House Wrap And Siding: A Two-In-One Replacement Project?

Whether or not you need to replace house wrap when replacing siding is a question that has been asked by many homeowners. The answer depends on a few factors, including the type of house wrap currently installed, the condition it is in, and the climate in your region.

Tar paper vs. Tyvek

When replacing siding, it is not always necessary to replace the house wrap. However, if the existing house wrap is damaged or inadequate, it may be advisable to do so.

House wrap, also known as building paper or felt paper, is a weather-resistant envelope that performs several important functions. It protects the building's interior during construction and cladding renewal, insulates the home, and acts as a moisture barrier if the siding is damaged.

There are two main types of house wrap: traditional building paper (tar paper) and synthetic house wrap (Tyvek). Here is a comparison of the two:

Material: Tar paper, also known as building paper or felt paper, is made by saturating paper with waterproofing asphalt. Tyvek, on the other hand, is a synthetic material made by DuPont using spun synthetic fibres bonded by heat and pressure. These fibres are approximately ten times thinner than human hair.

Moisture Protection: Tar paper provides a waterproof barrier that prevents wind and moisture from reaching the interior of the building. It is self-sealing around nails, provided they are driven in straight. However, it does not allow the building to breathe as effectively as Tyvek. Tyvek is permeable to water vapour, allowing the building to breathe, but it is also impervious to liquid water.

Installation: Tar paper is generally easier to install than Tyvek. Large sheets of Tyvek must be joined together using acrylic pressure-sensitive tape, hot glue, or solvent-based single-component polyurethane, making the installation process more time-consuming. Tar paper, being a traditional material, is preferred by many contractors due to its familiarity and proven effectiveness.

Durability: Tar paper is known for its durability and can last for decades if properly installed and maintained. Tyvek, while also durable, has a shorter lifespan when exposed to sunlight and wind for extended periods. It is recommended to install the siding over Tyvek as soon as possible to prevent degradation.

Cost: Tar paper is generally less expensive than Tyvek, making it a more economical option for house wrapping.

In summary, both tar paper and Tyvek have their advantages and disadvantages. Tar paper is more cost-effective, easier to install, and highly durable. On the other hand, Tyvek allows the building to breathe more effectively, is flexible and tear-resistant, and is recommended for use in exceptionally cold and exposed locations. Ultimately, the choice between the two depends on specific project requirements, local climate conditions, and personal preferences.

The importance of vapour-permeability

Whether or not you need to replace your house wrap when replacing siding depends on the type of wrap your house currently has and whether it is in good condition. For example, if your house has tar paper wrap, it is not vapour-permeable, and you may want to replace it with a vapour-permeable wrap.

Vapour permeability is an important characteristic when choosing a house wrap. It refers to a material's ability to let water vapour pass through it. If water vapour escapes from inside the house or liquid water gets behind the house wrap from outside, vapour-permeable house wrap allows the water vapour to escape through the exterior. This helps to protect the sheathing of your house by preventing the build-up of moisture vapour, which can lead to mould and rot.

The vapour permeability of a material is measured in units called "perms". The higher the perm number, the more vapour-permeable the material. According to building codes, a house wrap must have a perm rating of at least 5. However, the optimal vapour permeability range for house wraps is debated, with some sources recommending 10-20 perms. It is important to choose a house wrap with the appropriate vapour permeability for your climate.

In addition to vapour permeability, other factors to consider when choosing a house wrap include water resistance, durability, air resistance, and whether it is perforated or non-perforated.

Advances in housewrap membranes

Housewrap is an important component of a well-designed and well-constructed building. While it adds cost and time to a building project, it is a crucial step in ensuring the long-term protection, durability, and performance of the structure. The synthetic housewrap acts as a moisture barrier, preventing wind-driven rain and water from reaching the sheathing and framing, and helps to reduce heating and cooling costs by preventing air infiltration.

Over the years, there have been significant advances in housewrap technology. For instance, the latest drainable housewraps, such as those that provide a minimum one-millimeter gap, can be up to 100 times more effective at removing bulk water from walls compared to standard housewraps. These drainable housewraps incorporate a water-resistive layer and a drainage gap, facilitating the efficient removal of water from behind the exterior cladding system.

