Making Mistakes (Part 8)
For our continuing mistakes discussion, we’ll close out the year with a look at one of the most pervasive types of errors made in the estimating process. It is perhaps the most observable type of blunder yet it is arguably the most overlooked type made by the inexperienced, or for that matter, experienced estimator. Difficult, unusual and atypical conditions encountered on the job site and determinable from the design documents can and do add considerably to the burden of the major cost factors of:
• Labor • Material • Equipment
Out of sight, out of mindThere are a wide variety of conditions that must be considered when evaluating/analyzing for cost. Very often, an estimator must read between the lines in order to comprehensively account for all costs—both real and imagined. In estimating, “conditional costs” are both real and imagined.
A good example of this sort of recognition is found when dealing with concrete structures. There is a considerable difference in the strength/hardness of mature concrete as compared to new or green concrete.
A graphic depiction of strength vs. time for concrete would reveal that typically concrete used in construction reaches its design strength after 28 days of curing. However, rather than leveling off at 28 days, the curve on the graph travels off into infinity at a very gradual but steady incline.
This attests to the fact that concrete never stops getting stronger over time. Thus, a shot, anchoring device, etc., that will easily penetrate green concrete may bounce off a 60-year-old cinder concrete deck like a rubber ball. This reality represents a burden on the cost of anchoring to the concrete floor/deck and must be considered. It may be that a heavier load in the shot would suffice but perhaps not. It may be a requirement to “drill and anchor” to the existing concrete. For suspended ceilings, it might be necessary to expose the re-bar embedded in the concrete deck and attach directly to it. Bottom line, mature concrete represents a condition whereby additional/supplemental costs will be encountered. Therefore, such burdens must be considered carefully in your cost analysis. To not consider it is to commit the deadly sin of omission.
Form follows functionVery often, the structural system of a building is, in and of itself, the most revealing means by which an estimator can determine conditional costs. I was once working on an estimate for an old loft building conversion in lower Manhattan. A review of the drawings revealed that the floor structure was composed of Terra Cotta arches spanning between cinder concrete-encased steel beams—typically about 6 feet, 0 inches o.c. (this was a common structural system used in the early 20th century). The specification was clear and concise: attachment to the existing Terra Cotta arches was forbidden; it did not elaborate further. Terra Cotta is a clay-based material that is brittle and easily shattered—it would not support any load imposed on it for the walls and ceilings to be constructed. Thus, attachment for walls and ceiling anchors had to be directly or indirectly achieved via the concrete/steel beams between the arches. In effect, this meant creating a sort of “sub-system” of black-iron channels (CRC) in between the beams to provide sufficient support.
This was a very considerable cost. As I suspected, my price and one or two others were far a field from the rest of the pack of about 10 bidders. Reason being these other low bidders failed to recognize this situation and the considerable cost inherent in the condition.
On another project, a World War II-era warehouse in Brooklyn being converted to offices, the structure itself was the Achilles’ heel—almost. The building was massive. It had 1 foot, 0 inches thick cinder concrete floor slabs that you could drive a truck over. With the building about 50-years old at the time, I knew that the concrete was mature and posed a problem for attachment, which was fairly obvious. However, it was the support columns that would prove to be the condition that caused the most concern and contributed to the cost considerably.
On the floor plans, the columns—which were about 15 feet, 0 inches o.c. in each direction—were depicted as simple 30-inch diameter by 360-degrees round full-height columns. The various rated and non-rated wall assemblies typically ran along the centerline of these columns in each direction. The interface of the wall and column was well detailed but still depicted a round concrete column, nothing more. This was a 10-story building with a large “footprint” so there were to be many such interfaces of walls and columns. I accounted for the interfaces by a count of each condition but it was as a simple round column from floor to deck. When I was reviewing a 1/8-inch scale transverse building section, my radar went off. It depicted, ever so slightly in that small scale, that the round columns were not monolithically round from floor to deck. As it turned out, all the columns had a “Y”-shaped base and capital—only the shaft (the portion between the base and capital) was uniformly round. The architect cut the floor plans and the interface detail at the level of the shaft, thus the true shape of the column was not readily recognizable. Luckily, the building section depicted the columns in elevation, the only place on the drawings to do so.
This condition required that every time a wall met a column, the wall had to be “scribed” to follow the profile of the column. In the field, this meant making a template of the profile and transposing it to the framing and drywall at each interface. Needless to say, this entailed a major cost for both labor and material, much more than for a uniformly round column as first thought. On the job, it all went well having had the foreknowledge of the column condition as it truly existed. The money to cover it was included in the estimate but had it not been, the job would have been a bust.
It is this kind of recognition and accounting that separates the novice from the professional estimator. Next time, we’ll continue our discussion of conditions and mistake making into the New Year. My best wishes to you all for a happy, healthy and successful 2003. W&C