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Hello Everyone,
It is generally noted and as per this: http://www.ronwinterconsulting.com/rabaseline.htm point #92 that having having a Lag in a FS is not a good practice. Can someone pls provide more insight into my situation as below (Construction Project):
The predecessor is finishing on 10/02/15 while the successor will have to start on 10/04/15. I have a FS with 59d lag but a colleague (who is a planning consultant) advises that a lag should NEVER exist in FS relationship. Please assist in shedding more lights.
Thanks.
Ade.
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All of this discussion is excellent, and I agree with what zoltan and Gary have written. However, there is one thing I think it is important to add:
Lags on FS and FF relationships are like activities and, if they are on the critical path, will usually have drag and drag cost, which should be computed.
Lags on SS and SF relationships usually represent volume lags (even if the software does not have the functionality to distinguish between volume and time lags). As such, it is the volume of work in the predecessor activity that is adding the time to the project. To shorten the project, that volume of work in the predecessor must be performed faster (i.e., dig the first 100m. of trench faster so as to start laying the pipe). So the lag on an SS or SF relationship that is on the critical path will usually represent drag and drag cost that is in the predecessor activity.
Fraternally in project management,
Steve the Bajan
Thanks Zoltan,
All clear now.
the first part was about proper scheduling technique the rest of the post gave a detailed explanation of what to do. Which was the same thing that Gary said later.
the part that I mentioned about incorporate the delay into the schedule with lag is this.
what I said was is that "you are trying to incorporate a delay into the schedule using a 59 day lag"
which meant that you know the activity was going to be delayed by 59 days so instead of putting in the detailed activities that make up the 59 days with the proper logic you just wanted to use a lag of 59 days to represent your delay.
think I said the same thing seveal post ago
"or better yet add that whole chain of activities that comprise the 59 days."
also explained why not to use lags
"lag is generally not a good scheduling practice technique to use"
Hi Gary,
You mentioned-
"Whatever the duration, you should replace the lag with a new activity called "client design approval", and link it between design and site clearance"
That point nailed it all. I appreciate your guidance.
Thanks to you all.
I would expect that a defined period for client approval would be in your contract, in which case use that instead of 59d
If there is no defined period you have to make your own assumption, but 59d seems very long to me. Anything more than 4 weeks would be unusual in my experience.
Whatever the duration, you should replace the lag with a new activity called "client design approval", and link it between design and site clearance
As previously stated, I regard no FS with lag as not a good rule, since there are genuine cases for it's use such as concrete curing.
Instead, I follow the rule that any use of lag (regardless of relationship type) should be justified and documented.
Often (as in this case), the lag is there to replace an activity. This is poor planning practise.
Hi,
I really appreciate all commenters; you guys are awesome,
To shed more lights, the project is a Design and Build where it seems somehow difficult to accurately measure the exact duration to get client approval on designs. The 59d lag was added with an assumption that approval will be received within that horizon. Any better ethics to provide for such rolling-wave will be appreciated.
Besides- I need clarification on NO FS with LAG. Is it a valid rule before i cast it on my mind?
Thanks.
PS: I am not receiving email alerts from planningplannet posts. Admin pls assist on this.
Hi Idris
I only use lags on a FS link to show drying or curing periods.
They must be set to a 24/7 calendar.
Best regards
Mike Testro
Idris,
You still need to go into more detail about these "site issues" before we can advise your properly.
-What precisely are these "site issues"
-Do these "Site isues" have anything to do with approval of design?
-Explain in detail the sequence of events that has to happen in order for setting out to start on 10/04/15
-Explain in detail why these events cannot happen sooner
Once we have this info, we can advise you on how best to reflect the situation in the programme.
as FS relationships with a 59 day lag is generally not a good scheduling practice technique to use. One of the main reasons is that the lag is not defined anywhere and you will have to reduce the lag as time marches on. A lag this large is nebulous and can and will case confusion. Who other than you knows why the lag was put into the schedule ? you can not filter on a lag. it is difficult to trace back dates with a large lag in the schedule. What if the lag becomes larger or smaller ?
You have the solution in your second post. I do not understand why you do not add an activity with a 59 day duration for "design approval" or better yet add that whole chain of activities that comprise the 59 days. This will then be clear to all parties involved in the project and will give you the ability to track the delay or each item that makes up the 59 day "LAG"
it appears that you either did not have enough detail in the original schedule to track the design approval or you are trying to incorporate a delay into the schedule using a 59 day lag.
even with the posts above concerning the 7 day lag to use for curing this also has issues. What calendar does the curing lag use ? Does it use the 5 days per week calendar ? You can set relationship lags to either use the successor activity calendar, the predecessors calendar, a 24 hour calendar or the default calendar. HOWEVER this setting is for ALL lags not individual lags such as curing.
you could also add an activity for curing and make sure that the curing activities are on 7 day calendar because curing does not stop on the weekends. Then this is clear to everyone.
Hi Gary,
Thanks for your input,
Regarding my case, I am using lag because- Setting Out activities cannot start due to some site issues till after 59 days of completing the predecessor (design approval) but the consultant is rejecting on the basis of NO FS WITH LAG rule.
I agreed with your illustration regarding required lag for curing after casting but I got more confused due to this clause from the referenced link above {CAUTION: It is highly unusual for Finish-to-Start (FS) relationships to have positive lags.}. Can you give further analysis on what this means?
Pls advise.
Ade.
Lags never existing on an FS relationship is a little over the top in my view. -A classic example of proper use of a (time) lag is to allow for the curing time after a slab has been cast before putting anything on it, and this would typically be an FS+lag relationship.
With your situation, you need to provide a bit more info before we can properly advise you:
Why does the sucessor have to start on 10/4/15?
Email: PPadmin@planningplanet.com
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