With ocean waters rising and tidal storm surges growing both more frequent and more forceful, this century promises to be a challenging one for a coastal city with centuries-old architecture built mere feet above sea level. To its credit, Boston is facing down that forecast on two fronts: trying to slow climate change by reducing carbon emissions, and fortifying the city to protect life and property from the worst of its impacts.
After UN scientists last year said they expect sea levels to rise even faster than previously predicted, the latter strategy is taking on new urgency. Plans to make the city more resilient to coastal flooding include large-scale defenses such as sea walls, elevated parks and roadways, and living shorelines that can absorb surging tidewaters. But other strategies are meant to be implemented at the building level, particularly in areas most vulnerable to future flooding.
Building off the work of Climate Ready Boston, the city’s climate-change preparedness initiative, the Boston Planning and Development Agency created design guidelines to help homeowners and developers make their properties more flood-resistant. The guidelines are especially geared toward properties within a newly identified “zoning overlay” district — areas of the city likely to be at risk of flooding in the year 2070, assuming 40 inches of sea level rise. The overlay map includes portions of nearly a dozen neighborhoods, from East Boston to Dorchester.
New construction in this zoning overlay district may need to meet certain climate-resilience standards. For example, critical mechanical systems, like furnaces and boilers, electric panels, air ducts, and hot water heaters, would need to be located above the estimated elevation of a 100-year flood in the year 2070, or protected in place by flood-proofing measures.
Constructing big residential buildings to be climate-resilient is one thing. But most of Boston’s housing was built before World War II, and nearly a third of our living space is in one- to three-family structures, according to the BPDA — including the historic brownstones of the South End and Back Bay and the ubiquitous three-deckers of Dorchester and East Boston. So the guidelines also include case studies that illustrate how small-property owners can retrofit old, existing homes to weather more frequent and damaging floods.
The recommendations range from short-term, quick fixes to long-term strategies intended to be incorporated during a major remodel. For example, making a three-decker truly climate resilient might include abandoning the basement and filling it to grade, extending the foundation walls and elevating the entire building, and moving all heating and cooling systems to the roof or into utility closets on upper floors.
That’s a daunting amount of work. But there are also smaller, sensible steps that owners in flood-prone areas can take in the interim, such as raising mechanical systems off the floor, installing a sump pump with backup power, and putting in a backflow preventer valve, which stops sewage from flowing the wrong way when drains are inundated by stormwater.
We asked Chris Busch, assistant deputy director for climate change and environmental planning at the BPDA, what Boston homeowners ought to know about climate resilience and how much it costs to elevate a three-decker, among other questions.
(This interview has been shortened and edited for clarity.)
Q. Can you talk about the likely risks facing Boston homeowners, particularly in the flood-prone areas outlined in the new zoning overlay district, and why we need to start adapting our residential buildings to better withstand the impacts of climate change?
A. Up until this time, we’d been really utilizing the FEMA [Federal Emergency Management Agency] flood maps, which represent the extent of potential flooding with a 1 percent chance event. But the FEMA maps are only based upon historic storms of record, so they haven’t in any way incorporated future sea level rise. The mapping we use now represents areas of the city potentially inundated with that 1 percent chance event with about 40 inches of sea level rise.
These are areas of the city that, within the lifespan of their existing housing stock, could see some level of inundation with a major storm event — like what we saw back in 2018, with those nor’easters in January and March — floodwater inundating parts of the city that have never seen seawater before. I think we’ve seen a preview of what we can expect with a warming planet and rising oceans.
Q. What would you recommend to Boston property owners within this zoning overlay, and what are some of the key short- and long-term adaptations they should be thinking about to make their existing homes more climate resilient?
A. Just understand your level of vulnerability. We point people to that mapping tool that projects sea level rise. Are you fully within that area, or is just part of the property at risk? There’s also a top-of-water elevation — so based on your existing site grade, it could be just 6 inches of water you’d need to deal with, or it could be 3 feet, and that’s going to impact your considerations.
In near-term situations, where it’s just not feasible to keep the water out, it includes ensuring that hazardous materials are out of that basement. We’ve seen some nightmare situations where petroleum products create a toxic stew in people’s basements that are inundated, and that really increases the cleanup costs.
