Stone veneer is commonly used on commercial and residential buildings because it provides an attractive, durable exterior finish. However, even a well-installed stone veneer system can experience deterioration when it is repeatedly exposed to concentrated water from roof drainage.
Roof Water Can Become a Problem
Roof drainage systems are designed to collect and discharge large quantities of rainwater and snowmelt. When a roof drainage outlet discharges directly onto or close to a stone veneer wall, the wall can be exposed to concentrated and repeated water flow.
Over time, this can contribute to:
- Deterioration of mortar and joints
- Moisture damage to the supporting sheathing
- Loosening or displacement of stone veneer units
- Water accumulation behind the cladding
- Freeze-thaw damage during winter
- Localized deterioration around drainage outlets
The problem can be particularly significant on multi-storey buildings, where water from a large roof area may be concentrated at only a few discharge locations. A drainage outlet serving a five-storey building, for example, can expose the wall below to a substantial volume of water.
Calgary’s Freeze-Thaw Cycles Can Make the Problem Worse
Moisture-related deterioration can become more serious in climates with repeated freezing and thawing.
Water that enters or is retained within porous materials can freeze when temperatures fall below 0°C. Frozen water expands and can create stresses within the material. When temperatures rise, the ice melts and the process can repeat.
After many freeze-thaw cycles, vulnerable components of the cladding assembly may deteriorate.
This does not mean that every damaged stone veneer system is caused by freeze-thaw action. Proper investigation is necessary to determine the actual cause of deterioration.
Look at the Drainage, Not Just the Stone
When stone veneer is damaged below a roof drainage outlet, simply replacing the damaged stones may not address the underlying problem.
A proper assessment should consider:
- Where does the roof water come from?
- How much water is being discharged?
- Where does the water go after leaving the outlet?
- Does water remain against the wall or accumulate at the base?
- Is the drainage system directing water away from the building envelope?
- Are the sheathing, mortar, flashing, and supporting components still in good condition?
In some situations, extending or rerouting a roof drainage outlet may reduce the amount of water reaching the stone veneer and help prevent continued deterioration.
Repair the Cause, Not Only the Damage
There may be several approaches to repairing damaged stone veneer.
Depending on the condition, an owner may consider:
- Localized replacement of damaged stone
- Replacement of deteriorated sheathing
- Repair or replacement of mortar joints
- Improvement of flashing and drainage
- Extension or rerouting of roof drainage outlets
- Larger-scale replacement of the stone veneer system
The appropriate solution depends on the extent and cause of the damage.
A localized repair may be appropriate where deterioration is limited. However, if the source of excessive moisture remains, additional damage may occur in the future.
Engineering Assessment Can Help
At Solid Structural Design, we assess not only the visible stone veneer damage but also the supporting wall assembly and the conditions contributing to the deterioration.
A site review can help identify whether the observed damage appears to be localized to the cladding or whether there are concerns with the supporting wall system. Where roof drainage is contributing to the problem, we can also develop a separate engineering scope to investigate and design modifications to the drainage outlets.
A stone veneer wall does not only need strong materials—it also needs good water management.
Proper roof drainage, flashing, moisture management, and regular maintenance can play an important role in protecting the building envelope and extending the service life of the exterior cladding.