One example of a modern housewrap is DuPont™ Tyvek®, which is made of high-density polyethylene fibres. It is a lightweight, flexible, and breathable membrane that is wind-tight and water-resistant. Tyvek® is designed for use in new builds, refurbishment, or extension projects and can be left uncovered for up to four months while retaining full performance.

Another example of an advanced housewrap is the dimpled membrane, such as Benjamin Obdyke's HydroGap or Barricade's WeatherTrek. These dimpled housewraps are preferred by some over the "crinkled" varieties, as they are found to be easier to install straight and tight.

In conclusion, advances in housewrap membranes have led to the development of more effective and efficient products that offer superior protection against moisture and air infiltration. These modern housewraps not only enhance the durability and longevity of buildings but also contribute to energy savings by reducing heating and cooling costs.

Integrating housewrap with windows and doors

Integrating House Wrap with Windows and Doors

House wrap is a synthetic material that goes over wall sheathing and behind the siding. It is a building's secondary defence against air and water penetration. It is also a backup barrier that keeps water off the framing and structural sheathing and prevents air movement through the wall system.

When properly installed, house wrap can protect a building against air and water intrusion. It is particularly critical to preventing moisture and air intrusion around windows and doors. This is because water and air-tight windows and doors are essential in stopping the accumulation of moisture in the wall system and achieving an energy-efficient structure.

To integrate house wrap with windows and doors, you can follow these steps:

• Secure the wrap: Secure the house wrap firmly in place over the entire wall, including window and door openings. Use nails or staples to fasten the wrap every 12-18 inches along the vertical studs.
• Apply layers: Apply all layers of wrap in a shingle style, with the top layers overlapping the bottom layers.
• Create a top flap: At the top of the window or door, create a top flap. Install the head flashing under this flap and over the flange.
• Allow moisture escape: Do not flash the bottom of the window or door to allow any trapped moisture to escape.
• Trim the wrap: On both sides of the window or door, trim the wrap close to the flange.
• Secure the wrap: Secure the wrap to the flange with tape or caulk. Install side flashing over the wrap.
• Install head flashing: Install the head flashing and extend it out 3-4 inches to each side. Tape the flap created in step 3 over the flashing.

It is important to note that tape and caulk should only be used for securing purposes and should not be used as flashing material. Proper installation of house wrap around windows and doors will contribute to a healthy, durable, and energy-efficient home.

Ventilated rain screens

Ventilated rainscreens are an effective way to protect the structure of a building from moisture, rain, and condensation. They work by creating a cavity between the inner and outer walls, preventing water from infiltrating the building structure. The outer skin of a ventilated rainscreen protects against rain and moisture, while the space between the cladding and the building wall allows for drainage and evaporation. This drainage and evaporation are key to preventing water ingress into the building.

The air gap or cavity in a ventilated rainscreen system can be created in several ways. One common method is to use furring (battens, strapping) that are fastened vertically to the wall. Ventilation openings are then made at the top and bottom of the wall to allow for natural airflow through the cavity. This airflow helps to keep the insulation dry and maintain its efficiency over time.

The cavity in a ventilated rainscreen system is essential for its effectiveness. It provides a secondary line of defence against the elements and serves two main purposes. Firstly, it allows for the drainage of any moisture that penetrates the outer cladding. Secondly, it enables air circulation, which evaporates moisture from the surface of the air barrier and dries the cavity. As a rule of thumb, a minimum cavity of 25mm should be maintained to ensure sufficient air movement. For walls greater than 25m high, it is recommended to have a cavity depth of 1mm per meter in height.

In addition to superior waterproofing, ventilated rainscreen systems offer other benefits such as thermal efficiency and condensation control. The cavity between the inner and outer screens shades the structure and dissipates heat, preventing heat transfer into the building. The warm air rises and escapes through the top of the cavity by convection, drawing in cooler air at the base and insulating the primary wall structure. When properly designed and installed, condensation will form in the cladding cavity instead of within the wall structure. This condensation can then be drained or evaporated, preventing damage and mould growth.

Overall, ventilated rainscreens provide an effective solution for protecting buildings from the elements, with the added benefits of thermal efficiency and long-term durability.

Frequently asked questions