Semi- detached. A new row of tiles has been introduced to one roof just below the ridge.

The roofer/builder has increased the cover to the ridge basically by adding the extra course in, we do this when the cover the is shorter then the minimum current standards, and for guarantee reasons for ensuring their isn’t going to be a leak in very windy conditions. The bigger mortar bed is down to preference of the builder/roofer in charge, their is no right or wrong answer but again comes down to guarantee purposes and not wanting the ridge tiles to be blown off/leak in a storm, personally I like a bed of mortar between 25/50mm, anymore and it’s an eye sore any less and well I worry it could fail in high winds. If you are unhappy with the uneven appearance of the two different roofs, ask the builder/roofer for a quotation to do the same to your roof, you don’t add extra courses in for the fun of it, as it’s more time and money it’s always for a good reason and isn’t to spite anybody. Regards Frankie BT Roofing Services Limited

If the builder next door has put a new roof on he has probably dropped the gauge on the battening in to gain correct head lap on new tiles which can easily give you an extra course of tiles on a roof he should have put a bonding gutter to separate your roof from next doors making them detached from each other but still making both roofs water tight this is a common occurrence if the original tiles where put on at a stretched gauge then the builder would have to do this to make sure it doesn’t leak or have same problem again Thanks mark