Dimensioning For Success - Part 2
Designing and constructing a building is a complex undertaking. Designers draw hundreds of pages to convey their vision. Contractors are experts at bringing that vision to life. But sometimes it doesn't go as smoothly as everyone would like and dimensioning is one area that we think improvements can be made for the benefit of the entire project team.
In part one we discussed how installers of work both use and view plans, and we introduced the concept of offset gridlines. In part two, we will start our deep dives into specific areas of the building. As we are a contractor, this discussion will follow the construction sequence: excavation, foundation, framing, interior, and exterior.
At this stage of the project, everyone's goal is to have a building within the property lines that fits inside the hole. This seemingly simple task can be complicated by: property lines that are not perpendicular or parallel to each other, temporary shoring elements installed in right-of-ways, dedications, neighboring improvements on your property such as retaining walls and driveways, etc. When the face of the shoring is right at the property line, the stakes are high. Providing explicit instructions (dimensions) to locate building corners is essential for the independent design disciplines. Clear communication between the engineers, general contractor, surveyor, and shoring installer is critical.
When the shoring designer, structural (foundation) designer, and architect operate on a fixed set of gridlines, victory is one step closer. Shoring design and the major structural elements are often "finalized" well before the building design has been completed. Using a structural set of grid lines and an architectural set of gridlines that are specifically and permanently related is essential to success. This becomes even more important if you are contemplating phased permitting. It can reduce "clerical" revisions of the earlier designed / permitted elements.
Foundation / Parking Garage
The sub-structure is where the "structural" gridlines prevail. In general, concrete walls and columns work very well with traditional face-of-wall or center-of-column gridlines. These elements generally stack on top of each other through the parking garage up to street level. Above this point, architectural design and code requirements start moving vertical elements (walls and stairs) off the gridlines below. The separation or transfer level is where we see the benefits of separating the structural and architectural gridlines and where we start to really push for dimensioning the most critical element of any string.
As the architectural walls begin needing small adjustments (for various reasons), the original gridlines can often offset just enough to appear aligned, a true recipe for disaster. This is where having intentionally "offset" gridlines can bring real clarity when dimensioning what is important. For example: Is making the bicycle storage room exactly 17' 3" wide a priority? Or is the size of the parking space on the other side of the wall, with no callout, more important? We prefer to see a dimension for the parking space because its exact width is critical, and the bicycle storage room can fit in whatever is left over. Is having a generous 26' wide drive lane a priority? Or is the width of the adjacent stair core more critical? Dimension the stair core because its exact width is more important than the drive lane.
Elements that Stack
Offset gridlines work well for elements that stack within the building - shafts in particular. Shafts, whether stairs, elevators, or HVAC, often change wall types as they advance up the building. When a gridline is set at face-of-framing or edge-of-concrete, it can easily be lost as we progress up the building. While dimensioning off of varying wall types, 1 1/8" offsets can start to work their way into the design. Placing an offset line in roughly the middle of the shaft allows for clear dimensioning instructions as conditions change by floor.
This is the second of 5 articles that will explore ways of dimensioning a set of plans that can reduce the opportunity for errors.
Part 1 - Overview
Part 2 – Parking Garage and Building Core
Part 3 – Inside of the Building (Rooms/Units)
Part 4 – Inside of the Building (Other)
Part 5 – Outside of the Building