Dimensioning For Success : Part 3
Designing and constructing a building is a complex undertaking. Designers draw hundreds of pages to convey their vision. Contractors bring that vision to life. Sometimes, however, it doesn't go as smoothly as everyone would like and dimensioning is one area where improvements can benefit the entire project team.
In parts one and two we discussed how the installers of work both use and view the plans. We talked about the concept of offset gridlines, and we started our deep dives into specific areas of the building beginning with the parking garage and building core. As we are a contractor, this discussion will follow the construction sequence: excavation, foundation, framing, interior, and exterior.
At the top of the list for units is the overall distance from party wall to party wall. Typically, we see gridlines as center of party wall. How this can go wrong is when there is added shear in these walls and if there is a planned air gap in a double wall strategy. Has the architectural layout allowed for the shear panel at the party wall? Is the shear plywood allowed to "cannibalize" the airgap? If in the early throws of design, the double party walls were laid out with a 1.5-inch gap between them, the project team could avoid redesign as the design develops and perhaps even build a little tolerance into the system. We understand that there are constraints and issues for shrinking a unit voluntarily, even by half an inch.
It works well to think of each residential unit as its own module, an independent thing. If the module width of, call it 16 feet, works to accommodate a kitchen, a bath, and ADA clearances we can stay out of trouble by replicating the 16-foot box. Party wall to party wall, we build each unit within as a module, pulling measurements from the outside in. When planning the most efficient module we start by identifying the critical dimensions. It might be the clearance in front of the fridge to the hallway wall, not necessarily the width of a bedroom. If the plans show the bedroom width dimension, it could happen that by meeting that dimension, space is stolen from the minimum clearance required in front of an appliance.
Bathroom clearances are obviously a huge driver. If we know the toilet depth and the tub depth, we can quickly quality check to see if we're getting into trouble, especially when considering complicated wall types. We often have a double wall, furred wall, or shaft wall as part of the enclosure around a bathroom. Sometimes these atypical walls also have shear on them, and sometimes they don't. These tricky wall types are a recipe for disaster if a project is designed using the minimum clearance approach.
If it's at all possible, try to avoid pulling dimension chains for any purpose from complicated wall types. When there is a complicated configuration of wall types coming together next to a bathroom, it becomes much easier to identify an issue if the designer provides the interior clear distance required between the bathroom elements (toilet, tub, counter) and the complicated wall.
Here understanding the design intent is key and the nuances of installing the specific material can be critical. If features need to align, flush out, or terminate symmetrically with another element, then it's always good to discuss it early and get it on the plans. If we get to the point in the project where those finishing touches are being installed and no one has talked about alignment, the design becomes subject to the infamous "carpenter's choice".
Which Clearances Matter and Why
There are all kinds of information and numbers on a set of plans. Usually, most dimensions provided are framing to framing. Designers often focus their attention on those dimensions. But at the end of the day, it is mostly the benign seeming internal dimensions that make a space dysfunctional or unbuildable: the 36" clear between the kitchen island and the hallway wall, the unit entry door area, and one of the ADA clearance square callouts in the bathroom. These are the really important ones.
To avoid creating a kitchen with an unusable 10" wide drawer stack, we can stretch the kitchen. It is critical to understand how that may unintentionally affect other neighboring elements. Did we just inadvertently shrink our unit entry clearance? There are a million things that can go wrong with the best of intentions. If the plans tell us specifically what is most sacred, the team is better suited to adapting when "little" things come up.
This is the third 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