Forum Discussion
Accounting For Known Delay's When Planning a Project
- ACSkoz,
As I said there are two ways to handle the uncertainty of subcontractor start dates, with a constraint or with a lag. Normally constraints are not good practice as they disrupt the schedule dynamics (i.e. non-continuous logic path) but if there is no valid predecessor task, putting a start constraint is the best option.
I see in your schedule you have chosen to use lag but I question whether the predecessor upon which you added the lag is indeed valid. For example, is plumbing really a driver for the mechanical work? Certainly plumbing drain lines have slope requirements to work properly but duct work normally requires the most free space in limited chase runs. The point is, links between tasks should be true requirements not just for convenience.
With the constant change and uncertainty in construction, I think your best bet is to make your best guess on subcontractor start dates based on your experience with each subcontractor. If you try to keep up with constantly changing estimates you will spend a lot of frustrating time scheduling.
As far as a "more proper" way of handling schedule delays, I think you have a good handle on it, so press on and good luck with your plan.
John
The span of time (duration) a subcontractor bids to do their work is independent of the day they start the work. So if a sub says 5 days to do the job, make that the task duration. When that 5 days starts is best handled by either a constraint (Start-no-earlier-than) placeholder or possibly a lag from another task (e.g. framing can't start until the foundation is complete). When you get a firmer start date for the sub, adjust the Constraint Date or lag in the predecessor link.
If a sub quotes a 5 day duration for their task but you know from experience that sub typically takes more or less time than their quote, you can certainly adjust the duration value to include a contingency "pad". What actually happens is accounted for when you enter progress in the Actual Work and Remaining Work fields.
You mention entering delays as "slack". Project has two slack fields, Free Slack and Total Slack, both of which are calculated by Project and not editable by the user so I'm not sure what you mean by "slack".
Hope this helps.
John
Thanks John; however, this is more the time from when one trade finishes and second begins. Most or our subs finish their task in the time allotted, the challenge is do they start on the day they are supposed to. We call them 3 weeks out, 1.5 weeks out, 3 days out, and then the day before and many times they still say they will be there tomorrow, in which that night I get an email or text saying it's going to be another day. There also is the scenario where the sub tells us in advance that he can't start the day we have him scheduled. In either case, these are delays we know are going to occur before we even start, thus I want to build it into the schedule.
I said slack, but what I meant is I currently enter 2 or 3 days of lag (Finish to Start). I set it up on my predecessor so that the 2 days does not show as duration of the task, but as blank time. I've attached a screen shot of what I'm referring too. I've got 2 day extra for the Plumber, HVAC Sub, and Electrical sub to be late to start their work.
Now that I've been working with it these past few days, it does accomplish what I need from visually looking at the gantt, I'm wondering if it will cause me issues elsewhere in my reports, or if there is a more proper way of doing it.
- ACSkoz,
As I said there are two ways to handle the uncertainty of subcontractor start dates, with a constraint or with a lag. Normally constraints are not good practice as they disrupt the schedule dynamics (i.e. non-continuous logic path) but if there is no valid predecessor task, putting a start constraint is the best option.
I see in your schedule you have chosen to use lag but I question whether the predecessor upon which you added the lag is indeed valid. For example, is plumbing really a driver for the mechanical work? Certainly plumbing drain lines have slope requirements to work properly but duct work normally requires the most free space in limited chase runs. The point is, links between tasks should be true requirements not just for convenience.
With the constant change and uncertainty in construction, I think your best bet is to make your best guess on subcontractor start dates based on your experience with each subcontractor. If you try to keep up with constantly changing estimates you will spend a lot of frustrating time scheduling.
As far as a "more proper" way of handling schedule delays, I think you have a good handle on it, so press on and good luck with your plan.
John- Thanks for your help John.
