House Wrap: A Comprehensive Guide
Have you ever wondered why homes under construction tend to look like a wrapped Christmas present? House wrap is a common sight during home construction, though most people aren't sure what purpose it serves. However, this simple air and moisture barrier plays a crucial role in improving your home's energy efficiency and boosting its thermal performance. In this in-depth product guide, we will look at what house wrap is, why it's essential, and then look at some of the most important considerations when choosing the best type of house wrap for your home.
The vinyl siding, brick, or other exterior cladding options for our homes certainly play an essential role in protecting our home from the wind, rain, and other external elements. However, hidden beneath the cladding, house wrap also contributes to keeping our home dry, comfortably cool or warm (depending on the season), and otherwise protected.
What Is House Wrap?
House wrap is usually made from a synthetic material wrapped around the plywood of the home exterior. House wrap ensures that moisture does not infiltrate into your inner wall assembly. Its expansive nature makes application quick and can also be overlapped and sealed to improve your home's building envelope.
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So why exactly do homes need to be wrapped up in a synthetic barrier? First and foremost, No matter what type of exterior cladding option you have, cracks and fissures can occur over time. During times of driving rain or when your roof gutters get clogged and end up leaking, water can penetrate your exterior siding. This water penetration can cause significant damage to your interior wall assembly.
Excess amounts of water and moisture can cause mold to grow on your plywood or drywall or even weaken the structural stability of your house frame. If water gets into your inner-wall insulation, it can cause compaction, thus lowering the R-value of your home and driving up your energy bills.
In the past, contractors tended to prefer asphalt-treated paper or asphalt-saturated felt. These options were heavier and harder to apply to the building exterior before they installed the external cladding. The asphalt-treated paper also risked lowering your indoor air quality. It could increase the volatile organic compounds (VOCs) in your home, especially if the building envelope were not air-tight. According to the Occupational Safety and Health Administration (OSHA), exposure to asphalt fumes includes headaches, skin rash, sensitization, fatigue, reduced appetite, throat, eye irritation, cough, and skin cancer. These side effects are not exactly what you look for in a healthy home.
Today, most builders prefer the more lightweight synthetic house wrap options. This type of house wrap is easier to apply and broader than traditional asphalt paper.
Besides stopping water from infiltrating your home, house wrap also plays a vital role in letting your home "breathe." Most of the house wrap options being sold today allow water vapor from inside your home to flow through to the outside. This feature can help regulate your home's humidity levels and ensure that your wall sheathing does not suffer from excess moisture that could lead to rot or mold. As long as the contractor ensures that the house wrap is carefully connected and sealed at the seams and overlaps, the house wrap can also act as an air barrier. House wrap, then, is a crucial element in ensuring a sealed building envelope. A solid building envelope can help to lower your home's heating and cooling bills while providing a comfortable indoor environment.
What Types of House Wrap are Available?
All house wrap options intend to serve as a weatherization membrane for your home. However, there are different styles and types of house wrap available to builders and homeowners, which include:
- Asphalt-impregnated paper: This option, also known as felt paper, used to be the most common option, though it is less common in new home construction.
- Micro-perforated, cross-lapped films: These types of house wraps ensure that there are "micro-holes in the product to allow air permeation for a healthy respiration rate for the home.
- Films laminated to spun-bond nonwovens: Both CertaWrap and Typar house wraps are made from this type of material. This type of house wrap is engineered to resist water infiltration while allowing water vapor to pass through. It is generally the most stable type of house wrap to avoid long-term degradation.
- Films laminated or coated to polypropylene wovens; Supercalendered, wet-laid polyethylene fibril nonwoven: Tyvek, the most common and popular type of house wrap, is made from this type of material.
- Drainable house wraps: this type of house wrap is designed to provide a continuous drainage gap. This feature ensures that water will not be trapped behind the wrap and will permit water to escape from the wall system if infiltration does occur quickly.
