PERFORMANCE REQUIREMENTS AND CRITERIA FOR BASEMENT ENVELOPE SYSTEMS AND TESTING N. SAHAL, E. OZKAN

CIB World Building Congress, April 2001, Wellington, New Zealand Page 1 of 11 PERFORMANCE REQUIREMENTS AND CRITERIA FOR BASEMENT ENVELOPE SYSTEMS AND TESTING N. SAHAL, E. OZKAN Istanbul Technical University, Faculty of Architecture, Istanbul, Turkey ABSTRACT Basement can be a difficult environment in which to build a livable space. It is surrounded by soil that may be damp, wet or frozen. The temperature of the ground surface remains nearly in phase with that of the air, however; below surface, in summer it decreases and in winter it increases linearly with depth. Basements are exposed to dead and live loads of the building as well as the lateral soil loads and sometimes the hydrostatic pressure due to the high levels of groundwater. Therefore, below grade envelope systems are subjected to more temperature changes, structural and moisture loads than that of the above grade; yet, the interior environment is expected to be the same. Basement problems occur because of the poor concordance between users expectations of basements, their construction and the environmental forces with which the basements must meet. Solutions that reduce both building and operational costs while improving indoor environment can only be achieved by establishing performance requirements for basement envelope systems. And also, predicting the behavior of the system under actual in-service conditions by performance test methods. In this paper; the user requirements for basements and the functions of the basement envelope systems are established. The thermal and moisture regimes as well as the structural loads of the basement envelope systems related to the inside and outside environmental agents are identified. The resulting structural and environmental problems are reviewed. How the basement envelope systems are expected to perform under which circumstances are laid out as the performance requirements of the system. The performance criteria of the materials within the envelope system that address the performance requirements is determined. A test method which has been developed to evaluate the performance of strained bituminous waterproofing membranes under hydrostatic pressure is mentioned as an example for performance testing. Finally, the test results are presented and evaluated on the basis of whether the requirement and criteria are attained. KEYWORDS: Performance requirements; performance criteria; performance testing; basement envelope systems; waterproofing. INTRODUCTION Basement is somewhat invisible and the envelope is sometimes ignored component of the building. Until now, the primary concern of the designer and the builder was to meet the safety requirement of the user; therefore, the only function of the basement envelope was established as structural adequacy. The user requirements such as health and comfort were ignored or the environmental agents that affected the basement envelope were not fully recognized; thus, less attention was given to separate the basement indoor climate from the outdoor soil climate. As the basement envelope was exposed to below-grade environmental agents, it often failed to respond to the them and its performance proved to be unacceptable. Leaky and damp basements, cracked walls, frost-heaved walls, the smell of mould and mildew were some of the leading basement problems. These problems not only damaged the basement envelope materials but they also represented a real health hazard. On the other hand, the occupants of most buildings expected that the basement indoor climate would provide a prime living space. In order to achieve an effective control of indoor climate, the occupants took some precautions such as using humidifiers during the winter and dehumidifiers during the summer to maintain an acceptable indoor relative humidity, re-excavating the soil around leaky basements, using extra

CIB World Building Congress, April 2001, Wellington, New Zealand Page 2 of 11 equipment for heating and cooling and in extreme cases, rebuilding the basement envelope. In the end, the cost of these precautions passed on to the homeowners. Therefore, the occupants increasingly demanded that the basement envelope should provide an effective environmental separation besides structural adequacy. Today s home buyers want a healthy and energy-efficient home which they can not only afford to buy but, also afford to live in. In order to develop a better understanding of the intended role that is to be played by the basement envelope for the people designing and constructing it, the need to establish performance requirements and criteria as well as developing performance evaluating techniques for the systems and the materials have arisen. PERFORMANCE REQUIREMENTS FOR BASEMENT ENVELOPE SYSTEMS The aim is to build a livable and usable basement indoor environment that satisfies user requirements. The user requirements for basements are determined as thermal comfort, safety and tightness. The other user requirements, such as visual comfort, acoustic comfort, hygiene, etc. are excluded as they are usually treated in the context of the entire building. According to the specified user requirements, the overall function of the basement envelope system, in conjunction with above-grade, is to provide environmental separation, strength and stability to the loads of the building and structural support to the loads that are generated from environmental agents such as groundwater. The basement envelope system can be capable of functioning as intended, if performance requirements are satisfied. Performance requirements for basement envelope systems are developed from the performance analysis of the system; where the environmental agents that affect the system are identified, they are than related to the corresponding properties of the system and the processes involved in the interaction of the system with its environment are analyzed, as the moisture regime, thermal regime and the loads of the system. The moisture regime of the basement envelope system The environment that surrounds the basement envelope is the soil mass and the indoor climate; therefore, the sources of water that build up the moisture regime of basement envelope system are splash water, water vapor in the soil, seepage water, capillary water, groundwater, adsorbed water, moisture in concrete after construction, exterior humid air that enters the basement and condenses on cooler surfaces and water vapor from interior sources, Figure 1. The forces which drive the moisture into the openings in the building envelope from the exterior are, gravitational forces, capillary suction, vapor pressure and differences in air pressure. Differences in air pressure and vapor pressure are also responsible for the penetration of moisture into the openings in the basement envelope from the interior. Figure 1. The Moisture Regime of the Basement Envelope System

