What Causes Roof Condensation And How You Can Prevent It

What Causes Roof Condensation?

Moisture can be sneaky.  If you’ve got a roof that doesn’t leak, you may think you’re protected from moisture damage.  But the truth is that condensation is one of the chief forms of moisture damage in roofing systems.

The straightforward way of determining roof condensation causes is lack of ventilation.  But that answer raises many questions, like how to vent roofs well enough or what to do when roofs can’t be vented.

There are two different roofing paradigms when it comes to these issues: one for steep slope and one for low slope.  The physics are the same for each (obviously), but the concerns and practices for each differ.

In steep slope roofs with attic space, ventilation is a reasonable tool to counter the risk of condensation.  But in low slope roofs with no attic space, ventilation is typically inadequate.

The Physics of Condensation

The air around us contains water in its gas phase (water vapor).  Temperature determines the amount of water vapor air can hold.  When temperature decreases enough, the water vapor condenses into its liquid phase.

Remember how the mirror fogs up when you step out of the shower?  The mirror is a cold surface (condensation needs a surface), and the warm water vapor condenses as it lands on this cold surface.  The same thing frequently happens in roofing systems and attics, causing all sorts of damage.

The temperature at which vapor condenses is the “dew point.”

Imagine outside temperature is 45 degrees and inside your home is 70 degrees.  There will frequently be a dew point between those two temperatures, which means that at some point between the inside and outside of your home, water vapor condenses as hot travels to cold.

Roofs and attics are of particular significance since vapor can be carried by air, and air rises.  Without adequate air barriers enveloping your home, warm air with vapor will contact a cold surface and condense.

Vapor diffusion is the method by which vapor flows through solid material.  So, even if air travel is blocked, vapor can still travel through objects and condense on their cold surfaces.

For steep slope homes, the strategy for reducing the risk of condensation is by ventilating the attic.  We want the attic temperature to be as close to the temperature of the outside as possible.  If it is not, there is likely a dew point at some point in the attic (often noticed on underside of nails holding down shingles).  This can result in a roof going bad before the roofing shingles go bad, because the sheathing can rot.

With enough attic ventilation (both intake and exhaust), the risk of condensation on the roof underside can be significantly reduced.  But in that case there is still a dew point somewhere between the conditioned living space and the attic.

With a vapor barrier enveloping the living space and enough insulation in the attic for heat transfer resistance, the amount of vapor that gets into the attic can be minimal.  And the vapor that does can be swept away by the ventilated space.

Signs your roof may have condensation issues

  • Get into your attic.  Is it warm?  It should be really close to the same temperature as the outside
  • On a frosty morning, can you see the rafters outline from the outside?  Is the frost on one part of your roof melting that probably shouldn’t (not in direct sunlight)?  Are the overhangs frosty while the roof above living space is not?
  • Perform the smoke candle test.  Light a candle and put it up to your soffit intake ventilation (usually bird blocks beneath your gutters).  Find where that smoke goes.  If it exits your mushroom vents near the ridge of your roof or out of a ridge vent (depending on which you have), then ventilation may be good.  Otherwise it is probably not.
  • Is your roof overly mossed?  Sure some moss can be normal, but if you have a lot or if it seems to be in spots it maybe shouldn’t be, condensation can be feeding it from below the roofing shingles.
  • Do you have bird blocks?  Sometimes these are adequate intake ventilation, but often they’re not. Smart intake vents like Cobra IntakePro may be needed.
  • Is insulation blocking your soffit vents along the eave line in your attic?

Addressing flat roofs with no ventilation

Most commercial roofs (and some residential) are flat or low slope and don’t have much ventilation.  These roofs require a bit more sophistication to counter condensation.

As the roofing industry improves, understanding of condensation in roofing systems increases and our ability to solve it improves.

The strategy is to use a vapor retarder on the roofing substrate.  There is some difference of opinion on whether a retarder or barrier is best.  Because vapor does get through even the most well designed systems, it is believed a retarder is best because they have some level of breathability that can allow vapor to exit more easily.

Overlapping rigid insulation should go in the middle and the roofing membrane over the top.

This creates a roofing system with vapor retarder/barrier on each side and strong thermal resistance through the middle.  With the dew point in the insulation, the idea is for there to be little diffusion of vapor to a surface on which to condense.

And when that does happen (because no system is perfect), the roofing membrane itself plays a pivotal role in reducing damage by how it heats up.

It is well understood that some amount of water just finds its way through so many large, flat roofing systems.  But that water can dissipate seasonally (or daily) when the roofing membrane reheats by absorbing solar rays.

In recent years, white roofs for large, flat buildings have become wildly popular.  White is very reflective and much of the solar radiation that hits it isn’t absorbed.  The popularity of white roofs may be for environment-related concerns, but there’s an irony in that the reflective nature of white roofs may be causing unnecessary damage, which in turn costs energy to fix.

Gray is an option growing in popularity because of this.  It is less reflective than white and does have some ability to reheat.

But it may be the case that the only way to robustly protect against condensation in most flat roofs is by using a dark material, like modified bitumen.

Even then, there isn’t true certainty.  For homes and businesses alike, ventilating the living/working space may be required.  Even the smartest roofing system can’t avoid condensation if there is too much vapor in the conditioned space.

