Roof Vapor Retarder Purpose

When we use a vapor retarder in a roof system it will also act as an air barrier as long as it is sealed at all perimeters and penetrations and is tied to the wall air barrier.

Roof vapor retarder purpose.

Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful. Damage from water condensation due to water vapour movement called water vapour drive can wreak havoc on even the sturdiest of built structures and threaten the effectiveness of insulation. Vapor diffusion should be considered as a secondary moisture transport mechanism when designing and building roofs. The purpose of a vapor retarder is to minimize or reduce water vapor diffusion into a low slope roof or wall system.

Everyone knows that water in roof systems is never a positive. Vapor barrier unseen yet essential depending on where you live and what materials you are using for your construction project a vapor barrier can be a very important part of your structure. Low slope underlayments vapor retarders an important element to maximizing roof performance longevity and building protection on low slope roof systems is the understanding of underlayments and vapor retarders. Vapor barriers are not typically intended to retard the migration of air.

A vapour barrier is an important component in building construction. Without a vapor retarder the deck board sometimes called a roof board or substrate board under the insulation layers has much less utility. Its purpose is to help prevent water vapour from reaching building walls ceilings attics crawlspaces or roofs where it can condense and cause building materials to rot or grow mould. Specific vapor retarders are often unnecessary if appropriate air movement control is provided or if control of condensing surface temperatures is provided.

Considering that some deck board products may be vapor semi impermeable omitting this component will save cost and may foster greater drying potential toward the conditioned building interior. 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. And since most vapor barriers are not obvious to the homeowner they are an often neglected part of many do it yourself construction projects.

A vapor retarder is a material or system that is designed as part of the roof system to substantially reduce the movement of water vapor into the roof system where it can condense.