How to Inspect the Exterior Course - Spheres

The instructions say

The triangular area formed by a tread, riser and guard should not allow passage of a 6-
inch-diameter sphere.

What it doesn’t say is whether that’s at the start of the tread (which I suspect) or the back of the tread. It seems if it’s the back of the tread, the guard is going to be very close to the tread…


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Not sure I understand the question, but this graphic may be helpful.

You graphic is different than the one in the training. Your graphic suggests the ball rests against the riser for the clearance test. The training isn’t clear on resting against the riser, or setting on the edge of the tread above the riser below it.


IMO, we are worried about the larger space, not the smaller. Anywhere a child’s head may get stuck.

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According to code, placement of the sphere does not matter. A 6" sphere cannot pass thru.

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It is not about treads width. It’s about measuring the space between spindles or balusters, which forms a triangle. I thought it was 4" inches.

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While code is still ambiguous, looking at it from a safety perspective makes it make sense to be the smaller space. Thanks…

I did not see the lower sphere between the top of a tread and bottom of the baluster stair rail. I concur. 6" inch limitation.

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? How so? Triangle formed by the riser, bottom of the tread and the rail shall not allow a 6" sphere to pass.

Larger space, smaller space…it does not matter as long as a 6" sphere cannot pass.


InterNACHI Inspector Outlet gives 4" & 6" foam spheres to members.
Follow the link.


I am not speaking for Tom but, I think Tom’s reference to ambiguous meaning was that, we as InterNACHI CPI’s do not inspect to and refer to code, Brain.

Ambiguous in that I’m looking for “go here, do that”! Some of these requirements/codes get to be a LOT of little things to know. Not being someone that installs handrails or guards, this is new information to me. I can see a triangle formed by either the back riser and the tread, or the front riser and the tread. Then there’s idea that 6" seems awfully small - or puts the guard close to the tread - not actually looking at a stair/guard installation. There may be more clearance than my mind is envisioning.

Also, you can’t rule out the “Tom’s a hardhead” angle!

But, looking at it in the lens of safety, and a 6" ball shouldn’t pass thru any part of any riser/tread/guard triangle puts it to bed.

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So true. It is a building process.

Our first priority is to put our client into a safe home. So, great question.

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I don’t understand the confusion here. The sphere should initially be touching the tread (Adjacent) and the riser (Opposite). If it does not touch the guard rail (Hypotenuse) to prevent it from passing through… IT FAILS!


My name is Brian.

Anyway, we are not code inspectors. To say we do not refer to code or inspect to code is just not true. Of course we do, code is a reference point or touchstone for all of us. Commonly referred to as “modern building standards”.

That is why we have spheres.


Sorry, Brian. I misspelled your name.
Not the strongest speller. Don’t take it personally.
One inspector did several years ago and disparaged me on the MB for years. What an ass. He’s retired now. Good riddens.

My mistake.

2.2. Exclusions:

I. The inspector is not required to determine: H:. compliance with codes or regulations.