Extra special thanks to the Roofing Contractor’s Association of Washington (RCAW).  Their series of condensation and ventilation related classes at the annual trade show of 2019 was a brilliant move.  When we saw the schedule, we were expecting them to be great.  And the classes turned out better than that.  Kudos to GAF’s James Willits, Owens Corning’s Rollo Gallion, and Wetherholt and Associates’ Ray Wetherholt for their informative presentations!

Ready for a beautiful new roof?  Call Chase Construction North West, Inc. today (253-445-8950) to schedule a free estimate.  Or complete our quick estimate form.  Join thousands of happy Puget Sound customers with gorgeous roofs that protect their homes!

GAF TimberCrest Bullnose Ridge Cap Shingle | Master Elite Roofer

GAF TimberCrest Bullnose Ridge Cap Shingle

In February 2019, GAF announced its new high-profile ridge and hip cap shingle: the TimberCrest Bullnose.

Most ridge cap shingles have a sharp leading edge, giving the ridge or hip a rough look from shingle to shingle.  But TimberCrest’s surface folds over and secures to the overlapped shingle, creating a rounded, smooth transition from shingle to shingle.

Each shingle has an alignment guide to ensure the cap lies evenly along the ridge or hip, and the guide hides beneath the overlaps after installation.

By securing tightly with Dura Grip Self-Seal Adhesive, TimberCrest cap shingles have reduced risk of blow off from high winds or intense storms.

Master Elite Roofer

Hiring a reliable and professional roofer is never easier than with GAF’s Master Elite program.  Only 3% of all roofing companies have qualified for this premier qualification, because GAF only certifies its select few roofers with a long track record of best roofing practices and customer satisfaction.

Chase Construction North West, Inc. has been a proud GAF Master Elite roofer since 2011, and we look forward to many more fantastic years of installing beautiful and dependable GAF roofs!

TimberCrest can make up the ridge and hip cap portion of GAF’s six-part Lifetime Roofing System:

  • Ridge and hip cap shingles
  • Attic ventilation
  • Starter strip shingles
  • Leak barrier
  • Roof deck protection
  • Lifetime field shingles

GAF at the RCAW Trade Show 2018When we install one of these systems, we include GAF’s Golden Pledge warranty.  While the term can vary, with for a single family home, the Golden Pledge warranty for a Timberline HD system comes with 50 years of coverage for leaks caused by material defect and 25 years for misapplication.  Complete our quick estimate form or call us today at (253) 445-8950 or to schedule your free estimate!


RCAW Trade Show 2018

Join Us at the 2019 RCAW Annual Trade Show

One of the most exciting events for roofers in the Puget Sound takes place today, Friday the 22nd, 2019: the RCAW Annual Trade Show.  Each year, the Roofing Contractors Association of Washington (RCAW) holds an exciting and informative event that you don’t want to miss.  Many roofing vendors connect to discuss cutting edge products, innovative new services, and industry techniques.  Last year, classes included a host of topics, including fall safety, best roofing practices, and condensation in roofing systems.

GAF Timbrcrest Ridge Cap unveiling?

Could this bullnose SBS-modified ridge cap shingle be the new best-choice accessory for Timberline HD roofing system?  It looks thicker, heavier, wider, and with a more appealing overlap.  We’re really looking forward to learning more at the 2019 RCAW trade show!  Stay tuned for the comprehensive description after the event!

We anticipate meeting our many friends in the industry and learning a ton.  Join us for this awesome event!

Vital Storm Protection with WeatherWatch® Leak Barrier

No matter how great your roofing shingles are, rainwater is bound to find a way beneath them.  If it were not for underlayments that act as a buffer between shingles and plywood, water damage would be more frequent and severe.  GAF’s Tiger Paw™ is our favorite synthetic underlayment to serve this important purpose. However, for the most critical areas on your roof, specialized leak barrier (also known as ice and water shield) is needed.

Similar to the popular Tiger Paw™, WeatherWatch® Leak Barrier resists wrinkling and provides a safe, gripping surface for roofers to walk on during installation. This top-of-the-line leak barrier excels in its self-sealing properties that transform what would be a perforated barrier with inferior products into a watertight seal with WeatherWatch®.

If your roof has traditional felt paper when high winds drive rain under your shingles, water will seep through the nail penetrations.  But it will stop in its tracks if instead the rainwater meets WeatherWatch® because it self-seals around nails and other metal fasteners.  If you’re one of the many homeowners who find evidence of water damage in their homes, it may be because of an absence of a leak barrier on the most vulnerable parts of your roof.

These areas include chimneys, pipes, perimeters, skylights, and valleys.  They’re uniquely vulnerable to water damage because they’re where shingles come to an edge and because they handle greater volume of rainwater runoff.  Special attention must be paid to these areas in order to ensure they’re as reliably resistant to the elements as the rest of your roof.  By installing leak barrier at these critical points, we ensure that when storms drive rain under shingles, it goes no further and your roof remains safe from damage.

WeatherWatch® Leak Barrier plays an integral role in the GAF Lifetime Roofing System.  We offer this awesome system and the phenomenal Golden Pledge® warranty to every customer who wants long-lasting peace of mind with their new gorgeous composition shingle roof.

Join thousands of satisfied customers in the Puget Sound area!  Schedule a free in-home estimate at 253-445-8950 or fill out our quick estimate form.  Our estimators know everything there is to know about composition shingle roofs!  Only 3% of roofing contractors qualify for GAF’s aspirational Master Elite® certification, and we’ve been leading the pack since 2011! Give us a call now because we are dedicated to ensuring that you receive the service and expertise that you want!