Understanding Why Wall Systems Leak

By definition, “envelope” is an encapsulating covering such as an outer shell or membrane. In simple building terms, it consists of the roof, above-grade wall system and the below-grade wall system. An envelope’s purpose is to provide protection from external elements, which in building construction means protection from moisture, air and temperature ingress and egress.

The definition sounds simple enough, but in reality — because of the thousands of complex products and systems specified and the multiple trades involved — the chance of error is high when diagnosing a water infiltration event.

This article will focus on structures that have water infiltration and the building owners believe they have eliminated the roof as the issue and know that the problem is not below-grade. The assumption then is that the problem lies in the above-grade wall system.

An above-grade wall system is comprised of exterior components from the grade up to and including the parapet wall. A fundamental understanding of above-grade wall systems and how different systems manage water infiltration is paramount.

A wall system can be classified in general categories: barrier walls and water-managed walls. A wall system may have characteristics of both a barrier and a drainage wall in various combinations. As defined in ASTM E 2128:

Barrier Walls—The mechanism intended to prevent leakage in this type of wall is blocking or interrupting the movement of water to the interior.

Water Managed Walls—The mechanism intended to prevent leakage in this type of wall is the control and discharge of anticipated and accepted amounts of water that penetrates the exterior surfaces.

The year the building was built provides an instant insight as to how the wall system may manage water infiltration especially with masonry structures. Structures built before 1890 are usually load-bearing mass masonry barrier walls. The massive masonry walls function as a reservoir to absorb and evaporate water (barrier wall). Common from the 1890s until World War II are transitional hybrid walls. These walls function as a reservoir to absorb and evaporate water (barrier wall), but the embedded structural framing is subject to a moist environment.

Structures built after 1950 are generally considered modern curtain walls. With these designs, the exterior veneer employs a drainage plane that allows incidental water that penetrates the exterior to be captured and redirected (water managed wall).

In addition to knowing the year the structure was built and reviewing the original drawings, the need for a site inspection is critical. Although the building owner may feel confident about the information they provide, it is important to have a “trust but verify” mentality.

Determination of which wall system the building relies on to resist water infiltration starts with determining the original design intent. Visiting the site and determining the year of construction can help, but the key would be to find the original drawings. The team also must review any alterations and repairs to the structure to see if any work altered the original design intent.

Overall, the general inspection can be broken down into four basic steps:

• Initial Walk About
• Knowledge
• GatheringInterior Symptoms
• Exterior Signs

STEP I: INITIAL WALK ABOUT

Beginning with the wall system, walk around the structure to get an understanding of the shape and makeup of the structure, materials used, as well as any features like balconies, cornices or ornamentation. Also, check to see how the building is terminated at-grade. Next, continue to the roof to see the layout—if it has a parapet, how the roof is terminated to the parapet, how the roof is accessed, and the roof system type. Finally, continue to the below-grade area of the structure to look for sump pumps, smell for dampness and determine the foundation wall construction.

STEP 2: KNOWLEDGE GATHERING

Start by asking for a set of drawings. Hopefully, they are available, but with older structures, they may not be found. If this is the case, the team can interview the management, the maintenance staff and tenants, as well as review the maintenance and project files. Warranties for the roof, the window systems and the below-grade waterproofing system also are important.

Review sections with details on the wall systems to identify the wall system as a barrier wall or a water-managed wall. If it is unclear or if it seems to be questionable, become suspicious of the design details. Next, check the details. If insufficient details are pulled out of the wall sections to show how to create terminations, penetrations and changes of plane for all of the particular wall system building materials, it immediately throws up a flag. Unless the project had a high level of quality field craftsmen or really good inspectors, there may be some challenges in the way field decisions were made in order to make these details work.

Also, shop drawings should requested – especially for the windows if there is a curtain wall. From the window shop drawings, try to determine how the window system is managing water. A lack of wall details or the lack of shop drawings at any time makes Step 3, Interior Symptoms, more important.

For the roof, always look at the system type and check if the construction drawings of the roofing system match the existing conditions. If they don’t, has there been any modification or repair? If there has been a modification, what, if anything, has been done to the parapet wall? Because parapets are exposed to weather on three sides, there is a greater chance of them having problems, especially if the modifications did not take into consideration the original design intent. Identify the number of drains and whether there is an appropriate roof slope to drain. How the through-wall scuppers are detailed always should be reviewed, especially if the scupper outlet is directly at the vertical expansion joint. Last, locate the system specified for the below-grade waterproofing and see if any details were made on termination, penetration and changes in plane.

STEP 3: INTERIOR SYMPTOMS

At this point, if the building is exhibiting signs of interior water infiltration, severe cracking of interior finishes or both, use the observations gathered in Steps 1 and 2 to identify symptoms in the interior. Look for the following list of symptoms:

• Staining of the interior wall surfaces, the wall system above the ceiling tiles or both
• Water-damaged insulation above the ceiling tiles
• Stained ceiling finishes
• Water-damaged window soffits, jambs and sills
• Water stains on the floor finishes, including rust stains from excessively wet steel stud baseplates
• Peeling of wallpaper
• Cracking of interior finishes
• Stains/dirt in operable window tracks
• Water stains at the perimeter of the AC units
• Mold
• Odors

Document the location of any interior symptoms so that correlations can be made to any exterior symptoms found during Step 4. Because water does travel, symptoms often are not simply on the exterior of the building. ASTM 2128 Standard Guide for Evaluating Water Leakage of Building Walls provides a tremendous resource.

