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Multi-Deck Design Considerations

Model Railroad Helix.JPG

The vast majority of my customers are either new to the hobby or have yet to embark on building their first layout.  More than half state that they would like a multi-deck format.   Layout configurations are neither good nor bad in and of themselves…..IF, and it’s a huge IF, the builder goes in with their eyes wide open and knows EXACTLY what the pros and cons are.  That’s my concern.  In most cases, entry-level modelers (and many more experienced ones) desiring multi-deck layouts don’t know what they’re biting off. The assumption is that they are a magic bullet, a simple way to quickly increase a layout's run length.  That’s not the case.

A double deck layout isn’t “slightly” more involved than a single deck one of the same surface area.  It’s not twice as complex.  There are so many factors in play that the complexity level is four, five, or maybe six times that of the single deck format.  The compromises to human comfort are numerous.  Construction methods are more complex.  There are a lot of hidden landmines that just aren’t immediately apparent when looking at a two-dimensional drawing.  The published plans you see in the press?  Many are thought exercises that have not been built.  Many have significant issues that aren’t addressed in the article.

Let’s do a dig deep dive into the ergonomic, engineering, and mathematical issues associated with multi-deck railroads.  Once you have a full understanding of them, you will be better positioned to make an informed decision before embarking on something that involves a significant investment of time and money.  If you are absolutely clear on the issues involved, are okay with the compromises they entail, and have built at least one single deck layout to gain experience….. then go for it!

Pros of Multi-Deck Railroads:

-Longer run length and more "model railroad" for a given amount of space

Cons of Multi-Deck Railroads:

-Neither deck will be at the ideal height.  This is a BIG deal.

-A significant amount of a train's run time will be spent spiralling around the helix coils.

-There are often issues associated with elements on one deck interfering with those on the other deck.

-The complexity of constructing the helix structure and the multi-deck bench work is significant.

-The amount of floor space a helix takes up is a factor.  This is space that can't be used for scenery or structures.

-There is limited access to track in the helix in terms of cleaning track and addressing rolling stock malfunctions.

Now, let's look at some of the more important engineering decisions, deck height and separation and helix dimensional design issues.

Deck Height and Separation

It’s in model railroaders’ DNA to push the dimensional limits in an effort to maximize their experience. They think that they’ll be fine with engineering compromises only to find out the hard way (and expensive way) that they made a tremendous misjudgment that drastically impacts how much they enjoy the layout.  A classic, and often disastrous, example of this are shortcuts and oversights with respect to deck separation and how elements on the two decks impact one another.

The biggest “shortcut” is what I call “mail slotting”.  Mail slotting is putting the decks too close together.  It's not obvious looking at a two dimensional design on paper, but the user experience is one of viewing or reaching through a mail slot.

Other considerations with deck separation aren’t so obvious.  If you have taller elements on the lower deck, such as grain elevators or hills, they will rise up tight against the bottom of the upper deck.  At best this looks odd, at worst you can’t see the model.   Another issue relates to grades.   If you have significant grades on a lower deck you run the risk of the track and scenery running too close to the deck above.  If you have significant grades on an upper deck, you run the risk of the track rising so high that it’s not comfortable to view or reach.


Bottom line. When evaluating deck separation, you also need to do the juggling act of paying attention to how taller structures, taller hills, and grades upset the apple cart.

By far the biggest engineering decision will be that of the deck heights.  Getting this right is crucial and will be one of the most important decisions you make because it will determine how comfortable it is to interact with and view the trains.  The only way to totally nail the correct measurements is to construct mock-ups on shelves, put a rail car on them, and see what you have in 3D.  That said, let’s look at some numbers as a starting point.  The height of the average person is five feet, nine inches.  People generally find that on a SINGLE deck layout, the track level they find most comfortable is about 50 inches above the floor.

With multi-deck layouts that ideal height is off the table.  Each of the two decks will be at a compromised height in terms of comfort.  One will be a bit too high, the other a bit too low.  The design process becomes an exercises in managing compromises.  To adequately see the elements of the lower deck, a good starting point is 40 inches.   After doing extensive mock-up testing, I came to the conclusion that a deck separation of around 18 inches is about right in terms of sight lines and comfort. Deck separation being defined as  the distance between the lower deck rail and the upper deck rail.  Doing some testing with mockups, the highest I could go with the upper deck, and still be able to see things was 58”.  There is a subjective element to this so you need to test things out with mock-ups given the theme, geography, and design of your specific project.  You also need to be aware of “deep drop-down” scenery features such as canyons and viaducts.  If you put them on the upper deck, they will drop right into the lower deck scene below.  In summary we have the suggested starting points:


Deck separation: 18 inches

Top deck height: 58 inches

Bottom deck height: 40 inches

Side view showing suggest deck heights and separation.