How Much Energy Does House Wrap Save?
Because it is almost always manufactured from synthetic material, house wrap does come with a sizeable embodied energy footprint. Despite this fact, when applied correctly, house wrap can play a major role in completely sealing your home's building envelope. This sealing lowers the overall energy use to heat and cool the structure.
It is worth noting that house wrap in itself does not replace the need for adequate, high-quality insulation. The Federal Trade Commission (FTC) recently called out certain house wrap manufacturers who incorrectly claimed that their house wrap product could increase the R-value of a home. When combined with high-quality insulation, house wrap can serve as an effective air barrier to reduce air leaks that reduce a house's energy efficiency and thermal performance.
Is House Wrap Part of a Healthy Home?
Having an air-tight, synthetic membrane wrapped tightly around your home can certainly reduce the probability of any air leaks occurring. However, what effects might this have on your home's indoor air quality?
Though many house wrap manufacturers claim that their products allow for some water vapor inside your home to penetrate to the outside, your home's synthetic membrane will certainly trap certain things inside. Most contaminants and pollutants that affect your indoor air quality come from inside the building itself. So, the application of house wrap as a weather protection barrier can significantly affect your home's indoor air quality.
Does this mean that homeowners essentially have to choose between energy efficiency and indoor air quality? Not at all! Today, several mechanical ventilation options can ensure that your household enjoys a steady supply of fresh air without compromising your indoor air quality. Depending on your climate, the home construction technique that defines your structure, and other site-specific considerations, a heat or energy recovery ventilator (HRV or ERV) could be worth considering. Check out this complete guide on the differences between HRVs and ERVs to help determine which is best for your home. In this Rise article, we also recommend some of the best ERVs and HRVs currently on the market for passive house design.
How Long Does House Wrap Last?
Because house wrap is covered by exterior cladding, it should last for as long as the house is standing. The main "durability factors" related to house wrap occur before cladding installation. Different house wrap products are rated by their resistance to ultraviolet (UV) light, their overall tensile strength, and their cold and surfactant resistance.
Some house wraps need to be covered within four months (120 days) because of UV exposure. In comparison, others can withstand nine months (270 days) of exposure to the sun and other elements. If this UV rating is exceeded, there is a chance that the house wrap could be more susceptible to damage and leaks.
How To Install House Wrap?
Unless you are building your own home from scratch, house wrap installation will most likely be your contractor's responsibility. If you want to offer some oversight while the contractor is installing the house wrap, make sure that the wrap is installed to the very top of the walls with no visible spaces or gaps. Also, make sure that your contractor is using high-quality building tape to seal all edges and overlaps. You can watch a more detailed explanation for installing house wrap in this YouTube video.
What Are The Best Types of House Wrap?
There are several different brands of house wrap on the market, with the standard "Tyvek" being the most common. When searching for the best house wrap for sustainability and health home indicators, consider the following characteristics:
- Water Vapor Permeability: To limit the possibility of mold and rot, house wraps that offer certain levels of vapor permeability are usually best. Look for products rated at 1 Perm (US rating) or 60 Ng (Canadian rating), as these are benchmark permeability rates for what defines a type II residential vapor barrier. The higher the perm rating or Ng, the quicker that moisture will evaporate.
- Self-Adhesive Membranes: These options also come with water vapor permeability. They are generally better (though more expensive) for ensuring an air-tight building envelope. Non-adhesive options can tend to "balloon" over time. The nail or staple holes also compromise the airtightness of the envelope.
What Are The Benefits and Drawbacks of House Wrap?
House wrap can play a significant role in protecting your home from unwanted water infiltration. This infiltration leads to many problems, including mold growth and even rotting of your interior wall system. When correctly installed, it can also help reduce air leaks and improve your home's energy efficiency and thermal performance. On the downside, house wrap and other essential air sealing techniques can cause reductions in indoor air quality if proper ventilation is not installed.
Article by:
Tobias Roberts
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.