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Building and Installing a Site-Built Balustrade: Assembling the Balustrade

Use off-the-shelf hardwood balusters to complete the railing.

By Scott Grice

Establishing baluster spacing

Calculating the baluster spacing is not difficult, but it does require a little back and forth. Unless the spacing between all the posts is perfectly uniform, it’s best to calculate the baluster spacing for each run separately. Typically, your eye will not pick up small differences in spacing from one run to the next but will immediately identify one space that is not the same as the rest in the run. To calculate the spacing, begin by measuring the distance between the posts (see photos below). To keep the measurements straight and to avoid error, it’s best to have a calculation sheet to write the measurements down on (see “Calculating the Baluster Spacing” below). To the distance between the posts add one baluster thickness.

1. Measure the distance between two posts to begin calculating the baluster spacing.
1. Measure the distance between two posts to begin calculating the baluster spacing.

2. Add the width of one baluster to the post spacing to get the overall distance.
2. Add the width of one baluster to the post spacing to get the overall distance.

 

Calculating the baluster spacing

  • Distance between posts + One baluster thickness = Overall balustrade distance x estimated baluster-unit distance = Number of units fraction
  • Round number of units up to the next whole number = Final number of baluster units
  • Overall balustrade distance x Final baluster units = Final baluster-unit distance

Note that the final baluster-unit distance is what you use to lay out the balusters, but if you want to check the exact distance between the balusters, simply subtract the baluster thickness from the final baluster-unit distance.

Quick Tip: Mike Guertin demonstrates an alternative way to easily lay out good-looking baluster spacing using a piece of elastic band as a measuring tool in this video.

 

The maximum distance allowed between balusters by code is 4 in., so set two balusters down with a 4-in. gap between them and measure the space between the balusters plus one baluster thickness. This is the estimated baluster-unit distance. Now divide the overall distance by the unit distance to determine the number of units. In this case, the number is about 7-1/2. Round up to the next whole number and divide it back into the overall distance to get the final baluster-unit distance. In this case the baluster-unit distance is just over 5 in..

3. Calculate the baluster-unit distance by adding 4 in. to the width of one baluster.
3. Calculate the baluster-unit distance by adding 4 in. to the width of one baluster.

4. Divide the overall distance by the unit distance and then round up.
4. Divide the overall distance by the unit distance and then round up.

5. Divide the number of spaces back into the overall distance.
5. Divide the number of spaces back into the overall distance.

 

Assembling and securing the balustrade

To increase efficiency and avoid mistakes, make a story pole of baluster spacing and clamp it in place with the actual balusters. Transfer the baluster layout to the rails, making an X for each baluster. Unclamp the rails and transfer the layout up the rails’ inside faces. By code, the maximum allowable gap between the decking and the rail bottom is also 4 in. To establish the correct baluster length, place a 4-in. (or less) spacer on the deck. Measure to the top of the post for the overall baluster length. Cut all the balusters and place them according to the layout on a top and bottom rail on the deck surface.

1. Clamp the story pole to the rails of a section positioned between the posts.
1. Clamp the story pole to the rails of a section positioned between the posts.

2. Transfer the layout from the story pole to the railings.
2. Transfer the layout from the story pole to the railings.

3. Continue the layout marks down the insides of the rails.
3. Continue the layout marks down the insides of the rails.

4. Place a spacer no more than 4 in. tall at the base of the post.
4. Place a spacer less than 4 in. tall at the base of the post.

5. Measure from the spacer to the top of the post to establish the baluster height.
5. Measure from the spacer to the top of the post to establish the baluster height.

6. Assemble the rails and balusters on the deck adjacent to their final position.
6. Assemble the rails and balusters on the deck adjacent to their final position.

Place the other top and bottom rails over the balusters, being careful to align the ends and the layout marks. To create a uniform assembly, mark the fastener location with a stop or marking jig at every baluster location. As it’s easy for the individual boards to shift before they are secure, use a square to flush the baluster bottoms and rail edges before predrilling the holes. Hold the assembly firmly while predrilling the holes. Check the assembly again for alignment and then drive the fasteners to secure the bottom part of the balustrade.

Rather than measuring for the fastener locations in the top rail, align the top rail next to the bottom rail you just secured and transfer the fastener locations with a Speed Square. Repeat the process of drilling pilot holes and driving fasteners to secure the balusters and top rails. Test-fit the assembled balustrade to make sure it fits properly before attaching it permanently.

7. Position the opposing rail on top of the balusters. Take care to orient the rails appropriately.
7. Position the opposing rail on top of the balusters. Take care to orient the rails appropriately.

8. Mark the fastener locations with a gauge to ensure that they are uniform. A slight depression from the awl will help guide the bit.
8. Mark the fastener locations with a gauge to ensure that they are uniform. A slight depression from the awl will help guide the bit.

9. Flush the rails and balusters with a Speed Square before drilling the pilot holes.
9. Flush the rails and balusters with a Speed Square before drilling the pilot holes.

10. Drill the pilot holes at each baluster location, taking care not to drive the bit into the decking below.
10. Drill the pilot holes at each baluster location, taking care not to drive the bit into the decking below.

11. Drive a fastener into each hole to secure the rails and balusters.
11. Drive a fastener into each hole to secure the rails and balusters.

12. Position the top rail adjacent to the bottom rail and transfer the baluster locations, again making a dimple with your awl.
12. Position the top rail adjacent to the bottom rail and transfer the baluster locations, again making a dimple with your awl.

13. Repeat the process of aligning and securing the rails to the balusters at the top of the assembly.
13. Repeat the process of aligning and securing the rails to the balusters at the top of the assembly.

14. Test-fit the baluster and make any adjustments necessary to achieve a snug fit.
14. Test-fit the baluster and make any adjustments necessary to achieve a snug fit.

 

trim router
Trade secret:

Keep a trim router fitted with a small roundover bit handy. As you finish each section, quickly give the sharp edges a pass to remove splinters and give the balustrade a more finished look.

 

To secure the balustrade at the top, first cut a short section of baluster and fasten it to the post in the center. At the bottom, cut the top of the block at an angle to shed water and prevent rot, and then attach it where the bottom rail meets the post.  Slide the rail in from the side just above the blocks and then guide it down into place. Flush the top of the rail to the post top. If everything fits, you shouldn’t have to do more than some gentle tapping to persuade it into position. Finally, use fasteners to secure the rails to the blocks. Be careful with this process because the short blocks tend to split if you overdrive the fasteners or neglect to drill fastener pilot holes.

15. Fasten short lengths of baluster material to the posts between where the rails intersect the posts.
15. Fasten short lengths of baluster material to the posts between where the rails intersect the posts.

16. Angle the top of the blocks where they are exposed to the weather. This will help shed water and prevent rot.
16. Angle the top of the blocks where they are exposed to the weather. This will help shed water and prevent rot.

17. Slide the balustrade in from the side just above where the rails intersect the blocks.
17. Slide the balustrade in from the side just above where the rails intersect the blocks.

18. Slide the balustrades down into position so that all four blocks are hidden behind the rails.
18. Slide the balustrades down into position so that all four blocks are hidden behind the rails.

19. Flush the top of the rail with the top of the posts. Double-check to make sure the balustrade is aligned the way you want it.
19. Flush the top of the rail with the top of the posts. Double-check to make sure the balustrade is aligned the way you want it.

20. Secure the balustrade with fasteners at each of the four blocks.
20. Secure the balustrade with fasteners at each of the four blocks.

 

Photos: John Ross

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Previous: Building and Installing a Site-Built Balustrade: Cutting the Posts and Rails Next: How to Make Rot-Resistant Deck and Porch Railings

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