A Design Review of Waterproofing Codes

Transcription

1 A Design Review of Waterproofing Codes Section 1807 of Chapter 18 of the International Building Code addresses waterproofing under the section title of Dampproofing and Waterproofing. The section defines the essentials of waterproofing design as when it is to be applied, where to apply it and drainage issues. The code also provides a good description of what is considered waterproofing and what is considered dampproofing, while defining where they are required. The intent of this article is to include some of the waterproofing codes that pertain to design elements and provide interpretation Where required. Walls or portions thereof that retain earth and enclose interior spaces and floors below grade shall be waterproofed and dampproofed in accordance with this section. With the exception of those spaces containing groups other than residential and institutional where such omission is not detrimental to the building or occupancy. Ventilation crawl spaces shall comply with Section This section implies that all occupied below-grade spaces require the application of a waterproofing or dampproofing material. The exception is to all unoccupied spaces. Once is has been determined that waterproofing or dampproofing is required the next important decision is to determine where it is required. Typically, waterproofing or dampproofing should be applied over all below grade concrete surfaces (walls and floors). There are several established building components that require waterproofing or dampproofing protection, they are: Underground structures Elevated structural slabs over underground spaces Structural slabs below grade Structural slabs above grade Foundations Lagging walls Plazas Terraces Promenades Planters

2 Ground-water control. Where the ground-water table is lowered and maintained at an elevation not less than 6 inches (152 mm) below the bottom of the lowest floor, the floor and walls shall be dampproofed in accordance with Section The design of the system to lower the ground-water table shall be based on accepted principles of engineering that shall consider, but not necessarily be limited to, permeability of the soil, rate at which water enters the drainage system, rated capacity of pumps, head against which pumps are to operate and the rated capacity of the disposal area of the system. This section implies that dampproofing is required if the water table is maintained a minimum of six (6) inches below the bottom of the structure. If the water table is maintained within six (6) inches of the bottom of the structure or if hydrostatic pressure exists, than waterproofing is required. It is the designer s responsibility to review site-engineering analysis for water table conditions and soil analysis to determine if and what type of dampproofing or waterproofing is required. The section also implies that the ground-water table must be lowered by implementing a drainage system that is designed to meet the following engineering principles: 1. Permeability of the soil 2. Rate at which water enters the drainage system 3. Rated capacity of the pumps 4. Head against which pumps are to operate 5. Rate capacity of the designed area of the system Dampproofing required. Where hydrostatic pressure will not occur as determined by Section , floors and walls for other than wood foundation systems shall be dampproofed in accordance with this section. Wood foundation systems shall be constructed in accordance with AF&PA Technical Report No. 7. This section implies that dampproofing is required to all below grade floors and walls where hydrostatic pressure will not occur. ASTM defines dampproofing as the treatment of a surface or structure to block the passage of water in the absence of hydrostatic pressure. Fundamentally, it only has the ability to resist vapor migration. If soil analysis concludes that there is no hydrostatic pressure or if the water table is more than six (6) inches below the lowest floor, than dampproofing may be considered.

3 Dampproofing is always applied at the exterior (wet) face of the wall. The most common dampproofing material for walls is a bituminous coating, either solvent-based (cutback asphalt) or emulsion, brushed, sprayed, roller-coated or troweled on the substrate. Dampproofing systems may also include membranes. The general difference between waterproofing systems and dampproofing systems is that dampproofing membranes maximize at 10-mil film thickness and waterproofing membranes exceed this thickness. The section also implies that wood foundations shall be constructed in accordance with AF&PA Technical Report No. 7, Basic Requirements for Permanent Wood Foundation Systems Waterproofing required. Where the ground-water investigation required by Section indicates that a hydrostatic pressure condition exists, and the design does not include a ground-water control system as described in Section , walls and floors shall be waterproofed in accordance with this section. This section implies that a waterproofing application is completed when the site ground water table is maintained at an elevation of not less than six (6) inches below the bottom of the ground slab. The section states that waterproofing is required when hydrostatic pressure will occur. It is the responsibility of the architect or designer to make certain that the waterproofing component is in compliance with the applicable Federal, State or Local codes. The primary distinction of the codes in regards to water table and hydrostatic pressure. A proper engineering study of the grounds is required to establish this criterion for the design phase. ASTM states that dampproofing or waterproofing is required for slabs on ground and foundation retaining walls Floors. Floors required to be waterproofed shall be of concrete and designed and constructed to withstand the hydrostatic pressures to which the floors will be subjected. This section implies that all floors that require waterproofing shall be constructed of concrete and shall be of structural integrity to withstand hydrostatic pressure. The waterproofing applied to the floors shall consist of one of the following membranes: Rubberized asphalt Butyl Rubber Fully adhered/hdpe 6-mil+ polyvinyl chloride (PVC) The membrane joints shall be lapped a minimum of six (6) inches and shall be applied in accordance with the membrane manufacturers latest printed requirements.

