“‘We Cannot Save Everything’: A Historic Neighborhood Confronts Rising Seas” from yesterday’s Times hits a number of important points. Because of the history of settlement and travel in the US, a lot of old historic neighborhoods are near the ocean, bays, or sea-level portions of rivers. The buildings in those neighborhoods are increasingly vulnerable to flooding as well as being vulnerable in general.
“Dry flood-proofing” is exactly what it sounds like: improving a building so that it can withstand the pressure of flood water and remain dry on the inside. It is what most people think of when you say “flood-proofing.” The fact that the interior of the building will remain dry is as simple and obvious a benefit as there is. The problem with it is that old buildings typically have masonry foundations, which are not waterproof and not particularly strong when subjected to out-of-plane forces. Applying waterproofing to the inside face of a masonry foundation makes the masonry – particularly the mortar – weather faster than if it’s not waterproofed, so you’re trading flooding for increased difficult maintenance.
“Wet flood-proofing,” as described in the article, involves letting the lower portion of a building flood so as to reduce the lateral pressure from water. The “Flowing Through” animation in the article shows the concept, but this is a terrible idea for an unimproved original foundation. Allowing water to flow through a masonry foundation causes rapid deterioration of the mortar and is likely to result in displaced masonry units (stones or bricks) and possibly partial collapse of foundation walls. The picture above shows houses in Mantoloking, NJ after hurricane Sandy destroyed portions of their foundations. So wet flood-proofing an old building effectively means building new foundations below it, which is to say the least disruptive and expensive.
Similar to wet flood-proofing, “floatation” works far better with modern buildings that have positive and robust connections between their various pieces, which rules out masonry foundations, walls with nogging, mortise and tenon connections, and a lot of other old details that work fine only when the forces go in the direction that the building was design for.
The article does a pretty good job of describing the good and bad points of elevating buildings, but is focused on neighborhoods like the one described, with free-standing houses. Elevating a strong of rowhouses, or even a single building that has lot-line walls abutting its neighbors would be far more difficult.
I obviously recommend reading the article to get a sense of the complexity of the issues at hand. Ultimately, we may be forced as a society to triage neighborhoods and cities, and I doubt that the values of historic preservation are the ones that will be used to decide what to save and what will be lost.
