How can you tell if you have a warped door or not?
There is an industry standard method of determining whether your door is warped or not.
To determine whether you have a warped door or not you will need a length of string (longer than the length or height of your door) and a measuring stick or tape measure.
a) Tape one end of the string to the edge of the door and the other end to the opposite edge of the door.
b) Measure the gap between the string and the door’s surface area.
If the gap is greater than ¼” your door is warped (according to AWI standards for 1-3/8 to 1-3/4 inch doors 3’-0” to 3′-6″ x 7’-0”).
c) If the length exceeds 7 ft. AWI standard applies to any 7 ft. section. Apply string to any 7 ft. span.
Contact your door maintenance company and send them two photos.
d)  Photo of the length of the string which shows as much of the door in its entirety, or at least from one end of the string to the other. Then  a closeup photo of your measurement of the gap.
Armed with these two photographs, which can easily be emailed to the millwork or door maintenance company of your choice, the recipients will be able to determine how best to approach the repair or replacement of your warped door.
You might consider replacing your warped door with a professional door which has Sing Core inside which can be guaranteed not to warp, bend twist or otherwise fail so as to avoid this pitfall in the future.
For more information, see: Door Warping vs. True Flat
What if my door with Sing Core inside is warped?
The same standard method of determining and measuring any door with Sing Core inside is used just like any other door (as noted above).
Contact Sing Core about your concerns about your door being certain to include the two photos as noted above.
If you have purchased a professional door with Sing Core inside, you may be the recipient of a replacement Sing door.
Note that upon arrival and un-crating of a door with Sing Core inside, a door may appear warped (and indeed it will be measurable). This is normal for a door which has been packed and in transit. Stand your door on its edge at least twelve inches away from any adjoining surface area, allowing it to acclimatize for up to 72 hours. Measure your door again and you will find it to be straight and true. If not, document for warp (as above) and contact Sing Core.
In the event that a professional door with Sing Core inside is warped (which is highly unlikely) your help in determining the cause of the door’s warping is appreciated. Please assist documenting the chain of custody of your professional door with Sing Core inside, including the millwork or door company which finished the door, and the installers who installed the door, to help us insure your replacement door remains warp-free.