Integrated wall retrofits: Solutions for existing masonry construction for commercial buildings

Evaluating scenarios against 
pre-determined parameters
The nine retrofit scenarios were evaluated against the six pre-determined parameters identified at the expert review. Data for the scenarios came from multiple sources:

• 
cost data for the scenarios were obtained from a contractor;
• 
thermal performance and moisture durability were evaluated using the simulation software THERM and WUFI, respectively;
• 
mold probability was used as a metric to evaluate the indoor air quality and was identified using WUFI-Bio;
• 
air leakage data for the scenarios were based on the standard air leakage rates obtained from ABAA; and
• 
parameters of constructability-analyzed factors (e.g. interior floor space consumed by the retrofit, ease of construction, and time and labor required for installation) were obtained by speaking with a general contractor.

The data collected for each parameter had different units, all of which were normalized to a range from ‘0’ to ‘1’ to facilitate objective evaluation. The normalized data values were then applied with the respective weighted percentages for each parameter, which were then added and compiled in a final performance evaluation matrix to provide overall performance for each scenario.

As shown in Figure 3, three top-performing scenarios were identified through the performance evaluation matrix, to be evaluated through the next stage.

First-place scenario
The first scenario involved retaining the existing insulation and gypsum wallboard, and installing 50 mm (2 in.) of polyisocyanurate (polyiso) foam board insulation with taped seams on the existing wall.

Second-place scenario
In the scenario that ranked second, the existing insulation, steel studs, 
and drywall would be removed. Then, 63.5 mm (2 ½ in.) of polyiso foam board insulation would be installed, with a separate air barrier layer applied on the inner face of the concrete block.

Third-place scenario
For the third scenario, the existing insulation, steel studs, and drywall would again be removed. This time, 90 mm (3 ½ in.) of closed-cell sprayed polyur-ethane foam (SPF) would be used, of which 38 mm (1 ½ in.) is installed as a continuous insulation (ci) layer on the inner face of the concrete block.

Laboratory test evaluations
The three top-performing scenarios were then constructed as mockup walls and tested at ORNL for thermal performance (in accordance with ASTM C1363, Standard Test Method for the Thermal Performance of Building Assemblies by Means of a Hot Box Apparatus) and air leakage (per ASTM E283, Standard Test Method for Determining the Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen).

The results obtained for the two tests were used as inputs for an existing energy model created by ORNL for the two-story research platform. This energy model provided potential energy savings and payback period for the three scenarios, and their performance was evaluated against two baselines (Figure 4):

1. Baseline with no existing insulation on the interior of the masonry wall. (R-value for baseline assembly was R-0.88 K·m²/W [R-5 h-sf-F/Btu]; air leakage was 8 L/s-m² [1.6 cfm/sf].)

2. Baseline with existing fiberglass batt insulation on the interior of the masonry wall. (R-value for baseline was R-1.85 K·m²/W [R-10.5 h-sf-F/Btu]; air leakage was 8 L/s-m² [1.6 cfm/sf].)

The results for the two laboratory tests and the estimated payback periods for the three scenarios were evaluated for compliance against the previously defined metrics for the project. Two top-performing scenarios chosen based on this evaluation are shown in Figure 5.

The closed-cell sprayfoam scenario provided a high payback against a baseline with existing insulation—however, the payback against a baseline without existing insulation bordered on the range of 10 to 15 years. Along with the fact sprayfoam provided the highest energy savings, this resulted in selecting this scenario for the next stage of the project.

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Insulation