The Secret Moisture Control Leak - a dynamic new strategy.
Foundation insulation may be easy to overlook as many building professionals may be going under to old adage, "if it ain't broke, don't fix it." The serious reality is that in cold weather climates any structure that has a foundation that touch soil such as basements or frost walls needs to viewed differently in regards to moisture management.
Foundation insulation can be used for a variety of reason but the most important is R-Value. This is where it gets interesting - what does Moisture Management have to do with R-Value? Its all about building performance in real world applications.
We can explore permeability and the Laws of Thermodynamics and go very technical but for now most people know that when insulation gets wet, the R-Value of the insulation is reduced. This lowering of R-Value is a performance issue.
A new way to view and understand foundation insulation comes from a moisture study. This study looked at the two most commonly used insulation for below grade - XPS (Extruded Polystyrene - pink or blue) and EPS (Expanded Polystyrene - white). Three relevant items of note come from that study. First, XPS lost about 1/2 of its R-Value below grade and EPS held almost all of its R-Value. Second, it was found and further studied that EPS takes on a little more moisture than XPS but EPS insulation has the ability to dispel it. Third, for some anomaly in physics, that we don’t quite understand, EPS even with moisture, tends to hold its R-value. (Learn More from the research)
So now that we know what happens to insulation below grade how does that all tie back into Moisture Management? If you are not going to 100% envelope or water proof your below grade insulation or below grade wall system, EPS insulation should be used 100% of the time. Remember, the goal of Moisture Management - keeping a building lasting longer and performing properly - Its all about performance. If you want your below grade insulation performing properly and its going to be left “unenveloped," the best Moisture Management choice is EPS.