CIB World Building Congress, April 2001, Wellington, New Zealand Page 3 of 11 Seepage water is the water that drains from the soil after a rainfall by the force of gravity acting on it. Water seeping along the basement wall-soil interface may find an easier path along a crack through the basement wall and penetrate into the basement envelope due to the gravity. When seepage water collects within the pores of the soil on a strata, the forces of gravity cause a build up of hydrostatic pressure within the bulk water. When groundwater stands against the basement walls and floor, hydrostatic pressure will develop which can force large quantities of water through pores of the material used in the envelope into the basement. Capillary water is the water that moves by capillary forces above the water table. This water may be drawn into the porous materials used in the basement envelope under the action of capillary suction. Once in the wall or floor, the capillary water can evaporate to the interior of the basement. Capillary suction is related to the porosity of the materials used in the envelope as well as the fine cracks in the envelope. Dampness of basements is often attributable to capillary water. Splash water may deposit a film of water on the above-grade portion of the basement wall and porous materials may also draw the water into the envelope by capillary suction. The air in the soil and the air in the basement contain water in the form of vapor. At times, vapor can diffuse from the wetter soil through the envelope toward the dryer basement interior, at times from the basement toward the soil and most of the time both kinds of diffusion are found at the same time but in different parts of the basement envelope; the driving force being the vapor pressure differential. In most houses, a stack effect is created when warm air in the basement rises. This induces a negative pressure on the basement and draws vapor in the soil in through any cracks in the basement envelope. Adsorbed water is water that is relatively firmly held by surface forces developed between the polar water molecules and hydrophilic materials. The amount held by a surface in this state depends on the relative humidity of the environment. It is responsible for part of the water diffusion through building materials. It plays an significant part in moisture in construction and seasonal storage of water in building materials. In summer time, basement windows may be opened for fresh air. If the outside air is warm and humid, it will condense on the cool basement wall and floor surfaces. Leakage will occur on the surface of the wall or condensed water will accumulate on the floor. Water added to fresh concrete performs two functions; to provide workability and to react chemically with the cement. Unfortunately, the amount of water required for workability exceed the amount required for chemical reaction. Most of the unreacted water will be lost by drying. The moisture regime of the basement envelope system often results in moisture problems such as decay of organic and inorganic materials, water leaking on walls, standing water on floor, dampness, humid air, odor, mould and mildew, deterioration of basement finishing materials, efflorescence, etc. The thermal regime of the basement envelope system Besides the moisture regime, the thermal regime also influences the performance of basement envelope system. The environmental agents that build up the thermal regime of the system are soil temperature and basement indoor air temperature. Soil temperature is affected by many factors; terrain features such as vegetation and slope orientation, the properties of soil such as thermal conductivity and water content, and meteorological elements, primarily, snow, solar radiation and air temperature. Outdoor air temperature changes from day to night, from day to day and from season to season. Soil temperature also varies, only here the rate of change is slow while the amplitude of change is reduced. Soil temperature change reflects outdoor air temperature change, only here it can take a long time before air temperature change is reflected in the soil; the farther we go from the soil surface the longer it takes. The time lag is due to the thermal inertia of the soil and its water content. The time lag is minimal close to the ground surface. Assuming that the basement air temperature and humidity are the same as those outdoors in winter and in summer and the temperature of the uninsulated basement envelope approaches the temperature of the soil adjacent to it; in winter, the soil temperature between the basement floor and usually one meter below grade is usually higher that the basement air temperature, so that heat flows from the soil into the basement interior. In summer, it is in the opposite direction to the heat flow in winter. In both cases, the energy consumed for heating and air-conditioning increases. The temperature of the soil adjacent to the basement envelope is important not only because of its impact on heating and airconditioning loads but also because it has an effect on the direction of vapor diffusion between the soil and the basement interior. In summer, warm, moist air in the basement interior may condense on cold wall and floor surfaces as the soil temperature may be below the dewpoint temperature of the outdoor

