A vapor barrier (also called a vapor retarder
Retarder
A retarder is a device used to augment or replace some of the functions of primary friction-based braking systems, usually on heavy vehicles. Retarders serve to slow vehicles, or maintain a steady speed while traveling down a hill, and help prevent the vehicle from "running away" by accel…
Where are vapor barriers required?
A vapor barrier is likely required if the building is cladded with absorptive material and if the structure is in United States climate zones 4C, 5 through 8. If you are building in a colder climate, check local laws or consult with your architect if a vapor barrier is required.
When did vapor barriers become code?
Since 1948, building practices have changed Although building code requirements for vapor barriers were totally unjustified when they were first established in 1948, there have been three technical developments since then that have changed the way interior vapor retarders affect wall performance.
What happens if you don't install a vapor barrier?
Without poly beneath the drywall, water vapor hits the drywall and diffuses through to the drier (in summer) indoor air. By installing a sheet of poly there, you cut off that drying mechanism and water that finds its way into walls can stay there longer and do more damage.
Is a vapor barrier necessary behind drywall?
No, you don't need a vapor retarder, Class I or otherwise. By the time you paint the drywall, though, you've brought it into the Class III vapor retarder range (between 1 and 10 perms), and even less water vapor will diffuse through. Seal the air leakage pathways.
Can I use Tyvek as a vapor barrier?
Housewrap products like Tyvek are made with one of the highest ratings of 58 perms so they can easily allow water vapor to pass through them.
Is a moisture barrier necessary?
When moisture penetrates your flooring, it can cause mold, mildew, and the potential for water damage. A moisture barrier helps control the water vapor's movement to help protect your floors. Therefore, if you're installing floors in an area that sees moisture, even a little, a vapor barrier is needed.
Is an interior vapor barrier necessary?
Vapor barriers protect against mold and rot inside structures by preventing condensation and moisture from building up and damaging building materials. If a home is being built in a very humid climate, a vapor barrier can be an essential source of protection from problems caused by excess moisture.
Are crawl space vapor barriers necessary?
Yes. You need a vapor barrier in your crawl space. What's more, a moisture barrier is the minimum amount of protection that you should have in your crawl space. A vapor barrier helps you to avoid expensive repairs.
Does blown in fiberglass insulation need a vapor barrier?
Fiberglass Insulation Like other batt-type insulation, fiberglass has a predictable R-value if not compressed but is difficult to fit around obstacles without leaving gaps. In most climates, it needs a vapor barrier.
Can you use plastic sheeting as a vapor barrier?
Reinforced polyethylene plastic sheeting (poly) comes in a variety of thicknesses and strengths. A 6 mil thick poly is commonly used as a vapor barrier and offers short-term savings to the homeowner.
Do vapor barriers cause mold?
One of the more common problems with crawl spaces that do not have a crawl space vapor barrier system is that they create high moisture levels, which may result in mold growth – as dampness creates the ideal environment for mold growth.
What is the difference between a vapor barrier and a moisture barrier?
Moisture barriers function to help in preventing water from entering inside of the wall cavity. On the other hand, vapor barriers basically prevent water vapor from the interior of the house to filter through the wall and condense on the warm side of the insulation.
What do you put behind drywall?
Wires. Electrical cables are usually behind drywall, either running horizontally through holes in the studs or stapled vertically up the sides of studs. Outlet cables tend to be about 12 inches high. Light switches are around 48 inches high, so expect to see electric cables around that area.
Do you have to put a vapor barrier in basement walls?
If a basement wall system is designed and built to keep an interior space dry, then interior vapor barriers should be avoided regardless of where the insulation is located. If the basement is not properly insulated, hot basement air can seep into the foundation.
Where do you put vapor barrier in walls?
Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions: the inner surface in colder climates and the outer surface in hot, humid climates. In existing spaces, oil-based paints or vapor-barrier latex paints offer an effective moisture barrier.
Should basement walls have a vapor barrier?
Steve Bliss, of BuildingAdvisor.com, writes: The short answer is: Don't use a vapor barrier in a finished basement. This is asking for trouble, especially with a full bathroom, which generates a lot of humid air. Rigid foam board on the interior, like you have, is the ideal insulation.
