The popularity of vinyl siding is due to its durability, affordability, ease of maintenance, and ability to provide exterior insulation to the entire house. Since vinyl siding is water-resistant, is there really any need for siding underlayment?

The answer is YES. House wrap is the most popular underlayment for vinyl siding installation. Also, you have the opportunity to install new vinyl siding over the existing siding and reduce labor and cost since you don’t have to rip the old siding off first.

Vinyl siding installation

House wrap is an exterior sheathing with a design and purpose to keep moisture and water infiltration away from the home, while at the same time allowing water vapor to escape out of the house. Some house wrap materials help to keep the cold air from blowing into a house, and that way provides an energy-efficient home. It is recommended to apply housewrap at the beginning of your project because once the siding is installed it will cost you a lot of money and labor to rip it of and install it again.

How does it work?

House wrap is a material with very tiny perforations that are so small so that water molecules cannot pass through. Even if the water manages to get past your vinyl siding there is no chance to get into your home, because the house wrap will form the water-resistant barrier.

However, this wrap will not “suffocate” your house because the holes in the sheathing are large enough to allow moisture in vapor from the pass-through. This gives protection from extreme weather elements without creating mold or water problems inside the home.

Benefits of house wrap

There are several benefits of house wrapping:

  • Reduce mold problems;
  • Prevent moisture damage;
  • Improve the energy efficiency of your home;
  • More comfortable home;
  • Increase a home’s value;
  • Comply with local building codes

Installing house wrap under vinyl siding

Installing house wrap is a straightforward process and won’t require an unreasonable amount of time for your installing vinyl siding project. It is vital for this sheathing to be installed properly or you won’t get the optimal performance from this material. Improper installation of house wrap is not going to cause damage to your sheathing or to the vinyl siding necessarily, but it will end up as a waste of money and materials.

If your entire house is being wrapped and will be exposed to sunlight for a significant amount of time, then you should invest in a material that will resist UV rays for longer than average. Regular house wrap should be installed and covered with vinyl siding as soon as possible because it is not designed for direct exposure to sunlight.

Working with an experienced contractor will ensure that the wrap is placed from the lowest point to the top edge properly, secured with stapling nails and that all seams are taped.

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New siding over old siding

In new construction, builders may just choose vinyl siding from the beginning but with a renovation, the cost of removing the existing siding can cut into the cost savings of the project. So the unique approach is installing new siding over top of the old.

Installing vinyl siding over the existing siding (wood siding for example) had a lot of benefits.

Unfortunately, the existing siding is not flat or level. Before putting vinyl siding you need a flat surface in order to apply the new siding. That’s why siding underlayment is necessary, to smooth out the existing surface and give the vinyl a level finish to adhere to.

Energy efficiency

If the new siding material is not pre-insulated then siding underlayment may be needed to provide an additional layer of thermal protection, especially with new construction. Exterior insulation is so important to increasing interior comfort and lowering energy bills. The installation of new siding is an ideal time to add to the insulation and increase the energy efficiency and value of your home.

Vinyl siding installation

Even this is not an article that deals with vinyl siding installation, I think that it will be useful to say a few words about how this method works.



Vinyl siding should be installed over a sheathing that provides a flat and smooth surface. Check local building codes for sheathing requirements. Vinyl siding should not be installed directly to wall studs without sheathing. Rigid foam board installation can be an alternative siding underlayment.

Sheathing nailability

Vinyl siding installation could be over common wood sheathings such as plywood, oriented strand board (OSB), or other material. The thickness of wood sheathing counts toward the total thickness that the fasteners must penetrate into nailable material, usually 1 1/4” (32mm). But foam plastic sheathing does not contribute toward holding the fastener, so its thickness cannot be counted toward the total. In this case, the fastener would have to be long enough to penetrate through the sheathing and 1 1/4” (32mm) into the wood framing.

Water-resistive barrier

Vinyl siding installation should be over a water-resistive barrier to stop the intrusion of incidental water. Check your local building codes for requirements in your local geographic area.


Code-compliant flashing should be integrated with the water-resistive barrier and applied around windows and doors, and other openings. Flashing should also be applied to inside and outside corners, and the intersection of walls and roofing to prevent water to come in.

Estimating required materials

  • Sided area can be determined by measuring the height and width of the exterior walls, including windows.
  • Total all of the measurements for the areas to be sided. Windows and doors are not usually deducted.
  • To estimate the amount of starter strip required, measure the linear feet around the entire base of the home.
  • Add siding to all materials estimates to allow for waste, depending on the pitch of the roof and other specific factors.
  • To estimate the total pound of fasteners required, multiply the total square feet of the vinyl siding by 0.005 for aluminum nails and 0.01 for roofing nails, staples, and screws.
  • Every 100 square feet (9.29 square meters) is called a “square” for ordering purposes.

The amount of siding needed/waste generated for a vertical siding job will be determined by the height of the wall versus the length of the panels.

Fastener choices

Use aluminum, galvanized steel, or other corrosion-resistant nails, staples, or screws when installing vinyl siding. Aluminum trim pieces require aluminum or stainless steel fasteners. All fasteners must be able to penetrate a minimum of 1 ¼ (32mm) into nailable material such as wood and framing.

When the fasteners must penetrate through a non-nailable material such as foam insulation, the thickness of that material does not count toward the total. In such cases, the fastener will need to be long enough to penetrate through the non-nailable material and then 1 1/4 (32mm) into wood framing or other nailable material.