CIB World Building Congress, April 2001, Wellington, New Zealand Page 4 of 11 air. Further, in winter, vapor in the relatively warm moist soil may diffuse through the basement envelope into the basement interior, in response to a vapor pressure gradient which is in the opposite direction to the summer gradient. In winter and in summer, the materials used in basement walls will experience different thermal movements varying with depth in response to the variation of soil temperature with depth. Further, the maximum soil temperature difference between winter and summer occurs 0.05 m. below grade; therefore, the basement wall may undergo the highest thermal movement at this depth, Figure 2. If these thermal movements are restrained, stresses may induce within the material or between the materials used in the wall, resulting in deformations such as crack formation. Figure 2. The Thermal Regime of the Basement Envelope System The loads of the basement envelope system The loads that affect the basement envelope system are the dead and live loads of the above-grade structure, lateral soil loads, hydrostatic pressure due to the high level of groundwater and heaving pressures that is generated from frost action. One of the loads acting on basement wall is the sum of the dead, live and wind loads of the above-grade structure which is transferred to it vertically. Besides, the basement wall and floor have self-loads; their own weight and user loads. Basement wall is also exposed to the lateral loads from the soil. The lateral loads on the wall depend on the height of the fill, the soil type, soil moisture content and whether the building is located in an area of low or high seismic activity. If groundwater exists, water may exert hydrostatic pressure against the basement wall and floor area depending on the height of the water table, Figure 3. If the sum of the water pressure and the bearing capacity of the soil which has lessened as much as the water pressure exceed the dead load of the building, the building may float. When the basement envelope can not withstand the vertical, lateral, hydrostatic pressure and self loads and can not transfer the loads to the ground in such a way that the stresses developed in the material are not within the safety limits of strength of these materials and within the safety limits of soil bearing capacity, deformations may occur. The deformations which lead to basement envelope failures are bowing, vertical or horizontal cracking of basement walls or floor and distortion of window and door frames. Frost heaving of unheated basement may occur if the envelope is placed above the frost line. During ice lens growth at the frost line, most of the volume change results in an upward displacement of the frozen layer. The heaving displacements are transmitted to the envelope and displacements of the basement envelope occur unless the dead load of the building exceed the uplift force. Adfreezing may occur if the soil freezes to the surface of the wall of the unheated basement. Heaving pressures developing at the base of the freezing zone are transmitted through the adfreezing bond to the basement wall, producing uplift forces capable of vertical displacements which leads to structural damage.

CIB World Building Congress, April 2001, Wellington, New Zealand Page 5 of 11 Figure 3. The Loads of the Building Envelope System Basement problems occur because of the poor concordance between occupants expectations of basements, their design and construction and the environmental agents which the envelope must contend. In order to avoid the failures, how the envelope is expected to perform under the dictated conditions to satisfy the user requirements, must be stated. The statements are the performance requirements for the basement envelope system which are given in Table 1. As there are various building systems, the two functions of the basement envelope system which are to provide strength and stability to the loads of the building and structural support to the loads that are generated from environmental agents are considered separately. In a load-bearing wall structure, the basement wall serves as the structural as well as the external division element; therefore, it must fulfill both functions. On the other hand, in a framed structure, the structural component of the basement wall is the column which must fulfill both functions; while, the external division element must only provide structural support to the loads that are generated from the environmental agents. Durability is a major issue in basement envelope systems. Basement envelope system must create a protective environment for its components where they will be able to preserve their properties without any degradation and perform as intended over the service life of the system. PERFORMANCE CRITERIA FOR THE COMPONENTS OF BASEMENT ENVELOPE SYSTEMS The performance requirements are the key elements of the envelope design. In the design process, the performance requirements that will be addressed must be determined according to the intended use of the basement and the external agents. For instance, if the basement will serve as a structural foundation only, then the envelope must be designed to address the performance requirements related to the structural functions. The floor which separates the basement and indoors is now the envelope that must address all performance requirements. The envelope has a structural component which must resist the vertical loads of the above-grade structure, lateral soil loads, hydrostatic pressure due the groundwater and self-loads and must transfer the loads to the ground safely in such a way that the stresses developed in the material are within the safety limits of the strength of these materials, the bearing capacity of the soil is not exceeded and the settlement of the structure is not excessive. For frost-heaving and adfreezing to occur, there must be three conditions; the soil must be frost-susceptible, water must be available in sufficient quantities and cooling conditions must cause the water and soil to freeze. If any one of these factors can be controlled, frost action can be prevented. Since it is seldom economically possible to control soil temperature, frost action is usually prevented by separating the envelope from the surrounding soil with a drained zone of material such as gravel or a thermal insulation material installed on the exterior of the wall.

