Dangerous deck (C) Daniel FriedmanDeck Guardrail or Stair Railing Baluster Installation Procedure
Deck Design-Build Online Guide

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Guardrail baluster installation: how to buy or make and then install balusters to enclose a deck or stair guardrailing. We describe baluster materials, choices, and how to space the balusters, giving three options for handling tricky baluster spacing problems. The article continues with details and pros and cons for several methods for attaching balusters to the top and bottom rail or to the deck, ramp, porch or balcony structure itself.

We explain why some popular pre-cut bottom guardrail designs invite rot and are actually unsafe. This article series describes critical safe-construction details for decks and porches, including avoiding deck or porch collapse and unsafe deck stairs and railings.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Deck Guardrail Baluster Installation Steps

Dangerous deck (C) Daniel Friedman

Balusters are commonly made with 2x2 lumber and installed vertically. You can buy precut 2 x 2s or milled balusters in lengths that will fit standard railings

. If you want to save a few dollars, you can cut your own balusters from long 2 x 2s. If you have access to a table saw, you can also rip balusters from straight 2 x 4s or 2 X 6s.

Another choice for wood balusters is 1 X 4s or 1 x 6s. If you want to maximize privacy, use wide boards and space them closely together.

If you cut your own balusters, make sure they are all the identical length. The most efficient way to do this is to use a power miter saw and construct a simple stop block. Lengths of baluster material are fed under the saw against the stop block, making rapid chopping of equal lengths easy and uniform.

Balusters attached to the sides of rails and to the exterior of the rim joist (page top photo and photo at left) look much nicer (and shed water better) if the ends are beveled.

Keep the size and angle of the bevels consistent from baluster to baluster by making the end cuts using a power miter saw

. This installation method is rapid and easy because you don't face the difficulties of abutting and securing balusters to the under-side of the rail nor to the top of a horizontal guardrail bottom segment. You may need to pre-drill balusters to avoid splits.

If post bottoms will be visible on the deck, try to match the proportion of the bevels on the posts with those on the balusters.

How to Calculate the Deck Guardrail Baluster Spacing

Metal balusters too far apart (C) Daniel FriedmanBuilding codes usually allow a maximum gap of 4 inches between balusters.

The metal balusters shown here are unsafe and improper, with a gap of more than 5-inches of open space.

Chances are good that using that 4-inch gap will not result in evenly spaced balusters across the entire balcony, porch, or deck surface.

Common solutions to this little problem include:

Baluster spacing using the split-the-difference method (C) Daniel Friedman

This method is shown at a guardrail and baluster demonstration at Menards in Duluth, MN (photo at left).

If the split-the-difference approach results in a too-small end space problem you can do what roofers do to adjust shingle courses near the ridge. Starting several baluster gaps away from the ending newell posts at either run, adjust the baluster spacing in by a small amount, say 1/8? or 1/4", such that you end up with the desired end or last space. A 1/4" adjustment will give you an extra 1-inch in the last space, and so on.

For consistent spacing, do the following math. Add the width of one baluster (I 1/2 inches for a nominal 2 x 2" baluster) to the maximum allowed spacing (typically, 4 inches). This total (the width of an individual baluster plus the 4-inch desired opening) becomes the unit width used in calculations that follow.

Divide this total (5 1/2 inches, in most cases) into the measured distance between two posts (68 1/2 inches for example). Finally, round up the result (12.45) to the next highest whole number (here, 13) to find the number of balusters you will need between the posts.

Now that you have the number of balusters, you can figure the exact baluster spacing.

Multiply the number of balusters (13) by the width of one (13 x 1 1/2 inches = 19 1/2 inches). Subtract that number from the distance between the posts (68 1/2 - 19 1/2 = 49) and divide the result by the total number of spaces, which is always one more than the number of balusters (thus, 49 divided by 14 = 3 1/2 inches).

The result is the ideal spacing between balusters. Make a spacer as close to that figure as you can (if necessary, convert the number to its fractional equivalent). Double-check your math by making sure your result is less than the maximum baluster spacing allowed by code.

Watch out: If the distance between posts varies by a very small amount, you should not have to calculate different spacings for the balusters. People are not likely to notice small differences in the spaces between balusters. But you must keep all the gaps between balusters, or balusters and posts, at or below the maximum allowed by your code. But if the distance between post spacings is too large this whole scheme will have been a lot of trouble for nothing.

For these reasons, on a large deck with imperfect post spacings or other obstructions in the baluster and guardrail path, I recommend using option 1 or 2 above - much simpler and just about equal in cosmetic appearance.

Framing Tip: for Spacing Deck Railing Balusters Uniformly Use a Spacer Block

Attaching balusters will proceed much more quickly if you make a spacer. Rip a piece of plywood or 1 X 4 or 1 X 6 lumber to match the desired space between rails. Make the spacer long enough to span from the top to the bottom rail. Press the baluster against the spacer and the neighboring baluster or post as you drive the fasteners.

How to Attach the Deck Guardrail or Stair Rail Balusters

How to Build Wooden Guardrails with Balusters Screwed to the Sides of Top & Bottom Rails

Wood baluster installation detail at rim joist (C) Daniel Friedman

For strong, easy-to-assemble railings, it is hard to beat the system, install posts, add rails on edge, and finish with balusters. In some areas, building codes insist on this technique.

