Detailing The Grade Condition

Having developed details for the floor edges, windows, corners, columns, and parapet, we now address the matter of how the building meets the ground. We would like to get the brickwork close to the ground in order to avoid showing large expanses of the foundation walls. The foundation walls must have Thermal Insulation, preferably located on the outside for Outside-Insulated Thermal Mass. We have a rough detail from the structural engineer that shows the structural slab of the ground lloor supported on the top of the concrete foundation wall and doweled to it with reinforcing bars. We begin the design of this intersection by sketching a freehand detail on tracing paper laid alternately over the typical spandrel detail and the structural engineer's detail, trying to bring the two together. We rest the backup wall on the structural slab and the brick facing on the top of the wall, but we must increase the engineer's 12" wall to a 16" thickness to make this work. We bring 2" of polystyrene foam insulation up the outside of the foundation wall and find that it meets the flashing at the bottom of the brick facing in an awkward way. There is also a large thermal bridge parapet, creating a rather long path that heat must travel through concrete and masonry in order to move in or out of the building.

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Trial desiqr\> -for Qvode Condition through the edge of the slab and the top of the foundation wall.

Looking for a better alternative, we abandon this sketch for the moment and try another, this time using the same shelf angle detail as in the rest of the wall. Suddenly the particulars of the detail all fall into place: The concrete wall drops back to the desired 12" thickness. The insulation that emerges from the ground can be turned back under the shelf angle to form a Thermal Break. We adopt this detail and finish it: The basement wall must be damp-proofed before the insulating boards are applied. Where the insulation is exposed above ground level, we can protect and finish it with galvanized stucco lath and the same polymer-modified stucco materials used in EIFS cladding. We leave a space between the foam and the angle, protect it with an Overhang and Drip on the flashing, and seal it with a backer rod and sealant. We make a note to be sure that grade never approaches closer than 6" to this joint, to protect the angle from corrosion and to keep the weep holes clear at the base of the brick facing. We assure good Foundation Drainage by sloping the ground away from the buildings (Wash) and by installing a porous drainage panel on the outside of the insulation that will conduct groundwater to a system of drainage pipes around the footings.

Checking for Thermal Bridges We examine the perimeters of the conditioned spaces on all the exterior details, looking for thermal bridges. The polystyrene foam insulation does a remarkably good job of wrapping the building. The only serious breach in diis insulating layer, as we noted earlier, is where the backup wall emerges through it at the parapet. The masonry ties and shelf angles throughout the wall are also thermal bridges but constitute such small cross sections of metal that they conduct very little heat.


┬┐Jtrugle Sealant

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Elevation Studies In designing these preliminary details, we have made many decisions that afTcct the appearance of the building both inside and out. We have laid a grid of movement joints onto the facades, have designed a parapet coping and window surrounds, and have detailed the way in which the building meets the ground. Now we visualize the cumulative effect of these decisions by overlaying a tracing paper sketch on one of the original design elevations. When we first drew the design elevation, before the design of the details began, we had only a vague idea of how the building would be put together. Now we are working with a tangible, buildable reality, and we find ourselves in the powerful position of knowing how the building is put together and how to change it to make it exactly what wc want it to be. We summarize our work on the design of the details in a set of accurately constructed drawings.

Partial E:\evwtion Stuty

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