Ever heard of the mushroom de- sign? It was Richard Benjamin who first invented and carried out the concept of two decks attain- able from different sides. But is was John Armstrong (who had seen Richard Benjamin's layout in 1985) who isolated the principle out of Richards example and broadcasted it by a couple of articles in MR magazine. But honestly said it was only when Joe Fugate published the plans for his new Siskiyou line layout in January and February 1997 that I really understood the advantages and potentials of the idea.
For a long time model railroaders have meditated about possibilities to make extensive use of the third dimension provided that there is enough clearence in the railroad room. Double or even multiple deck designs do have the draw back that only one of the decks (if any) can have the optimal height for to be looked at and operated.
The idea of Richard Benjamin was that this draw back can be eliminated at least at locations which are accessible from both sides. This is mostly the case in peninsulas. The illustration above shows a cross-section through a penisula. Normally the space between the two facing scenes is occupied by scenery or by a double sided back drop. In the mushroom design this space is made accessible by means of a duck under and a couple of steps lead to a raised floor.
From this raised floor the visitor/operator can look at the scenes on the upper level of the layout which are more or less above the lower ones. These secenes sticking out to the sides of a "stem" in the middle look indeed a little like a mushroom, don't they?.
When I was given that terrific basement with 8' head clearence I began immedeately to reckon about how to make the best use of that high room. Of course the mushroom design which I had studied in the pages of Model Railroader came to my mind at once. But as I have mentioned in a previous chapter I needed ample space for several workshop places under the layout. A mushroom does not offer any space under the layout, or maybe a little under the raised floor.
If you have a mushroom peninsula you look at the lower levels from the exterior and at the upper levels from the interior. My idea was to turn the mushroom inside out, to invert it.
An inverted mushroom pensinsula has the same exterior width as the original mushroom but offers considerable space under the layout. The lower graphic shows the actual cross section AA through the peninsula on my BAE III layout.
No draw backs? Oh yes. Clearence under the layout is more or less limited. As a consequence there is very limited clearence above the railroad scenes on the lower level. A room 10' high would emiminate this of course.
Anyway the additional space gained is enormous. Not less than five workshop places could be installed under the peninsula.
In order to make best use of the space under the layout special construction methods have to be applied. The common open grid benchwork would spoil this completely. I fabricated several long contoured spans up to 3 1/2' long by laminating two layers of 3/16" plywood back to back.
This picture shows workshop places #1 and #2 at the end of the pensinsula. The under side of the layout construction and scenery is still to be concealed in some way, but the space is obvious, isn't it?
The train visible to the left is standing on a piece of track that marks the level of the future "lower level" of the layout. Outside the workshop areas this lower line (the St.Andreasberg branch) will be fully scenicked.
Track on the upper level is shown in faded outline on this plan of the lower level. The inverted mushroom design offers enough space on the lower level for a long branch line plus 6 workshop places.
While the workshop places are already in good use the branch line is still to be built.
The maroon arrow shows the location of the above photo.
This chapter is a shortened and modified version of my article "The Inverted Mushroom" in the Layout Design Journal (LDJ) No 38. LDJ is the quarterly magazine of the Layout Design Special Interest Group within the NMRA.