Construction impacts are common, we all know it. They are common because projects are complex and there are a lot of moving parts.  More importantly, they are common because there are so many people and/or entities involved.  From laborers, to subcontractors, project managers, designers, architects, decision makers, legal entities, government regulators, just to name a few!  Each one of these has a role and/or a responsibility, and if they don’t perform their role/responsibility in accordance with “the plan”, something gets impacted.  Impacts happen all the time, and as they mount, construction projects change.  The schedule changes, progress changes and performance changes - all of which will likely impact cost for all parties involved.  Impacts can be very costly to the various stakeholders involved on construction project, and for that reason, they need to be studied.   No one wants to have to pay for an impact that they didn’t cause.
I have worked with many clients who have attempted to study impacts in an effort to ensure they are not paying for something that they didn’t cause. One thing I have learned is that there is the right way to do this analysis and there is a wrong way.  Unfortunately, in my experience most companies attempting to perform impact analyses are doing it the wrong way - with a cost based approach as oppose to a schedule based approach.  I have seen that quite often construction professionals think the logical approach is to study cost overruns through the cost system and then come up with the reasons why the cost was impacted.  While I understand why most construction professionals would default to this logic, it just isn’t the correct way to do this type of analysis.  An analysis of cost overruns without taking into account the schedule will only lead to incomplete, unsubstantiated findings, and often results in a disagreement from another party.  This is the case because the cost system does not contain interrelations between one cost code and another; Interrelations are important, because impacts in construction often result in a domino effect across multiple scopes/stakeholders/contractors. Therefore, pinpointing the root cause of the impact and the follow on effect is very important.   That is why the schedule needs to be the vehicle for studying impacts first, and from there, cost overages need to be assessed. 
Every activity in the schedule represents a portion of work that needs to be performed to complete the project – and these activities are typically tied together with relationships (logic); meaning that each activity is essentially a piece of the time and cost equation in construction.   Since schedules contain activities and interrelations among activities, it is the perfect place to start when analyzing impacts.  Therefore, in order to be successful in understanding impacts and the resultant cost overruns, the cost system must be aligned with the schedule system.  
In order to do this, one must do the following:
1. Resource and cost load the Baseline CPM schedule to align with the original budget;
2. Capture good data on the project every day and associate it to the particular activity that it represents.  Data includes manpower, progress, impacts info. equipment utilized, etc.  Daily reports are a good place to do this.  
3. Compare planned versus actual manpower, equipment cost, and duration's to assess performance.  All of the above can be converted to actual cost, enabling the analyst to compare planned versus actual cost while taking into account variances in time, along with reasoning for the impact.
The absolute most important proactive measure anyone can take on any construction project is capturing good progress/performance data and associating this data with a particular activity in the project schedule (or a summarized version of the schedule.
While this may seem like a tedious task, it is not.  I do it for all my clients and once the system is set up, the information captured is GOLD to any construction organization, particularly as it relates to real time delay/impact management on active construction projects.  In addition, this information is paramount towards resolving disputes and/or correcting any internal issues a construction company may have. I know this because I have been capturing, studying and utilizing this type of data on behalf of my clients for 15 years and I can assure you the knowledge gained has saved clients enormous amounts of money.
If you want to learn more and/or try a software solution that will automate this type of data tracking and analysis, check out SmartPM at  www.construxsolutions.com .