We already know that brick walls are not waterproof. Once the water is behind the brick veneer, we need to capture it and redirect it to the exterior of the wall so it can't cause damage. This is the job of flashing material. Flashings are not easy to install correctly. This is especially true at inside and outside corners. The flashings need to be overlapped and cut in such a way so that water will not enter through the seams.
What's more, the water resistant membranes such as tar paper or the new, fancy water barriers need to overlap the flashings. This practice requires work above doors and windows. The flashings need to be "laced" behind the water membranes.
Flashings also need to be placed at door sills, window sills and any other place where the brick has a horizontal break or interruption.
Quite possibly the best brick flashing I have seen is one made by the Grace Construction Products. It is called Perma-Barrier.
The Water Pathway
Mortar droppings can easily clog the narrow space behind brick. The droppings accumulate as the brick wall gets taller and taller. If this space becomes clogged, then the water can't easily escape through the weep holes below. There is only one product I have seen that permits water to easily find its way to the weep holes. This product is called Mortar Net. It is a plastic mesh product that looks like a saw-toothed shingle. This product can be found at companies that sell brick.
These are the simple drain holes at the base of walls or on the first course of brick above a door or window. Without weep holes, there is no easy way for water to escape from behind brick walls. The Brick Industry Association recommends weep holes be placed on 2 foot centers. Most model building codes permit a spacing of 4 feet on center. In my opinion, you can't have too many weep holes.
I have seen unknowing homeowners caulk these holes closed. Don't do it! They are important and must be left open at all times.
Masonry Wall Ties
Non-professional bricklayers often create hazards by not installing a sufficient number of masonry wall ties in brick veneer work. A wall tie is a connector. These simple metal devices attach the brickwork to the wood frame structure. Without wall ties, a brick wall can simply fall down and away from the house. The model building codes are very specific in the spacing of wall ties. They tell you how often they should be spaced vertically and horizontally. Sometimes they will specify a minimum amount of wall ties per square foot of brick work. The building codes also tell you how far each nail should penetrate into the wood sheathing or wood studs. Pay attention to this specification!
This is going to be your biggest challenge. I would like to see you have your bricklayers make their mortar like the old timers. The premixed mortars used today are simply too strong. That is fine for today's higher strength brick, but it is unnecessary in brick veneer work. A low strength mortar with a high lime content is what you want. The extra lime in the mortar actually will help prevent water from getting between the brick and mortar contact zone. A great low strength mortar that you might try can be mixed using the following proportions: 5 measures of sand, 3 measures of lime and 1 measure of Portland cement. This mortar mixture is an absolute necessity if you decide to use used brick on your house or chimney.