One of the best parts of working on a construction site is being there the day after they pour a concrete floor slab. Although the concrete is still curing, the sense of sure-footedness is quite pleasing after months of walking (and tripping) over metal decking. It's at this point in the project where you pause and take it all in. The sheen on the new slab resembles a clean slate, and the possibilities for the project are as limitless as the concrete expanse. But be careful, sometimes the concrete is so new, the contractor hasn't had time to install barricades around the slab openings. So note to self: when walking on a new concrete slab, be careful where you walk. You don't want to go over the edge - the slab edge, that is.
When putting together a set of construction documents, an architect should show equal care when working on the slab edge drawing. Here too, one has to be mindful of the gap that occurs between the architect and consulting engineers. That gap can quickly become a canyon on a job site unless the architect can create a bridge with his or her consultants during CDs (construction documents). As discussed in previous 'Note to Self' blogs, these relationships are key components to a successfully executed project. For this reason, the architect needs to fully understand how the structural documents impact the slab edge drawing, and how the slab edge drawing is shaped by the building systems. While neglecting this drawing type is the construction equivalent of living on the edge, ignoring it completely is like driving off a cliff - a financial cliff, that is.
Simply put, although the slab edge drawing has elements of structural engineering, it truly lives in the domain of the architect's office. Here's why.
Once the slab is poured, there's no going back without having to chop out concrete and possibly relocate steel. Either way, the owner will incur change orders and delay claims from the contractor. To avoid this problem, the architect needs to address two issues during the CD phase.
1. Review the structural set for the engineer's slab edge details. These details indicate the relationship between the steel beams and edge of slab and should form the basis of the slab edge drawing. If the structural engineer uses a typical or generic slab edge detail without dimensions or is missing a detail for a unique condition, he or she must provide you with that information in order for you to complete the slab edge drawing. In composite construction (metal decking, shear studs, or concrete), have the structural engineer verify the load capacity of metal decking if it extends past the beam flange.
2. Determine the dimensions of the spatial and geometric requirements of the building system defined by the slab edge (i.e. shafts). Below is a sample list of building systems that will impact the slab edge. Your list will vary depending on your building type and program.
Warning: Cure time for concrete may be shorter than this list.
• HVAC Shafts – In addition to the size of duct risers within a shaft, consult your mechanical engineer for duct accessories including insulation and support framing as well as the space needed between the ducts within the shaft.
• Electrical Shafts – Verify the size and quantity of conduits within a shaft with the electrical engineer. Ask him or her how the conduit will be arranged and how much space is needed between each conduit. Also verify the size of the framing needed to support the conduit risers. Although the conduit is most likely in a rated shaft, there may be circumstances where additional fire-rated wrapping is required that could impact the size of the opening.
• Elevator Shaft – Aside from the obvious shaft requirements supplied by the manufacturer or vertical transportation consultant, verify the support bracket sizes and location (attached to slab edge or beam). Additionally, verify the size and depth of the elevator and sump pits.
• Fuel Oil/Gas Riser Shaft – Requirements vary depending on jurisdiction. Contact your local building code official or utility company.
• Stair Openings – Check your egress calculations to ensure proper width of stairs. Verify if the stair walls are load bearing down to the foundation or supported at each floor slab. If supported at each floor, how is the slab edge finished? Study the framing at intermediate landings. Sometimes they have tricky hangers that need to be located relative to the slab edge and stair walls.
• Façade – Fully dimension the edge of slab along the perimeter and locate the edge of slab relative to the column lines and property lines. Pay special attention to building setbacks or if the angle or curvature of the façade changes. Understand the relationship of the envelope system relative to the slab edge and meet with the structural engineer to address the façade's impact on the spandrel beams and slab edge. Tangential to this geometry, your structural engineer must anticipate the amount of deflection at the slab edge since this affects the tolerances of façade systems (i.e. hanging lintels or curtain wall).
• Slab Elevation Changes – Clearly label and fully dimension all slab elevations including slab depressions. Understand how changes in slab elevation affect partition types and wall finishes as well as installation of building components such as walk-off entrance mats and commercial kitchen flooring. Make sure the structural engineer is aware of all slab elevation changes since this will impact the structural detailing at these locations.
• Foundation – Verify size, quantity and location of pits within the slab on grade or mat foundation. Meet with your MEP consultants to account for all utility pits including but not limited to sumps and house traps. Take into consideration not just the size of equipment within the pit, but that someone needs to be able to access the pit to maintain the equipment. Also, most pits require some type of waterproofing.
• Roof Openings – Working with the MEP consultants, inventory all equipment on the roof with special emphasis on air handling units and exhaust fans. Find out exactly what the engineers need in terms of space for ducts to transition up into the equipment and if any dampers are required. Dampers have motors that need to be accessed and oftentimes steel beams framing out the slab edge opening block this access. Finally, check the opening for elevator and stair bulkheads as well as smoke hatches.
