Roof design Documents

BSD-013: Rain Control in Buildings by John Straube — last modified 2008/09/09

Moisture is one of the most important agents leading to building enclosure deterioration. Understanding and predicting moisture movement within and through the enclosure is therefore of fundamental importance to predicting and improving building enclosure performance, particularly durability. Since driving rain deposition on walls and roofs is quantitatively the largest single source of moisture for most walls and roofs, it is no surprise that controlling rain penetration is one of the most important parts of a successful moisture control strategy. In fact, failure to control rain is likely the oldest and most common serious building enclosure performance problem. Commentators as long as Vitruvius (70 BC) bemoaned the challenges of controlling rain penetration. This document will consider rain control from a general to a specific level. The following sections will cover: basic moisture control principles that should be employed in the design of above-grade building enclosures; driving rain as a moisture load on walls; a classification system of the various rain control strategies available for walls; and finally, good design practises for walls. The rain control of roofs will be covered in more detail in another BSD.

BSD-102: Understanding Attic Ventilation by Joseph Lstiburek — last modified 2008/08/20

Attics or roofs can be designed and constructed to be either vented or unvented in any hygro-thermal zone (Map 1). The choice of venting or not venting is a design and construction choice not a requirement determined by the physics or by the building code. The model building codes allow both vented and unvented roof assemblies. The applicable physics impacts the design of attic or roof systems as does the applicable building code but neither limit the choice.

BSD-105: Understanding Drainage Planes by Joseph Lstiburek — last modified 2008/08/20

Controlling rain is the single most important factor in the design and construction of durable buildings and in the control of mold. Drainage planes are used in the design and construction of building enclosures to control rain. All exterior claddings pass some rainwater. Siding leaks, brick leaks, stucco leaks, stone leaks, etc. As such, some control of this penetrating rainwater is required. In most walls, this penetrating rainwater is controlled by the drainage plane that directs the penetrating water downwards and outwards.

BSD-106: Understanding Vapor Barriers by Joseph Lstiburek — last modified 2008/08/21

The function of a vapor barrier is to retard the migration of water vapor. Where it is located in an assembly and its permeability is a function of climate, the characteristics of the materials that comprise the assembly and the interior conditions. Vapor barriers are not typically intended to retard the migration of air. That is the function of air barriers.

BSD-111: Flood and Hurricane Resistant Buildings by Joseph Lstiburek — last modified 2008/08/21

We learn our lessons from disaster. Hurricane Andrew taught us about wind. Hurricanes Charley, Frances and Jeanne taught us about rain. The Red River of the North Basin taught us about floods. Hurricane Katrina had it all: wind, rain and flood. That we will rebuild, and rebuild in the same place, is not in doubt. This is what we do – for better or worse. If we are to rebuild and if we are to rebuild in the same place how should we rebuild?

BSD-115: Wood Pitched Roof Construction by John Straube — last modified 2008/08/20

Pitched roofs of either wood rafter and joist or truss construction are used in the construction of literally millions of homes and small commercial buildings each year. There are variations in these roofs, but there are relatively few primary options. The following digest describes the most common types of wood pitched roofs, their enclosure functions, and common modes of failure.

BSD-135: Ice Dams by John Straube — last modified 2008/08/20

Ice dams are a common roof performance problem in buildings that experience snowfall and at least a month of below freezing temperatures. The combination of sufficient roof pitch, adequate insulation just above the exterior wall, and air sealing at the wall-roof assemblies transition are all essential to prevent ice dams. But ice dams can occur even in properly detailed roof assemblies from differential solar snow melt. This digest outlines both the causes and solutions to ice dam problems.

BSD-149: Unvented Roof Assemblies for All Climates by Christopher Schumacher — last modified 2008/09/09

A brief description of different types of unvented roof assemblies and the benefits of unvented roof construction.