r/solarpunk • u/Uncivilized_n_happy Scientist • 1d ago
Discussion Green roof biggest limiting factor?
I asked some places around my city if they’d be interested in me installing a green roof for free. They said that the buildings are so old they’re worried the ceiling will cave in. I’d love to discuss ways this hurdle can be overcome!
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u/GreenStrong 1d ago
This hurdle can be overcome by a structural engineer and the installation of additional steel. Roofs are rated for snow and wind loads- most commercial buildings can support a green roof but not necessarily a green roof plus a once in a century snow load. Building codes are very specific with wind and snow requirements for each region. This is one reason commercial and industrial solar installation is less common than residential, structural and electrical engineers have to do it and then work with code inspection to justify certain choices. For regular homes, the project is small enough that they can just issue blanket approval for every house with modern construction to host a certain amount, as long as the parts are appropriate for the climate. For example, everything in South Florida has to survive hours of hurricane wind, they can have solar panels but need extra strong brackets so they don't become projectiles.
This is the first test; enthusiasm for a better world meets the complexity of existing systems. Keep going find the next idea, maybe rain gardens. Maybe lightly constructed trellises that vines can climb to block summer sun from walls but the vines will shed leaves in winter to allow solar heat. I take a photo of a nice one at an Architect office tomorrow if you like, it is planted in jasmine and it smells like heaven for a month every summer.
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u/CorpusculantCortex 1d ago
If the building isnt built rated for like 30+ pounds per sq ft above what it is built for then it would be negligent to do this.
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u/ARCHFUTURA 1d ago
Uh liability? How much do you know about green roofs? Are you a structural engineer? I mean if you’re really trying to learn then do some peoples sheds. No way you’re doing a proper job for free. No way you’re doing it without proper experience and engineering approval and proper materials and a substantial budget on anything commercial ever.
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u/hollisterrox 1d ago
Sure, it's called an engineering retrofit. California firms do it all the time for buildings that weren't built to seismic code, a similar process and slightly different outcome could reinforce an existing roof for the extra load.
Depending on the building you are starting with, that retrofit might look like an exoskeleton with some penetrations to put wide-flange beams across the soffit of the roof, or potentially an exoskeleten with arches over the top from one side to the other and suspension support, or for very wide buildings (think tilt-up 2-story/3-story commercial warehouse structures) there would just need to be a bunch of internal columns added to carry the load to the foundation, and probably penetrations in the existing foundation to build a better piling for that load.
There's a significant amount of engineering involved in these solutions, because all the details of the building matter: roof and wall construction techniques, age of the materials, foundation construction style and current state, and the soil characteristics under the building would all have to be evaluated.
All completely possible, there's nothing magic required, it's just work & money.
It might be easier to talk to new build owners about adding 2% to their initial cost to incorporate a green roof, because they are already doing 98% of the engineering and construction required, setting a higher load requirement for the roof up front barely changes the engineering effort and adds nominal cost to construction. Way, way less expensive and disruptive than a retrofit.
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u/Henri_Dupont 1d ago
Yeah the structure is the barrier. Structures are built for a certain load (roof, rain, snow loads) and the green roof will hold not only soil and plants, but water. Water is heavy. At minimum a review by a structural engineer would be reqpired.
The second issue is the use case. What problem does the green roof solve or benefit does it accrue? Any smart client has limited capital and should decide to use it for the most benefit. A green roof reduces stormwater runoff and reduces heat island effect. The former could possibly be an economic benefit in special cases, the latter is a diffuse benefit to the community but lxttle direct benefit to the owner. Sure, it could cut their AC by a smidge, but the same money put into attic insulation would save far more.
Is a green roof project the best bang for this client's sustainability buck? In fifteen years as a LEED certification consultant, not one of my many clients could pencil out a green roof and make it worth the investment. We built solar arrays and high efficiency HVAC and superinsulation and zero-net-energy buildings, but never once a green roof.
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u/Varro-Reborn 1d ago
Come out here and build one. I've got space for experimentation.
Are you anywhere near West Virginia?
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