Types of Vapor Retarders
Vapor retarders are typically available as membranes or coatings. Membranes are generally thin, flexible materials, but also include thicker sheet materials sometimes called "structural" vapor retarders. Materials such as rigid foam insulation, reinforced plastics, aluminum, and stainless steel are relatively resistant to water vapor diffusion.
Installing Vapor Retarders for New Construction
In mild climates, materials like painted gypsum wallboard and plaster wall coatings may be enough to impede moisture diffusion. In more extreme climates, higher-perm vapor diffusion retarders are advisable for new construction.
Installing Vapor Retarders in Existing Homes
Except for extensive remodeling projects, it's difficult to add materials like sheet plastic as a vapor retarder to an existing home. Obtaining an energy assessment and thoroughly sealing any leaks it reveals is are very effective for slowing moisture movement in and out of your home.
Water Resistive Barriers
An air barrier/vapor retarder attempts to accomplish water vapor diffusion and air movement control with one material. This type of material is most appropriate for southern climates where keeping humid outdoor air from entering the building cavities is critical during the cooling season.
Why does water vapor form in the air?
Because the temperature of the container falls below the dew point temperature given the relative humidity of the surrounding air. So water vapor in the air around the object condenses, or the air molecules come together forming water droplets.
Do we need a vapor barrier in California?
We need vapor barriers in California Climate Zones 14-16. In some climate zones , an air barrier allows currents of air to help prevent water vapor from forming. A vapor barrier is likely required if the building is cladded with absorptive material and if the structure is in United States climate zones 4C, 5 through 8.
What is smart vapor retarder?
A smart vapor retarder is a vapor retarder material with the unique ability to react to changes in relative humidity by altering its physical structure.
Do you need a vapor retarder?
Whether or not you need a vapor retarder hinges on three main factors your climate, your home and the location of the wall you're insulating.
Can a vapor retarder be used in a wall?
In certain climates vapor retarders can be a vital part of the wall construction. However incorrect use can lead to additional moisture problems. Consult an insulation professional in your area if you are unsure where or how to install a vapor retarder or consider a vapor retarder that provides some degree of additional flexibility, like a smart vapor retarder. A smart vapor retarder is able to adapt its permeability to allow the wall to dry should moisture get trapped in the wall cavity.
When are air barriers considered vapor barriers?
In the strictest sense air barriers are also vapor barriers when they control the transport of moisture-laden air. An excellent discussion about the differences between vapor barriers and air barriers can be found in Quirrouette (1985).
What is vapor barrier?
Vapor barriers installed on the interior of assemblies prevent assemblies from drying inward. This can be a problem in any air-conditioned enclosure. This can be a problem in any below grade space. This can be a problem when there is also a vapor barrier on the exterior.
What is the unit of measurement used in characterizing the water vapor permeance of materials?
The unit of measurement typically used in characterizing the water vapor permeance of materials is the “perm.” It is further proposed here that there should be several classes of vapor retarders (this is nothing new – it is an extension and modification of the Canadian General Standards Board approach that specifies Type I and Type II vapor retarders – the numbers here are a little different however):
Why is it so difficult to keep water vapor out?
No chance. It gets complicated because sometimes the best strategies to keep water vapor out also trap water vapor in. This can be a real problem if the assemblies start out wet because of rain or the use of wet materials. It gets even more complicated because of climate.
Why is there confusion about vapor barriers?
Confusion on the issue of vapor barriers and air barriers is common. The confusion arises because air often holds a great deal of moisture in the vapor form. When this air moves from location to location due to an air pressure difference, the vapor moves with it. This is a type of migration of water vapor.
Why are vapor barriers bad?
Incorrect use of vapor barriers is leading to an increase in moisture related problems. Vapor barriers were originally intended to prevent assemblies from getting wet. However, they often prevent assemblies from drying. Vapor barriers installed on the interior of assemblies prevent assemblies from drying inward. This can be a problem in any air-conditioned enclosure. This can be a problem in any below grade space. This can be a problem when there is also a vapor barrier on the exterior. This can be a problem where brick is installed over building paper and vapor permeable sheathing.
What is the principle of control of water in the liquid form?
The fundamental principle of control of water in the liquid form is to drain it out if it gets in – and let us make it perfectly clear – it will get in if you build where it rains or if you put your building in the ground where there is water in the ground. This is easy to understand, logical, with a long historical basis.
What is a Vapor Barrier?
