Ridge height and rafter spacing decide whether a shelter works. Cover material is the third decision, not the first.
| Date | Area | Low | Sky | Shelter | Heat | Edge work |
|---|---|---|---|---|---|---|
| 27 Feb | Iron Co, WI | 3°F | Overcast | Tarp and brush lean-to | Box stove | Pot hanger, eight tent stakes |
How high should the ridge be?
For a fire-facing lean-to, between 34 and 38 inches. High enough to sit up under, low enough that the sloped face still throws heat back down onto the bed.
The number comes from two constraints pulling against each other. Below about 32 inches you cannot sit up, which sounds like comfort and is actually about how long it takes to do anything inside. Above about 40 inches the back wall stops reflecting fire heat onto the sleeping platform and starts throwing it over your body into the trees behind you.
On the 27 February camp we built at 42 inches by accident, having eyeballed it against a taller person. The stove made the mistake invisible that night. Two weeks earlier, with an open fire and no stove, the same error had shown up as a cold chest and warm feet, which is the diagnostic signature of a ridge that is too high.
What sets rafter spacing?
The cover, entirely. Boughs need rafters every 8 to 10 inches. A tarp is happy at 16 to 20 and gains nothing from more.
| Cover | Rafter spacing | Ridge height | What fails if you get it wrong |
|---|---|---|---|
| Spruce boughs, shingled | 8 to 10 in | 34 to 38 in | Boughs sag between rafters, water tracks through the gaps |
| Leaf and duff debris | 6 to 8 in | 30 to 34 in | Debris falls through, then the whole face slumps |
| Tarp, pitched taut | 16 to 20 in | 34 to 38 in | Nothing structural, but extra rafters cost build time for no gain |
| Bark slabs | 12 to 14 in | 34 to 38 in | Slabs cup and lift in wind without enough bearing points |
| Canvas, heavy | 14 to 16 in | 36 to 40 in | Frame deflects under wet snow load |
The relationship worth internalising is that spacing is a function of how far the cover can span unsupported. It is the same logic as shingle exposure on a roof: a cedar shake and a sheet of steel cover the same rafters completely differently, and nobody would build one frame for both.
Where the drip line lands
Almost nobody plans for it, and it is the most common reason a well-built shelter produces a wet night.
Water leaving the lower edge of the cover does not fall straight down. It carries forward, and on a steep pitch in wind it can land a foot beyond where you expect. If the bed is under that line, the shelter is working perfectly and you are still wet.
The fix is a scratch in the dirt before the roof goes on. Stand where the lower edge will be, drop a stick from it, add a hand’s width forward for pitch and another for wind, and put the front edge of the bed behind that mark. It takes thirty seconds and it is the cheapest insurance on the whole build.
Everyone measures the ridge. Almost nobody marks the drip line, and then they blame the cover. Scratch the line in the ground before you put a single rafter up, because after that you will not want to move the bed.
Maren Aho, forest research field technician, Baraga County
The order these numbers get decided
Bed first, then ridge, then spacing, then cover. Deciding the cover first is what produces frames that have to be rebuilt.
- Lay out the bed and mark its footprint. Everything else is measured from it.
- Set the ridge height from the bed, at 34 to 38 inches for a fire-facing build.
- Choose the cover from what is actually standing within a short carry.
- Set rafter spacing from that cover, and only then start cutting rafters.
Ridge height is the number people copy from a video, and video builds are framed to look good rather than to sit in. Measure it against the person who is sleeping there, kneeling, with a hand above their head.
Wendell Tokarz, retired outdoor program instructor, Marquette
Working the other way is how our first winter went. We cut a dozen rafters at a spacing that suited a tarp, then found no tarp-friendly anchor points and switched to boughs, and every one of those rafters was in the wrong place. That build took three hours. The same shelter now goes up in fifty minutes.
- Mark the bed footprint before any pole is cut.
- Measure the ridge against the person who will sleep in it, not against whoever is building.
- Count the rafters you need before cutting any, because trimming a long pole is fast and lengthening a short one is impossible.
What the frame asks of your tools
Twenty two poles cut to length and six seats cut clean. That is a saw job and a knife job, and doing either with the wrong tool shows up in the frame.
Length control is the quiet half of this. A rafter cut roughly never seats flush against the ridge, and a stack of poorly seated rafters is a face that flexes in wind. The joinery side of it is counted out in the notch write-up, and which tools to bring in the first place is in knife, axe or saw.
- A saw gives square ends, which is what makes a rafter sit still.
- A knife finishes the six seats and puts points on stakes.
- An axe does neither of those well and is only worth its weight when the wood is big.
The full structure is on camp craft.