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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What Insulation is the Best in Roofing?
- R-Value
R-value is more than the R-value per inch. Polyisocyanurate (ISO), starts out with a higher r-value per inch, but then the blowing agents escapes and the R-value is reduced. (learn more) Expanded Polystyrene (EPS) has a lower R-value per inch but can be make thicker to match any R-value requirement. EPS’s R-value increase in colder temperature while ISO decreases. Many would give ISO the edge because of R/inch, but taking into consideration overpaying for R-value that does not stay stable in lower temperature, the advantage has to good to EPS.
- Environmentally Friendly
- Combustion
- Cost
- Design Flexibility
- Moisture Retention
Expanded Polystyrene, when compared to polyisocyanurate, certainly has more reason to be use in roofing. It seems over the last few years, many designer have lost sight of the purpose of insulation and the importance of R-value long-term. Some designer only considered combustibility and its superior importance, when in all likely hood this physical property will never ever be used. A feature such as long-term R-value, which performs daily in that system, or even moisture expelling capability, get lower considerations. When all of the major features of insulation are considered, EPS seems to be the clear winner.
Steady Wins the Performance Race
In high school, I remember watching the track team race around the track. One runner Peter, a farm kid, was fascinating to watch as he always grabbed the early lead. Peter always looked so fast but in the end he would typically finish in 3rd or 4th place. In that moment, early in the race, Peter looked like a world class athlete that would easily win gold at the Olympics. In those early moments, that frozen time, the measure of performance was perfect.
Thirty-six years later and I see the same thing happening in the rigid insulation market. Its like watching Polyiso, and XPS insulation running just like Peter, getting off to a tremendous lead regarding R-value, but then fading out at the end. That perfect moment in time is when that R-value gets measured and they look like superheroes but in reality they just “blowhards.” Pardon the pun as the blowing agent escapes and lowers the r-value. (LEARN WHY)
When it comes to below grade or roofing insulation, Polyiso and XPS start out with really good R-value numbers but they don’t last (LEARN MORE). Unfortunately, you pay for these early performance numbers, sometimes as much as 50% more. Paying for performance isn’t bad but not knowing that the product will fade out is a different matter.
The old idiom, “slow and steady wins the race” really holds true in insulation. EPS might start out slow (or lower r-value) but is consistent through its life and ultimately wins the race. Not only does EPS (Expanded Polystyrene) have a steady consistent R-Value but when compared with XPS and Polyiso, it also performs better in the field. XPS and Polyiso, when wet, hold the moisture and loss much of its r-value. EPS has the ability to hold its r-value and even expel moisture under exsiccate conditions.
Next time, when you’re looking to specify or install insulation on a project, remember that Polyiso and XPS look great at the beginning but EPS is the steady performer and the best value in rigid insulation. Your customer deserves the winner - EPS.
Value Engineering - A Win-Win Strategy
Experience in the industry has shown that it takes designers and architects several years to catch up and change their project specifications based on new information. This opportunity window allows for roofing contractors to provide a wonderful service and offer "Value Engineering." (Get a copy of - "Value Engineering Tips and Tricks for Roofing")
The recent research has shown that polyisocyanurate (ISO) insulation provides an R-value of 5 R/inch at 40ºF and 4 R/inch at 25ºF. Contrast that to Type VIII Expanded Polystyrene (EPS) that has an r-value of 4.2 R/inch at 40ºF and 4.4 R/inch at 25ºF. Now, take into account that the cost difference between ISO and EPS insulation. ISO Insulation can cost up to 60% more. This really spotlights EPS as the best r-value/inch value. Substituting EPS insulation in for ISO in a value engineering premise is quite simple as the numbers speak volumes. The real trick is how it can be accomplished in an environment that is so "Pro" ISO?
Ultimately, the building owner can win by saving money and yet the contractor can win by proving his professionalism and closing more work - a real Win-Win.
LTTR - What does long-term R-value mean
Early this year, the National Roofers Contractors Association, made a recommendation to it's members that Polyisocyanurate Insulation revise "its design in-service R-value recommendation to 5.0 per inch thickness." This declaration was the second time Polyisocyanurate's R-value was downgraded in the last 2 years. For some of us "Energy Aficionados," who understand the principles of insulation off-gassing, determined it was time to re-examine LTTR testing (View Technical LTTR Bulletin).
LTTR really looks at Long-Term Thermal Performance of insulation as 5 years. Do we expect a building to last only five years? How is 5 years a true quantitative analysis of R-value performance?
We do not replace insulation in a building every 5 years, why would we think that is long-term? Most building in the U.S. are built to last 50 years, some 100 years. Long-term R-value should be figured at 50 years… right? We know off-gassing continues to happen after 5 years. Let's re-evaluate what we are doing as an industry and modify Long-Term Thermal Resistance to at least 50 years.
The Shrinking R-value of Polyisocyanurate Insulation
The real question maybe why? and why another change after last year’s change? The answer is independent testing. According to research conducted by BSC (Building Science Corporation) and others, “the thermal performance of some insulation materials changes as they age. The R-Value of Polyisocyanurate decreases as some of the gasses … diffuse out and are replaced by air.” This is known by several names - Thermal Drift, Gas Replacement Process or Off Gassing.
What the research has shown is that unlike EPS (Expanded Polystyrene) Insulation that increases its R-Value when the temperature decreases, ISO Insulation R-Value actually goes down. Bottom line: In the north, when you need the r-value the most, its not there like we thought.
Solutions
• If you need to use ISO - the BCS Recommendation is to use it in a “hybrid insulation approach” with a cold stable R-Value insulation like EPS.
• Try to substitute out ISO Insulation and use EPS or the New Neopor Plus Insulation.