Now you’re ready to build green. The questions begin- linoleum or bamboo flooring? Skylights or solar tubes…or both? And finally the roofing…green design offers so many alternatives sometimes it can be overwhelming. Today I would like to run through some of the competing benefits of a solar roof verses a living roof. This would seem to be fairly simple and straight forward but many factors are involved. For sake of argument let’s stick with the purely environmental benefits.
-The idea with a solar roof is that the power you produce on your roof doesn’t have to be produced via petroleum, at a coal fired plant, or by some other harmful means somewhere.
-The idea with a living roof is a little more nuanced- in that you are recovering the space for flora (carbon reduction) which has been displaced by your residence, improving your insulation, cooling your roof, all while mitigating the urban heat island effect.
So which green design is actually more beneficial for the environment? Guess what- It is somewhat a matter of perception and is very involved if one is trying to quantify. It comes down to a complicated equation. (doesn’t it always?)
First you have to figure out how much power your hypothetical solar roof will create over the course of it’s lifetime. Then you consider how many emissions would be produced if that power was created via conventional means. This is how many emissions aren’t being created because you aren’t consuming the power that would have necessitated their creation. However the energy expended in the production and disposal (or recycling) of solar panels (and their batteries) creates it’s own set of emissions and pollution which must be subtracted from that original total-emissions-avoided number. So what your left with is the total amount of carbon emissions which aren’t being created due to the total lifespan of your solar panels. This emission reduction is the environmental benefit of your hypothetical solar roof. (There are geopolitical and personal benefits as well but they are beyond the scope of this article)
On the green roofs side you must calculate the entirety of carbon emissions and pollution which are being breathed and processed by your rooftop plants in the course of your roofs 40 to 80 year lifespan and ad to that the carbon emissions avoided from the energy savings reaped from your enhanced insulation and roof cooling benefits. The complexity of variables such as plant type and energy-use-avoided go on and on. That’s why I pose the conclusion that it simply isn’t generally feasible to quantify/compare the ‘exact benefit’ of these two alternatives because there are so many ancillary factors involved. There are a few definite things to consider though when making your choice;
- A living roof is going to be beneficial in an urban setting in the sense that it provides a place for plants where there is none. This is also where the “urban heat island” exists. (not to mention storm water mitigation, and air quality improvement)
- Foot per foot over equal time periods the emission reduction/avoidance is probably greater from a solar roof when you consider how that energy might otherwise be produced in the current social environment. (see next bullet) On the other hand theoretically this energy can also be produced elsewhere or by other renewable means whereas the flora that is able to grow on a living roof in a city would otherwise have nowhere else to grow in that urban area.
- So many little factors are involved. Before you build green you really need to consider how optimal your location is for either or both. If your in a sunny rural area (with high energy prices) solar may be the way to go. If your in a predominantly cloudy urban setting then your a great candidate for certain living roofs. One thing to consider is that if your just going to be using much of that solar energy on extra power for air conditioning or heating, then a living roof might be just as good in terms of ‘cutting out the middle man’ and naturally keeping your house a little cooler, and/or better insulated.
So in reality the world of green design is not so cut and dry. Solar roofs have the added benefit of directly producing energy- living roofs don’t carry all the industrial baggage and both will play a big role in transforming the world into a better more sustainable place to exist.