Houston area builders love arches
So do Houston homebuyers and sellers. Many of the arches are what I call shallow arches. Shallow arches are not self-supporting.
The code is even more stringent – arches, shallow or not, must be supported by a noncombustible lintel. No exceptions.
There is a very good reason for this: arches without a lintel to support the brick are at a higher risk of failure. This is even more the case when the foundation is sitting on expansive soils. Brick arches in expansive soil areas frequently will show openings and cracks in brick arches, especially shallow arches.
It The myth of the self-supporting arch
Most builders believe brick arches are self-supporting. There is a grain of truth in this, but only a grain.
Arches can be self-supporting under certain conditions, but those conditions are rarely met in modern residential construction. For instance, the arch is supposed to be “well buttressed.” When an arch is designed by an engineer a key part of the design is the weight of the buttressing. It is rare for a residential masonry arch to be “well buttressed.”
In addition, the design includes assumptions that are unrealistic. It is assumed that the joints between the brick units are completely filled with mortar to obtain maximum bond strength and a more even distribution of stress in the joints, the mortar used must have high compressive and bond strength, the foundation is stable, etc.
In reality, mortar joints are rarely fully filled with mortar. Only the front is filled. Masons do this for the simple reason that no one will know and the future problems that emerge will do so only long after the masons have moved on.
Foundations on expansive soils move as the moisture level in the soil changes. Cracks in masonry arches are inevitable as the house ages.
What to do about cracked arches
The safe thing is to hire a steel fabricator to create a custom steel lintel to support the arch.
Another option is to repair the visible cracks. In my opinion, this is not a viable option if the shape of the arch is distorted.
Many people think that a steel lintel will not look good. The arch and lintel in the photo below look fine to my eyes.