Subject: Insulations levels in a passive solar house
Question: I’m interested in building a passive solar house using Insulated Concrete Forms (ICF) walls, R-60 ceiling. What’s appropriate for under-slab in total R value?
Answer: I’ll quickly point out that a passive solar house of the 70′s and 80′s is quite different from a home built to the Passive House Standard [click here for more info on that subject].
Now, back to your question, the answers that I may offer will vary, depending on your goals for the project. If the goal of the project is to meet the Passive House (PH) standard of efficiency, I recommend that you have a qualified Passive House Consultant enter the project plans into the appropriate energy-modeling software. This is the only way one can ascertain appropriate R-values for the various components within a project.
The super power of the PH approach is that the designer and the builder will know exactly what each specification needs to be, and why. Cost/benefit tradeoffs become easy to model, and in the end it can be said with a high level of confidence how much heat will need to be delivered by the home’s mechanical system, whether or not the home will overheat in the summer, etc. There is no prescriptive path that will achieve the PH standard, because every home represents a differing set of climate conditions, design elements, and site conditions.
Please note there is are very real benefits to hitting the PH standard of efficiency: the home can be heated with a source that is equivalent to a hair dryer, and saving money by nogs will payt installing typical or higher cost mechanical systems will free up funds that are better spent on the home’s thermal envelope. In a PH, the energy saving for thermal upgrades in a just a few years. After the point of breaking even financially, energy savings will accrue to tens of thousands of dollars over time. Actually, in some homes, the homebuyer can save money up front when ‘going Passive’ vs. other methods of construction. The trick is to work with qualified designers and builders and to perform Passive House Energy Modeling as part of the process.
Database of Certified Passive House Consultants in the US: www.passivehouse.us/consultants.php
Posted on November 30, 2011