My wife and I are in the process of building a house in the New England area and wanted some opinions on vapor barriers. We are looking to build an energy star rated house with a geothermal heating and cooling system, 2x6 construction. I would like to stick with fiberglass batts R21 or blown in. We did not budget for the added expense of using foam insulation. I am not sure if I want to use a poly vapor barrier of use kraft faced figerglass insulation. The thought of using plastic as a vapor barrier makes me nervous because of what I have heard adn read of people having problems with moisture and mold. I have researched online which has not helped much. I find one article that recomends using a plastic vb and then an article that says to stay away from plastic vb. Just looking for some help inmaking my decision. Thanks Bernie

Use & placement of vapor retarders is very climate-zone specific- there is no "universal" method that's right for all climates, ergo the confusion.

In Manchester CT you don't need a separate vapor retarder, but you do need to make keep the most vapor-retardent layer in the stackup on the warm-in winter side of the assembly, and make it air-tight to keep humid room air from entering the wall cavity to condense on the colder parts of the studs or sheathing. This can be done with caulked gypsum board & vapor retardent paint on the interior surface. You could use poly vapor retarder on the inside of the studs if you wanted to, but you have to religiously foam-seal/tape/caulk seal any tears or penetrations it develops during construction. Read more about use of vapor retarders here:

http://www.buildingscience.com/documents/information-sheets/3-water-management-and-vapor-control/info-sheet-310-vapor-control-layer-recommendations

http://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers (download at the link)

http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design

Air sealing the place can work great without any special materials if you install the sheathing, doors & windows first, then set up a blower door and run around with cans of foam sealer & caulk sniffing out and sealing all of the exterior leaks as you go.

Then blow wet-spray insulation rather than batts once the electrical is all roughed-in. If you're sticking with fiberglass a sticky wet-blown wool like JM Spider etc. SUBSTANTIALLY outperforms batts with good margin, since it conforms to all irregularities and will fill even the narrowest of micro-cavities in the odd framing around corners, windows doors, etc. Wet-blown won't sag over time like dry blown either, since it's locked in place by adhesive. Cellulose has some advantages (significant thermal mass, lower internal air convection, hygric buffering), but the structure will have ~5-8% lower R value with wet blown cellulose than top-end blown fiberglass. But wet blown cellulose may/may not outperform blown fiberglass, depending on a lot of the structural and climate particulars. Wet blown fiberglass will dry out a lot quicker though- wet-blown cellulose may take weeks if done in winter. Both are likely to be cheaper than half-pound spray foam, and will perform similarly to half-pound foam if wet-sprayed.

When the gypsum goes up caulk/tape every seam, then repeat the blower-door method of finding & fixing any leaks that my have cropped up from electrical/plumbing, etc. work.

You might consider double-wall construction using 2x3s & batts for the interior, 2x4 & wet blown (blown-in-bag method) for the outer (structural) wall & gap fill. That way you get a very good thermal break at the studs, enhancing the overall R-value by quite a bit. The more common alternative for the thermal break is to use extruded polystyrene sheathing on the exterior, between the structural sheathing and the siding. Thermally breaking the studs has a significant effect on the whole-wall and clear-wall R-values, and is well worth doing. Play around with this tool a bit:

http://www.ornl.gov/sci/roofs+walls/AWT/InteractiveCalculators/NS/SimCalc.htm

If you're going for EnergyStar, don't forget to insulate the foundation. Insulated Concrete Forms (ICF) is less labor intensive than some other methods, and there are several vendors with suitable product. Be sure to foam-insulate & seal the band joist & sill to make the thermal envelope continuous, and air-tight. (It won't break the bank to do this in foam, since it's not huge volumes, and it WILL outperform other stuff. DON'T use fiberglass here, since room air will convect in/through the insulation, creating mold conditions against the wood.) If going ICF, make it at least R15. Assymetric ICFs with more insulation on the exterior eg: http://www.quadlock.com/green_building/building_shell_superinsulation.htm or http://www.varianthouse.com/house_building_system/ ) are preferable, since you then get the benefit of the thermal mass of the concrete being mostly inside the thermal envelope, moderating diurnal temperature swings considerably.

I don't want to upset the plan completely, but if you have access to natural gas you may be WAY better off from a cost & carbon-footprint point of view going with the micro-cogenerator systems from Climate Energy See: http://www.freewatt.com/ You're close enough to theirDedham MA (Boston area- south) home base that you can probably get them to serve you, otherwise Depco in Farmington CT are certified installers:

DEPCO
PO Box 727
Farmington, CT 06034
860-747-0079

By generating electricity & net metering most of the heating season your annual power bill can be extremely low (especially if you're going out of the way to EnergyStar the lighting & appliances). Even in summer if you're heating your hot water with the cogenerator you get significant payback. (And it'll be half the upfront cost of a geo system.) It's worth at least considering, before signing off on geo.

Also, in this climate the rationale for geo over high-efficiency air-source heat pumps isn't as great as in colder (or much hotter) regions. CT is heating dominated, but at barely ~6000 heating degree-days with a design-day heating temps above 0F, in a well heated house a cold-weather heat pump. Daikin and Sanyo both have air source heat pumps that maintain a COP of 2.0 at least down to 0F, and I'm sure there are others.

