What are the Building Codes For Drainage Around A House?
Building codes for drainage around a house are specific and haven’t changed much over the last several decades. The International Residential Code (IRC) is the most used model code in Texas as well as most other states in America. It is the knowledge base from which home inspectors draw their expertise whether they know it or not.
The State first adopted the IRC in 2000 and maintains the decision today. Its predecessor was the CABO Code, which was almost identical. However, the IRC relinquished enforcement requirements to the Counties to enact if they so choose. Even then local municipalities have the right to pick, choose and revise it to fit their area needs.
Unfortunately, many counties do not have the budget to enforce a building code. Doing so makes homebuilding outside of major municipalities open range. In rural areas homebuilders are regulated by their liability insurance carriers (if they have any) and the courts if a homeowner can prove they were neglectful in some way.
building codes for drainage around a house IRC R401.3
Site drainage around a house is addressed in the Foundation Chapter of the IRC because proper drainage is critical to foundation performance. Maintaining drainage, landscaping and irrigation should be a priority for every homeowner. This section is simple and comprehensible. It is a requirement, not a recommendation. There are no gray areas unless there is an obstruction within ten feet of the foundation that prevents sloping. The building codes for drainage around a house even recognizes sidewalks and other impervious surfaces should be sloped to prevent water from flowing toward the foundation. IRC Subchapter R401.3 Drainage addresses general drainage.
The code states: “Surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection that does not create a hazard. Lots shall be graded to drain surface water away from foundation walls. The grade shall fall a minimum of 6 inches (152 mm) within the first 10 feet (3048 mm).”
R401.3 Lot Drainage Exception
The IRC recognizes that houses are often constructed less than 10 feet apart. To address those subdivision lots IRC Subchapter R401.3 Drainage offers an Exception in the building codes for drainage around a house.
The code states: “Where lot lines, walls, slopes or other physical barriers prohibit 6 inches (152 mm) of fall within 10 feet (3048 mm), drains or swales shall be constructed to ensure drainage away from the structure. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped a minimum of 2 percent away from the building.”
Using Swales To Control Drainage
There are other tried and true ways to control site drainage when there is an obstruction within ten feet of the foundation. They can be found in the building codes for drainage around a house. For instance, swales are a commonly used strategy found for subdivision lots due to the proximity of the houses. A swale is simply a shallow ditch, which collects the ground water and sends it away from the foundation. The idea is to spread the water out so as not to unevenly saturate the bearing soil at and under the foundation.
The problem is builders sometimes do not provide adequate sloping to the main storm drainage system. Improperly constructed swales allow ponding within ten feet of the foundation contributing to foundation failure. Another concern with swales is some builders allow the landscapers to form them along the foundation behind the planting bed. Although this might be considered as esthetically pleasing it almost always leads to excessive foundation movement. Measured success might be possible if the swale was lined with an impervious material making it a gutter instead of a ditch.
Another approach is to provide an underground drainage system. Those include a series of collection boxes connected to pipes buried underground thereby discharging the storm water a safe distance away from the foundation. There are multiple problems with these. The most common issue being they are usually undersized. Another concern is the inlet drain box being too close to the foundation so actually directs surface water toward the foundation instead of away. They are almost always poorly maintained, making them useless.
IRC Subchapter R801.3 Roof Drainage
The code states: “In areas where expansive or collapsible soils are known to exist, all dwellings shall have a controlled method of water disposal from roofs that will collect and discharge roof drainage to the ground surface at least 5 feet (1524 mm) from foundation walls or to an approved drainage system.”
Note the addresses drainage in areas where expansive or collapsible soils exist. This includes most of Texas and is especially true in southern and eastern parts of the state. These soils can also be found in other areas even where rock is predominant. This detail is important because soil conditions affect a house foundation.
How Can Roof Drainage Be Controlled?
There are ways for roof drainage to be controlled to comply with building codes for drainage around a house. The best answer is by installing gutters or rain disperser systems. When doing so it is highly recommended for them to be installed all around the house. Partial installation can lead to uneven soil moisture density next to the foundation. The foundation can experience tilting, sloping, settlement, heaving and other adverse conditions if the bearing soil is not consistent on all sides.
The EPA recognizes moisture problems can occur in homes. Elevated moisture wicking into concrete and up into the house contributes to fungal concerns. They recommend roof drainage be placed at least five feet from the house. Those little concrete splash blocks do not achieve the intended goal.
Downspouts should be connected to a flexible pipe in areas, especially where the supporting soil is expansive. The pipe should discharge the water at least five feet from the foundation or directly into a swale where obstructions are within ten feet of the house.
Final Thoughts on Building Codes For Drainage
Our experience has found poor site drainage to be the number one cause of foundation failure. Give us a call if you would like an inspection and advice on this subject. The Wildcat Inspections Team will be happy to assist you.
