The dispute: While these grid-system roofs have been installed on a limited basis for about 30 years here, they are more common in California.
On one side of the discussion are the folks who don't like this process: Some are pest-control consultants, many are roofers (who may happen to be selling other products), roof consultants, firefighters and municipal building departments.
Supporters note that the process does not violate any national building codes. Contractors and manufacturers installing and selling these systems insist that there is simply an abundance of ignorance out there, with education being the key to wider acceptance.
They point to their many happy customers and insist their track record is fine. And so far they appear to be right — I haven't found evidence of significant problems.
Here's more on the arguments from both sides:
The opponents: Thomas Bollnow, director of technical services for the National Roofing Contractors Association (NRCA), says this method of re-roofing is "contrary to NRCA guidelines," which does not recommend covering wood shakes or wood shingles with any roofing product.
This point of view is supported by roofers who say that fastening battens over shakes is difficult to level and assure the fasteners are tightly secured to the frame of the building.
While no municipal building official wanted to be quoted with regard to a particular contractor or product, two interviewed had concerns with previous installations in their municipalities.
Rot "inherent in the shakes can spread to the battens and structure beneath," one said.
"I think it is ridiculous to leave all that rotting kindling up there if you can tear it off for a relatively small amount of money. When it goes bad, you then get two roofs to replace," said another building-department official.
Roofing consultant and engineer Ray Wetherholt with Wetherholt & Associates in Kirkland is not a big fan of this roofing method, but says he has seen no failures.
Wetherholt agrees that condensation will occur beneath, and that rot (and subsequently the damaged wood ) is a potential problem. But if the work is done correctly and all details attended to, the process should work, he says.
Then there's the bug argument. "If metal roofing is installed over cedar shakes, there is a possibility that carpenter ants could colonize the old roofing material," according to Dan Suomi of the Washington Department of Agriculture — the state's point man on pest matters.
"The condensation issue is a real one, and this would make the shakes more conducive to the establishment of wood-destroying organisms such as rot fungus and carpenter ants." (On the other hand, at least leaving the older roof in place keeps pest-infested wood from falling into the attic during removal, as commonly occurs.)
The proponent: On the other side of this discussion is the fact that a very large percentage of older houses in our area have composition shingles laid directly over the original wood shingles. Yet these homes generally suffer no consequences beyond the reduced roof life typical of any layered roof system.
Chuck Schillings, president of Lifetime Roofing Technologies in Bellevue, has been installing Gerard brand stone-coated steel roofing directly over cedar shakes for the past 10 years.
During installation, Schillings says he leaves the existing attic venting in place, extending it to the exterior above the steel roofing and adding more venting to it if necessary.
The area between the steel roofing and shakes is ventilated via the battens from above, below, and all sides. The shakes dry out, the moss dies and rot does not spread after drying. (Contrary to popular folk wisdom, "dry rot" needs moisture). Condensation is not a great risk, he says, first because of excellent venting, and second because the drier shakes act as a reservoir for changes in humidity levels.
Schillings insists pests have never been a problem in any of his company's hundreds of installed roofs or in any other similarly installed product.
Firefighters: Now the fire issue.
Some roofers and firefighters say they worry that a grid system can create a chamber between the decaying wood and the newer roofing, creating a chimney effect for fire.
Schillings maintains that fire does not spread as quickly when the material is "capped and in a lowered oxygen level, keeping it smoldering longer."
For that matter, Schillings believes firefighters could stand longer on a shake roof covered with metal than a shake roof alone.
But Phil Lyons, a lieutenant with the Tukwila Fire Department, raises other concerns. Lyons says a fire may take longer to detect with this system because heat or smoke is held in the attic longer and is harder for firefighters to vent.
"It's not a plus as far as I can see," he said. "Having a hard shell over a cedar roof will cause the fire to spread laterally and heat more areas of the attic. This gridwork creates a chase and aids the spread to more roofing material."
So, would I consider stone-coated steel roofing on my roof? Absolutely. But despite the added expense, I would lose the old shakes first. |