CIB World Building Congress, April 2001, Wellington, New Zealand Page 6 of 11 The penetration of seepage water into the basement wall can be prevented by controlling the amount of rainwater or surface water entering to the soil adjacent to the basement wall, controlling the number of openings or holes in the wall and/or controlling the driving force which is gravity. In order to control the amount of rain or entering to the soil adjacent to the basement wall, overhangs must be designed around the perimeter of the roof, gutters must collect rainwater falling on the roof and downspouts must direct water away from the soil adjacent to the basement wall. Ground must slope away from basement wall in order to redirect surface runoff. An impermeable material must be used for backfilling the upper portions of the basement wall. Gravity can be controlled by the use of a drain screen immediately adjacent to the basement wall linked to the perimeter subsurface drainage system. The most common examples of the drain screen is free-draining backfill material, drainage mats and thermal insulation materials with drainage properties. A dampproofing material can be installed on the exterior of the basement wall to eliminate the openings or holes in the wall. The dampproofing material must also be linked to the perimeter subsurface drainage system where perforated drainpipes in a gravel bed along the footing or beneath the slab are located to drain water to a sump. These strategies will also prevent the development of groundwater in the soil adjacent to the basement wall and floor; but, in sites where groundwater already exists, the penetration of water into the basement envelope will be prevented by the provision of a continuous waterproofing membrane installed on the exterior of the basement wall and floor. surface drainage must also be provided to prevent the rising of the water table. A designer can prevent the penetration of capillary water into the basement envelope by controlling the availability of capillary water, sealing capillary pores, and/or making capillary pores larger. The traditional way is to use a material that does have any pores such as a dampproofing material applied onto the exterior surface of the wall where it breaks the capillary continuity between the soil and material used in wall; or to use materials that does not support capillarity as a result of their large pore size such as granular pad placed under the floor slab. The control of heat flow is an essential element of environmental separation. All the components of the envelope have more or less thermal resistance and all of them are involved in heat transfer. But, an effective thermal resistance of the assembly can be achieved by the provision of a continuous thermal insulation material with adequate thermal resistance within the envelope. The key question in the design process is whether to place the insulation inside or outside the basement wall and floor. Rigid insulation placed on the exterior surface of a wall and floor has some advantages over the interior placement in that it can provide continuous insulation with no thermal bridges, protects and maintains the other components of the envelope, minimizes moisture condensation problems, prevents thermal movements and does not reduce interior basement floor area. Interior insulation is an alternative to exterior insulation and it is mostly popular for retrofit situations. It is simpler to install on existing wall and floor and thermal insulation material costs may be low since almost any insulation material may be used. In general, vapor diffusion retarders are located on the exterior of the wall to retard the inward flow of vapor by diffusion from the surrounding soil into the basement interior. Dampproofings typically have high resistance to vapor flow; therefore, they act as vapor diffusion retarders. Vapor diffusions from the surrounding soil into the basement wall can also be controlled by thermally insulating the wall from the exterior. Vapor diffusion under the basement floor is controlled by installing a vapor diffusion retarder between the slab and the granular pad. Vapor diffusion from the basement interior into the wall and is controlled by locating a vapor diffusion retarder to the interior of the wall. Interior moisture levels can be controlled as well. Diffusion of construction moisture from concrete walls into the basement interior can be controlled by locating a vapor diffusion retarder at the interior surface of the wall. Another practice is to apply the finishing materials to the interior surface of the wall after the drying of the construction moisture is over. The key factor in the design process is that balance of vapor flow is achieved in every point within the envelope without condensation occurring. The moisture in the soil or basement interior air can also be transported as a result of air movement. The air movement from the surrounding soil into the basement interior or via versa can be controlled by controlling the openings or holes in the assembly as well as air pressure differential. As most of the materials used in the envelope are relatively air impermeable such as polyethylene, concrete, the key factor in the design is to provide the continuity of the materials within the envelope.

