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1. Expert Member
   Dana Dorsett | Jun 30, 2016 01:38pm | #1

   Vapor barriers in the ceiling of a vented attic space are completely unnecessary anywhere south of US climate zone 7, which is the opposite of "warm and humid". Making the ceiling under the attic insulation air tight is important to limit stack effect infiltration, but there is no advantage to installing vapor barriers, which would be more likely to create problems than solving them.

   ICF is a fairly expensive way to insulate, and susceptible to insect damage. In many warm humid climates SCIP is often cheaper, and has substantial benefits. With SCIP the EPS insulation is between two thin layers of wire mesh reinforced concrete (shot-creted in place with the same type of equipment used for swimming pools), where the EPS won't be accessible to ambitious ants. Where concrete spray equipment isn't available and labor is cheap it can be done by hand, or with much smaller hand opereated stucco spray equipment. The concrete then serves as the scratch coat for a stucco finish on the exterior, and a hard plaster or clay finish on the interior. There is more labor involved than ICF, but a lot less concrete, yet still enough concrete to have a significant thermal mass benefit, and fairly good hurricane & earthquake resistance. Even a 2" EPS core SCIP is plenty of insulation for any location in the tropics, (or even warmer areas up to 35 degrees north or south latitude) which is half the amount of EPS in a minimal ICF.

   Spending the difference in cost on rooftop solar & inverter sufficient to run a 3/4 ton mini-split heat pump during the sunny hours makes sense in some high energy cost areas, even if it's off grid with only the absolute minimum of battery necessary to stabilize the inverter. This is a much cheaper option now than it was even five years ago. On a lifecycle basis it's cheaper than island diesel genset power.