This is a job I was brought in to complete after the customer had already built their raised timber decking, having handled replacing the deck from scratch themselves. My task was to fit all the safety railing around the outer edge, including two staircase sections. It was a satisfying project that tested both my joinery skills and my patience for precise measurement. Here’s exactly how I approached it.
I recently did a similar job, fitting wooden garden railings for an elderly customer, if you want to see another approach.
What You’ll Need for This Job
Skill level: Intermediate. You need to be comfortable with basic joinery, accurate measuring and using power tools. The spindle spacing calculations require patience and precision.
Time: Allow a full day for a deck of this size. Two days if you are including stair sections and siding.
Tools
- Mitre saw (I use a Evolution Power Tools R185SMS+ Compound Saw)
- Sliding bevel (I recommend this one – Presch Sliding Bevel)
- Spirit level
- F-clamps
- Set square
- Tape measure and pencil
- Pocket hole jig (I use a Kreg)
- Impact driver
- Combi drill
- Hammer
- Socket set
For my Impact driver and Combi drill, I personally like DeWalt, but other quality brands include Makita and Milwaukee.
Materials
- Newel posts
- Spindles
- Top and bottom rails
- 120mm coach bolts
- Decking screws
- 50mm galvanised nails
- Exterior wood glue
The Job Spec
The decking measured roughly 3,600mm x 4,000mm, with two sets of stairs, each with three steps. The bannister had to run around the full outer perimeter, including down both stair sections.
The materials list came to:
9 newel posts, approximately 82 spindles, top and bottom rails cut to run between each post, coach bolts (120mm) for securing the posts to the frame, decking screws, 50mm galvanised nails, and wood glue. Total material cost across the whole deck was around £800. (£370 for the railings).
Step One: Fixing the Newel Posts
The newel posts go in first. I secured each one directly to the decking frame using 120mm coach bolts, tightening them down with a socket set. Getting these absolutely plumb and level is critical. If a post leans even slightly, the distance between the top and bottom rail will be different on each side, and you’ll notice it immediately when you come to cut your spindles.
I used a spirit level on every post and took my time here. Any time you spend getting the posts right saves you double the time later.
Step Two: Top and Bottom Rails
Once the posts were solid, I cut and fitted the top rails at a height of 900mm, which is the standard minimum for a raised deck in the UK. The rails were fixed to the posts using a Kreg pocket hole jig, which meant no visible brackets or fixings on the outside face. It’s a small detail but it makes a big difference to how clean the finished job looks.
I left a 50mm gap at the base before fitting the bottom rail. This keeps spindles clear of the deck surface and allows for drainage and movement.
Step Three: Working Out Spindle Spacing
This is the part that catches most people out, and it is worth taking seriously. UK building regulations require that no sphere greater than 100mm can pass through the balustrade. In practice, that means your spindle gap cannot exceed 100mm.
I aimed for roughly 80mm between spindles, but because each bay (the distance between two adjacent newel posts) was slightly different, I had to calculate the spacing individually for each one.
Here is the formula I used:
Bay width minus spindle width divided by number of spindles plus one equals the gap between each spindle.
For example: if the bay is 1,300mm wide and you are using 40mm spindles, fitting 10 spindles gives you:
(1300 – (10 x 40)) ÷ 11 = (1300 – 400) ÷ 11 = 900 ÷ 11 = 81.8mm per gap
You adjust the number of spindles up or down until you land on a gap that is comfortably under 100mm. Around 80mm is a good target.
You then adjust the number of spindles up or down until you land on a gap that is under 100mm and as even as possible. Being a millimetre or two out compounds across the whole bay, so precision really matters here. I measure twice before committing any cut.
Stair Sections: The Angle Changes Everything
The stair sections need a different approach. Because the spindles run on an angle, the effective width of each spindle as measured along the slope increases. A 40mm square spindle on a staircase angled at around 38 degrees effectively reads as closer to 50mm in the spacing calculation.
I used a sliding bevel to find the exact angle of each stair run, then factored that into my calculations. The spacing I achieved on the stairs was still within the 100mm maximum, but the numbers were different to the flat sections and I treated each stair run as a completely separate calculation.
