When we assess the urban sustainability of a neighborhood, what are the conditions that lead us to decide to demolish it?
if it does not meet the sustainability criteria, is this when we should demolish it ?
Lots to unpack. First decide what metrics are appropriate to measure "sustainability". There are lots of papers on these, but I would include both embodied and operational carbon (energy is only a proxy for carbon), consider the toxicity of construction and demolition, and any material scarcities, at minimum. Then you must decide the time-period to measure by. A 50 year analysis may produce different answers to a 100 year analysis. The general consideration will be whether the operational carbon savings of a new neighborhood will outperform the negative cost of embodied carbon for new construction. The embodied carbon/impact of the existing construction (not counting maintainence) is a sunk cost. All of this said, I would assume that in most cases upfits to existing structures to improve energy efficiency and/or convert energy sources to renewables will be both the most impactful and most cost-effective. The carbon ratio between solar and gas can be as high as 40X. This is where picking your metric is so crucial. Energy use is not bad, the bad part is all of the externalities associated with current energy systems. Hope this helps.
Thanks for this replay, it's very interessting, in fact i have created my own tool of sustainability evaluation and i compared between tow neighberhoods, one of them is sustainable, the other one is not sustainable , it doesn't replay to any criteria ! i was wondring if i we should decide to demolish it in case of it's not sustainable, the neiberhood is very old , but we can find alos some new constructions, unfortunatly all the green spaces had degraded and become builded also. i really i'm confused what to propose !
MAKING SOME EDITS FOR CLARITY...
Gotcha. Social issues will probably play a role in removing an entire neighborhood. Where will people go? Assuming these residents are the most vulnerable in society, there is a large chance they will be negatively impacted, and may not recover. Maladaptation and green- or eco-gentrification are real problems. Again, if there are other ways to address sustainability, through up-fitting, new technology, etc. it may be possible to improve sustainability and keep families/communities intact.
To be more blunt, unless the buildings are physically unsafe, I can't imagine a scenario where solar/wind farms + battery storage won't address the carbon footprint of an existing area more effectively than would demolishing and rebuilding. You still need to switch energy sources -- why not start there. An energy efficient neighborhood powered by gas/coal is worse than probably any reasonably built (but less efficient) neighborhood powered by renewables. This is simple ratios. Coal/Gas to Solar offers 20-40 X carbon reduction. You will never get that factor of energy savings unless you're in a building with holes or 0 insulation. In that case, a mix of upfit and energy transition might be best.
If you want some food for thought, check out our paper in Landscape and Urbanism on carbon-neutral neighborhoods. Its a bit radical and I'm sure many will think it bad-policy, but unless 500 million people are going to move out of the MENA region, we have to find ways to become carbon neutral there.
Thank you, very interessting , i have seeing your articles work, seems very important , i'll read them and i would like to discuss your results later.
for my case study, it's a traditionnel neighberhood but in arid climate area, so i may find some responses in your work. i'll come back to you in the coming days. thanks so much.
I believe that the ideas of sustainability seek to preserve things and seek alternatives to update or modify them as little as possible, so demolishing is not the best option since it is unsustainable, investing resources to demolish and then rebuild, that is unsustainable.
Leticia Peña Barrera Thanks for this replay dear researcher, i really was thinking that sustainability means to restaure and to renovate and reform instead of destroying to build again because it's not good economically and ecologically even in the social plan because it represents a part from their memory . but the case study neighberhood is in bad state, all the gardeen become houses now, a lot of houses are not planified builded without architects so there is no study for that , i have found some spaces so i can propose a green parc but for the houses what can we propose and especialy that esthitically and spatialy and energeticaly are not good !
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