A vapor barrier is a material that retards or restricts moisture vapor penetration and is also known as a moisture or vapor retarder. To be considered impermeable, a vapor barrier or retarder requires the permeance of 0.1 Perms IMP or less. True moisture or vapor barriers have a permeance of 0.00 Perms. A common practice is to use a thin layer of polyethylene (plastic) sheeting as a vapor barrier.
What is the minimum vapor barrier required for concrete?
Concrete slabs that will be within heated structures must have a vapor barrier. Subsection R506.2.3 of the 2018 IRC states that a minimum of 6-mil polyethylene vapor retarder be used between the concrete and the base course or prepared ground. It also requires seams or joints in the barrier to have a minimum 6” overlap sealed with compatible material.
How thick should a moisture barrier be?
A moisture retarding barrier needs to have a permeance of 0.06 Perms or less. It should also be at least 6 one-thousandths of an inch thick to withstand punctures and tears during the concrete pour. The IRC identifies 6-mil polyethylene as the minimum acceptable barrier for under concrete, and the ACI states 10-mil poly as their minimum recommended choice.
What is the best material to use for vapor barrier?
A common practice is to use a thin layer of polyethylene (plastic) sheeting as a vapor barrier. The permeable nature of concrete allows ground moisture to penetrate upward to flooring or anything in contact with the concrete.
Why do vapor diffusers have string?
Many of the thicker vapor diffusers or barriers have reinforcement cord or string within the polyethylene layers to give them greater tensile strength. The increased strength makes them easier to move around and more durable when placing concrete. The added thickness also makes the sheeting more resistant to punctures.
How far should vapor membrane go up walls?
It should be the last layer before the concrete – even on top of any rigid foam insulation. The barrier should go 3” to 4” up any walls and be sealed to the foundation concrete with appropriate binders, or extend 4” to 6” beyond the formed framework.
Why do you need a vapor barrier on a concrete floor?
A vapor barrier under the concrete decreases the amount of moisture that can wick through the concrete and into the living space.
What is a Class III vapor retarder?
The Class III vapor retarder provisions in Climate Zones 7 and 8 are differentiated and strengthened to address an inadvertent error in prior codes that treated Climate Zones 7 and 8 the same.
When was the IBC code published?
Published on February 3, 2021. The newly published 2021 IBC and IRC codes include some important advancements to water vapor retarder provisions. These relate to properly coordinating the use of cavity and continuous insulation materials used for energy code compliance with water vapor retarders used to comply with the building code.
What is missing from the IRC code?
One significant consideration still missing from the IRC and IBC water vapor retarder provisions is that the code lacks a means of controlling the vapor permeance on the interior and exterior side of wall assemblies that do not include continuous insulation to control water vapor. For example, the code provisions in Figure 2 for walls with continuous insulation (see Figure 1) rely on compliance with underlying “insulation ratios,” which vary by climate, to ensure the inside of the wall stays warm and avoids the dew-point temperature or high humidity levels. For walls without continuous insulation (see Figure 3), the ratio of permeance of outer and inner layers of the wall must be controlled in a similar manner by use of permeance ratios that also should vary with climate. However, such a methodology remains absent from the code.
What is the perm rating for fiberglass batts?
Kraft-faced fiberglass batts, vapor retarder paint, or other approved materials applied in accordance with the manufacturer’s installation instructions for a perm rating greater than 0.1 and less than or equal to 1.0.
Does condensation damage construction?
Construction where accumulation, condensation or freezing of moisture will not damage the materials.
How far up must a vapor barrier be?
Where barriers overlap, the seams must overlap by 6 inches and be sealed. The barrier must extend at least 6 inches up the walls of the crawl space and be sealed to the side walls or to the insulation on the side walls.
What is a Class I vapor barrier?
The Class I vapor barriers, such as 6-mil-thick polyethylene sheets, stop moisture migration from the bare earth into the house. Many people believe that it is a good idea to cover the earth with a vapor barrier even if you do meet the 1 square foot to 500 square feet requirement.
What is the International Residential Code?
Advertisement. Today, after much work by builders and building scientists, the International Residential Code allows for both vented and unvented crawl spaces. The IRC is a model building code, which means that states and local jurisdictions can use it to develop their own building codes, but are not required to do so.
How many square feet of vents should be in a crawl space?
There should be vents on all crawl space walls. They should provide a minimum of 1 square foot of vent area for every 500 square feet of crawl space area.
