News From Go Plymouth Foam

Stopping Condensation in Metal Roof - What's the Secret?

Metal roofs over the past 10 years have exploded onto the construction sites. The ongoing problems and frustration for building contractors and design professionals of condensation in metal roofs has only increased exponentially. Solving this issue can be very difficult. Let's explore the benefits to rigid insulation and a secret, not known by many, in the building industry.

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 and metal roofs

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.

View our Metal Roofing Products

What Insulation is the Best in Roofing?

I get asked this question all the time, but the answer is much more complicated. Its fun to go back historically and look at why insulation was introduced into roofs in the first place. It was fairly simple back then, the waterproofing was to keep water out and the insulation was to keep people warm. Today, insulation is so much more and that is why to answer which insulation is the best, we need to look at the most important attributes of the two most popular roofing insulations - Polyisocyanurate and Expanded Polystyrene.


      • 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
ISO uses a “harmful” blowing agent which escapes into the surrounding area and no one knows for sure what the health effects are on humans. EPS does not use harmful blowing agents and is known as the “safe insulation.” EPS insulation is also 100% recyclable where ISO is not. EPS is by fair the greener product. (learn more)

      • Combustion
This gets complicated because EPS has a fire retarder that is in the product and thermal boards, like drywall can be used to make it even more fire resistant. Remember, EPS can go Direct to Deck and has UL approved. ISO by its very chemical makeup is more fire resistant. The question maybe, if ISO does catch on fire what is the chemical by-product that are produced when that product burns and how harmful is that to humans? ISO has the slight advantage on fire but EPS has the advantage on by-product. (learn more)

      • Cost
You can’t have a material discussion without looking at the cost element. This is not even close EPS is a much better value than ISO any way you measure, including cost per R-value inch. (learn more)

      • Design Flexibility
Roof design can be looked at in numerous ways such as thickness restrictions and tapered possibilities. ISO is very limited in thickness per board. High R-value systems make ISO more labor intensive as it need so many layer to comply. One EPS board can go up to 200 R. ISO is limited in tapered slope possibilities usually 3. EPS on the other hand is almost unlimited. EPS can use insulation shapes (example rounded) that ISO just can’t match. Design flexibility goes to EPS.

      • Moisture Retention
Roof leaks can cause moisture to enter into a roofing system. When exposed to the same test as EPS, ISO absorbs much more moisture and has a difficult time expelling it. The ISO glass facers are even more prone to moisture absorption. EPS can absorb moisture but two anomalies make it so desirable - one it can expel moisture and two moisture has little effect the R-value. EPS has the advantage. (learn more)

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. (

Battle of the Polystyrenes

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

Recently, much has been written on the new r-values of polyisocyanurate insulation spurred on by the NRCA Tech Talk. What hasn't been talked about is what does it mean for the consumer? or What opportunities are available for advanced roofing contractor that are willing to educate clients? or How can a Win -Win scenario be used to Win More Jobs?

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

What is your definition of long-term - 5, 10, 25 years? How should we judge the R-value of insulation long-term? LTTR (Long-Term Thermal Resistance) is a measure to quantify a comparative method of R-value in an attempt at trying to help architects, specifiers, builders, inspectors and owners. This measurement is achieved by the test methods ASTM C1303 or CAN/ULC-S770. I applaud the effort of developing these testing to quantify thermal performance, however a major adjustment may need to take place or at least the building industry need to understand these measurements - what they are and what they are not.

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

What happen to the old days when were told that ISO (Polyisocyanurate) Insulation had an R-Value of 7, 8.3 or 9 per inch. Those days are over! In fact, this last month the “NRCA (National Roofers Contractors Association) has revised its design in-service R-Value recommendation to 5.0 per inch.” (Article)

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.

Polyiso insulation RValue decreases in colder temperatures

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.

• 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.