Referencing Techniques: Wall-Type Schematic Schedule (Part 1)
I have been involved with many of the architectural construction trades during my career as an estimator, but my focus and area of expertise is and always has been drywall construction systems. In particular, for high-rise and complex projects--the kind New York City is famous for. By its nature, drywall construction involves the assembly of disparate component parts typically including framing members, gypsum panels, insulation, adhesives, fasteners, finish (tape and spackle) and caulking. Each of these components has multiple variations that are applicable to multiple assemblages.
For example, framing members come in a wide variety of types, sizes, configurations, strengths and spacing requirements. Gypsum panels are manufactured in a variety of thicknesses, fire-resistance ratings, applications, etc. To deal with this complexity, I always create a wall-type schematic schedule. This schedule plays a key role in both the quantity survey and cost analysis phase(s) of the estimate. Basically, it condenses the complete wall-type schedule into a matrix format that is readily available for quick and easy reference.
A wall by any other nameOne of the most common mistakes I find on architects' drawings is the title/reference to the partition schedule. This is a misnomer. The proper terminology should be wall-type schedule. In drywall construction, a partition is commonly defined as a single row of framing with gypsum board panels applied/finished on each side of the framing. Thus, walls like chases, furring and shaftwall are mistakenly being called partitions when in fact they are not. The generic term "walls" defines the wide variety of drywall assemblies and should always be used as the defining terminology.
This said, it is important to have a clear understanding of the types of walls commonly found in drywall construction and their variations. A short list would include--but not be limited to--the following types:
* Partitions: balanced, unbalanced, rated, non-rated, acoustical, bearing and non-bearing.
* Shaftwall: elevator/mechanical shaft, stair (one-, two- and three-hour rated), vent (solid).
* Furring: direct, framed, laminated, exterior wall.
* Chases: single, double, rated, non-rated, freestanding, area separation.
* Exterior wall window: head, sill, jamb (return).
* Partial height: knee/pony walls, kitchen pass-thru.
Needless to say, each of these types can and does have multiple variations. For example, a partition that is non-rated can be full height (frame and board to deck), to underside of finish ceiling (frame and board), or framed to deck and board to above finish ceiling. To this mix can be added the absence or presence of various types of insulation and multiple floor-to-deck heights. Here we can begin to see the need to sort out the apples from the oranges.
It is now the schematic's job to clarify and define each wall type and its variations based on the architect's schedule drawing(s). A target or a tag with an alpha, numeric or combined alpha-numeric code is typically used on the floor plans to define the wall types. Often, a wall type with a series of variations is given a numeric-decimal code such as 3.1, 3.2, 3.3, etc. Let's look at an interesting example of one type of wall-type target/tag that is all inclusive (no formal schedule drawing), in the diagram.
Cracking the codeThis is one of the most unusual wall target/tag types I have ever encountered. First, it is inclusive not only for both drywall and masonry walls but also includes metal and glass partitions (H) and combination gypsum board and glass partitions (A). Note that the first-letter prefix applies to only the gypsum board (G, L, X and C), gypsum board and glass (A) and glass partitions (H); none applies to the masonry walls. It is logical to assume that the masonry walls are indicated by a lack of this first-letter prefix in the code. Also, note that the code G refers to a gypsum board partition and X to a wall with gypsum board on one side only. Thus, the proper definition of a partition applies to all G designated walls. X codes refer to furred wall conditions and/or single-chase walls that are defined as being finished on one side only. However, the code C for chase walls can be for either or both single- and double-sided chase walls only.
There is a gray area concerning the definition of a furred wall and a freestanding single-chase wall. In my experience, a furred wall is either directly applied to a substrate or is in close proximity to it--close enough to be braced back to it (usually the structure or another wall). Single-chase walls are usually freestanding with mechanical/ electrical/plumbing (MEP) roughing between it and a substrate, and braced (if required) diagonally to the deck above. Double-chase walls are typically freestanding with the roughing between and internally braced. In this job, both furred walls and single-chase walls were referred by target/tag code as X; it was left to me to distinguish the two types from each other. For wall types A and L, further investigation into the drawings is required to determine heights, assembly details, etc.
