5.6 Sint Maarten: The Impact of Design Performance Level on Emissions Savings

Program Details

Housing in the Caribbean island of Sint Maarten was severely affected by Category 5 Hurricane Irma in September 2017. Build Change worked with the country’s National Recovery Program Bureau (NRPB) to provide technical assistance to their housing recovery program.

Given the limited funding available and the large number of damaged houses, the NRPB favored a program which would support as many of the country’s homeowners with the highest socio-economic vulnerability as possible. From an engineering perspective, most of the houses selected to receive grant funding for repairs had masonry walls that were well built and had little hurricane damage, but their roofs lacked sufficient capacity, and had moderate to severe damage.

Build Change worked with the NRPB to design a housing repair and improvement program that would have two principal levels of intervention depending on the existing condition of the house:

• Life safety: For small houses that did not meet minimum requirements for earthquakes and wind, we implemented a full retrofit that would bring the whole building—walls and roof—up to a code-compliant, life safety performance level. Life safety means that for wind speeds up to and including the design level, the building may experience damage, but not to such an extent that there will be loss of life.

• Risk reduction: For larger houses that had not been severely damaged, we implemented a risk reduction intervention. Strengthening for risk reduction does not bring the whole building up to minimum code requirements for life safety, but it brings the most critical components up to (or close to) a life safety performance level. A risk reduction intervention still improves the overall resistance of the building to hurricanes and earthquakes. For the houses in Sint Maarten, this meant that we mostly intervened in the roofs by providing additional capacity to the framing elements and to the connections, as well as repairing or replacing the covering.

Improvements for habitability were included regardless of the intervention level, and included new windows and doors, and replaced electrical wiring and panel boxes. This has not been calculated in the embodied carbon.

Houses in Sint Maarten are typically one to three stories high and comprise masonry walls (partially reinforced, often with reinforced concrete columns at wall intersections) and a ring beam above all exterior walls. Roofs are typically pitched with timber framing and clad with galvanized metal sheets, or solid reinforced concrete slabs.

Findings

Overall, home improvements in Sint Maarten saved 76 percent of the emissions of equivalent new construction. On average, strengthening existing homes in Sint Maarten as part of the NRPB’s program saved 40 metric tons of carbon dioxide per house (0.2 tons per square meter).

The savings in Sint Maarten are some of the highest of all design groups due to the higher quality of the existing houses, the cultural acceptance and prevalence of lightweight roofs, and the design performance level. The design and construction quality of the foundations and walls of existing housing in Sint Maarten meant that there was less damage to these elements that required repair, nor was there substantial need for strengthening. In general, most of the damage was to the roofs.

The design performance level can have a significant impact on embodied carbon emissions. The two intervention levels in the Sint Maarten program provide an interesting comparison of the impact performance level can have on the emissions of a housing retrofit program. Comparing the sample of 37 repaired and strengthened houses to equivalent new construction, the savings by strengthening to a risk reduction and life safety performance levels were 85 percent and 69 percent, respectively.

In addition to the carbon savings, risk reduction interventions are typically cheaper than full life safety interventions. Risk reduction interventions are also quicker and less invasive, which means homeowners are displaced from their homes for shortened periods of time (if at all) and have less superficial redecorating to do after the structural work is completed.

In contexts where the design and construction quality of housing is already reasonable, designing housing interventions for risk reduction rather than life safety performance can be an effective way to balance the financial and environmental cost of interventions with the need to minimize damages in future disasters.