STEP 4: EXTERIOR SIGNS

Once information has been gathered from the previous three steps, the inspector will have a better understanding of what to focus on during the review of the exterior signs. For walls, the obvious big three are bulging, spalling and cracking. Following is a partial list of other exterior signs to consider:

• When the wall system has a cavity wall but the flashing cannot be seen. Note, even if drawings and inspection drawings indicate a flashing, if the flashing cannot be seen to the naked eye in the field, the installation and or functionality is suspect.

If any of these signs match with any symptoms identified in the previous steps, there is a very good chance that the building envelope faces some challenges. The exterior signs without interior symptoms do not mean there is not a challenge; however, – it’s just a matter of time. In most cases, the interior symptom will occur at some point in the life of the structure, so it is important to continue to monitor these conditions.

While obvious building envelope problems are easy to identify, in order to identify the not-so-obvious signs, especially if the interior symptoms have not occurred or have not been identified, experience in the restoration of building envelope deficiencies is priceless. Combining this experience with the knowledge of architectural details, engineering basics, good waterproofing practices and the inspection plan as outlined above will give the owner the best possible information about the building envelope. The information can be used as a tool to purchase a building, create capital projects or develop a maintenance plan.

DILLON COUNTY CASE STUDY

The Dillon County Courthouse (DCC) located in Florence, South Carolina was built in 1911 and was built with a barrier wall system. Water infiltration, structural deterioration, façade distress, and leaks were reported and thought to be associated with a defective roof system. The above- grade wall system consisted of load-bearing brick, terra cotta, and carved stone masonry and the roof system consisted of a two-ply modified bitumen membrane applied over a well-sloped wood plank deck.

The roof system at the property consisted of modified bitumen membranes applied over a sloping wood roof deck system. The facility managers had been dealing with water infiltration at the upper floors of the building for many years. The roof system had reportedly been replaced several times, but the leaks continued. In 2008, the contractor was asked to review the façade and roof system. STRUCTURAL requested that the building envelope design professional assist them in assessing the issues, developing repair construction documents and reviewing the installed work.

During the initial inspection (which followed the steps outlined above), façade distress was noted at numerous locations – mainly associated with the parapet wall. The roof membrane had been extended up the backside of the masonry parapet wall, but no through-wall flashings were installed at the parapet. Numerous blisters and other deficiencies were noted in the roof system and leaking drains and gutters were also noted. The contractor and engineer determined that the source of the leaks was mainly related to deficiencies at the parapet wall.

The parapet wall had been modified several times, but the previous repair attempts did not reflect a through understanding of the wall system and how the parapet functions as a part of the wall system as well as an overall part of the building envelope.

PARAPET WALL REPAIRS

Upon removal of the vertical wall flashings, the suspicions of the contractor and engineer were confirmed – the masonry parapet had been saturated with moisture because the flashings prevented drying. The uncovered masonry was found to be previously painted and parged as well, which also may have contributed to additional moisture retention. Once the walls were uncovered, they were allowed to dry and the masonry was verified to be sound.

The terra cotta coping was removed at the entire perimeter of the building and a new continuous copper through-wall flashing was installed beneath the terra cotta. Each section of terra cotta was numbered, stored, cleaned, and then re-installed over the new flashings. New stainless-steel cleats were installed by using traditional dovetail stone anchors in a horizontal application. The cleats were necessary in order to prevent the terra cotta from sliding on the flashings. Once the terra cotta was re-set, the skyward facing joints were sealed with caulking over backer rod and the sealant joints were protected with an embedded lead cap.

RAINSCREEN CLADDING

As a counter-flashing for the roof system, protection for the masonry and as a mechanism to allow the masonry to dry, a metal rainscreen was installed on the backside of the parapet. A 30-pound building felt was placed over the wall as a drainage plane behind the metal panels. Steel hat channels were attached to the masonry using nail-in expansion anchors and the metal panels were secured to the hat channels using standing-seam metal roof system clips.

The installation of the rainscreen met the goal of allowing the parapet to dry out while keeping the driving rain from saturating the masonry. Because of the intricate nature of the parapet wall, numerous transitions and various panel sizes were necessary. A patina green copper finish was selected to maintain a historic appearance consistent with this building’s age. Once the rainscreen was installed, the new through-wall flashing beneath the terra cotta coping was used as a counter-flashing for the top of the rainscreen, and capped off the system.

CONCLUSIONS

The Dillon County Courthouse project was completed in January 2010. The project that took nearly two years to plan only took about four months to complete, including the mock-up process. By working as a design-build team, the engineer and contractor expedited the process and could effectively address unforeseen conditions as a team during construction. The end result of the project did include the replacement of a roof system; however, the replacement of the roof alone would not have addressed the challenges.

The parapet wall repairs and the installation of the rainscreen were the critical component of the project. Development of the approach as a team effort convinced the owner to proceed with this repair and detailed explanations of the building science behind the repairs enhanced the owner’s knowledge about the project. The end product addressed the issue and restored the facility to a watertight condition.

SUCCESS WITH MOCK-UPS

Mock-ups – a detailed, full-scale sample of part of a project to be completed — were an important part of the construction process. In this case, mock-ups were not just part of the submittal process in order to verify the contractor’s ability to install a given product in accordance with the specifications; they also provided the owner with a sample of the final product, so that they could understand what they would eventually be purchasing.