The second digit in the code is the number that describes the stud (framing) size or block (CMU) size. Since a G preceded it (gypsum board partition), we know it is not 4-inch CMU but is 4-inch framing. However, two critical elements relevant to metal-framed walls are not indicated: gauge and spacing. We must make further inquiries into the specifications, manufacturer's recommendations, floor-to-deck/limiting heights, etc., to determine the appropriate selection of gauge/spacing for all framing components since it is not given here.
The third digit in the code is again a letter prefix describing the height condition(s) for the framing, gypsum board or masonry walls. Apparently, there is a raised floor condition (F and R) so an investigation to determine the height differential(s) will be required. If the target/tag indicated a fire-rated wall and had either letter prefix F or R it would in all likelihood be a mistake by the architect. A fire-rated wall must extend vertically from structural slab to the underside of the structure's deck to maintain its integrity. Thus, a fire-rated wall should always have the letter prefix S (to structure). I would qualify any fire-rated walls so designated F or R to extend from slab to deck--not from raised floor. Since this is a life-safety issue, it would be irresponsible to do otherwise.
If applicable, the fire rating of the wall is at the bottom of the target/tag--below the framing/block size. The asterisk at the top denotes "double-layer gypsum board each side of the partition." This implies either a two-hour rated partition or chase, but it is not necessarily so. Often, particularly in apartment buildings where, in NYC for example, a one-hour partition is required, a double/double partition is used for acoustical purposes. Thus, the asterisk could be present with a one-hour wall indicated and it would be correct in such a situation.
The alternative to the "double/double" between apartments is an unbalanced wall (two layers one side, one layer the other) that achieves the required one-hour rating. This is more economical and is effective at diminishing airborne noise since sound (being wave energy) does not travel evenly through uneven surfaces.
God is in the detailsOutside the target--starting from the top--the R & F applies exclusively to masonry walls. Our only interaction with masonry walls occurs when the number 1 (for furring x(1)side) or 2 (for furring x(2)sides) appears below R & F. Without 1 or 2 below it, the implication is an unfinished masonry wall. At the bottom, the code S denotes the requirement for acoustical insulation. Basically, there are two types of generic acoustical (blanket) insulation: sound attenuation blanket and sound attenuation fire blanket. Both contribute equally to a wall's sound transmission coefficient but the latter contributes to and is part of a wall's fire-resistance rating.
The presence of the letter prefix F to the left of the prefix S indicates the requirement for a sound attenuating fire blanket. To the right of the prefix S, the STC rating achieved by the assembly is indicated. Note that walls without acoustical insulation can and do achieve STC ratings so the presence of the STC rating need not accompany the prefix letter code(s) for acoustical insulation.
Needless to say, this kind of wall-type target/tag can be easily confusing, misinterpreted and exponential in possible combinations. In this case, the best way to deal with it was not to create a wall-type schedule schematic as I normally would. Due to the custom nature of this type of coding, whereby every wall potentially has its own unique characteristics, a wall-type schedule schematic is ineffective. Rather, I cut out the detail from the drawing I found it on, made a photocopy of it and taped the detail back onto the drawing.
I posted the copy on my bulletin board next to my desk and constantly referred to it as I encountered the various wall types during the quantity survey. As the survey progressed, I became less dependent on the copy since I was becoming familiar with the code. But it was a difficult process to deal with the multitude of drywall assemblies on a job that was very complex to begin with.
Fortunately, this type of target/tag is infrequently used. More common is a drawing(s) dedicated to the wall types that consecutively lists each wall by type along with variations of the type, usually as a series. Accompanying this schedule drawing will usually be found common details relevant to the walls, including wall mounting details or penetrations through walls. It is from this type of schedule that we can establish the criteria for creating a typical wall-type schematic schedule. Next month, we shall do exactly that via a working example.