What Do Architects Have To Consider When Designing A Building?
There are a few basic science truths that architects , engineers and contractors have to contend with among the many variables that need to be taken into account in the construction of a building envelope. These, when overlooked, cause the most waterproofing issues.
The walls, roof and floor foundations (including below-grade walls and slabs-on-grade) form a building envelope. For each of these, different exposure factors lead to different designs and materials being chosen to waterproof each person.
BASIC TRUTHS OF SCIENCE
The design professional and contractor must not neglect the basic laws of physics and thermodynamics in order to build a weatherproof construction envelope. No matter what new materials are created, there are some essential truths that have always been and will always be behavior that must be accommodated in the design and construction of building envelopes. The following are some of them:
Water must check for the lowest amount. If it appears to "bottom out" at the head or sill of a window or door or at the base of a wall cavity, it must be guided back to the outside until it can come into contact with the components of the internal wall.
Differential pressures generate wind. These pressures can push rain through an external wall that seems to be waterproof and into the interior of a house. Air moves from high to low pressure, and quite a lot of water can be pushed by the pressure through very tiny cracks in an external veneer.
From hot to cold, air molecules move. More moisture than cold is retained by warm air. As humid, moist air is cooled to the dew point (the temperature at which the air can't retain the water molecules), condensation develops. The temperature at the dew point depends on the relative humidity of the air. Areas with low humidity would have a lower temperature at the dew point than areas with high humidity. In order to condense moisture, the arid desert air must cool to a much lower temperature than the humid air of a tropical climate.
By capillary motion, water flies. Wind in a masonry or plaster veneer will push rain into cracks. Skin friction between the crack sides and the water molecules makes it possible to wick the moisture into the material and into the wall.
Materials grow and contract with temperature increases. However, some materials are more durable than others. The skin of walls and roofs may be stressed by these differentials in temperature shifts, resulting in tiny microscopic cracks or large openings. Also small cracks in masonry or plaster walls can allow for water penetration directly into the wall from capillary action or rain.
Okay, so we've developed that water, whether due to movement fractures, blowing wind and capillary action or construction fault, will get through the exterior veneer and into the wall cavity. What now? The solution is to provide the blinking, which guides water back out, with a secondary weather resistant barrier as a drainage plane.
For walls, the exterior veneer is the first line of protection. As the only defense from the elements, it should not be relied upon.This secondary wall membrane was also designed in the old days to shed water with lapped shingle type paper (asphalt impregnated sheets). The selection process has been made more complicated by new items and code regulations.
Water may come into contact with the sheathing layer (the outer face of the wall behind the veneer) once in the cavity space and transfer to the insulation, the inner wall layer and the internal base molding. Water decreases insulation efficiency. If any of these materials are organic, mold can grow (such as the paper layer on gypsum board, plywood sheathing, wood foundation, wood studs).
In the last few years, we have all learned a lot about mold. This has become a particular concern as codes have needed "tighter" buildings and homes in an attempt to increase energy efficiency. For energy conservation, blocking air infiltration is fine. If these air barriers, however, often serve as a vapor barrier, then there may be trouble.
While effective as air barriers, humidity in the wall can be trapped by vapor barriers. Both vapor barriers are barriers to air, but not all vapor barriers are barriers to air. Water molecules are larger than water vapor molecules, so an effective air barrier may be a specific material, but it does not block moisture vapor. When choosing and installing a secondary weather resistant membrane to provide double protection, all of this must be considered.
FLASH, FLASH, FLASH
Some construction professionals and contractors have somehow forgotten to flash. To guide water outward, this essential element must be mounted.
Flashings start six to eight inches above the base of walls, heads of windows and doors and above shelf angles at the outside wall sheathing and spread through the cavity space. It is important to overlap the flashing top with the secondary drainage membrane. Under the exterior veneer, the outside edge of the flashing material must stretch. Weep holes must be created at regular intervals through the exterior veneer to allow water to drain. And, please, joint sealants are not a flash replacement.
The involvement in water infiltration and mold litigation has earned EIFS (Exterior Insulation & Finish System) a great deal of notoriety. The issue is not related to the EIFS, but to the absence of flashes and drainage. For all types of products, not just EIFS, these errors occur. Water is going to get in and the flashes have to direct it out.
SELECT & INSTALL WISELY
In order to make a suitable selection regarding the installation of secondary weather resistant membranes and flashing materials, the design professional and contractor must be fully aware. Know the planned use of the material by the producer and any product constraints. And follow the instructions from the manufacturer for installation.
BASICS FOR OWNERS
Members, know your contractor and your design expert. The distinction between a fruitful project and a headache can be implied by an accomplished architect , engineer and contractor.
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