The depth of the bench work and scenery factors in, especially with respect to the upper deck.  In this example I'm assuming a cross section depth of 5 1/2"


Scenic elements that drop significantly downward vertically need to be accounted for.  Ideally they should be placed on the lower deck.  If you put them on the upper deck, they'll encroach on any layout features below.


You need to pay close to grades with multi-deck layouts.  Rising track on a lower deck ramps up towards the bottom of the upper deck bench work.  Rising track on an upper deck can climb out of sight.


You run into sightline issues when you place taller elements (such as hills and structures) on the lower deck.  You may not be able to see the upper portion and overall it's an odd look. If you have the option, place taller features on the upper deck.

Helix Engineering

Run Time and Helix FootprintMulti-deck layouts require some way of getting from deck to deck.  In most cases, this will entail a helix. When contemplating a double deck format, it’s crucial to have your eyes wide open as to the amount of track that will be in the helix, the travel time it takes to traverse that distance,  and the significant room square footage taken up by its frame.  Realistically, it will take five helix coils to go from deck to deck.  At a minimum, the track length per coil will be around fifteen feet.  That means you will have 75 feet of track in the helix.  Trains on multi-deck layouts will spend a very significant portion of their run time “spiraling” within the helix.  It’s crucial to understand that and be okay with it before making the decision to go multi-deck.  The minimum diameter of a soundly designed helix frame is roughly 5 feet in diameter. If you have forty foot long basement, that’s not significant.  However, if the layout is in a spare room, and many are, a noticeable percentage of your available layout floor space will be taken up by the helix frame.

Helix Math

When engineering the helix you need to pay attention to:


-Coil separation

-Coil radius 

-Car overhang

Grades: When I was writing my design book for Kalmbach,  I polled the most experienced modelers I knew in terms of what was an acceptable maximum grade.  The answers were all over the place  driven by variables such as train length, type of locomotives, amount of curvature (curves add drag and reduce the workable grade), and the length of the grade.  Looking for a common theme, and relying on my own testing, the number seemed to be in the range of 1.75 per cent to maybe 2.00 percent if the trains are shorter.

Coil Separation: If you don't have enough separation between helix coils, obviously the cars won't fit inside.  You need just enough room to reach into the coils if need be.  On the flip side, if the spacing is too much, the grades will become unworkable.  Ultimately the spacing will depend on the height of cars you plan to run.  Assuming no cork in the helix, and code 83 rail, the following is a starting point.

Standard Height Cars: 3 3/8" coil spacing

Excess Height Cars: 3 3/4" coil spacing


Coil separation for standard height cars.


Coil separation for excess height cars

Radius and Car Overhang:
Short cars will typically negotiate a curve radii of 24 inches, or even less.  We can't use that metric in a helix.  Why?  Small radii means shorter run length in the coil, the end result being grades that are too steep.  As a starting point use the following:

Shorter rolling stock (50 foot cars, 4 axle power): 27 inch coil radius (2.00 per cent grade)
Longer rolling stock ( 60 foot plus cars, 6 axle power: 33 inch coil radius (1.85 per cent grade)

If your helix design contains double track, you need enough parallel track separation so that car overhang doesn’t result in side-swiping.  In a similar vein, you need to make sure that you have enough distance between the outermost track and the helix support frames to provide adequate car overhang clearance.


Helix radii for average or shorter rolling stock.


Helix radii for long rolling stock.

Helix Construction Considerations:
Once a helix is constructed, access to the components is extremely limited.  The last thing you want to deal with is rail popups, buckled rail, failed feeder connections, etc.  I spike all helix track down with Atlas 1/4" spikes spaced every six inches or so.  I also leave a 1/16” rail gap every six feet or so.

Other Design ConsiderationsOp. Session considerations.

Planning for Operating Sessions: One of the design "best practice" standards for the formal operating session crowd is to avoid having operationally intense design elements, such as yards, towns, or industrial parks across the aisle from one another.  Things get crowded in  in a hurry if you don't stagger their location.  Double deck layouts add another wrinkle to the issue.  You also want to avoid having operationally intense elements over one another vertically.  Having a crew working a yard on one deck, and then having another yard directly above it with its own crew, becomes unworkable.  In other words, with multi-deck layouts you don't want operational intense elements across the aisles from each other nor directly above one another on the other deck.


Deck support:

With most route formats you can hide the upper deck vertical support columns behind the backdrop.  Be aware that in some situations there won’t be a backdrop to hide them, a stub-ended peninsula for example.  You’ll either need to have the post extending upward from the lower deck scene or have one heck of an ingenious overhead long-span rafter design.


Life has gotten much easier in this regard.  LED tape lights are bright, inexpensive, thin, and easy to work with.  They're the way to go.


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