I know reading a blog like this is like watching concrete dry, but it really comes down to just two basic things: understanding the relationship of the steel framing to the slab edge, and then determining the size of the opening or geometry required to support the building system. Do this and you won't be living on the edge.
When putting together a set of construction documents, an architect should show equal care when working on the slab edge drawing. Here too, one has to be mindful of the gap that occurs between the architect and consulting engineers. That gap can quickly become a canyon on a job site unless the architect can create a bridge with his or her consultants during CDs (construction documents). As discussed in previous 'Note to Self' blogs, these relationships are key components to a successfully executed project. For this reason, the architect needs to fully understand how the structural documents impact the slab edge drawing, and how the slab edge drawing is shaped by the building systems. While neglecting this drawing type is the construction equivalent of living on the edge, ignoring it completely is like driving off a cliff - a financial cliff, that is.
Simply put, although the slab edge drawing has elements of structural engineering, it truly lives in the domain of the architect's office. Here's why.
Once the slab is poured, there's no going back without having to chop out concrete and possibly relocate steel. Either way, the owner will incur change orders and delay claims from the contractor. To avoid this problem, the architect needs to address two issues during the CD phase.
1. Review the structural set for the engineer's slab edge details. These details indicate the relationship between the steel beams and edge of slab and should form the basis of the slab edge drawing. If the structural engineer uses a typical or generic slab edge detail without dimensions or is missing a detail for a unique condition, he or she must provide you with that information in order for you to complete the slab edge drawing. In composite construction (metal decking, shear studs, or concrete), have the structural engineer verify the load capacity of metal decking if it extends past the beam flange.
2. Determine the dimensions of the spatial and geometric requirements of the building system defined by the slab edge (i.e. shafts). Below is a sample list of building systems that will impact the slab edge. Your list will vary depending on your building type and program.
Warning: Cure time for concrete may be shorter than this list.
• HVAC Shafts – In addition to the size of duct risers within a shaft, consult your mechanical engineer for duct accessories including insulation and support framing as well as the space needed between the ducts within the shaft.
• Electrical Shafts – Verify the size and quantity of conduits within a shaft with the electrical engineer. Ask him or her how the conduit will be arranged and how much space is needed between each conduit. Also verify the size of the framing needed to support the conduit risers. Although the conduit is most likely in a rated shaft, there may be circumstances where additional fire-rated wrapping is required that could impact the size of the opening.
• Elevator Shaft – Aside from the obvious shaft requirements supplied by the manufacturer or vertical transportation consultant, verify the support bracket sizes and location (attached to slab edge or beam). Additionally, verify the size and depth of the elevator and sump pits.
• Fuel Oil/Gas Riser Shaft – Requirements vary depending on jurisdiction. Contact your local building code official or utility company.
• Stair Openings – Check your egress calculations to ensure proper width of stairs. Verify if the stair walls are load bearing down to the foundation or supported at each floor slab. If supported at each floor, how is the slab edge finished? Study the framing at intermediate landings. Sometimes they have tricky hangers that need to be located relative to the slab edge and stair walls.
• Façade – Fully dimension the edge of slab along the perimeter and locate the edge of slab relative to the column lines and property lines. Pay special attention to building setbacks or if the angle or curvature of the façade changes. Understand the relationship of the envelope system relative to the slab edge and meet with the structural engineer to address the façade's impact on the spandrel beams and slab edge. Tangential to this geometry, your structural engineer must anticipate the amount of deflection at the slab edge since this affects the tolerances of façade systems (i.e. hanging lintels or curtain wall).
• Slab Elevation Changes – Clearly label and fully dimension all slab elevations including slab depressions. Understand how changes in slab elevation affect partition types and wall finishes as well as installation of building components such as walk-off entrance mats and commercial kitchen flooring. Make sure the structural engineer is aware of all slab elevation changes since this will impact the structural detailing at these locations.
• Foundation – Verify size, quantity and location of pits within the slab on grade or mat foundation. Meet with your MEP consultants to account for all utility pits including but not limited to sumps and house traps. Take into consideration not just the size of equipment within the pit, but that someone needs to be able to access the pit to maintain the equipment. Also, most pits require some type of waterproofing.
• Roof Openings – Working with the MEP consultants, inventory all equipment on the roof with special emphasis on air handling units and exhaust fans. Find out exactly what the engineers need in terms of space for ducts to transition up into the equipment and if any dampers are required. Dampers have motors that need to be accessed and oftentimes steel beams framing out the slab edge opening block this access. Finally, check the opening for elevator and stair bulkheads as well as smoke hatches.
I know reading a blog like this is like watching concrete dry, but it really comes down to just two basic things: understanding the relationship of the steel framing to the slab edge, and then determining the size of the opening or geometry required to support the building system. Do this and you won't be living on the edge.
