Your ready to put on the exterior finish on your shed, if your going to be applying some type of siding over your sheds exterior your probably wondering if you should use some type of building wrap under the siding.
House wrap, otherwise known as WRB or Weather Resistant Barrier, is a good idea for your shed. After all, your shed will be subject to the same weather conditions as your home, and you don’t want your shed to develop mold, mildew or moisture damage any more than you do your home.
Since it doesn’t really add too much to the cost of your shed materials and is not hard to install, it just makes sense to have this extra protection for your shed. Additionally, if you plan to insulate your shed, the house wrap will help your insulation do a better job of keeping outside temperatures outside. If you plan to heat or cool your shed or both, the house wrap will help keep your utility costs down.
What is the Purpose of House Wrap?
House wrap is a material that goes under the siding. It can be made of fabric, paper, or board material. Many materials used in siding are not completely efficient at keeping water out, especially rain driven by wind. Vinyl siding in particular is recommended to have house wrap installed underneath.
If water or moisture does get under your siding, the house wrap will shed the water and keep it from going any farther into the wall structure. However, since water vapor can pass through the wrap, it permits the vapor to go in the other direction to the outside of the building.
How Many Types of House Wrap are There?
There are several main types of house wrap. Each has its own properties. There are paper and several types of plastic, perforated and non-perforated, woven and non-woven. You may want to consult your supplier to find out which one works best for your climate, as the types are not “one size fits all.” If your house has been recently built, you can ask your builder what was used on your house. What was used there will certainly be good for your shed.
One of the most common is building paper or tar paper. It is also called asphalt felt and is basically the same material you use for roofing paper, albeit in a thinner form. It’s one of the least expensive forms of house wrap. Since it is more sensitive to damage from freezing, it’s usually installed next to the interior wall material rather than under the siding as most WRBs.
Plastic or polyethylene house wrap is also very common, and not much more costly than tar paper. It’s made from the same type of plastic that forms most plastic bottles and is entirely recyclable. While it’s usually white or tinted, some companies make a clear form to make it easier to see just where you’re placing it.
Tyvek is a very popular type of house wrap. While it looks like it’s made from plastic, it’s actually made from a material developed by the company. It’s a type of spunbond olefin. Like other plastic or plastic-type wraps, it is woven, which allows moisture to escape.
Does House Wrap Help with Insulation?
Insulation effectiveness is expressed as the R-value. This is the resistance factor as far as being able to resist heat flow through its material. The factor is determined by multiplying the material’s thickness in inches by its rated R-value per inch. The higher the R-value, the greater the insulation’s resistance. There are maps available showing the International Energy Conservation Code’s recommendations for R-values according to eight climate zones.
While house wrap can’t be used as a replacement for insulation, it does help the insulation you choose to do its job better. It increases the R-value by providing control of air and moisture, and also prevents water from accumulating in the walls, which can lead to all sorts of problems.
More importantly, moisture actually decreases the R-value of installed insulation. For instance, in tests using a moisture content of just 20%, the R-value of fiberglass insulation was reduced by 55%, quite a significant amount. If your thinking about insulating your shed you can read my article What’s the Best Insulation for a Shed? [Batt, rigid or loose fill?] for more information and options.
Is House Wrap Required by Code?
Many building codes don’t require house wrap in general, but if one is installed, it must meet the 2018 International Building Codes for water resistance and vapor permeability. The only time the wrap is actually required is when vinyl siding is installed. Even so, not all building authorities require it for vinyl siding, although some of the siding manufacturers recommend it. Better to be sure than pay a big fine later, get more information on permits in my article Can I Build a Shed Without Getting a Permit?
Can Tar Paper be Used as House Wrap?
Tar paper, or asphalt felt, is a common choice for house wrap, but it does have its drawbacks. It is easily torn and must be installed carefully to prevent holes or rips. Usually, the tar paper used as a house wrap will not be a thick as the material used as roofing paper.
Building codes may specify that it be installed with tacks rather than tape, as some other materials are. Also, since tar paper can crack if exposed to freezing temperatures, it is sometimes installed on the interior side under the wall materials instead of directly under the siding.
How to Install House Wrap on a Shed
Tar Paper – You’ll need a helper for this job. Start at the bottom, installing the felt so it extends an inch or two below the sill plate. Using chalk lines will help you locate the studs, which is important if you’re using cap nails. Start with a length of eight feet or so, checking that it is level and aligned with the bottom.
Use a hammer stapler to speed things up, and don’t skimp on the staples, especially if you live in a windy climate. Overlap seams by at least six inches. Trimming around doors and windows can be done with a utility knife, as can cutting around odd shapes such as a gable shape. Seal all the seams using the recommended tape or sealant.
If you haven’t installed your window or door yet, secure the paper over the opening. Make horizontal cuts along the top and bottom openings and a vertical cut near the center between the two cuts. At each corner, make an eight-inch cut diagonally. Fasten the paper to the edges, making sure it is taut, then wrap the pieces around the opening and staple. Trim away the excess. Following the manufacturer’s instructions, install your flashing over the tar paper.
Tyvek – You’ll need a helper here as well. There are two main types of Tyvek. The ThermaWrap helps keep the indoor temperatures consistent, while the DrainWrap features vertical grooves to aid drainage if you live in an area that experiences heavy rain on a more or less regular basis. Your supplier can help you choose the right product for your area. He can also recommend the proper fasteners for you to use, whether washer head nails or staples. You may be able to obtain Tyvek imprinted with stud marks printed at a specified width to help you line up your installation with the studs.
Place the edge of the roll along one corner leaving a six to twelve-inch overlap and plumb with the bottom sill plate. If you have printed stud marks, line them up with your first stud. Unroll the Tyvek, keeping it taut but not so tight that it stretches or tears when you fasten it. Your helper should fasten the material every 6-18 inches over the wall studs.
While it’s best to install the Tyvek before installing windows or doors or their flashing, when installing Tyvek, go ahead and cover the doors and windows or their openings. Any overlaps should extend at least six inches. If you need to get up high, scaffolding is recommended rather than a ladder. Tyvek rolls are large and can be slippery, so secure footing is important.
Use a utility knife to cut the excess from corners or odd shapes such as gables. Cut windows out in an X shape, fold the flaps inside and tack them down. If your flashing has already been installed, cut out the entire window outline. Cut the door in the shape of the letter I. The top and bottom should be about eight inches from the top and bottom of the door opening.
Cut a horizontal bar partway across the top and bottom of the first cut, then another cut from the edge of these horizontal cuts to the corners of the door. Fold these flaps down and fasten them over the frame.
You will need either Tyvek tape or a recommended sealant made for Tyvek to form an airtight seal. Seal any overlap seams and the whole window opening except for the sill. Inspect your Tyvek for any tears or punctures that may have occurred during installation and seal them also.
Some people tend to treat their shed as an afterthought, and don’t seem to think that the building needs the care or materials that their house does. However, if you want your shed to last (and who doesn’t), it needs as much protection from the elements as you can give it. The expense and work involved in repairing sheathing or flooring damaged by moisture far outweigh the cost of installing a WRB. You can save on your heating costs of your shed with building wrap, read my article How Much Does It Cost to Heat a Shed? for more information.
Conclusion
Not only does sufficient insulation and moisture protection keep your stored items safer from mold and mildew, but shed usage tends to change over the years. Once the kids are grown and gone, you may want to get rid of the summer toys and turn your shed into a workshop with heat, and the added care you took in building will pay off in energy savings. Don’t shortchange your shed and it will serve you well.