CIB World Building Congress, April 2001, Wellington, New Zealand Page 7 of 11 In the design process of basement envelope, the achievement of effective environmental separation function is usually a difficult practice as the prevailing conditions such as climate changes on a hourly, daily and seasonal basis. Using one component in the envelope which address a requirement for a prevailing condition at a period may cause failure in the envelope in the following period in which another condition prevails. For example, when the basement air temperature and humidity are the same as those outdoors in winter and in summer and the temperature of the uninsulated basement envelope approaches the temperature of the soil adjacent to it; the heat flow from the soil into the basement interior in winter or the reverse in summer, may be controlled by thermally insulating the wall from the interior. But condensation between the interface of the wall and the thermal insulation material which has high vapor permeability can be expected in the summer. Therefore, in the design process, the roles of each material within the system must be evaluated on a full year basis. Basement envelope system involves multiple materials or system of materials which one of them must at least satisfy one requirement of the system. Some materials address a single requirement; for instance, thermal insulation material placed on the interior of the wall only controls heat loss. Some materials address multiple requirements; for instance, a bituminous liquid applied on the exterior of the wall surface will serve as a dampproofing as well as a vapor diffusion retarder. One material can address most of the requirements depending on how stringent the requirements are for that particular circumstances. For the materials to meet the given role in the envelope system, the expected property or the properties of the material must be stated as the performance criteria of the material. The components of the basement envelope system which address the performance requirements and their expected properties in order to satisfy the requirements, namely, the performance criteria of the components are given in Table 2. The basement envelope as a system will achieve satisfactory performance when all the components that address the needed performance requirements are put together and that all of them work together as intended. PERFORMANCE TESTING: AN EXAMPLE After the fundamental performance requirements for basement envelope systems are derived from the user s needs, the performance criteria for the components of the envelope which address the requirements are established. In order to find out, whether or not the requirements are met by the performance criteria, performance evaluation techniques have to be developed in which the typical conditions of real use are simulated. In the following section, a test method which has been developed to evaluate the performance of bituminous waterproofing membranes under hydrostatic pressure will be mentioned as an example for performance testing, (Sahal, 1999). Basements wall and floor of a new constructed building are sometimes exposed to water that exerts hydrostatic pressure from the outside due to the existence of high level of groundwater. The basement envelope system is expected to resist the hydrostatic pressure loads as well as to prevent the penetration of water under pressure. The structural components of the system resist the hydrostatic pressure loads; therefore, they have to provide strength and stability to the loads. When the groundwater is the concern, the basement wall and floor are designed as reinforced concrete walls and reinforced concrete structural slab. Bituminous membranes are used as one of the waterproofing materials in order to prevent the transmission of water under pressure; therefore, they are expected to have low permeability. To perform satisfactorily, bituminous waterproofing membranes must surround the entire structure continuously. To resist the effects of hydrostatic pressure, the membrane, weak in itself, must be loaded by a mass of material at one side and must be protected from damage at the other side. Therefore, the bituminous membranes are sandwiched between two layers in an external tanking arrangement where the tanking is protected by a protective layer on the excavation side with the structural wall and floor slab internally, Figure 4. In the actual service conditions of the membrane, the membrane remains under compressive pressure between the structural floor slab especially under the columns where the loads are relatively high and the concrete blinding. Thus, the plastic bituminous membranes follows the structural deformation. In external tanking, tensile stresses are developed within the reinforced concrete structural slab in contact with the membrane; therefore, membranes are subjected to tensile stresses and they deform as

CIB World Building Congress, April 2001, Wellington, New Zealand Page 8 of 11 the reinforced concrete slab. During construction; after the pumping out of the groundwater is stopped, the rising water will fill the air pockets and push the air to the membrane. The air under pressure will force the membranes which may not be airtight and as a result, air will penetrate through the membranes providing easy access for the water afterwards. The concrete blinding in contact with the membrane, may be attacked by harmful chemicals that are found in the groundwater such as sulphates. Sulphates will react with the hardened cement paste of the concrete to form either ettringite or gypsum which eventually will cause the cracking and spalling of the concrete unless preventive measurements are taken. Shrinkage may occur in concrete building elements when concrete losses its construction moisture. The resultant movement is another cause of cracking