I have researched insulation for months asked on several forums, have bids from multiple contractors... I can't make a decision. My local design temperature is -4. I have an outdoor wood boiler bought to heat my run down 4500 sqft home.

My house is OLD and crappy. EST 1830s that has haphazardly been added on to up until the 2000's

I am essentially keeping the first story and ripping the second story off all new windows, doors, siding etc, have redone some of the house (1/3) that is almost entirely new except a savable piece of the old foundation. I need to make a decision on insulation. I am living here for the rest of my life so its important to me that this is done right.

• I KNOW that closed cell spray foam is great insulation HOWEVER I fear the moisture issues that it can cause, especially on old/new hybrid construction. Its also extremely expensive. I do not believe that spray foam insulation contractors are out for the best interest of the homeowner with their bids, they cover absolutely everything possible (rather than pointing out where foam is helpful and where it is not) and they don't KNOW how to mitigate moisture issues in the cielings for example (IE icicles coming out the soffit vents)
  

• I KNOW that fiberglass is less than ideal and should be avoided because there are so much better options.

Some problems:

I have scissor trusses making a vaulted cieling. This unfortunately was a bad decision as far as thermal efficiency goes. I only have 8" or less at the pinch point where the truss rests on the sill. My contractor neglected to mention or offer "Energy Heels" to allow for more insulation. Is this is a big deal? how should I approach insulating this cavity?

Moisture mitigation: I am avoiding spray foam because the old house meeting the new house repairs etc. Plus I am doing my own HVAC so I don't think I can afford an HVAC air exchange system that is required with spray foam

Does anyone have any suggestions for a COST EFFECTIVE insulation choice that I won't regret in energy losses?

Thank you very kindly for your help in this.

Dense packed cellulose is the insulation of choice for cost and effectiveness among many/most high performance builders, with some blown in fiberglass and various assortments of spray and sheet foam, and rock wool (Roxul) thrown in. Fiberglass batts should be completely off your list for many reasons. the exact insulation with vary with the location; spray foams may be necessary in speciific situations like your truss edge; sheet foam in basement or very moist areas.

The most important factor in thermal efficiency for your house, though is not the type of insulation, it is very careful and thorough air sealing. The air sealing must be a separate "project" apart from insulation. The biggest mistake you can make is to assume that some type of magic insulation will air seal your house. Air seal it before you insulate and have a blower door test done to check it so you can make the necessary repairs before you insulate.

You'll get lots of replies with recommendations for various insulations and it does get confusing. The reality is that they all work is some situations and the comparative cost depends on the insulation contractors in tour area. However, no brand, no type of insulation takes the place of careful and thorough air sealing.

Bob, thanks for your reply. This prompted more research into air sealing.

We have taken several precautions to get a good air seal including getting special outside wall "sealing" type electlrical boxes. I have a full wrap of tyvek. I have special sealing tape around each window. Doors and windows will be installed with expanding foam in the gaps. I'm using casement instead of double hung windows that are more efficient due to a better air seal. Everything thats NOT concrete will be like this. I will probably do a Mooney wall where I will keep old 2x4 studwalls to make for 2x6 walls with a thermal barrier to transfer through the studs.

One of the most confusing and totally Democrat or Republican things that is holding me back from pulling the trigger is how to vent the cieling. If I go with dense pack cellulose with a vent tray I will only have approx R12 at the heels on on the sill of the structure. Do I need vent tray products that allow air circulation on the bottom side of the roof from the soffit to the ridge vent? Or do I (as some people say) fill it to the top and pack it as tight as possible with no vent? People place very very high R-values in the cieling, yet vent it for airflow, rendering the R-value recognized to be marginal because there is airflow through these non-sealed insulation types. Some sources say having insulation against the bottom of the roof damages the roof.

I cant find standard, accepted methodologies on this.

Cellulose insulation should not touch the roof sheathing. With scissors trusses you probably have an air space above the R60 cellulose insulation (+/- depending on exact climate) in the center - that area should be vented. Where it would touch the sheathing, do a "hot roof" (unvented) with 4" of closed cell (CCSF) and 4" of cellulose which will give you about an R40 there. As you go up the slope, increase the depth of cellulose. When you get to where you have an air space and 18" of cellulose you can stop the spray foam.