Our photo (left) shows the top baluster connections along a stairway guardrail. The square cut end of the baluster abuts the under side of the deck (or in this example stairway) guardrailing flat top cap and the baluster is fastened to the guardrail using construction screws.

Notice that the Menards installers building this example used Method #1, the "ignore-it" rule of baluster spacing - they started at the left with 4-inches of spacing and let the right end of the run come out however it might.

Wood baluster installation detail at rim joist (C) Daniel Friedman

At its bottom the beveled end of the baluster faces down and out as shown at left.

If you are not installing a top cap along the deck guardrail then you will want to use cut beveled ends at both top and bottom of the balusters and to connect them as shown in our Baluster Spacing Method #2 above.

Begin the installation by grasping a baluster and the spacer in one hand. Hold the spacer tight against the post while driving two screws or nails into each end of the baluster.

Move the spacer to the other side of the baluster, pick up another baluster, and repeat the process. Having a helper hold each baluster in place while you work the drill for pilot and screw driving can speed the process.

Baluster Drilling Tips: If you mark and pre-drill pilot holes for the baluster screws ahead of time with all of your balusters laid flat on a work surface the job will go still faster.

Lining up the baluster screw location on a consistent horizontal plane is worth the effort as it will be quite noticeable if your screws are not at consistent locations across the deck.

Finally, don't pre-drill your balusters by placing them directly on the deck surface. It's tempting but you'll drill holes all over the deck. You will see this mistake and will be sorry as soon as you pick up the balusters.

How to Cut the Correct Top & Bottom Rail Lengths of a Guardrail

The top and bottom rail length will need to be longer than the space between the supporting posts if you are going to mortise the rail ends into the posts. Increase the railing length by more than the exact measurement so that you can trim the rails for an exact fit during assembly.

How to Build Wooden Guardrails with Balusters Placed Between Top Rail & Bottom Rail

Dadoed top and bottom deck railing design (C) Daniel Friedman

Assemble the Deck Railing a Section at a Time

If your code is less strict, and your taste differs, you may prefer the look of a railing with balusters installed between flat rails. This type of railing takes more time to build, and it works best when the posts are perfectly plumb and evenly spaced.

These railings are best assembled in full sections, which then are attached as units between posts.

Balusters should be cut to identical lengths. To keep them from spinning in place, you can cut a 1/2-inch-deep channel along the underside of the top rail just wide enough for the balusters to fit. (Or plan on toe-nailing each baluster with galvanized finishing nails.

Some writers on deck building suggest that to strengthen the assembly, plan to set the rails into 1/2-inch- deep dadoes cut into the bottom guardrail as well. In fact pre-dado-cut top and bottom railing assemblies are available at most lumber suppliers so don't use this project as an excuse just to buy a new router.

Baluster dadoed bottom rail (C) Daniel FriedmanIf you use this double-dado approach shown above, the dados are 1/2" deep so the the balusters should be cut 1 inch longer than the space between the horizontal railings. The dadoes are easiest to cut with a router or table saw before the posts are installed.

Watch out: The dado 'ed guardrailing approach works very nicely for constructing the top railing of a guardrailing or stair railing, but for the bottom rail ... well that's another matter.

I do not recommend this approach (shown above) because the dado groove in the bottom rail, facing up, will collect water and speed rot, splits, and aggravation throughout the entire (and short) life of the railing.

Watch out: break-away balusters due to rot or poor connections are very dangerous and can permit someone to fall off of the deck, ramp, or stairway the balusters were intended to enclose.

Baluster abutting flat bottom rail (C) Daniel Friedman

Your guardrail and its balusters along a deck or stairway will be more durable if the bottom ends of balusters abut on a flat, or better still, double-angled bottom rail that provides better drainage.

The flat abutment is easiest to assemble. Just drill and screw up through the bottom of the rail into the bottom of each baluster.

You'll need two galvanized finishing nails in the top end (and maybe bottom) of the balusters to prevent them from rotating in place (a problem the stupid dado-approach does solve, I admit).

If you use a flat bottom rail (shown at left), before setting the rail assembly in place between its supporting posts, use a block plane to chamfer the upper edges of the bottom rail.

Baluster connections to a beveled bottom rail (C) Daniel Friedman

For a well-drained, long-lasting bottom baluster rail assembly you don't need a slope as steep as I've shown in the sketch (left) though the steeper you make the slope the more resistant the baluster will be to rotation.

Use 4d galvanized finishing nails to secure the baluster bottoms in place.

You'll want to pre-drill the holes for your galvanized 4d or 6d finishing nails used to secure the baluster bottoms to avoid splits.

When all of the parts have been cut, assemble a railing section on the deck. Position the balusters with a spacer.  Drill a pilot hole at each baluster location, and then attach the baluster with 3-inch deck screws driven through the top and bottom rails into the center of the baluster.

Once the balusters have been attached to the rails, lift the section into place, sliding the rail ends into the post dadoes if you took the dado approach. (Ick!).

Fasten the railing assembly to the posts with 3-inch deck screws driven at an angle through each rail into the post.


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