Same with mechanical systems that have to be taken offline because they’re inundated with saltwater. If those systems were elevated, people could potentially just come back the next day and have an occupied home, and instead it takes weeks and weeks and folks have to find other places to live. Your water heater or boiler may be getting old, so when you think about replacing those things, consider where you could relocate them ... in some cases it’s just a large closet. Through zoning, the intent is to allow variances for building setbacks or side yards if people want to do a minor expansion of their footprint to accommodate these systems.
If you have a major rebuild or a teardown or redevelopment, in that case we’re getting into major foundation work, and we’ll think about elevating the building. And we’ll have a zoning allowance for how height is defined — currently the measure is by existing grade, but within this overlay, height would be measured from sea level, so you wouldn’t need to take a haircut. The height allowance is for projects undergoing resilience review.
Thinking about other shorter-term interventions, there are deployable measures like flood shields to put around the foundation to keep the water out. If you’re doing a revamp to your landscaping, on garden-level units you could be putting in a knee wall with planters, something along those lines, to get up to the new elevation.
Q. I think the idea of “dry flood proofing” makes intuitive sense to people: You keep the water out. But can you explain “wet flood proofing,” where flood vents intentionally allow water into a crawl space or basement (as long as it’s built using flood-resistant materials, like concrete or tile)?
A. The intention with wet flood-proofing, when you’re letting water in and out, the idea there is to equalize the hydrostatic pressure. Think about when you’re on a beach, getting hit with a wave, and the force of the water. If you’ve got 2 to 3 feet of water piling up on a foundation with nothing but air on the other side — a lot of foundations are not designed to withstand that. So the intent is you let the floodwaters in and allow that pressure to equalize inside and out, and you maintain the structural integrity of the foundation.
Q. The design guidelines offer some ballpark cost estimates for various resiliency retrofits. For example, installing backup systems, such as sump pumps and backflow preventers, and raising a foundation. (I can’t even fathom the cost of elevating an entire three-decker.) Can you talk about the costs and any financial incentives associated with these strategies?
A. Cost is most definitely a serious consideration with any of this. It can vary a lot based on building type and age, everything from relocating mechanical systems, which could likely be in the thousands of dollars, to a full reinforcement or foundation elevation, which could be hundreds of thousands of dollars.
But take mechanical systems, for example. When you’re replacing and upgrading those systems, there could be substantial efficiency upgrades as well, so you could realize some cost savings and improve longevity. If you’re within the current FEMA flood area, if you have a federally backed mortgage, you need to carry flood insurance, and if you’re taking measures to fortify your home or to meet these standards, you can see reductions in your flood insurance rates. But that doesn’t apply yet to these locally applied future flood zones.
Q. In the South End case study, one long-term solution includes building a rooftop addition to compensate for the loss of the basement-level living space. Is that feasible?
A. We’re just trying to prevent having residential units, highly occupied spaces, beneath these flood elevations. The intent is to ensure property owners maintain their buildable, occupiable square footage … to make up for space that’s lost over time, as long as there are resilient strategies being employed.
We had a couple of meetings with the Landmarks Commission, who would be involved and engaged with any type of exterior alterations in historic landmark neighborhoods. [Initially] we’re going to focus on projects that are 20,000 square feet and larger, and for smaller projects, brownstones, we’re going to have to have another more nuanced level of discussion in those neighborhoods. We’re relying on the design community; they have some creative solutions in terms of meeting future site elevations and elegantly integrating these types of design parameters.
Q. I imagine cost is just one hurdle, though, right? For example, a lot of Boston’s older housing is nonconforming — that is, grandfathered in and not up to current building codes. Could taking on some of these retrofits require an owner to make other improvements to comply with current fire or accessibility codes, for example?
A. We want to push these elements with major renovations and new projects, have them built in when other project upgrades are going on. But we’re trying to reduce the inhibitions from a zoning standpoint to ensure we facilitate these types of upgrades ... that we don’t have people getting tripped up through the zoning variance process.
As we get into this we’re going to be hiring someone who has an architectural background and will be able to work with property owners and designers to come up with the types of solutions that may be needed. And we want to have a pilot project somewhere, potentially in East Boston, where we can look to a rehab of an existing two-family to see a living, breathing example of how these things can be done.
Jon Gorey blogs about homes at HouseandHammer.com. Send comments to email@example.com. Follow him on Twitter at @jongorey. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.