in the attic space. Use sealed wind baffles at all eaves, allowing for channel ventilation over the top.

Gorgeous day today, until the wind wrecked it.

Again, I think the foam against the bottom of roof decking is a bad idea. In walls is good. If someone came up with a plan to foam on top of the ceiling surface, I think that would be a winner....a look in the attic would reveal any leakage problem and the roof structure wouldn't be in danger. The idea that water could get trapped between foam and the roof deck seems like a real time bomb to me, especially since it could go on for a looong time without you knowing.

Worthy, is this correct or a misprint?

Ah, er, I was just testing to be sure you were paying attention.

Here is a link that might be useful: Cellulose vs. fiberglass

For the 2x4 walls, you could do 1" of spray foam (to make a nice air seal) and then dense pack cellulose on the inside. Another option would be "spray cellulose" - it makes a dense, non-settling cellulose material in your walls.

For the attic, I would choose cellulose over fiberglass - there are "wind washing" problems with fiberglass.

klaire, what do you mean by "wind washing" problems?

Is the spray cellulose you are talking about the cellulose that is applied wet? Does this type of cellulose not settle?

I am leaning towards closed cell in the 2x4 walls and then open cell or wet cellulose in the 2x6 and 2x8 walls. For the attic, I would like to spray an inch of foam and then cellulose over the rest.

If I do the foam (even an inch), would applying the airtight drywall approach be repetitive/overkill?

Wind washing occurs when the the attic ventilation allows enough air movement to syphon off some of the insulation value of the insulation. Fibreglass has more air in it than cellulose, so it is more affected by wind washing.

Another place wind washing can occur is at the heel height of the rafter, if you dont have solid baffles installed in the heels.

Stabilized cellulose has a water based glue/adhesive mixed in with it in its dry state. Adding water to the mixture activates the adhesive so that settling is eliminated.

Of course, too much water is a bad thing in a stud cavity also, but for the most part, it requires very little water to insulation ratio to activate the adhesives.

Why spray any foam in the attic, other than places that can leak air, like wall partitions, electrical openings and recessed cans?(recessed cans require special treatment if you are going to foam them.) You can also build a drywall box that seals over top of each recessed can in the atic and make it 100% airtight. The drywall ceiling is air tight enough, and you have the ability to add all the loose fill insulation of choice on top, once you addressed the air leakage areas.

"If I do the foam (even an inch), would applying the airtight drywall approach be repetitive/overkill?"

Yes and no. With the ADA, the air barrier is on the warm side of the insulation, which is correct for your climate.

I am down to two choices with our insulation in the 2x4 walls. I can either go with 3 inches of closed cell (and would then probably go 3 inches in the 6 and 8 inch walls, too) and leave the remaining cavity empty or blow in 1.5 inches of closed cell and fill the remaining 2 inches with an R-8 batt.

But, one insulation sub has told me I would need to put poly over the batts (which, he said, is expensive and would bring the cost close to doing 3 inches of closed cell). He also said it would be virtually impossible to blow in 1.5 iches of closed cell and then blow cellulose or fiberglass over the top of that.

I am not going to put any foam in the attic and, in the sloped attic portions, I can either put foam (probably open cell) or a netting and blow-in cellolose/fiberglass.

Does this sound right about the poly over the fiberglass batts? What about blowing in the cellulose over the closed cell?

Have you considered adding insulation outside the walls? If you're siding isn't up yet, you could add a layer, or two, of 4x8 sheet foam boards. Keep in mind this make siding a tiny bit slower, as they require longer fasteners.

Also, if you haven't locked in siding, you could look at CraneBoard. It's a vinyl extruded board with a solid core of foam. Goes on like regular clapboards. It's R-4 or R-6 ish.