Seam Peaking in Carpet Installations
Seam peaking is normal when installing and joining carpet and then stretching the carpet into place. Adequate carpet stretching is necessary to ensure that the carpet does not ruck (waves in the carpet) and to ensure that the carpet performs in accordance with the manufacturers warranty.
Seam peaking occurs when a carpet is stretched because the combined carpet backing (primary backing + secondary tape backing) absorbs the forces of stretching at the seam. As the stretch forces are applied to the seamed area, the seaming tape is pulled upward to align itself with the approximate centre of the combined carpet backing. This creates an elevation in the carpet along the seam which consequently causes the pile to open in a v-configuration. When the main source of light falls at an angle across the peaked seam, the pile on the side closer to the light source reflects more light, resulting in a shade similar to the effect of a shadow falling on the carpet.
Seam peaking often eases once the carpet has been installed for a few months as normal traffic and wear causes the carpet to settle down.
To recap, seams are not invisible. But they should not be feared. Almost everything has visible seams, and carpet is no exception.
For further information, view the Carpet Institute of Australia factsheet.