4 Walls. Walls required to be waterproofed shall be of concrete or masonry and shall be designed and constructed to withstand the hydrostatic pressures and other lateral loads to which the walls will be subjected. This section implies that all walls that require waterproofing shall be constructed of concrete or masonry and shall be of structural integrity to withstand hydrostatic pressure and lateral loads. The waterproofing applied at the walls shall consist of one of the following membranes: Two-ply hot moped felts 6-mil+ polyvinyl chloride (PVC) 40-mil polymer modified asphalt 6-mil polyethylene The waterproofing should be applied a minimum of 12 inches above the highest point of the ground water table. The membrane joints shall be lapped in accordance with the membrane manufacturers latest printed requirements Surface preparation of walls. Prior to the application of waterproofing materials on concrete or masonry walls, the walls shall be prepared in accordance with Section This section implies that the wall substrate must be properly prepared to receive waterproofing materials. The wall must be free of all voids, openings, cracks, honeycombs, fissures and other imperfections prior to the application of the waterproofing material. Concrete walls can be repaired using bituminous materials or other products approved by the material manufacturer. Masonry walls shall be parged below ground level on the exterior surface using not less than inch (9.5 mm) of Portland cement. The only exception is approved for application directly to the masonry 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.

5 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.

6 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 Subsoil drainage system. Where a hydrostatic pressure condition does not exist, dammproofing shall be provided and a base shall be installed under the floor and a drain installed around the foundation perimeter. A subsoil drainage system designed and constructed in accordance with Section shall be deemed adequate for lowering the ground water table. This section implies that a subsoil drainage system is required in instances where hydrostatic pressure does not exist. The subsoil drain shall be installed by applying a base layer under the floor and installing a drain around the foundation perimeter. Proper below-grade waterproofing design must include a system for collecting, draining, and discharging groundwater away from the structure. The most effective way to properly collect and discharge groundwater is through the use of foundation drains. Foundation drains can be field-constructed drainage systems or prefabricated soil drainage systems.

7 Field-constructed drainage systems consist of a perforated pipe (typically PVC) that is set in a bed of gravel at the bottom of the foundation. The perforation in the pipe is applied downward to allow the water to flow into the gravel bed. A drainpipe is installed next to the structure slightly above the bottom of the foundation to prevent the soil under the foundation from washing away. The pipe is set to slope the water towards drain fields, bare soil or sump pits. A layer of coarse gravel is set around the drainage pipe for additional water accumulation. In some cases, meshes and/or mats can be applied over the top gravel layer to prevent soil build-up from interfering with water flow to the drainage system. The biggest disadvantage with these systems is that they rely on proper field construction (not always completed properly) and over time they become clogged with dirt, soil and contaminants. It is the designer s responsibility to review site-engineering analysis for water table conditions and soil analysis to determine if and what type of dampproofing or waterproofing is required. The section also implies that the ground-water table must be lowered by implementing a drainage system that is designed to meet the following engineering principles: 1. Permeability of the soil 2. Rate at which water enters the drainage system 3. Rated capacity of the pumps 4. Head against which pumps are to operate Rate capacity of the designed area of the system Foundation drain. A drain shall be placed around the perimeter of a foundation that consists of gravel or crushed stone containing not more than 10-percent that passes through a No. 4 (4.75 mm) sieve. The drain shall extend a minimum of 12 inches (305 mm) beyond the outside edge of the footing. The thickness shall be such that the bottom of the drain is not higher than the bottom of the base under the floor, and that the top of the drain is not less than 6 inches (152 mm) above the top of the footing. The top of the drain shall be covered with an approved filter membrane material. Where a drain tile or perforated pipe is used the invert of the pipe or tile shall be placed higher than the floor elevation. The pipe or tile shall be placed on not less than 2 inches (51 mm) of gravel or crushed stone complying with Section , and shall be covered with not less than 6 inches (152 mm) of the same material.

8 This section provides the requirements for foundation drain placement. requirements and provides a basis for design: The section is precise in the Foundation Drain: 1. Apply a drain around the perimeter of the foundation that consists of gravel or crushed stone. The gravel or crushed stone shall be a minimum of 4.75 mm or larger. 2. The drain shall extend a minimum of 12 inches (305 mm) beyond the outside edge of the footing. 3. The thickness shall be such that the bottom of the drain is not higher than the bottom of the base under the floor, and that the top of the drain is not less than 6 inches (152 mm) above the top of the footing. 4. Cover the top of the drain with an approved filter material. 5. If a drain tile or perforated pipe is used the invert of the pipe or tile shall be placed higher than the floor elevation. 6. The pipe or tile shall be placed on a minimum of two (2) inches of gravel or crushed stone. The gravel or crushed stone shall be a minimum of 4.75 mm or larger Backfill. The backfill in the annular space around columns not embedded in poured footings shall be by one of the following methods: 1. Backfill shall be of concrete with an ultimate strength of 2,000 psi (13.8 MPa) at 28 days. The hole shall not be less than 4 inches (102 mm) larger than the diameter of the column at its bottom or 4 inches (102 mm) larger than the diagonal dimension of a square or rectangular column. 2. Backfill shall be clean sand. The sand shall be thoroughly compacted by tamping in layers not more than 8 inches (203 mm) in depth. 3. Backfill shall be controlled low-strength material (CLSM). This section implies that backfill material shall be in accordance with code requirements. This section was originally contained in the Waterproofing and Dampproofing Section of the BOCA code. In it s original form it addressed backfill around foundations a pertinent component of a waterproofing application. Therefore, it provides relevance and requires addressing from a waterproofing perspective. This section implies that the excavation outside of the foundation shall be backfilled with soil that is free of all organic material, construction debris and large rocks. The backfill shall be placed in lifts no more than 8 inches (203 mm) in depth and compacted or tampered in a manner that has no adverse effect or cause damage to the substrate or the waterproofing or dampproofing material.