on the surface of the structural floor slab and reinforced concrete walls. Due to the cracking, a narrow part of the membrane may strain excessively. Concisely, the mechanical agents that are generated by the construction strain the bituminous membranes excessively. The mechanical properties of the bituminous membranes may withstand the stresses satisfactorily but on the other hand it is not known whether the strained bituminous membranes will still maintain its low permeability property efficiently or lose its watertightness integrity under water pressure. Therefore, the performance of both strained and unstrained bituminous membranes under water that exerts pressure must be determined by a convenient test method. Figure 4. External Tanking Current test methods that determine the resistance of bituminous membranes to water pressure have been examined and it has been found out that these methods were testing for the purpose of quality control, they were not testing for the purpose of predicting in-service performance. Therefore, a test method has been developed where the effects of the mechanical agents on the membranes are simulated, one side of the strained membranes are then exposed to water pressure and whether or not water molecules has penetrated through the membrane is determined from the other side of the membrane. Besides, the amount of transmitted water molecules either in liquid or vapor form is measured in order to calculate the coefficient of permeability constants of the membranes according to the D arcy Law. The test apparatus consists of a hydrostatic testing equipment and a measurement system. Hydrostatic testing equipment includes, a chamber, a rubber gasket, a steel plate which has a gap in the body, a clamping bracket and fasteners to tighten the clamping bracket to the chamber. The strained bituminous membrane is placed between the rubber gasket and the steel plate. The measurement system consists of an absolute humidity sensor, a signal conditioning circuitry and a multimeter. Several tests have been conducted on the commercially available oxidized and modified bituminous membranes; but, the results of the two tests will be mentioned here. The samples used in both tests are polyester reinforced (180 gr/m 2 ), APP modified bituminous membrane with a thickness of 3 mm. In one of the tests, to simulate the strain of the membranes when subjected to the compressive pressure under the column bases, one of the membrane samples was strained at 0.5 N/mm 2 of compressive pressure in an universal testing machine. The same simulation was conducted on the other sample where the compressive pressure was 0.8 N/mm 2. Then one side of the strained membrane sample (0.5 N/mm 2 ) was exposed to a 0.25 N/mm 2 of air pressure for 2 hours; then, the same side was exposed to a 0.25 N/mm 2 of water pressure for 96 hours in the hydrostatic testing equipment. Meanwhile, the amount of water molecules (gr/m 3 ) that have been transmitted through the

CIB World Building Congress, April 2001, Wellington, New Zealand Page 9 of 11 membrane to the other side was collected in the steel plate s gap which is tightly sealed from the outer environment and measured per minute for 96 hours with the measurement system. The measured data is recorded and stored in a computer program to be evaluated periodically. The same test was conducted on the other membrane sample. The test result of the membrane sample which was strained at 0.5 N/mm 2 of compressive pressure showed that it maintained its low permeability property under these conditions as there was no increase in the amount of water molecules in the gap. The test result of the membrane sample which was strained at 0.8 N/mm 2 of compressive pressure is given in Figure 5. From the figure, it can be seen that after 77 hours, the membrane has started transmitting water molecules into the gap. Water in the gap condenses depending on the air temperature of the gap. In the test, approximately 14 gr. of water molecules have been transmitted within 4 hours and then condensation had occurred in the gap. In external tanking, the amount of transmitted water molecules in vapor state may increase the moisture content of the reinforced concrete structural slab or water may condense in the slab depending on its temperature. This may lead to the corrosion of the steel reinforcements. In winter, the capillary water may be absorbed by the thermal insulation material depending on its water absorbing property, leading to deterioration of the insulation. In summer, condensed water may dry into the basement interior if the thermal insulation material has high vapor permeability. It can be concluded that the performance criteria of the bituminous membranes will meet the performance requirement of the basement envelope systems when they are only subjected to compressive stresses between 0.1-0.5 N/mm 2. Figure 5. The Performance of Strained Bituminous Membrane Under Hydrostatic Pressure Absolute humidity (gr/m 3 ) 28,00 26,00 24,00 22,00 20,00 18,00 16,00 14,00 12,00 10,00 8,00 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 Tim e (hour) CONCLUSION There are many different approaches to building a basement envelope and more are emerging every year. All should be capable of functioning as intended, if performance requirements and criteria are satisfied under the dictated conditions. The benefits of the satisfactory performance of basement envelope system will be creation of more comfortable above-grade spaces, reduction in homeowner s utility bills, creation of more usable, comfortable below-grade spaces as well as avoidance of costly moisture and structural problems. REFERENCES Sahal, N., Ozkan, E. 1999. Performance of strained bituminous waterproofing membranes under hydrostatic pressure. In Proceedings, 1999 Durability of Building Materials & Components 8,1156-1165.

