Roof Vapor Retarder Purpose

The purpose of a vapor retarder is to minimize or reduce water vapor diffusion into a low slope roof or wall system.

Roof vapor retarder purpose. 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. Vapor barriers are not typically intended to retard the migration of air. 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. Everyone knows that water in roof systems is never a positive.

The purpose of vapour barriers. Vapor diffusion should be considered as a secondary moisture transport mechanism when designing and building roofs. 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.

Without a vapor retarder the deck board sometimes called a roof board or substrate board under the insulation layers has much less utility. 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. 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. Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful.

In other words it is used to prevent the formation of condensation in a low slope roof or wall system. 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. Specific vapor retarders are often unnecessary if appropriate air movement control is provided or if control of condensing surface temperatures is provided. 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.

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.