During construction change happens. If the change is for a reason outside of your control i.e. not of your making there should be a remedy within your contract to enable an adjustment of the completion date and/or the contract sum.
The contract should list the change events under which you can make a claim. It is therefore important when conducting your initial contract review that you ensure this list is complete. The contract will also tell you which changes events you are able to claim only time and which you can claim both time and cost. Again, check to make sure these are correct.
It is vital that you understand the protocol under the contract for claim change. There can be time bars, conditions precedent and formats that you need comply with for your claim to be valid. Be aware.
As always it is important to follow the rules of the contract. Things may be going well with the Employers current team, claims for change are being agreed without the proper paperwork being in place but what if that team changes and the new team are sticklers for following the rules of the contract. Without the proper paperwork in place you are in a very risky position.