Referencing Techniques: Wall-Type Schematic Schedule (Part 2)
Last month, for our introduction to understanding the purpose for and creating a wall-type schematic schedule, we examined an unusual type of wall-type target. This target or tag contained an all-inclusive code that defined the various parameters and components of the wall assembly--but in a limited and ambiguous way. Since there could be an exponential number of variations of the code, a wall-type schedule schematic would not be feasible. This month, we begin our discussion of the more common delineation by architects of wall types and their schedules, as well as the effective use of a wall-type schematic schedule to define and explain it.
Déjà vu all over againSimilar to our previous discussion of color coding for reference purposes whereby, at the time, I was working on a large, complex project (a hotel in Times Square) that lent itself to the technique, this month's topic is well timed. I recently completed work on a very large and complex multi-use building in mid-town Manhattan. There were several parts to the bid--basically broken down by use and/or location, but the "core and shell" work for all parts of the building shared a common wall-type schedule--it was three full pages of the drawing set. My height schematic had revealed multiple heights, even on the same floor(s), so I knew I would have to be thorough in my survey and account for all types of conditions. Ironically, the problem that needed to be overcome quickly occurred in the most unexpected place: the typical office floor cores.
There was much repetition of the basic layout of the office floor core plan(s), with some variations that I could easily account for. The dilemma I faced concerned the architect's choice of wall types--there were just too many that were redundant. For example, a typical one-hour rated partition had six variations--with only the gauge of the framing--not the size, and the spacing or "on center" requirement changing. The sequence for this variety of gauge/spacing was as follows:
* <3A>~25GA/24 inches OC
* <3B>~25GA/16 inches OC
* <3C>~22GA/24 inches OC
* <3D>~22GA/16 inches OC
* <3E>~20GA/24 inches OC
* <3F>~20GA/16 inches OC
Except for the shaft walls, this scenario was typical for most of the wall types.
The architect was strictly following the limiting height criteria set forth by the industry for determining the GA/OC. Each wall in a series was given an LH based on its unbraced vertical span and allowable deflection for that span. To be given an LH is not uncommon. What was uncommon and unusual was that the architect had apparently coordinated this criteria with the actual floor-to-deck heights of the floors to a degree not normally encountered. Typically, the LH serves as a generic guide to the architect for the selection of GA/OC very often with the wall types exceeding the minimum requirement. The selection of a wall type from a wall-type series such as the one above appeared to be based strictly on the LH criteria and was reflected on the core plan(s). Thus, a core for one floor that was identical in every way to another floor could or would have wall types of the same series but of a different designation based on the LH criteria for GA/OC--even if the height difference was just a few inches.
I could not fault the architects. They were playing by the rules, but it was making my life very difficult and I needed to meet a bid date (at the rate I was going, I would not). With all these variations of wall types for the same core plan(s), I could not take advantage of duplications and symmetry that help expedite the quantity survey. After consulting with my client and getting his approval, I resolved the problem to everyone's satisfaction--I took the worst-case scenario: 20GA/16-inch OC, as the standard GA/OC for framing where this scenario occurred.
By doing so, I eliminated the problem of multiple variations of the same wall type by condensing six into one. Considering there were about 10 wall types with this scenario, I reduced what would be 60 wall types into just 10. Needless to say, it was a tremendous help in completing the quantity survey and improving its accuracy. In reality, it was no great stretch to do this since 20GA/16 inches OC was the most commonly required GA/OC. To simplify and standardize both the survey and the field application, 20GA framing would inevitably be used on such a job. The option to frame at 24-inch OC--if it met the LH criteria, would be a cost-saving field condition.
To add to the mix, 25GA and 22GA framing would only serve to complicate and confuse the situation--just as it did for me in the quantity survey. The additional labor and material cost for 20GA framing is irrelevant considering the benefit gained. By setting a standard, snafus that would more than likely occur during purchasing, loading and installation are eliminated. This decision to standardize at the early stage of the estimate reflects the reality of the actual field application--something an estimate should always do.
Battle wonBy always exceeding the minimum requirements set forth by the LH criteria, I am consistently in compliance with it. Had I chosen 22GA/16 inches OC for example as the standard GA/OC, I would have complied with the LH criteria for only those floors with deck heights less than or equal to the 22GA/16 inches OC maximum unbraced height span as defined by the wall-type schedule for each wall type/series. Floors requiring 20GA/24 inches OC and/or 20GA/16 inches OC would be non-compliant and unacceptable as a field application. The only alternative would be internal/external bracing to offset the violation of the LH. Neither my client nor I wanted to go down that road. It would require submittals/approvals and add significantly to the labor cost. When confronted with a choice between additional labor or material costs, always choose material--you have more control of it.
There is an analogy to this type of situation that, unlike this GA/OC scenario that is common but infrequent, concerns the standardization of gypsum-board panels.
It is standard requirement that all fire-rated wall assemblies include fire-rated gypsum-board panels--these contain what is known as a Type X core. Contrary to this, walls not required to achieve a fire rating typically do not require such a core and standard gypsum panels suffice. Thus, a job may require a large percentage of board to be rated and the balance to be standard, non-rated panels. This can be a dangerous combination.
In New York City, as elsewhere, it is standard practice by most drywall contractors to use only fire-rated gypsum board panels for all applications--rated or not. Correcting the misapplication of standard, non-rated panels to fire-rated wall(s) can be a very expensive proposition. Also, there is the issue of life safety and potential liability. So you see, it is better to spend a little to save a lot. As with the framing components, standardizing the type of gypsum panels make purchasing, loading/distribution and application a no-brainer. Very often, when the quantity is large enough and/or delivered to the job by the trailer load, the cost difference between rated and non-rated panels is negligible.
As with exceeding the minimum requirement for GA/OC, the exclusive use of rated gypsum panels is considered an acceptable practice since it meets or exceeds the minimum requirement(s) and is very conservative by its nature. My wall-type schematic schedule revealed to me early on the GA/OC situation, but it was not until I got into the survey that the true depth of the problem came to the surface. It is in the creation of the schematic schedule that potential complexities, problems, conflicts, errors, omissions, etc., are encountered and first dealt with. This is the primary function of the schematic schedule.
Next month in our continuing discussion, we will take a look at a fairly typical example of a wall-type series and discuss it in detail as it relates to setting up a schematic schedule to define and explain it.