Key Detail: Ridge Beam

The original roof is symmetrical

The pitched rafters lean against each other

Like stacking playing cards in a tower

There is a timber “ridge plate”

But it doesn’t hold weight

It’s just for buildability

But adding a dormer

Breaks the symmetry of the roof

Pitched rafters would push the flat roof sideways

Unless the ridge is strong and holds weight

So it needs to be a “ridge beam”

A steel holding up the roof

The key detail is here (right).