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Roof Drainage Building Codes & Standards

International Code Council - International Residential Code 2006

Ch. 8 Roof-Ceiling Construction: Section R801

R801.3 Roof Drainage

"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."

International Residential Code 2000 Commentary - Vol. 1

"Saturated expansive or collapsible soils can lead to foundation failures because their additional loads are imposed on the foundation wall. To minimize the potential for the soil adjacent to the foundation wall to become saturated due to roof drainage, the code requires that the roof drain 5 feet (1524 mm) from the foundation."

Ch. 4 Foundations: Section R401.3

R401.3 Drainage

"Surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection so as to 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)."

Exception:Where lot lines, walls, slopes or other physical barriers prohibit 6 inches (152mm) of fall within 10 feet (3048 mm), the final grade shall slope away from the foundation at a minimum slope of 5 percent and the water shall be directed to drains or swales to ensure drainage away from the structure. Swales shall be sloped a minimum of 2 percent when located within 10 feet (3048 mm) of the building foundation. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped a minimum of 2 percent away from the building.

International Residential Code Commentary - 2000

Along with the proper support for a structure through the foundation system, adequate preparation of the building site is necessary to keep water drainage away from the supporting foundations. Proper site drainage is an important element in preventing wet basements, damp crawl spaces, eroded banks, and possible failure of a foundation system.

One of the most important considerations is the arrangement of structures on a building site in a manner that retains natural drainage patterns and minimizes the alteration or disturbance to existing grades. If the designer keeps such factors in mind, the result will be a reduction of ground surface stabilization problems and opportunities for differential settlement through the reduction in the use of fills. A detailed treatment of drainage design is beyond the scope of this document; therefore, only rough guidelines can be provided for areas where a more comprehensive set of grading regulations does not exist.

As illustrated in Commentary Figures R401.3(1) and R 401.3(2) , drainage patterns should result in adequate slopes to approved drainage devices that are capable of carrying concentrated runoff. In some cases, control of concentrated roof runoff by gutters and downspouts may be needed, and if gutters and downspouts are used, provisions should be made to discharge runoff in order to prevent soil erosion. Refer also to Section R801.

Diagram of approved downspout extension.

Texas Administrative Code

Title 22............Examining Boards

Part 23............Texas Real Estate Commission

Chapter 535....General Provisions

Subchapter R..Real Estate Inspectors

Rule 535.228: Standards of Practice: Inspection Guidelines for Structural Systems

(a) Foundations - the Inspector shall:

(8) report as in need of repair conditions or symptoms that ay indicated the possibility of water penetration that are present and visible, such as improper grading around foundation walls or plumbing leaks; and

(9) report as in need of repair conditions that are present and visible and may be adversely affecting foundation performance, such as erosion or water ponding.

(h) Roof, roof structure and attic. The inspector shall:

(11) report as in need of repair deficiencies in visible installed gutter and downspout systems.

International Code Council- International Residential Code 2006

National Association of Home Builders

NAHB Model Green Home Building Guidelines

Version I, Section 2.2 Enhance Durability and Reduce Maintenance Install drip edge at eave and gable roof edges. Intent: The drip edge directs roof runoff water into the gutters and away from the fascia and roof sheathing. Install gutter and downspout system to divert water at least 5' away from foundation and from there into the overall onsite drainage area. Intent: Moisture intrusion of foundations is avoided by moving runoff water beyond the foundation.

U.S. Green Building Council

LEED for Homes Program

Water Efficiency: Credit #1 Water Reuse - Maximum Points: 2

There are no mandatory requirements.

Optional requirements include:

1.1 Design and install of rainwater harvesting system which includes the collection of surface and roof run-off for irrigation uses. (1 Point)

1.2 Design and install gray water re-use system, with minimum of dedicated clothes washer with 2 inch drain directed to subterranean drain field for landscape irrigation. (1 Point)

USGBC Rationale: 50% of potable water use in a home may be for maintenance of lawns and gardens. This credit promotes the re-use of indoor waste water and rainwater to help meet landscape water demands.