Step Four. Cutting and Fitting the Spindles
Once I had my spacing worked out for each bay, I cut the first spindle to length on the mitre saw and used it as a template for all the rest in that bay. I set up a stop block on the saw fence so I could replicate the cut every time without measuring each piece individually, and if you aren’t sure which mitre saw to buy I’ve compared budget and premium options in detail. If you are cutting 82 spindles by hand with a tape measure, you will lose your mind and probably your accuracy.
For spacing, I cut small filler pieces of timber to the exact width of each gap. These slot into the groove on the underside of the top rail and act as spacers, pushing each spindle into the correct position automatically. You fit the filler piece, drop in a spindle, nail and glue it, then fit the next filler piece, and so on. No guesswork, no drift.
Each spindle was fixed at the top with a nail and a small amount of exterior wood glue, and secured at the bottom by screwing up through the bottom rail with a decking screw. Once all spindles were in place, the bottom rail was then fixed to the posts.
Step Five: Fixing the Bottom Rail
Once all the spindles were in place, I secured the bottom rail to the newel posts. Leaving this until the spindles are all fitted means you can adjust the rail position slightly if needed before committing it. I repeated the whole process for each bay in sequence, working around the full perimeter of the deck.
Finishing
Once all the spindles and rails were in place I went back over the whole job, checking for anything out of level and tightening any fixings that had moved during the build. Everything was in good shape.
I advised the customer to leave treating the wood for a month or two. Fresh sawn timber needs time to settle and lose moisture before it will take a preservative properly. Rushing this just wastes product.
What This Job Cost
I was brought in to fit the railings, stair sections and siding only. The customer had already built and installed the decking frame and boards themselves, which kept their overall project costs down considerably.
For the railing installation alone the job came in at £360, which was 1.5 days of work. With the stair sections and siding included the full package was £600 across 2.5 days. Materials for the whole deck came to around £800.
If you are based in Cornwall and need something similar priced up, get in touch, and I’ll come out and take a look.
Lessons Learnt: What Will Make or Break This Job
After completing a perimeter railing across a deck this size, with two stair sections and 82 spindles, here is what I would pass on to anyone attempting something similar.
Get your newel posts perfect before anything else. Every measurement in this job flows from the posts. If a post is even slightly out of plumb, the distance between your top and bottom rail will be inconsistent and your spindle lengths will all be different. Use a spirit level on every post and take your time here. It costs nothing but pays back double.
Spindle spacing calculation is where most people go wrong. A millimetre or two of error at the start of a bay compounds across every spindle and becomes very obvious by the last one. Work out the spacing for each bay individually, since the distance between posts will rarely be identical. Use the formula in Step Three, check your numbers twice, and cut your spacer blocks as accurately as you can. Precision here is what separates a professional-looking result from one that jars.
The stair sections need separate calculations. Do not assume the same spacing works on the stairs as on the flat sections. The angle increases the effective width of each spindle, which changes the gap calculation entirely. Measure the angle with a sliding bevel and treat each stair run as its own job.
A mitre saw with a stop block is not optional on a job this size. Cutting 82 spindles individually by hand is slow, inconsistent and exhausting. Set your first cut, lock in a stop block, and replicate it every time. The same applies to your spacer filler pieces.
Always use galvanised fixings outdoors. Standard screws and nails will rust within a season, stain the timber and eventually fail. The small extra cost is not worth arguing about.
Use F-Clamps as an extra pair of hands. When working with multiple pieces of wood at the same time, a set of clamps is essential, especially when working alone.
Use exterior wood glue on every join. It adds strength and longevity to any fixing point and costs very little extra across a job of this size.
Leave fresh timber before treating it. New sawn timber needs time to lose moisture before it will absorb a preservative properly. Leave it for at least a month or two before applying any treatment, otherwise you are wasting product.
Ready to Get Your Decking Railing Fitted?
A job like this takes precision, the right tools and a good understanding of the regulations around spindle spacing. If you would rather have it done properly first time, I cover Cornwall and the surrounding areas.
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