CIB World Building Congress, April 2001, Wellington, New Zealand Page 10 of 11 User Requirements Table 1. Performance Requirements For Basement Envelope Systems, (B.E.S.). Agents Functions of the B.E.S. Main Sub-Agents Agents Performance Requirements To provide structural support to the loads that are generated from environmental agents Dead loads Lateral soil load B.E.S. must resist lateral loads from the soil. Safety To provide strength and stability to the loads of the building To provide structural support to the loads that are generated from environmental agents Loads Gravity Vibration Live loads Soil pressure The loads of the above structure and self-loads User loads Hydrostatic pressure due to the groundwater Seismic loads B.E.S. must transfer load evenly to the soil. B.E.S. must resist the loads of the above structure and must self-support. B.E.S. must resist user loads. B.E.S. must resist the hydrostatic pressure due to the groundwater. B.E.S. must resist the seismic loads. Tightness Thermal Comfort To provide effective environmental separation Water Air Heat Heaving pressures generated from frost action B.E.S. must prevent adfreezing; frost penetration control. Splash water B.E.S. must prevent the penetration of splash water. Capillary water B.E.S. must prevent the penetration of capillary water. Soil Seepage water B.E.S. must prevent the penetration of seepage water. Groundwater B.E.S. must prevent the penetration of groundwater. Water vapor B.E.S. must control the vapor flow and prevent condensation. Basement interior Water vapor B.E.S. must control the vapor flow and prevent condensation. Basement wall and Released moisture of B.E.S. must control the released moisture of the floor construction construction. B.E.S. must control the air movement. Soil temperature B.E.S. must control the heat flow and thermal Basement indoor air temperature bridges must be avoided. Durability.

CIB World Building Congress, April 2001, Wellington, New Zealand Page 11 of 11 Table 2. Performance Criteria for the Components of Basement Envelope Systems, (B.E.S.) Performance Requirements Components of the B.E.S. Performance Criteria B.E.S. must resist lateral loads from the soil. B.E.S. must transfer load evenly to the soil. B.E.S. must resist the loads of the above structure and must self-support. B.E.S. must resist user loads. B.E.S. must resist the hydrostatic pressure due to the groundwater. B.E.S. must resist the seismic loads. B.E.S. must prevent adfreezing; frost penetration control. The structural components of the B.E.S The structural components must resist and transfer loads such that strength of materials and soil bearing capacities are within safety limits. Provision of a drain screen, subsurface drainage, thermal insulation material Maximum drainage capacity, effective thermal resistance B.E.S. must prevent the penetration of splash water. Dampproofing, waterproofing, Low capillarity, low permeability B.E.S. must prevent the penetration of capillary Dampproofing, waterproofing, provision of granular Low capillarity, low permeability water. pad B.E.S. must prevent the penetration of seepage water. Dampproofing, waterproofing, provision of surface drainage, drain screen and subsurface drainage Low capillarity, low permeability, maximum drainage capacity B.E.S. must prevent the penetration of groundwater. Waterproofing, provision of surface drainage Low permeability, B.E.S. must control the vapor flow and prevent Vapor retarder, dampproofing, waterproofing, High vapor diffusion resistance condensation, (vapor in the soil) B.E.S. must control the vapor flow and prevent Vapor retarder, provision of thermal insulation High vapor diffusion resistance condensation, (vapor in the interior) B.E.S. must control the released moisture of the Vapor retarder, dampproofing, thermal insulation High vapor diffusion resistance construction. B.E.S. must control the air movement. Air impermeable materials, provision of continuity Low air permeability B.E.S. must control the heat flow and thermal bridges must be avoided. Thermal insulation materials Effective thermal resistance