Materials and Resources: Credit #4 Durability Plan - Maximum Points: 3

The mandatory requirement is:

4.1 Prepare a detailed durability plan per the design process in Exhibit MR4-A.

Optional requirement:

4.2 Verify implementation of durability plan via third party inspection as described in Exhibit MR4-C.

The synergy between durability, energy efficiency, and indoor air quality are inextricably linked in high performance homes. Moisture management becomes more critical as energy management reduces the buildings overall drying potential."

Moisture can be a major cause of indoor environmental problems (e.g., mold)". The point value of this credit therefore reflects the related indoor environmental benefits of improved water management at the foundation, exterior walls, and roof.

Water management of the property (i.e., both lot and structure) is a combination of surface and ground water management, with the dual goals of protecting the structure from water as well as keeping as much water as possible on the site in order to limit the burden on municipals infrastructure, recharging the aquifer, etc. To the greatest extent possible, the site and landscape should be designed with these goals in mind. The durability plan is intended to prevent damage to the home by water - both surface and ground - that can not be effectively managed at the site level, as well as to protect the structure from other damage functions.

USGBC Rationale is that durability problems can substantially shorten the life of assemblies, systems, and/or materials in a home and indeed the home itself. While the development and implementation of a durability plan can not guarantee improved durability, there are a number of precedents in the insurance industry, in particular, supporting the premise that a prescribed process aimed at improving durability can indeed correlate to improved performance, as measured by decreases in warranty claims for durability-related building defects and failures.

Energy Star

Indoor Air Package Pilot Specification - April 4, 2005

1. Moisture Control Required Measures References Water Managed Roofs

1.1Provide Minimum No. 30 roof felt under layment or equivalent.

1.2 In IECC 2004 Climate Zones 5 and higher, provide self sealing water protection membrane ice flashing over the sheathing at the eave extending 2 feet inside the exterior wall plane.

1.3 Provide metal drip edge at all exposed roof decking.

1.4 Provide self-sealing bituminous membrane at all eaves, valleys and penetrations except in climates with less than 20 inches annual rainfall.

1.5 Provide Insulated wind baffle or other air barrier to block wind washing at all attic eave bays in roof assemblies with soffit vents.

1.6 Provide step flashing at all intersections of roof and walls with the exception of continuous flashing at metal and rubber membrane roofs. Metal "kick-out" flashing shall be provided at the end of roof/wall intersections to direct water away from wall. Drainage plane above shall be directed water flow onto and not behind flashing. Intersection wall siding shall terminate a minimum of 2 inches above roof. HUD/NAHB specs for gutters and downspouts

1.7 Direct roof water from house with either:

Guttering and downspouts shall empty to lateral piping that deposit(s) water on finish grade a minimum of 5 ft. from foundation, or in limited spaces, deposit to underground catchment system that carries water 10 ft. from foundation.

In dry climates with less that 20 inches annual rainfall as shown in EEBA Builder Guides, provide minimum 18" roof overhangs that deposit water to grade sloped away from home.

References

Copper Development Assn. Design Handbook, Sec. 4

Moisture Control Handbook
IRC

EBBA Builder Guide
Moisture Control Handbook

EEBA Builder Guide
EEBA Water management Guide

IRC code 801.c
EEBA Builder Guides

HUD/NAHB specs for gutters and downspouts
Moisture Control Handbook
IRC

Also see:

Texas Minimum Construction Standards

2.3 Drainage
Surface drainage shall be diverted to a storm sewer or other approved point of collection that does not create a hazard. Lots need to be graded to drain surface water away from the foundation at a minimum slope of 6” within the first 10’. Where lot lines or other physical barriers prohibit this, drains, swales, and/or rain gardens shall be constructed to ensure drainage away from the structure. Use of alternative drainage methods must be approved by TDHCA.
Rain gutters shall be installed if none exist. Gutters shall slope 1” for every 20 linear feet with downspouts installed at a minimum every 40’. Downspouts shall discharge water at least 5’ from the foundation. Special care must be taken to not discharge water onto adjacent properties.

   

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