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 kilometres, 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 Canada, ClimateData.ca, supported by Environment and Climate Change Canada and partners, provides downscaled projections of temperature, precipitation, degree days and other variables for any location. The 2025 editions of the National Building Code and National Energy Code for Buildings use updated climate data that reflect projected future conditions, the first time Canada's model codes have done so. The National Research Council's Climate-Resilient Buildings and Core Public Infrastructure initiative produced much of the underlying research, and CSA Group has published standards and guidelines on flood resilience, including CSA Z800 on basement flood protection and CSA W204 on flood-resilient design of new residential communities. The National Research Council's National Guide for Wildland-Urban Interface Fires (2021) sets out construction and planning measures for areas at risk of wildfire, and FireSmart Canada provides guidance for homeowners and communities.

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 C of local warming (synthetic data)
import math, random
random.seed(11)
def year(shift=0.0):
    days = []
    for d in range(365):
        seasonal = 8.9 - 13.5 * math.cos(2 * math.pi * (d - 15) / 365)   # daily mean, C
        days.append(seasonal + random.gauss(0, 3.5) + shift)
    return days
def stats(days):
    hdd = sum(max(0, 18 - t) for t in days)
    cdd = sum(max(0, t - 18) for t in days)
    hot = sum(t >= 24 for t in days)
    return hdd, cdd, hot
for label, shift in (('Recent climate', 0.0), ('2050s, +2.5 C', 2.5)):
    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 >= 24 C: {hot:4.1f}")

Recent climate  HDD  3657  CDD  360  days with mean >= 24 C: 20.7
2050s, +2.5 C   HDD  3014  CDD  619  days with mean >= 24 C: 44.8

In this synthetic illustration, 2.5 °C of local warming cuts Harrowgate's heating degree days by about 18 %, but raises cooling degree days by about 70 % and more than doubles the number of very hot days. The recent-climate HDD of about 3,650 is close to the 3,600 used in Lesson 5. 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

Water damage, much of it from basement and sewer-backup flooding, is the leading cause of home insurance claims in Canada, and 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 likely flood level; 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 modelling 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

Government programs that help pay for resilience change over time. In Canada, the federal Disaster Mitigation and Adaptation Fund has supported large infrastructure projects, the National Adaptation Strategy (2023) set out goals for resilient buildings and infrastructure, and the federal government has been developing a national flood insurance program for high-risk households. Provinces and municipalities run their own programs, such as subsidies for backwater valves and sump pumps. Insurers increasingly price resilience, and some offer discounts for flood-proofing or ember-resistant construction.

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.