Building a construction schedule can sometimes be as daunting as the physical construction itself. You basically have to construct the project in your mind in advance. Scheduling theories abound. I call my approach to scheduling "Logical Progression". Some prefer the Shotgun schedule, where you throw all the trades onto a project and let them fight it out. Kind of like a turf war. Eventually the project gets done but at what price?
By using the logical progression approach you know at all times who needs to do what and where they need to do it. There are some obvious elements in this theory because it is very basic. Certain things need to happen before the next phase takes place. But unlike other scheduling technique, with logical progression you can have several things taking place at the same time.
Another term for this is "critical path management". This means that there are certain elements that are critical to the overall time frame of the schedule. Other elements can move around these critical ones without major impact on your finish date. These non critical elements give your schedule flexibility.
A schedule must also be flexible so that as unforseen circumstances arise you can work around the "hiccup" so to speak. There are elements in every project that even the best project manager or superintendent cannot control. Bad weather in one part of the country might affect shipping dates on vital equipment. Just recently we had a concrete shortage in the United States on the east coast that brought a lot of projects to a crawl. So you need the flexibility in your scheduling process to work around the things you have no control over.
Site conditions play an enormous role in how you set up your project schedule. If you have a huge site with lots of space for staging equipment etc. you have a little more wiggle room in how you time your building elements. However if your building is shoehorned onto a tight lot, your schedule has to be very exacting or you will find yourself in a gridlock situation where you have no room to get materials and equipment into or off the site. So by carefully considering your "staging" areas you can utilize your schedule potential to its fullest.
In order to schedule properly you need to envision your building on a multi-dimensional level. Unless you are putting up a string line on a batter board there is nothing linear to building. No two things can occupy the same space at the same time. So when working up your schedule you need to make sure that your trades are layered properly.
Establish elevations that make sense for each trade involved. Overhead work layers from the ceiling up to the joists or structure above. Underground work starts at the floor and goes down. On multi-story projects you have to consider both of these factors at the same time when layering between floors. Which trade has more flexibility to maneuver between bar joists? How much room does a light fixture require? What size is the air conditioning duct "after" it is insulated? How much room does a "P" trap require? What elevation does the building plumbing tie into the city main? Do your homework and get your trades where they belong.
The same goes for horizontal layering. Just as in establishing elevations vertically you need to make sure that your elements work together side by side. As I mentioned earlier no two things can occupy the same place at the same time. The more you can envision your building three dimensionally the better you can schedule and the better you can run your project.
When developing a complete site, layering your underground utilities is important to your schedule also. Fire lines and water mains, sewer, drainage, electrical, all need their own space. Which of these elements has more flexibility? Some have "required" depths to meet code requirements. Know your utiilities. When scheduling site work, I start with my deepest items and work up as much as possible. There are going to be conflicts from time to time. But by installing your deeper trades first you avoid a lot of headaches. It pays to make sure that each trade is marked in the field and on an "as-built" plan as it is installed also.
Going along with the "Layering" premise is the fact that you need to know and understand your materials. Knowing exactly where the bottom of your structural beams and joists are make life a lot easier when establishing your layers. This can really come to play in wall cavities also. Whether dealing with masonry, conventional framing, tilt-up panels or whatever, you only have so much room to work with. No offense to Architects meant, but oftentimes the structural elements get overlooked in the name of "creative license". Changes in roof elevations can drastically affect how the trades make the transition from room to room. Being able to visualize how that elevation change takes place can eliminate a lot of headaches in the field during construction. Sometimes an architect or engineer will show a "cut-through" elevation that seemingly will work on paper. Don't take it for granted. Break each element down to the exact inch, do the math. Electrical engineers are good for showing a run of piping with one dotted line but when you look at his schedule you see that this line represents a bank of conduit that fills a six foot by six foot trench eight feet deep. Plumbing inverts calculations are important also. A sewer line will change elevation at up to a quarter of an inch per foot, this can add up in a long run. You will be surprised at how often ceiling heights,wall locations, structural, and trade requirements do not work as shown. The more of this you determine in advance the better your bottom line at the end of the job and the more fluid your schedule becomes.
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