Climate resilience and adaptation

A building finished this year will face a different climate by mid-century than the one its codes were written for. Heavier rainfall overwhelms drains and floods basements, longer and hotter heat waves endanger occupants in buildings without cooling, wildfire seasons are longer and smoke travels thousands of kilometers, and wind, snow and freeze-thaw patterns are shifting. Mitigation, the subject of most of this course, reduces the emissions that cause climate change; adaptation prepares buildings for the changes that are already locked in. Resilience is the ability of a building and its occupants to withstand, adapt to and recover quickly from disruptions. BIOL-208 (lesson 12) describes the ecological side of climate change; this lesson covers what builders need to know about designing and constructing for a changing climate.

Climate hazards for buildings

Hazards also combine and cascade. A heat wave can trigger a power outage that disables cooling, elevators and water pumps in a mid-rise building; a wildfire can cause smoke days that force windows closed during heat; a storm can flood a basement electrical room and leave the whole building without power for weeks. Resilient design therefore looks at the building as a system and asks what happens when several things go wrong at once.

Designing for future climate

Building codes have traditionally used climate data from the past, such as design temperatures, rainfall intensities and snow loads derived from historical records. With a changing climate, past records underestimate future conditions over a building's life. The main tools for looking ahead are climate projections, produced by running global climate models under different emissions scenarios, called Shared Socioeconomic Pathways (SSPs) in the latest IPCC assessment, and downscaling the results to local regions.

In the United States, climate projections are available from federal and state sources and from universities, and the National Climate Assessment summarizes regional impacts. Design standards are beginning to incorporate future conditions: ASCE 7-22, the standard for minimum design loads referenced by the International Building Code, added tornado loads for critical facilities in tornado-prone regions and updated snow, wind and flood provisions, and ASCE 24 sets requirements for flood-resistant design and construction. FEMA's Flood Insurance Rate Maps define the base flood elevation, the level with a 1 % annual chance of being reached or exceeded, but they are based mainly on historical data and many are out of date, so many jurisdictions require freeboard above it. NOAA Atlas 14 provides rainfall frequency estimates used for drainage design, and its successor, Atlas 15, is designed to account for climate change. For wildfire, the International Wildland-Urban Interface Code and California's Chapter 7A requirements set ember-resistant construction standards.

Designers commonly choose a future time horizon matched to the life of each component: perhaps 2050s conditions for mechanical equipment that will be replaced in 25 years, and late-century conditions for the structure, foundations and drainage that will last much longer. Projections carry uncertainty, so robust designs work reasonably well across a range of futures and can be adapted later, for example by leaving space for larger cooling equipment or drainage upgrades.

# Heating and cooling degree days for Harrowgate today and with 2.5 F (2.5 C) of local warming (synthetic data)
import math, random
random.seed(11)
def year(shift=0.0):
    days = []
    for d in range(365):
        seasonal = 48.0 - 24.3 * math.cos(2 * math.pi * (d - 15) / 365)   # daily mean, F
        days.append(seasonal + random.gauss(0, 6.3) + shift)
    return days
def stats(days):
    hdd = sum(max(0, 65 - t) for t in days)
    cdd = sum(max(0, t - 65) for t in days)
    hot = sum(t >= 75.2 for t in days)
    return hdd, cdd, hot
for label, shift in (('Recent climate', 0.0), ('2050s, +4.5 F', 4.5)):
    runs = [stats(year(shift)) for _ in range(30)]          # 30 synthetic years
    hdd, cdd, hot = (sum(r[i] for r in runs) / 30 for i in range(3))
    print(f"{label:15s} HDD {hdd:5.0f}  CDD {cdd:4.0f}  days with mean >= 75 F: {hot:4.1f}")

Recent climate  HDD  6755  CDD  593  days with mean >= 75 F: 20.6
2050s, +4.5 F   HDD  5579  CDD 1042  days with mean >= 75 F: 44.7

In this synthetic illustration, 4.5 °F of local warming cuts Harrowgate's heating degree days by about 17 %, but raises cooling degree days by about 75 % and more than doubles the number of very hot days. The recent-climate HDD of about 6,750 is a little above the 6,480 used in Lesson 5, partly because the US base temperature of 65 °F is slightly higher than 18 °C. For Cedar Row, that means heating loads fall, which helps the energy budget, but cooling becomes essential, overheating risk grows and peak summer electricity demand rises.

Flood resilience

Flooding is the most common and costly natural disaster in the United States, and standard property insurance usually excludes it, so owners buy separate coverage through the National Flood Insurance Program or private insurers. Underground parking and electrical rooms make mid-rise buildings vulnerable. Resilient measures include grading the site so water flows away from the building; backwater valves on sanitary and storm connections; sump pumps with battery or generator backup; raised thresholds and curbs at garage ramps and entrances, with deployable flood barriers where needed; locating electrical switchgear, transformers, generators and elevator controls above the design flood elevation plus freeboard; flood-resistant materials such as concrete, closed-cell insulation and tile in areas that may get wet; and sealing below-grade penetrations. Many of these measures cost little when included in design but are expensive to retrofit.

