Stopping Condensation in Metal Roof - What's the Secret?
The biggest concern of condensation and its effects can be quit worrying for building owners and construction professionals. Water that forms in a system can cause damage such as:
✓ Corrosion of metal panels and components which can structural weaken the system
✓ Degraded and wet insulation reducing thermal performance
✓ Mold and/or mildew growth that can increase health risks
✓ Insect infestation which can contaminate systems
Condensation tends to occur in noticeable quantities and cause problems at surfaces where there is a sudden change of permeance, which causes an increase in local relative humidity sufficient to create dew point conditions. Condensation in metal roofs can be caused by air leaks around units, holes in vapor barriers/retarders, gaps in insulation just to name a few and no system is bullet proof. “Moisture moves by several mechanisms, including bulk drainage, diffusion (absorption), surface diffusion (absorption), capillarity, osmosis and convection.”
Condensation can occurs on a hygroscopic surface, such as wooden sheathing or insulation, then moisture is absorbed, lowering the vapor pressure and increasing the vapor pressure gradient, driving more moisture toward that surface.
Picking an insulation that is resistant to moisture and help stop condensation is important, but no insulation is 100% waterproof. When Polyisocyanurate (Polyiso/ISO) or Extruded Polystyrene (XPS) gets wet, they dramatically loss their thermal effectiveness. Engineered Expanded Polystyrene (EPS) has the ability to resist moisture but when it get wet has the ability to expel moisture. Most metal roofing systems are not waterproof but rather watersheds. Therefore, air can travel and flow through the upper metal roof system allowing drying to occur. Learn More Here is the Secret: EPS is the BEST Insulation Solution for Metal Roofs because it can expel moisture caused by condensation. EPS's R-value will stay stable and be an overall better value.
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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.