hrv for cold climates erv for hot humid climates. it matters what your location is. adding fresh air or make up air is easy. how much to add, is the question. was a blower door test performed on the house? what were the air changes per hour? using the blower door numbers, & volume of the house, ach is calculated. once amount of air required is determined then you make choices of how to do it. La. for instance is hot humid climate. an energy recovery ventilator will cost you approx $1200 installed. but a better choice is a whole house dehumidifier with fresh air intake. for a few hundred more. there are other methods of adding fresh air like barometric dampers etc. some work very well. you'd do best to find out how tight the house is. and go from there. best of luck

Flash and batt is effective, but you need to be sure the foam is thick enough so that you don't form a condensing surface inside the wall. In the northeast 1" would not be enough, I don't know about VA, it might vary across the state. There are tables that will tell you the minimum thickness needed given the lowest temperatures you expect. Where we are the minimum is 2-3 in, at which point it's about a wash to just go with all foam. Another approach to consider (which may or may not make sense in a more moderate climate) is spray foam on the inside for air sealing and a rigid foam wrap on the outside to block thermal bridging across the framing members. That's been extremely effective in our house.

Nothing about your home should keep you up at night. If concerns about using a particular construction material or method will do that, then don't use it. However, if we never applied any new materials, systems, and construction methods in residential construction, our homes would be no more comfortable and perform no better than homes built in the 1700's. We wouldn't have, for example, air conditioning, which makes living here in coastal Virginia much more pleasant in summer and which keeps certain contractors in the Houston area employed. The energy crisis in the 1970s gave rise to the use of house wraps and vapor barriers which caused plenty of unintended consequences. That doesn't make polyethylene or house wrap bad materials, it's simply that the building science wasn't established at the time. We continue to rely on the researchers to thoroughly test new ideas (and real world testing is better than computer simulations) to minimize, if not preclude, unintended consequences. When considering the use of the latest and greatest materials homeowners would be well advised to remember the old adage: The early bird gets the worm, but the second mouse gets the cheese!

"He suggests closing ridge vent and soffit holes from inside with spray foam. Is that an acceptable practice? Do we need to replace the ridge vent with cap shingle from outside to prevent moisture damage to the roof under the ridge vent?" I retrofit spray foam insulation under the roof deck in my former home (climate zone 4c) to convert a conventional, vented attic to a conditioned, cathedralized attic. Based on my experience, you'll need to remove the ridge vent and install cap shingles (it was an easy path for insects to enter.) I'm not sure what type of soffit vents you have, but there is a possibility of spray foam finding its way through the openings as it expands and making a royal mess. "There is a website saying ridge vent is still needed with foam insulation. Do You Need Attic Ventilation With Spray Foam Insulation? (mcclellandsroofing.com) . Is ridge vent needed or not?" The website you linked is a great case in point illustrating that not everything you read is true--especially on the internet. The point of installing spray foam insulation on the underside of the roof deck is to create a conditioned attic. A conditioned attic does not depend on air exchange with outdoor air for ventilation. It does not require a ridge vent. That said, a vapor diffusion port is recommended to reduce the relative humidity in the attic. We didn't install vapor diffusion ports in any of the conditioned attics we've constructed to date, but each attic houses HVAC units and duct work which regulate the conditions. The first conditioned attic we installed was back in 2001 so we've got plenty of history and no problems thus far. "Foam insulation seals the house tight, would that reduce the air quality inside the house? I prefered batt insulation and breathable house out of this concern." Your house is not a living organism and it doesn't need to "breathe." The interior conditions do need to be controlled for both the comfort of the occupants and the sustainability of the structure. If your home is "tightly constructed," and spray foam implies such, you'll need a provision for fresh air exchange. A properly-sized energy-recovery ventilator is a must, in my opinion for occupant health and safety. "Is open cell foam insulation effective enough to reduce AC unit by 30%? Due to the hard-to-reach space in attics, I am not sure if close cell insulation is an option. Should HVAC be sized differently for open cell foam vs closed cell foam? If Open cell is applied multiple layers, would that achieve the same R value as closed cell foam?" HVAC systems are sized based on the insulation R-values and surface areas. You can achieve equivalent R-values with open cell, but it needs to be installed at much greater thickness. Ask to see the ACCA manual J calculations and the manual S equipment sizing to see if the required capacity is indeed reduced by 3 tons.