HI, I thinking of knocking through our kitchen on the gable end into our out house to make a larger kitchen. The opening span would be 1800mm in a wall with no cavity. (two hardbricks right up against each other as the house was build in 1890). There is only a bathroom above the kitchen with a pitched roof so it would be supporting one story. The walls thicknes is 200mm thick. Question is would two 2100x100x65 concrete lintels be sufficient. Or even 2100x215x65. are concrete lintel strong enough?