Table of Contents
House Wrap Functions
Building Protection
The most important function of house wrap is the protection of the home’s building materials from water and air penetration. It sits just behind the siding, which is capable of withstanding weather, and the house sheathing, which usually is not. Most house wraps are designed with channels that will let water flow down and out of the house if it manages to penetrate the siding. These channels are also important for air flow behind the siding since air flow helps building materials last longer. I would not recommend a product without channels unless you plan on using furring strips to set the siding off of it.
Permeability
The other important function of house wrap is to be permeable enough, its perm rating, to let air and dampness out of the structure. For example, plastic would have a perm rating less than 10. This means that, while it would keep water out just fine, it would prevent the air and humidity from inside the house trapped. Not only is this bad for building materials but it also produces a more uncomfortable environment for occupants.
A material such as Tyvek House Wrap has a very high permeability of 58. This shows that the product allows air and moisture from inside the structure to flow out easily. The air flow makes a more comfortable and long lasting house. Greenguard Ultra is another good option, with a perm rating of 48 and R-Wrap is even higher with a perm rating of 59.
Look for products with high perm ratings. If a product does not advertise its perm rating, I would be suspicious of it without more information. Avoid products like Raindrop, perm rating 10, or Pink Wrap with a perm rating of 14.
House Wrap Exposure Resistance and Toughness
UV Light Exposure
Not only does house wrap need to be excellent when it is fully installed underneath siding but it has to hold up to the elements when it is not covered as well. After all, the best builder in the world can’t properly side a house in a single day. Surprisingly, it isn’t the rain that is the toughest part to stand up to. The UV rays from the sun will break down the structure of the wrap even faster. Every product will be rated for a specific number of days that it can remain uncovered and still function just fine.
When I first learned about house wrap, I didn’t think they would last long in the sun. I was surprised to find that almost all are good to go for up to 120 days in the sun, or roughly 4 months. These include Tyvek House Wrap for residential use. Some are made to last even longer in the sun though. Greenguard Ultra is made to last up to 180 days in the sun and Tyvek for commercial use is made to last up to 270 days when exposed to UV light.
A low rating for UV exposure isn’t necessarily a bad thing. I would make sure that your house wrap meets a minimum of 120 days of UV exposure since this should give you more than adequate time to cover your structure. If you know that you will need longer, don’t hesitate to look for a better product.
Toughness on the Job Site
For a house wrap to function properly, it needs to be fairly resistant to physical damage during installation. The best house wrap in the world won’t function if you tear a hole in it while putting it up. Wrap can be damaged in many ways. Tears are simple to make if your roll is too large for you to handle easily. Don’t be afraid to cut the roll in half to make it easier to put up in one piece.
House wrap can also be damaged if it is put up with the wrong fasteners. Plastic cap nails or staples are the only way to properly put up house wrap. If there is no plastic cap behind the fastener, the wrap can easily be torn by the fastener driving through it. These fasteners can be put up with a hammer or with a Stinger brand hammer tacker. Of course, accidents happen and tears can be fixed with proper installation.
House Wrap Installation and System
Best System
Proper installation relies heavily on a complete system to install it. Since the system is so important, my favorite system is the Tyvek house wrap system. They have a part of the system that accounts for every gap and every penetration that comes through the wall. Tyvek provides not only house wrap but also tape, flex wrap, and straight flash that gives you a complete professional installation.House Wrap Installation
For more in depth installation instructions, check out this article, but I’ll tell you the most important parts. Install your housewrap from the bottom to the top so that the upper layers overlap. At vertical seams, make sure to overlap the wrap by at least 6 inches and tape. Pull the wrap tight but don’t tear it before you tack it to the house sheathing. Apply fasteners roughly every foot.
Make sure that each pipe is surrounded and taped so that the house wrap is completely secure at each. If you do have to cut the wrap to install a window (link to install a window article) or door opening, cut an X across the opening and leave the extra house wrap so that you can install windows and doors according to manufacturers guidelines.