Clearing Blocked Internal Storm Drains

Procedure code:
Thermal and Moisture Protection
Iron Roof Drain
Last Modified:



A. This procedure includes guidance on inspecting for and clearing out blocked internal storm drains. Prevention of potentially blocking debris from entering the drains via the roof is an important factor in preventing blocked drains. See 3.01 A.1. and A.2. below for preventive maintenance guidance.

B. See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:

  1. Safety Precautions
  2. Historic Structures Precautions
  3. Submittals
  4. Quality Assurance
  5. Delivery, Storage and Handling
  6. Project/Site Conditions
  7. Sequencing and Scheduling
  8. General Protection (Surface and Surrounding)

These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO).





A. Diagnostic Equipment: High performance durable camera/transmitter system equipped with small black and white camera head and pipe location transmitter; able to negotiate multiple 90 degree bends in 2" to 10", such as “SeeSnake Diagnostic Tools” (RIDGID), or approved equal.

Note: Complete system includes camera, push cable, 3" & 6" centering guides, cable drum and dolly, interconnect cable, 9" high resolution B&W monitor with integrated power supply, light dimmer and sunshade, operator’s manual, RCA to RCA video cable, BNC to RCA adapter.

B. Drain cleaning equipment such as an auger and/or saw tooth cutter (Ridgid), or approved equal, as required for the specific blockage type.



A. Examine the foundation and exterior of the building by walking around the building during a heavy rain storm. Look for blocked or broken storm drains, leaking or overflowing gutters or perforated downspouts. Notice where water is ponding on the ground around the building.

  1. Clean gutters and downspouts twice a year—in late spring and in late fall.
  2. Provide screen barriers at gutter outlets to prevent debris from entering into the downspout and storm drain system.
  3. Examine interior walls where internal roof drains run vertically, to identify staining, failed paint, failed plaster or other signs of water damage near the drains.


Caution: Do not attemt to flush drains with water to remove debris. Excessive pressure can create internal leaks, causing staining and damage to adjacent building materials. Inspect annually; open and clean-out accessible points periodically.

A. When there is apparent blockage and signs of water damage inside the building, use “low-tech” attempts such as routers to clear the drain. If these attempts are not successful, it is possible to identify the problem via new video tools.

B. Identify the problem through video inspection and determine the fault location as accurately as possible using a high-performance camera/transmitter system.

  1. Plug in the system and turn on the monitor.
  2. Push the camera head into the line and continue to slowly feed it through. Follow manufacturer’s instructions.
  3. Blockages will be evident on the video monitor as viewed by the camera.
  4. Once the blockage has been identified, use the location transmitter to accurately identify its location. Follow manufacturer’s instructions.

B. Remove blockages using a mechanical auger or tooth cutter as required for the type of blockage. Follow manufacturer’s instructions. If necessary, excavate the section of drain line in question and replace any cracked or broken pipe.

C. Test drain lines between catch basin and municipal storm drainage system.

D. Replace any missing drain covers to match existing.

Last Reviewed: 2017-12-11