Straw works nearly as well as sawdust for insulating ice and is available on any farm: pack dry straw in layers 20-30 cm thick around the ice, treading each layer down lightly, and expect it to settle so that the top needs refilling. Prefer dry straw to hay, and never use damp hay, because damp hay ferments and can heat itself to the point of fire. Straw also compresses and is harder to clean out than sawdust.
Part of Ice Houses and Cold Storage
Straw and hay are agricultural by-products, dry stalks and cut grass, used as loose insulation in ice houses where sawdust is not available.
Straw Is Hollow Stalks, Which Trap Air; Hay Is Green Grass That Can Rot
Straw is the dry stalk left after grain is harvested. Its hollow tubes trap air, it is low in nutrients and it dries and stays dry. Hay is cut grass or legumes, dried for animal feed. It holds more moisture and nutrient, rots more readily and attracts rodents. For insulation, straw is the better of the two.
The parent article gives straw 20-30 cm layers against sawdust’s 15-20 cm. That extra thickness is the cost of its slightly poorer performance.
What You Need
- Dry straw — from a threshing floor or a dry stack, golden and crisp, not grey and musty.
- A dry, rodent-proof store — a raised, roofed place.
- A fork — for placing and fluffing it.
- Sacking or boards — to retain it in a wall gap.
Method: Insulate With Straw
Step 1: Check it is dry. Squeeze a handful. It should rustle and spring back. A damp or musty smell means mould. Reject it.
Step 2: Pack the wall gap. Fill the gap behind the lining in layers, treading each one lightly to remove large voids without crushing it.
Step 3: Lay the floor and cap. Put 20-30 cm under the ice and over the top.
Step 4: Fill between blocks. Pack loose straw into the spaces between blocks and around the edges.
Step 5: Top up after settling. Straw compresses. Check the top and walls after a few weeks and refill.
Step 6: Clear out each year. Straw is harder to clean than sawdust. Remove wet or mouldy straw at the end of the season and replace it.
Worked Example: Thickness To Match Sawdust
The parent article gives 15-20 cm of sawdust and 20-30 cm of straw. The ratio of the thicknesses is 20 / 15 = 1.33 at the lower end and 30 / 20 = 1.5 at the upper end. So straw needs roughly a third to a half more thickness for the same protection. That is also more volume: for a 2.5 m pit, going from 17.5 cm to 25 cm of insulation (the mid-points) shrinks the ice core from 2.15 m across and 2.15 m high (7.8 m3) to 2.0 m across and 2.0 m high, which is pi x 1.0^2 x 2.0 = 6.3 m3. The pit then holds 1.5 m3 less ice, about 19 percent, which is the trade-off for using straw.
Common Mistakes
- Using hay — it ferments and rots.
- Damp straw — it conducts heat and moulds.
- Packing too hard — it loses air.
- Not topping up — the top settles and leaves a gap.
- Leaving straw to rodents — they nest in it and foul it. Keep it in rodent-proof stores.
Safety
Damp hay heats itself, mouldy hay harms lungs, and a sealed pit loses its oxygen
Hay stacked or packed damp can ferment and heat itself enough to ignite without any flame, and dry straw burns fast. Keep it dry and away from fires. Mouldy hay and straw release spores that can cause a serious lung illness known as farmer’s lung in people who breathe them, so cover the nose and mouth and discard mouldy material. Rotting straw in a closed pit uses up oxygen and releases carbon dioxide that pools at the bottom. Ventilate, tether and never test the air with a flame. See Ice House Construction.
What’s Next
- Learn next: Earth Berming — use the ground as insulation
- Combine with: Sawdust — the better material where it is available