Gap

[jmmrlm]

I heard somewhere that it is OK to leave gaps between sections (HO Scale) to allow for potential expansion.

How much gap should there be for HO Scale track ? Maximum/Minimum ??

Any easy way to measure this ?

Thanks.

[Len]

If your layout is in an enviromentally controlled room, expansion gaps aren't really necessary. If not, and index card thickness between sections should be enough.

Len

[jward]

If you are using a base that doesn't swell with humidity you really shouldn't need to worry about expansion joints. In 40 plus years of model railroading, i've only had one instance where expansion was a problem, and that was handlaid track built on Homasote in a damp basement. The section i had the most trouble with also butted up against an outside. Homasote attracts moisture, and the lessons learned here led me to rebuild the layout on pine planks that were much more dimensionally stable.

Most of us don't have our layouts set up in places of extreme temperature changes, so the expansion of the rails is not usually an issue. But using the wrong material as a base you built upon  can mean the difference between a good running layout, and one that is an endless source of frustration.

[Maletrain]

Gaps aren't a bad idea, even in "climate controlled" spaces.  Even in my house, summertime and wintertime humidity changes from something like 45% to 65% at extremes.  And, those extremes do not include what happens when there is a loss of power that kills the A/C or heat for a while.  And, in basements, there is the occasional flood from gutter problems, hot water heater problems, etc., etc.  So, my reasoning is "better safe than sorry."

Also, let's draw an distinction between electrical gaps and expansion gaps.  Electrical gaps are there to prevent short circuits or otherwise isolate track sections electrically.  It is important that those types of gaps do not close due to expansion.  So, typically, it is recommended that they be filled with some sort of insulating material.  A piece of plastic that is glued in-place and then trimmed/filed to match the rail contour is what is usually done.  But, then those electrical gaps cannot close, so they cannot absorb expansion.  So, additional gaps that are not filled with anything are used to accommodate expansion.

Some folks glibly cut electrical isolation gaps and do not fill them, and have neither short circuits nor buckled track.  They are lucky.  Some folks go to great lengths to use non-climate-sensitive layout materials and still cut expansion gaps.  They never seem to have problems with expansion.

[Maletrain]

The rail is not the only thing that expands and contracts with changes in various ambient conditions.  The layout base can also expand and contract at different rates than the rails.  If wood or other fiber materials are use for the layout base, humidity changes may be more significant than temperature changes.