In a well insulated or super insulated house in 06040 your sensible air conditioning loads will be quite low (practically non-existent except for a handful of days/year, but the latent load (humidity) is substantial. Still, a geo system sized to heat the place will be many times oversized for that summertime load and won't operate efficiently- it'll short-cycle. A right-sized AC or whole-house dehumidification system is more appropriate in summer than using the geo. Very tight houses also need active ventilation- a heat-recovery ventilator + dehumidification is probably sufficient to stay comfortable & healthy in summer.

Thanks for the helpful input. We already have the foundation in the ground and the framing is starting tomorrow. We do not have access to natural gas where we are building, we would have to go with propane which is more than natural gas. I wanted to go with geothermal to get away from using gas or oil in addition to reducing polution. I got tired of the sometimes big flucuations in gas and oil prices, where one winter it might cost twice as much for heat than the previous year. We are having 2 electric hot water heaters with one of them being powered and the other as a buffer tank connected to a desuperheater from the geo. We are going to stick with the fiberglass batt insulation with the paper vapor barrier. I just don't want to take my chances with poly. Foam, flash and batt and any other expensive types of insulation are out of the question. We are just getting started with buildign and want to stick with out budget and it is too early to start adding a little here and a little there. We are having a ventilation and heat recovery system which will help. The geo is goign to be a 2-stage system with 2 zones which I hope will help iwth short-cycling in the summer as you explained might happen. Thanks again for the input.

Blown/sprayed fiber insulation is usually/often cost-competitive with batts, and reliably outperforms batts due to the lack of voids, compressions, etc, and the ability to accommodate even micro stud-bays too narrow to stuff with batting.  Since it conforms perfectly to the available space, it always performs to spec, whereas batts inevitably have errors or impossible situations in real-world framing, and typically underperforms spec by ~15%. DO get it quoted several ways.

Also, don't ignore insulating the foundation- I doubt you can meet EnergyStar standards without it.  If it's still open on the exterior down to the footings you can insulate it from the outside and get the benefit of the thermal mass of the concrete walls.  An uninsulated foundation is typically 15-25% of the heat loss of houses in southern New England, yet often ignored. R10 of high density EPS or XPS would be the minimum (and still cost-effective with high efficiency heating systems.)  I did my place in Worcester MA with  R20 on the cheap, retrofitted from the inside using recycled fiber-faced iso board, which only takes up 3" of depth.  Recycled foam board is typically 1/3-1/2 the price of virgin goods.  There's a place in MA that handles recycled rigid foam in volume, and it might be worth the trip to Framingham to pick it up if they won't deliver in the quantities you need. See http://www.insulationdepot.com/

If it's already backfilled insulating it from the inside is still possible & desirable, but requires 1/2" gypsum or other thermal-barrier over it to meet fire code, and you can't used foil or poly faced stuff on the interior or you risk creating mold issues on the foundation sill &/or efforescence & spalling on the above grade portion of the exterior.  Using unfaced EPS, XPS (up to but not exceeding 2"/R10), or fiber-faced iso are all acceptable.  Studwall & batts are NOT an option for insulating foundation walls, since ground moisture inevitably creates mold conditions.  If you put at least R5 of semi-permeable foam against the wall, you can usually get away with up to ~R20 of batt-insulated studwall on the interior in this climate zone if you're trying to super-insulate. (Or a 2x4 studwall with up to R15 batts.)  If you go the foam+studwall & batts route, only use UNFACED batts, and be sure to use permeable paints on the interior so that the studwall can pass water vapor into the basement rather than trapping it in the studwall to feed the mold.

And how much are you paying for Electricity? Geo's are copious users of it. It's not too late to try and super insulate, and then dumping the Geo would be a no brainer. Listen to Dana, he's trying to help!

In most of southern NE if you're using electricity, you're using natural gas (at ~30-35% efficiency, with most of the energy going up the flues & cooling towers at the power plant), since most of the fossil plants hereabouts are NG fired. The retail price of electricty to ME in central MA fell by ~25% this year, largely a reflection of the crashing wholesale price of NG.  As regulated monopolies the volatility of electricity prices are somewhat less volatile than oil, but it still follows the economic trend lines (as it must.)  The pollution is still happening- just not on-site at the load the way a fossil-fired heating system does.

At current regional pricing using electricity in resistance heating isn't dramatically different from using propane in a condensing furnace. But with their COP, heat pumps, are cheaper to run than either resistance-electricity or propane.  But it needs to maintain a seasonal average COP over 3.0 to beat condensing fossil-fired heating appliances on total fuel-source efficiency.

With a propane fired condensing furnace & cogenerator like the Freewatt, if you're net-metered methinks you'd still kill geo on both operating & up front costs, since your electric bill basically disappears if you're miserly with power use. Earlier this year they were talking about releasing a propane fired version, and if you read the fine print the condensing furnace part is available today:

http://www.freewatt.com/products.asp?id=170&name=Warm

Don't know about the propane conversion for the cogen, but it's such a no-brainer kind of modifcation to get a natural gas internal combustion engine to run on propane I can't imagine it's not there yet.  (A guy in my office has the NG version running at his home- it has to be dead quiet in the house & neigborhood to hear it kick on.)

Still when it's said & done, for the $25K cost adder of geo you might have gone all PassivHaus on it, superinsulating the building envelope and you wouldn't NEED a heating system (!).  (But if the project is already rolling it would be a significant re-design to get you there at this point. Without significant basement-slab & foundation insulation even if you super-insulated the rest you wouldn't quite get there...)  The operating cost, maintenance & reliability of insulation has to be better than compressors.  When all else is equal, go with the higher performance building envelope over the higher performance heating system.