Reborn on the Bayou
- By Anne Hildenbr, Lisa W. Lamkin
- October 1st, 2012
The crown jewel of Houston Community College (HCC), the San Jacinto Memorial Building, is undergoing an extensive renovation. The building closed 18 months ago while preparations for the abatement and rebuilding of the entire interior of the building got underway. The exterior will be restored to its original glory. The renovation is planned for completion in the spring of 2014, in time for the centennial celebration of the building.
The renovation of HCC’s San Jacinto Memorial Building, which began life in 1914 as the South End Junior High School, provides architects with a unique challenge: bringing this historic building up to existing code while maintaining its original appearance and character.
The San Jacinto Memorial Building was designed in the Classic Renaissance style, complete with Doric columns, carved pediments, and copper spandrels. The building currently welcomes visitors to the Central College in the Houston Community College System, although it has served in many capacities and passed through many hands (including the Houston Technical Institute and the Houston Independent School District) in its almost century of life. Since its original construction in 1914, it has also had a major addition in 1927 and a second major addition in 1939, as well as other more minor renovations.
BRW Architects of Dallas, TX, is leading this $35M project. When completed in September 2013, it will include a historic renovation of the exterior; full interior demolition to structural frame; interior collegiate office and classroom construction; and additions of stair, mechanical, and elevator towers. It will also include a new state-of-the-art cardio/wellness center; the replacement of the building’s mechanical, electrical, and plumbing systems; and the installation of new information technology systems — all while meeting USGBC LEED Silver certification criteria and City of Houston building code requirements and finding generally more sustainable solutions for all the building’s needs.
In addition to those concerns, the project must address the existing mass wall with no drainage plane, the removal of existing coatings, and the existing interior plaster finish.
The cherry on the top of this challenging sundae is Houston’s notoriously hot, humid climate, making moisture control a top priority. This article will address that issue, including the various considerations, challenges, and proposed solutions.
Vapor Permeable or Impermeable Air Barrier?
As previously mentioned, moisture control is a priority. The question was whether to use a vapor permeable or impermeable air barrier. Vapor will move from the warm side of the wall to the cold side of the wall, and the greater the temperature differential, the greater the vapor drive. In addition, the more humid the air is, the greater the vapor drive. Houston’s hot, humid climate provides a perfect storm for vapor drive from the outside to the inside.
In order to find the best approach for combating this problem, it was essential to perform a dew-point analysis. When the air reaches its dew-point temperature, it can no longer hold water and that water condensates. For this project varying scenarios were analyzed, including variations for locating the air barrier, insulation, and outside air temperature.
The existing wall is comprised of a 4-in. cast stone veneer on an 8-in. hollow clay tile with no air space (see Figure A). To provide opportunity for thermal insulation, space for data and electrical conduit, and to provide a finished interior wall surface, a stud wall furring assembly at the interior is proposed (see Figure B). In all cases in the analysis, the most substantial jump in temperature was between the interior furred-out assembly and the insulation. The potential for condensation was always more within the existing masonry mass wall (exterior side of the assembly). Where a non-permeable vapor retarder was placed on the interior side of the 12-in. masonry mass wall, the dew point temperature and the temperature of the wall were within 1°F of each other (at an outside temperature of 85°F), thus posing the most risk of creating condensation in the wall.
All the dew-point analyses were run with a constant interior temperature of 72°F with a relative humidity (RH) of 50 percent and exterior RH of 85 percent. The calculations were run with exterior temperatures of 100°F and 85°F. When the outside air temperature was increased, the dew-point temperature was close to the wall temperature, creating a higher potential for condensation in the wall.
Because this project involves an existing, aged structure rather than new construction where conditions can be more tightly controlled, the vapor permeable air barrier is a more forgiving approach, allowing the wall to breathe. In addition, the dew-point analyses showed a greater risk for condensation in the exterior wall with a vapor impermeable air barrier.
In this case, the plan is to help keep the wall dry by actually allowing some vapor diffusion so that the moisture can escape and not build up in the wall. The permeable vapor air barrier keeps water bulk out but allows some vapor diffusion. Plus, the aged historic building is not “hermetically sealed,” as new construction might be.
Insulation: Spray Foam (Open or Closed Cell) or Other?
In addition, the insulation was also an important factor for preventing moisture build-up and still providing additional insulating value to support the sustainable approach. An application of spray foam insulation was considered.
There are two forms of spray foam insulations, open and closed cell. Both have pros and cons.
The open cell spray foam insulation is vapor permeable; more environmentally friendly for an interior application using a water-based blowing agent; has a soft, flexible composition; has an R-value of 3.7 per inch; is not meant to be exposed to bulk water; requires stable substrate (the existing masonry wall is rough in places); and does not qualify as an air barrier.
The closed cell spray foam insulation is an impermeable vapor barrier that meets the ASTM E2357 requirements of minimum 2.0 lb. density to also be considered an air barrier (thus not requiring application of liquid applied air barrier); requires special installation procedures; has a rigid, non-flexible composition and an R-value of 6.0 per inch; and can be exposed to bulk water.
Both spray foams did not completely address the issues. Therefore, extruded polystyrene (XPS) was considered. XPS allows vapor permeable application, more R-value than the open cell spray, is not damaged by bulk water, and can be applied to the unstable substrate of the existing wall. The application of 1-in. XPS rigid board sheathing (also adding an insulating R-value of 5) to the existing plaster wall with liquid applied vapor permeable air barrier was determined to be the best scenario for our described conditions.
The final proposed assembly of the exterior envelope is shown in Figure B.
Actions undertaken in restoring the San Jacinto Memorial Building include:
Removing the multiple layers of coating from the exterior masonry façade to expose original building intent;
re-pointing the masonry joints;
replacing the existing windows and doors with historically sensitive, energy-efficient windows and doors and treatment of existing lintels and minor masonry replacement and repair, including completely new window sill and jamb flashing;
adding a pre-manufactured metal coping system with factory pre-formed, mitered, and continuously welded corners;
applying 1-in. XPS rigid board sheathing (also adding an insulating R-value of 5) to the interior face of the existing masonry mass wall without disturbing the existing plaster;
the application of liquid vapor permeable air barrier to inside face of XPS; and
finishing with metal stud furr-out with painted gypsum board on interior, providing a chase for power and data for new technologies without disturbing the existing aged wall.
As part of the initial project research, considerable historical information has been discovered that has raised the building’s importance within the community, state, and nation. Based on the initial historical findings, HCC has decided to pursue a listing of the property in the National Register of Historic Places.
Although the San Jacinto Memorial Building has been remodeled and added onto several times during the last century, this project will dwarf those other renovations in scope and scale. When completed, the remodel will have recaptured the building’s architectural past while ensuring it has a long and productive future as a cutting-edge educational institution.
Lisa W. Lamkin, AIA, LEED-AP is a principal and Anne Hildenbrand, AIA, LEED-AP is a senior associate for BRW Architects, Inc.