Snow is water with air in it, so what it weighs is what the water in it weighs. Enter how deep it is on your roof and this gives you the load in pounds per square foot, and compares it with your maker’s rating if you have one.
Depth alone cannot give a weight, because a foot of dry powder and a foot of wet snow are not the same load. So the depth here is bridged to a weight by a figure a maker publishes: Keystone rates the roofs on its towables at 30 pounds per square foot, and states that as about two feet of snow. Thirty divided by twenty-four is 1.25 pounds per square foot for every inch of snow, and that is what the depth is multiplied by.
Two things about that figure, because it is one maker’s and not a law. It describes snow that has settled, so fresh powder weighs less and wet snow weighs more, which is why the result is the middle of a range rather than the top of it. And it is a rating for Keystone’s own roofs, so it tells you the weight on yours, not what yours is built to carry. That is what the rating box is for.
Two makers publish a roof figure for a towable, and between them they give you the scale even though neither is your roof:
| Maker | Figure | What kind of number it is |
|---|---|---|
| Keystone | 30 lb/ft² | A roof rating for its own towables, stated as about two feet of snow |
| Boxabl | 20 lb/ft² | A live-load rating for the flat roof of one factory-built towable |
Those are not the same kind of number as each other, and neither is your roof's rating. Taking the lower of two figures published for two other RVs does not produce a rating for a third: a roof with no published limit may be built to carry less than either. What the pair does tell you is roughly where the line falls for a light towable roof, which is in the tens of pounds per square foot rather than the hundreds.
If your manual publishes one, that figure governs and you can put it in the box above. If it does not, the honest reading of no figure is that the roof was built to shed water rather than to carry snow, and the safe move is to clear it earlier rather than later.
The same note gives the method, and it needs one piece of kit: a long cylinder with a flat bottom and a cap, deep enough to hold the snow. A capped length of PVC pipe works. Push it down through the snow all the way to the roof, turn it over, and let what you have caught melt indoors. The depth of the water left in the cylinder is your water equivalent in inches.
Measure on the roof if you can rather than on the ground. The note is explicit that snow depth varies a great deal over a short distance, and the depth on your roof is the one that matters.
Two things, and both are the note's own cautions rather than ours. It assumes the snow has aged the same way across the area, which is not always true, and it calls the result a rough estimate that should be used with care. Neither this tool nor the method behind it is a structural assessment of your roof, and if the number is close to a rating you have, the answer is to clear the snow rather than to keep measuring it.
The roof snow load guide covers what snow does to an RV roof beyond the weight of it, and what the makers rate their roofs at. The winterising guide is the plumbing half of the same season.