Metallizing How to Control Corrosion by Improving Design. Why is Stainless Steel Corrosion Resistant? An Introduction to Hydrogen Embrittlement. An Intro to Pipeline Corrosion in Seawater. Follow Connect with us. Sign up. Thank you for subscribing to our newsletter! Connect with us. Vapor Barrier. In areas where the climate is cold in the winter, the vapor retarder should be installed on the inner side of the wall near the warm interior space — or on the warm side in winter.
In humid climates or areas where there is extensive use of air-conditioning, if a vapor retarder is required, it should be installed on the exterior side of the wall.
The table below shows the perm rating of some common building materials that are consistent with the ASHRAE Handbook of Fundamentals and other industry sources. The latest research on moisture performance of walls and vapor retarders has significantly changed the vapor retarder requirements in the building codes.
Class III vapor retarders can be used on the interior side of the wall in the following climate zones in any of the conditions outlined. Logically, this means we need different strategies for different climates. We also have to take into account differences between summer and winter. Finally, complications arise when materials can store water.
This can be both good and bad. A cladding system such as a brick veneer can act as a reservoir after a rainstorm and significantly complicate wall design.
Alternatively, wood framing or masonry can act as a hygric buffer absorbing water lessening moisture shocks. What is required is to define vapor control measures on a more regional climatic basis and to define the vapor control measures more precisely. Part of the problem is that we struggle with names and terms. We have vapor retarders, we have vapor barriers, we have vapor permeable we have vapor impermeable, etc. What do these terms mean?
It depends on whom you ask and whether they are selling something or arguing with a building official. In an attempt to clear up some of the confusion the following definitions are proposed:. The current International Building Code and its derivative codes defines a vapor retarder as 1. In other words the current code definition of a vapor retarder is equivalent to the definition of a Class II Vapor Retarder proposed by the author.
Continuing in the spirit of finally defining terms that are tossed around in the enclosure business. It is also proposed that materials be separated into four general classes based on their permeance again nothing new, this is an extension of the discussion in ASHRAE Journal, February 02 — Moisture Control for Buildings :.
The following building assembly recommendations are climatically based see Side Bar 1 and are sensitive to cladding type brick or stone veneer, stucco and structure concrete block, steel or wood frame, precast concrete.
The recommendations apply to residential, business, assembly, and educational and mercantile occupancies. The recommendations do not apply to special use enclosures such as spas, pool buildings, museums, hospitals, data processing centers or other engineered enclosures such as factory, storage or utility enclosures. Avoidance of using vapor barriers where vapor retarders will provide satisfactory performance.
Avoidance of using vapor retarders where vapor permeable materials will provide satisfactory performance. Thereby encouraging drying mechanisms over wetting prevention mechanisms. Avoidance of the installation of vapor barriers on both sides of assemblies — i. Avoidance of the installation of vapor barriers such as polyethylene vapor barriers, foil faced batt insulation and reflective radiant barrier foil insulation on the interior of air-conditioned assemblies — a practice that has been linked with moldy buildings Lstiburek, Avoidance of the installation of vinyl wall coverings on the inside of air-conditioned assemblies — a practice that has been linked with moldy buildings Lstiburek, Each of the recommended building assemblies were evaluated using dynamic hygrothermal modeling.
The moisture content of building materials that comprise the building assemblies all remained below the equilibrium moisture content of the materials as specified in ASHRAE P under this evaluation approach. WUFI was used as the modeling program Kunzel, More significantly, each of the recommended building assemblies have been found by the author to provide satisfactory performance under the limitations noted. Satisfactory performance is defined as no moisture problems reported or observed over at least a year period.
This wall assembly has all of the thermal insulation installed to the interior of the vapor barrier and therefore should not be used in cold regions or colder. It is also a durable assembly due to the block construction and the associated moisture storage hygric buffer capacity. The wall assembly does contain water sensitive cavity insulation except where spray foam is used and it is important that this assembly can dry inwards — therefore vapor semi impermeable interior finishes such as vinyl wall coverings should be avoided.
In this wall assembly the vapor barrier is also the drainage plane and air barrier. This assembly has all of the thermal insulation installed on the interior of the concrete block construction but differs from Figure 2 since it does not have a vapor barrier on the exterior.
The assembly also does not have a vapor barrier on the interior of the assembly. It has a large moisture storage hygric buffer capacity due to the block construction. The rigid insulation installed on the interior should ideally be non-moisture sensitive and allow the wall to dry inwards — hence the recommended use of vapor semi permeable foam sheathing. Note that foam sheathing faced with aluminum foil or polypropylene skins would also be acceptable provided only non-moisture sensitive materials are used at the masonry block to insulation interface.
The drainage plane in this assembly is the latex painted stucco rendering. A Class III vapor retarder is located on both the interior and exterior of the assembly the latex paint on the stucco and on the interior gypsum board.
This assembly is a variation of Figure 3. It also has all of the thermal insulation installed on the interior of the concrete block construction but differs from Figure 3 due to the addition of a frame wall to the interior of the rigid insulation. This assembly also does not have a vapor barrier on the exterior. Applicability — all hygro-thermal regions. This wall is a variation of Figure 1 — but without the moisture storage or hygric buffer capacity.
This wall is also a durable wall assembly. It is constructed from non-water sensitive materials and has a high drying potential inwards due to the frame wall cavity not being insulated. It can also be constructed virtually anywhere. In cold climates condensation is limited on the interior side of the vapor barrier as a result of installing all of the thermal insulation on the exterior side of the vapor barrier which is also the drainage plane and air barrier in this assembly.
In hot climates any moisture that condenses on the exterior side of the vapor barrier will be drained to the exterior since the vapor barrier is also a drainage plane. It is important not to confuse a vapor barrier with vapor retarders.
Vapor barriers stop vapor diffusion, while vapor retarders only slow vapor diffusion. Historically, placement of vapor barriers typically polyethylene was on the interior wall and ceiling insulation to prevent vapor division into the wall systems during the winter months when the interior of a home is warmer than the air within the wall system. A hygroscopic building envelope can absorb and store moisture from the surrounding air. A permeable building envelope allows for vapor diffusion.
The study concluded that the presence of a vapor barrier did not produce significant changes in the moisture content of the wall assembly. Furthermore, of the four mechanisms for moisture transfer into the wall system, liquid flow, capillary suction, air movement, and vapor diffusion, vapor diffusion represented the smallest amount and so is less likely to cause severe damage to a home.
Not only do vapor barriers not significantly help a wall system stay dry, but they may also damage the integrity of the home. If moisture infiltrates a wall system, the low permeance of a vapor barrier may stop a wall system from drying. Insufficient drying within the building enclosure can lead to mold and rot, which is unhealthy to the occupants of a home and can damage the integrity of the house. The use of a vapor barrier on the interior or exterior of a building is dependent on the climate zone.
Southern climate zones 1, 2, and 3 do not mandate vapor barriers and retarder. Barricade Wrap is also impermeable to airflow, durable over the expected lifetime of the home, and has the stiffness and strength to resist the forces that act on it during and after construction.
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