Whether a resilience measure is worth its cost depends on the probability and consequence of the hazard, both of which are changing. A benefit-cost analysis compares the present value of expected avoided damage with the cost of the measure. Because floods are random, a Monte Carlo simulation of many possible futures shows not just the average benefit but also its spread.

# Benefit-cost of flood-proofing Cedar Row's below-grade level (illustrative, Monte Carlo)
import random
random.seed(1111)
years, rate = 50, 0.03                 # study period and real discount rate
damage = 1_200_000                     # cost of one basement flood: electrical room, elevator pits, cars
cost = 350_000                         # relocating switchgear, backwater valves, flood barriers, sump backup
reduction = 0.85                       # share of flood damage avoided by the measures
def p_flood(y):                        # annual chance rises from 2 % to 5 % over the period
    return 0.02 + 0.03 * y / years
trials = 20000
avoided = []
for _ in range(trials):
    pv = sum(damage / (1 + rate) ** y for y in range(years) if random.random() < p_flood(y))
    avoided.append(pv * reduction)
avoided.sort()
expected = sum(avoided) / trials
print(f"Expected present value of avoided damage: ${expected:,.0f}")
print(f"Benefit-cost ratio: {expected / cost:.2f}")
print(f"Futures with no flood in 50 years: {sum(a == 0 for a in avoided) / trials:.0%}")
print(f"Futures where avoided damage exceeds the cost: {sum(a > cost for a in avoided) / trials:.0%}")

Expected present value of avoided damage: $834,454
Benefit-cost ratio: 2.38
Futures with no flood in 50 years: 17%
Futures where avoided damage exceeds the cost: 72%

For Cedar Row, flood-proofing the below-grade level costs $350,000 and returns an expected $834,000 in avoided damage over 50 years, a benefit-cost ratio of about 2.4, but the outcome is uncertain: in about 17 % of simulated futures there is no flood at all, while in most futures the measures pay for themselves. The analysis does not count tenant disruption, displacement, health effects or insurance premiums, which would strengthen the case. Studies of hazard mitigation by the US National Institute of Building Sciences have similarly found that mitigation typically saves several dollars for every dollar spent, although results vary by hazard and measure.

Heat, power outages and passive survivability

Passive survivability, or thermal autonomy, is the ability of a building to maintain safe indoor conditions for a period without power or fuel. A well-insulated, airtight building with moderate windows, external shading and operable windows stays warm much longer in a winter outage and heats up more slowly in a summer heat wave than a leaky, heavily glazed one. Measures such as these, which also save energy, are some of the most cost-effective resilience strategies. For mid-rise buildings, designers also consider backup power for critical loads, such as at least one elevator, domestic water booster pumps, sump pumps, emergency lighting and a cooled common room that can serve as a refuge during a heat wave; batteries and on-site solar can supply some of these loads with less dependence on diesel generators.

Overheating risk assessment uses dynamic thermal modeling with future weather files to check how many hours indoor temperatures exceed comfort thresholds in each unit type, with and without cooling or during outages. Lesson 10 noted code requirements for cooling in some jurisdictions; the CAGBC Zero Carbon Building Standard v4 and LEED v5 both now ask teams to assess climate resilience, and LEED v5 includes it as a prerequisite.

Wildfire and smoke

Most homes lost in wildfires ignite from embers rather than direct flame contact, often days of embers landing in vents, gutters, decks and gaps. Ember-resistant construction uses noncombustible or ignition-resistant cladding and roofing, vents with fine metal mesh or ember-resistant designs, enclosed eaves, noncombustible material near the ground and around decks, and tempered or multi-pane windows, combined with defensible space that removes fuel near the building. Even buildings far from the fire are affected by smoke, which can raise outdoor fine particulate concentrations to hazardous levels for days or weeks. Airtight envelopes, MERV 13 or better filtration on outdoor air, the ability to reduce outdoor air temporarily and portable air cleaners for vulnerable occupants all reduce indoor smoke exposure.

Resilience and funding

Federal resilience funding has been unstable. FEMA's Building Resilient Infrastructure and Communities (BRIC) program, which funded hazard mitigation projects and code adoption, was canceled in April 2025; a federal court ruled the cancellation unlawful and ordered it reinstated, and in March 2026 FEMA announced it would revive the program with a revised focus. Other federal mitigation grants, state programs and local incentives continue, and insurers increasingly price resilience, with some offering discounts for fortified roofs, flood-proofing or ember-resistant construction. Builders should check the current status of any program before relying on it in a budget.

Opinions differ on how much resilience should be required by code versus left to owners and insurers. Supporters of stronger requirements argue that individual owners underestimate low-probability, high-consequence risks, and that resilience protects occupants and communities who did not choose the building. Critics argue that each requirement adds cost, that projections are uncertain, and that market signals such as insurance premiums can drive adaptation efficiently. In practice, codes are moving slowly toward future-climate design, and owners like Harrowgate Community Housing often go further because their tenants are vulnerable to heat and displacement.