A few years ago "hot" unvented cellulose insulated roofs were thought to be OK, and a number of houses were built this way. Then it was discovered that some moisture does migrate to the sheathing. Oops. Fortunately none of these homes have reported problems, and it is still a grey area. But, the building codes were rewritten to outlaw the practice so that's where we stand today.

the ceiling must be air sealed. After the wiring and plumbing is done, and before the insulation is installed, go up into the trusses and foam and tape all the penetrations. Use high quality tape.

Tyvek is not an air seal. Tyvek is not an air seal. (repeat) Tape* or caulk** all of your exterior plywood joints; caulk all the sills to the foundation. Do a BD test before you insulate. We've found that getting the building sealed to 1.0 ACH 50 is not difficult; above that and you've missed something. *SIGA Wigluv or equal, or ZIP tape over ZIP sheathing. **GeoCell, DAP 35, most good urethane caulks. Expect to pay $6/tube or more.

Since you only have R12 at the eaves if you go with a ventilated roof structure you pretty much have to insulate at roof deck to get any performance out of it. Putting the 4" of closed cell foam on the underside of the deck while effective, may be more expensive and less effective than going with a combination of rigid foam above the roof deck with fiber on the interor side- it just depends on the slope of the roof, and just how much of that closed cell spray you need to use.

Doing the exterior rigid + interior fiber in a location where -4F/-20C is the 99% outside design temp you're on the warm edge of a US climate zone 6 /cool edge of zone 5 type climate. If you put at least 5" of EPS above the roof deck (or 2' of polyiso, with 2" of EPS above that) , either of which is nominally R20, you can then safely add up to another R30 or a bit more as cellulose on the under side of the roof deck, with either a smart vapor retarder (Certainteed MemBrain, Intello Plus) on the interior side, or an interior layer of half-inch OSB, or gypsum painted with standard latex paint.This works because it raises the average temp at the roof deck sufficiently too not adsorb much wintertime moisture through the 1-5 perms (depending on which interior side option you use), yet has sufficient moisture permeance for the roof deck to dry toward the interior. With cellulose you also get the benefit of having the cellulose share the moisture load with the roof deck, reducing the moisture content of the roof.

Closed cell polyurethane runs about 17-18 cents per R per square foot.

EPS and poly iso run about 10 cents per R per square foot (but you have to factor in your scrap rates if it's a complicated roof like a hipped roof interrupted by dormers, etc.)

Dense packed cellulose in netting will vary from 6-15 cents per R per square foot, depending on complexity.

Open blown cellulose on the attic floor is about 3 cents per R-foot, clearly the bargain, unless you need to do a lot of square feet at 4"/R26, which would runs $4-$4.50 per square foot

Closed cell spray foam fixes more moisture problems than it causes. At 1" it's about as vapor permeable as OSB sheathing, 2" it's still more vapor-open than the kraft facer on a batt. There are reasons to avoid it (high global warming potential blowing agents, needs to be applied in lifts of 2" at a time and be applied when the temperature of the roof deck is right to avoid problems with adhesion- or SELF IGNITION as it cures), but from a moisture point of view it's usually more the solution than the problem. The thing to be extra-leery about are extremely low permeance materials such as polyethylene sheeting, foil facers, foil or vinyl wallpaper, etc. since improperly applied you can create moisture traps, or have seasonal moisture problems (from either interior or exterior side moisture drives.)

If using closed cell spray polyurethane on the underside of the whole roof deck, 2" with the rest as fiber is sufficient to be protective in any climate zone in the US lower 48, and most of populated Canada, and certainly any location with a -4F outside design temp. The IRC prescribes higher levels, but it's been amply demonstrated that 2" (about 0.6 perms) is enough. See:

http://www.buildingscience.com/documents/bareports/ba-1001-moisture-safe-unvented-wood-roof-systems