When it comes to premium roofing materials, slate is right up at the top, and it's joined by several metals, including copper and porcelain coated steel. If you're debating re-roofing with one of these beautiful - and pricey - materials, here's a handy comparison to consider before making a final decision.
1. WEIGHT
Usual weights for slate roofs are quoted as roughly 9 to 25 pounds per square foot. That would mean one of the thinner slate roofs choices for a roof on a large home would weigh somewhere in the range of 40 tons - and the heavier choices upwards of 100 tons! This is a serious consideration for a re-roof, since structural reinforcements may be necessary. And in seismic zones, having that much material over your head could be cause for concern.
A metal roof is far lighter, weighing in around 7 tons on a large home. Plus, many profile are interlocked together to form an additional sheer layer resisting movement of the roof structure. While no assurance that a significant earthquake won't damage a home, 30 plus fewer tons of dead weight above your head offers many order of magnitude of safety over heavier denser materials.
2. MAINTENANCE
The usual issues with slate roofs are cracking, "nail sickness," delaminating, damage from foot traffic and slippage. Repairs are difficult and expensive and rarely well-concealed. Moss is also something that is prone to growth on slate roofs as all of the edges and crevices provide a foot hold for the hardy plant. This is something that some people like to see (makes the home look old and rustic), but it actually contributes to the degradation of the slate roof assembly and will eventually lead to serious damage.
One of the advantages of metal roofs is that they're as close to zero maintenance as any building exterior can be. In addition to being light and rigid, there is no chance they'll accumulate moss - and even if it found a place to grow it couldn't crack the metal. Also, copper, zinc, or porcelain do not fade, and short of a tree falling on the house, will never need any attention.
3. QUALITY LEVEL
The usual range for decent quality slate roofs is $10-$20 per square foot, so being at the absolute low end of that scale begs a number of questions about the quality of the slate, the thoroughness of the installer, and the attention to detail of the estimator. Cutting corners - especially on the quality of the slate itself - is certain to increase the chances of maintenance issues down the road. When choosing slate, there are two primary considerations: thickness and grade. Generally, the thinnest is the 1/4' and better materials go up from there (to as much as a full inch). Buying at the low end of slate means choosing one of the thinner products and the thinner the product, the more prone to the problems of a slate roof (cracking, slipping, etc). Plus the cheaper grades are prone to fading from exposure to sun light. Especially if a black shade is important, you'll want to make sure that you're upgrading to a quality level of slate that is classified as "unfading."
The choice of metal in this regard is an easy one as our porcelain diamonds are completely fade-free and the black glass will just never degrade in the sun.
4. SOLAR GAIN
Energy efficiency is a major consideration when choosing a roof these days, and when you install a slate roof you're literally putting hot rocks next right next to your roof deck. This is exacerbated by choices of dark, "formal" colors. This heat can then be conducted into your attic and increase the demand on your A/C system.
One of the verifiable advantages of our porcelain diamonds installed over our thermal liner is that the combination of the air-space beneath the shingles and the insulation value of the liner means that a fraction of the heat that strikes the roof will be conducted into your home. This assembly also cools off very quickly once the sun stops striking the roof (due to the fact that the roof is just that much lighter than slate). Almost no other material in the color black can achieve any level of energy efficiency - except metal! In every case, the result of choosing a metal roof with a thermal liner is a more energy-efficient system. Your carbon footprint will be so much less with our metal roof system and you'll be reducing your contribution of greenhouse gases due to a lower energy demand from your home.
None of this is to say that slate is a poor choice - far from it! Versions of slate roofs have been around as successful roof coverings for centuries. But comparing to metal, there are definitely factors to be weighed.
Want to know more? Download our FREE re-roofing booklet, and learn about all of your roofing options.