Fastening procedure

Whether using a nail, screw, or staple to fasten the siding, the following basic rules must be followed:

  • Make sure the panels are fully locked along the length of the lower portion but do not force them uptight when fastening.
  • Do not drive the head of the fastener tightly against the siding nailing hem. Allow approximately 0.8mm clearance between the fastener head and the vinyl. Tight nailing, screwing, or stapling will cause the vinyl siding buckle with changes in temperature.
  • When fastening, start in the center of the panel and work toward the ends.
  • Center the fasteners in the slots to permit expansion and contraction of the siding.
  • Drive fasteners straight and level to prevent distortion and buckling of the panel.
  • Space the fasteners to a max of 16” apart for horizontal siding panels, every 12” for vertical siding panels, and every 8” to 12” for accessories. These distances may be increased if the manufacturer permits greater spacing based on wind load testing. Start fastening vertical siding and corner posts at the top of the uppermost slots to hold them in position. Place all other fasteners in the center of the slots.
  • If a nail slot does not allow centering/securing into a nailable surface, use a nail hole slot punch to extend the slot and allow centering of the fastener.

Screw fasteners

Screw fasteners if the screws do not restrict the normal expansion and contraction movement of the vinyl siding panel on the wall. Screws must be centered in the slot with approximately 0.8mm of space between the screw head and the vinyl.


If staples are being used instead of nails or screws, consult the manufacturer’s manual if you can use staples as an alternative to nails. Be sure to observe any limitations with respect to the wind load design pressure rating when you install vinyl siding with staples.

Cutting the siding

When cutting vinyl siding or vinyl soffit, follow the steps bellows:

  • Safety first!
  • With a circular saw, always install the fine-tooth (plywood) blade backward on the saw for a smoother, cleaner cut, especially in cold weather. Cut slowly. Do not attempt to cut materials other than vinyl with a reverse direction saw blade.
  • With tin snips, avoid closing the blades completely at the end of a stroke for a neater, cleaner cut.
  • With a utility knife or scoring tool, score the vinyl face up with medium pressure and snap it in half. It is not necessary to cut all the way through the vinyl.

Preparing the walls

A flat, level surface is necessary for proper vinyl siding installation. Install flashing before starting to apply the siding.

Unless already installed, a water-resistive barrier should be applied to the house prior to installing vinyl siding.

Make sure that the construction of the wall allows for a total of 32mm fastener penetration into wood material. If the wall is covered with foam plastic sheathing make sure that the nails will be long enough to penetrate 32 mm into the framing behind the foam. Make sure that any furring strips are thick enough to provide this penetration depth, or cover them with wood sheathing to provide the needed depth.

New construction

To reduce the possibility of floor-plate compression, drywall, roof, or other heavy building materials should be installed or stored prior to the vinyl siding installation. Floor-plate compression can result in a buckled siding at the intersection of the floor and the wall.


  • Nail down loose boards of existing siding and replace any rotten ones. Vinyl siding installation should not be performed over rotting wood.
  • Scrape off the loose caulk and re-caulk around windows, doors, other areas to protect moisture to penetrate.
  • Check all walls for evenness and install furring strips where necessary. When installing furring strips, take appropriate measures to establish a smooth and continuous surface.

In cases where the lower point of a horizontal siding panel must be trimmed so that it may be installed over steps, porches, etc., the panel should be built out for proper angle and rigidity. Utility trim can be used to seal the cut edge of the panel and then secured to the wall.

Outside and inside corner posts

  • A water-resistive material should be used to flash the inside and outside corners a minimum of 10” on each side before installation of the corner posts.
  • Inside corner posts can be a single or double j-channel, or a factory formed inside corner.
  • Place the corner post in position, allowing a ¼” (6.4mm) gap between the top of the post and the eave or soffit. Position a nail at the top of the top row on both sides of the corner post, leaving a gap of approximately 1/32” (0.8mm) between the nail heads and the corner posts. The corner post hangs from these nails. The corner post should extend ¾” (19mm) below the starter strip.
  • If more than one length of the corner post is required, overlap the upper piece over the lower piece by cutting away 25.4mm of the nailing flange on the top piece. Overlap 19mm, allowing 6.4mm for expansion. This method will produce a visible joint between the two posts but will allow water to flow over the joint.

Starter strip

In order for the siding to be installed properly in a level fashion, the starter strip at the bottom of the wall must be level.

  • Determine the lowest point of the wall that will be sided, from that point, measure up ¼” (6.4mm) less than the width of the starter strip and partially a nail at one corner.
  • Attach a chalk line, go to the next corner and pull the line taut.
  • Make sure the line is level by using a line level or a 4’ (1.2m) level.
  • Snap the chalkline and repeat the procedure around the entire home.
  • Using the chalkline as a guide, install the top edge of the starter strip along the chalkline, nailing at 10” (254mm) intervals. Allow space for the corner posts, j-channels, etc.
  • Keep the ends of the starter strips at least ¼” (6.4mm) apart to allow for expansion.
  • Nail in the center of the starter strip nailing slots.
  • For insulated siding, the starter strip needs to be spaced away from the wall to accommodate the thickness of the backing on the siding. Consult the manufacturer’s instructions for specific techniques.

When insulation or backer board is used, fur the starter strip, if necessary, to accommodate the thickness of the siding. In certain situations, it may be necessary to use j-channel as a starter strip, remember to drill a minimum of 3/16” (4.8mm) diameter weep holes no more than 24” (610mm) apart.

igor elenchevski
Author: igor elenchevski - is a prolific writer in many niches including music, home improvement and even psychology and addictions. His success is built around his in-depth research and understanding of a subject before putting pen to paper (or fingers to keys).