During some recent travels to work with builders, I spent time with a builder who was in the process of constructing walls and building envelopes with very little R value. These were thermal mass walls but with little R value. The builder was meeting the state energy building code through the performance path, which allows for more design freedom but involves more complex energy simulations and tradeoffs between systems, by using a highly engineered, very sophisticated, very expensive, high efficiency heating and air conditioning system.
The building when it’s completed will meet the code and the intent of the code which is to reduce energy consumption. However, the weakness of this approach is that the equipment which is being used to meet the energy reduction goal codes will eventually wear out. When that time comes, the owners of the building will be able to replace this high end equipment with a less expensive option since they are not under the jurisdiction or ‘watch’ of the building inspectors. This will decrease the energy efficiency of the building and possibly compromise its building code compliance.
This is one of the good things about the prescriptive path to the building code – that the elements that we choose, when properly installed, will meet the code and goals of energy reduction for the long term. Things like thermal insulation when installed during the initial construction will always be in place, will always work and will never wear out. It will continue to perform over the life of the structure.
So while it is good to have options, remember not all options will give you the desired result over the life of the structure and that is worrisome.