Principia published recently a chart that can help investors and dealers explain the nuances behind some of their inventory numbers.

The chart comes from a survey in which Principia asked dealers to identify the percentage of sales of particular items during the past 12 months that came out of their in-stock inventory. Roofing, exterior trim, and siding all had the highest percentages. That’s natural, Principia said, because those products tend to be more standard. In contrast, doors and windows tend to be much more customized, so there are far more special order sales than purchases made out of what’s on hand.

These differences help explain why one company’s inventory might vary markedly from another’s, even if both generate the same amount of revenue. It’s also a factor to consider when estimating how much storage space a dealer needs and how that space should be configured. Those differences could lead to differences in valuation at sales time.