This time of year I often get asked whether a metal roof can help someone avoid wintertime ice dams and the resulting damage to their roofs and homes. Generally, the answer to that question is “yes” but there are several things to keep in mind.
First, any time you re-roof your home, it is an opportunity to install an ice and water shield type of membrane around the bottom edge of the roof. Required by code in many places, this rubber or asphaltic membrane will help guard against water intrusion inside of your home if ice damming occurs. However, it does not help keep your shingles from being damaged.
Next, if you have interior damages from ice damming but in the spring your shingles look okay, that does not mean they do not need to be replaced. Some ice damage can be small cracks which, though barely visible, leave your roof extremely vulnerable to water intrusion and further damage.
Third, metal roofs due to their smooth surface and heat handling characteristics, tend to shed snow quickly. This helps avoid ice damming.
The interlocking nature of most metal panels also helps avoid problems due to ice dams.
Finally, if your home is prone to ice dams, when you re-roof is the time to see if you can increase your attic ventilation as well. Keeping your attic at a similar temperature to the outside will go a long way in keeping ice dams from occurring.
In many areas of the country, this has been a horrible winter for ice and snow. While this situation is a homeowner’s nightmare, it will keep roofing contractors very busy in the Spring.
Check out my podcast on ice dams. It will help you understand why ice and snow ends up being so damaging to roofs.
The worst situation for ice dams involves a lot of snow, not much sun, fairly cold temperatures with occasional warm swings, and little attic ventilation. This creatues a condition of compacting ice on the roof that can eventually work its way under shingles and into your home, usually around the outside perimeter.
Even more frustrating is that sometimes your roof can look fine but the drips inside your house, along with wet insulation and eventual mold inside the attic, tell a different story! And, if next summer you don’t replace your roof, you will be prone to even greater problems next winter.
Metal roofing for many reasons is great at protecting against ice dams and their resulting interior leaks and damage. However, any time you re-roof, regardless of the roofing material, it’s a great idea to look at increasing your attic ventilation — another big help toward avoiding ice dams.
I recently received an email asking:
“I hear differing opinions on installing metal over old shingles. Can the metal be too much weight on a home?”
My Answer:
Most metal roofs weigh from 40 pounds per square (aluminum) up to maybe 145 (for stone coated steel). A square is 100 square feet. Asphalt shingles on the other hand weigh from 275 – 450 pounds. When you get into products like slate and tile, weights can be pushing 2000 pounds per square!
These numbers show just how miniscule the weight of metal is.
Building codes allow two layers of standard shingles – that would be up to 900 pounds per square. Additionally, most homes are constructed to carry at least 3000 pounds of snowload for that area.
As asphalt (or fiberglass) shingles age, they lose weight. This is from granules that wear off and oils that evaporate. I have never seen any studies on this but it would not surprise me if an aged asphalt shingle has lost 30% of its original weight.
For that reason, in many cases, putting a metal roof over an aged shingle roof may still be less total weight than when the asphalt shingle was originally installed!
Now, while building codes say no more than two layers of roofing shingles, I have had many instances over the years when building inspectors have allowed metal as a third layer, because of the weight issues.
Someone sent me an email recently and asked the following:
“…will a fire explode out of the sides of the house rather than through the roof when a metal roof is on a home?”
My Response:
Good question. Most asphalt and fiberglass shingles get a Class A fire rating. Metal while it is extremely fire resistant to small burning brands that may land on it, still has a melting point. To obtain Class A, many metal roofs need a special fire resistant underlayment. My point of this is that metal is resistant to outside fires but, if there is a major fire originating inside the home, there’s a good chance it could actually melt through the metal roof faster than it would burn through asphalt shingles.
Additionally, fire fighters are trained on how to cut through a metal roof for venting an internal fire.
Now, all that said, there have been some concerns raised over the years when metal is installed over old wood shakes. The old shakes become like kindling as they age and there has been concern that an attic fire could spread quickly across the old shakes, faster than it would melt through the metal. This has not been a problem in my experience. I have heard only a few anecdotal stories about it in all my years and you never know what all factors were involved in anecdotal stories.
The melting point of aluminum is about 500 degrees lower than steel so, if someone has a concern and wants to install metal over their old wood shakes, they may feel more comfortable with a product like aluminum that has a lower melting temperature.
I hope this helps some. The bottom line is … metal has been used successfully on homes in the US for over 100 years at this point and, for the reasons stated above, there have not been problems with it containing home fires.
I was asked the following question:
I am looking at samples of several roofing products. Two of them claim to be 26 gauge, but they feel very different. One is clearly lighter than the other. Can I use a micrometer to test the thickness and figure out which one really is 26 gauge? Is there a chart that would tell me the appropriate thickness for the 29, 26 and 24 gauge of roofing materials? Please review and advise. This is very important to me.
My response:
As long as you gauge a flat area of metal, sure you can check it with micrometers.
I have long been a proponent of the industry looking at steel roofing in terms of decimal thickness rather than gauge.
Too many games can be played with gauge in regards to tolerances, with paint, without paint, etc.
You can find charts referencing gauge and decimal thickness but as you will see there is a wide range of tolerance on decimal thickness for each gauge.
A Homeowner Asked:
I have a contractor who is install a snap-lock system roof on my project. He used his roll former to create a “double male” panel which he then installed at the top of the hips on the roof. He did this because he did not feel that he could run his panels up the hip and keep them straight. This has cause an appearance issue where the panel attachments change. The panels, although they are made from the same material, look like they are different colors.
The contractor told me that using the “double male” panel is a standard detail throughout the roll forming industry, and the issue will go away once the roof gets dirty.
Is this type of installation standard to the roll forming industry?
My Response:
I would not say it is “standard” but I would not say it is unusual.
Some paint systems are more prone to “directionality” than others. That is what you are seeing. Metallics are especially known for this.
Will it diminish over time? It may. It is hard to say. Dust on the roof may mask it, but not make it go away.
