Clearing Blocked Internal Storm Drains

Technical Procedures Disclaimer

Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.


We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.



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 “See Snake 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 (Rigid), 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 attempt 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.