SECTION 1807.3.3

JOINTS AND PENETRATIONS

Joints in walls and floors, joints between the wall and floor and penetrations of the wall and floor shall be made water-tight utilizing approved methods and materials.

CODE INTERPRETATION

This section implies that all wall and floor joints must be properly waterproofed. Waterproofing application at joints includes approved sealants. Proper sealant application is completed using proper materials and application methods.

The success of the construction sealant is based on proper selection and use of the various sealant materials for a specific application. Sealant selection should be based on the adhering substrates. General recommendations for sealant selection typical in roof applications are as follows:

• Concrete-to-Concrete: Two-part Polyurethane
• Brick-to-Brick: Two-part Polyurethane
• Metal-to-Metal: Perimeter Silicone Sealant
• Metal-to-Brick: Perimeter Silicone Sealant
• Metal-to-Metal: Perimeter Silicone Sealant
• Metal-to-Brick: Perimeter Silicone Sealant

The sealant must have the ability to move with the adjacent building substrates while maintaining a watertight barrier. In application it is generally discovered that a thin bead of sealant will accommodate more movement than a thick bead. In joints where excessive movement is expected the building sealant should be no thicker than 1/2-inch and no thinner than 1/8-inch.

At typical building joints the ratio of joint width to sealant depth should be a minimum of 2:1. At building expansion joints the designed joint should be at least twice the total anticipated joint movement. However, due to construction tolerances and material variations it is recommended that the joint design be four times the anticipated movement.

Preparation of the Joints

The joint must be thoroughly cleaned prior to any sealant application. This can be completed by removing all foreign matter and contaminants such as grease, oil, dust, water, frost, surface dirt, old sealants and protective coatings.

Porous substrates can be cleaned by grinding; blast cleaning (sand or water) saw cutting or mechanical abrading. A combination of these cleaning methods can also be utilized. All dust and loose particles from these cleaning operations must be removed by vacuum or compressed air to leave a dry, clean surface for sealant application.

Metal, glass and plastic surfaces can be cleaned with mechanical or solvent procedures. Check the manufacturers latest printed specifications for the use of detergent or soap and water treatments, they are generally not allowed as suitable cleaning methods. Solvents should be wiped off with clean, oil- and lint-free cloths.

Masking

All areas adjacent to the building joints should be masked prior to sealant application. This is to allow for neat sealant lines. Masking the adjoining surfaces also guards against sealant contact with any incompatible surfaces. Uncured sealants can leave a film on a surface that may change the aesthetic surface characteristics of the substrate. In some cases, the only method of sealant removal may be grinding or saw cutting. Generally these surfaces can be cleaned with special cleaning solvents.

The masking should be removed immediately following the tooling of the sealant.

Sealant Application

Install all back up material or joint filler prior to sealant application. Backer rods and joint filler material must be in accordance with the manufacturers latest printed specifications. Open cell polyurethane foam or closed cell polyethylene are the recommended back up materials for most joints. Polyethylene tape may be used for joints that are too shallow for backer rod.

The sealant should be applied in a continuous operation using positive pressure to properly fill and seal the joint. Tooling should be completed in a continuous stroke immediately after the sealant application prior to the formation of the sealant skin. The sealant should be tooled with light pressure to spread the material against the back up material and the joint surfaces.

The tool should have a concave profile to keep the sealant in the joint. Contrary to popular opinion, a finger is not the proper tool for sealant application.

DAMPPROOFING AND WATERPROOFING

SECTION 1503.2  

FLASHING

Flashing shall be installed in such a manner so as to prevent moisture entering the wall and roof through joints in copings, through moisture-permeable materials and at intersections with parapet walls and other penetrations through the roof plane.

Section 1503.2.1 Locations: Flashing shall be installed at wall and roof intersections, at gutters, wherever there is a change in roof slope or direction and around roof openings. Where flashing is of metal, the metal shall be corrosion resistant with a thickness of not less than 0.019-inch (No. 26 galvanized sheet.)

CODE INTERPRETATION

These codes imply that flashings are required at all transitions, walls, perimeter areas and at all roof penetrations. The code provides requirements for metal flashings—“the metal shall be corrosion resistant with a thickness of not less than 0.019 inch (No. 26 galvanized sheet.)”—however; it is the responsibility of the designer to provide proper flashing materials. It is a best practice to use the system manufacturer’s flashing materials for system compliance.

The flashing element is the most vulnerable part of any roof system because it is the point at which the horizontal roof deck and vertical surface join. It is also the intersection of two different materials, such as at parapet walls. Flashings are also vulnerable because they are applied around all roof penetrations such as skylights, HVAC units, vents, expansion joints and all other areas where membrane is interrupted or terminated. The primary purpose of the flashing element is to seal the membrane at all edges; a task that is difficult enough without bearing any design inadequacies.

The material selected should have an in-service life expectancy that meets or exceeds that of the membrane. This is an important characteristic because the flashing generally has to perform in more severe conditions than the membrane. The selection of inferior materials to save money up front generally results in severe economic losses due to premature failures.
If the flashing material specified does not conform to the roof system and surface that it is attached to, then even the most detailed flashing plans will fail. It is essential that this material is compatible with all adjoining materials and that it has the capability and durability to last the lifetime of the system.

The material must also have the ability to withstand all thermal and load induced movements. An allowance must be made for differential movement between the membrane and all other parts of the application. Base flashing should not be anchored to parapet walls, unless the parapet and the substrate are continuously connected and cannot expand or contract independently. Counter flashings should not be connected to base flashings unless the possibility of relative movement between them can be positively prevented. If the flashing material cannot sustain the strains of the roofing system movement, cracks and tears will develop and deteriorate the flashing.

ROOFING

Building Enclosure  |  BuildingEnclosureOnline.com  |  Spring 2024

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