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How to Measure for Vinyl Siding

You’ll want to be sure that you buy enough vinyl siding to do the job right. Luckily, learning how to measure for vinyl siding is a pretty easy job. Installing it can take some precision, so you don’t want to rush the project. Here, the siding professionals at PJ Fitzpatrick tell you how to measure for vinyl siding, and list any additional accessories you need to finish the job properly. If you have any questions, just reach out to us. After all, we’re happy to help.

The construction industry will often speak in terms of a builder “square,” which is a unit of measurement that means 100 square feet. A box of vinyl siding will commonly have 2 “squares” in it, which means it will cover 200 feet of wall. Vinyl siding is generally purchased in 12-ft lengths. Siding accessories like corner posts usually run in 12-ft lengths, as well.

Measuring Your Home’s Walls

  1. Break your house into different sections, and start by measuring the walls that are purely square and rectangle. Measure the height and width, then divide by 100 to get the number of squares you need. H x W ÷ 100 = Number of squares to cover walls
  2. Then measure your gables, which is the rise to your roof. Height times width, and then multiply by 0.75 (to account for the angle). H x W x 0.75 = Number of squares to cover your gables
  3. To have enough siding for your dormers, measure your dormers’ height and multiply by width. Then multiply by 1.5 and you’ll have enough siding to cover the two sides of the dormer. H x W x 1.5 = Number of squares for your dormers
  4. When you’re determining the amount of siding to purchase, don’t subtract for regular sized windows and doors. The only exception? If you have a really large picture window on the house, and you can also subtract for a large garage door.

Pro Tip: Remember when you start applying vinyl siding to your home that it expands and contracts with various weather. Don’t nail it so tightly that it has no room to expand when temperatures climb.

Vinyl Siding Accessories

The next step in learning how to measure for vinyl siding is to determine what you’ll need for siding accessories.

  1. Corner posts: You’ll obviously need one corner post per corner, but remember to factor in the height of the corner post. If your corners are taller than 12 feet, and many are – be sure to factor in the 12-ft length, so order 2 or 3 if that’s what you’ll need.
  2. Starter strip: You want to measure around the base of your house to determine the length of starter strip to buy. All of the vinyl siding has a starter strip with it, but some people like to buy a steel starter strip. The steel ones are less flexible and may be easier to wield.
  3. J-Channel: Plan on 2 pieces of j-channel per window, and 1½ pieces for each regular sized door. Be sure to purchase j-channel for where the siding meets your gutter’s soffit.
  4. Z-bar flashing: Is your home’s foundation brick? Then you need to measure around the base of your house for z-bar flashing and use it. However, you don’t need z-bar flashing where the siding meets your deck.
  5. Windows and doors? Besides the j-channel, you’ll also want to measure the top of each window and door for drip caps.

Finishing Steps to Keep in Mind

These are the steps to keep in mind, so now you’ll be an expert on how to measure for vinyl siding. If you take the time when installing your vinyl siding, you’ll end up having a finished job that looks attractive, with all your corners flush and all the siding courses level. And the really good news? Once you’ve finished all your hard work, your house will look great for years to come!

Tools & Materials

  • Steel measuring tape
  • Pen and paper for taking notes
  • Calculator

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