Define zone-wrapper in Omega 4 and 960px
If you are using Susy, something like that will do the job:

$total-columns: 12
$column-width: 6em;
$gutter-width: $column-width / 3;
$grid-padding: $gutter-width / 2;
$container-style: fluid;

html {
  font-size: 62.5%;
}

.l-page {
  @include container();
}