Roof an ice house with two layers, an inner ceiling and an outer roof, separated by an air gap that vents the heat the sun puts into the outer layer before it reaches the ice. Build it peaked or domed, extend it at least 60 cm past the walls on all sides to shed rain and shade the walls, open vents at both ends of the gap, and lay 20-30 cm of sawdust or straw on top of the stacked ice below the ceiling.
Part of Ice Houses and Cold Storage
The ice house roof is the one surface the sun reaches directly. Its job is to keep rain and sun off the structure and to carry away the heat that collects above the ice.
The Roof Meets The Sun, So It Has To Shed Heat Before The Ice Receives It
An ordinary roof heats up in the sun and radiates down. In an ice house, that heat lands on the insulation over the ice. The solution is a second layer. The outer roof takes the sun and the rain. Beneath it, an air gap rises with hot air and leaves through vents, so the inner ceiling stays near the temperature of the air in the shade. The parent article calls for this double-layer construction.
What You Need
- Roofing — thatch, shingles or any roofing material. Thatch is a good insulator itself. See Thatching.
- Framing — rafters for the outer roof and joists for the inner ceiling.
- Vent openings — at both ends of the gap, screened against animals and insects.
- Insulation for the ceiling — sawdust or straw laid on top of the stacked ice.
- A pale surface — whitewash or lime wash on the outer roof where the material allows. See Lime Wash.
Method: Build The Roof
Step 1: Frame the inner ceiling. Span the pit with joists and close them with boards or poles to carry the insulation above the ice.
Step 2: Frame the outer roof. Raise a peaked or domed roof above the ceiling so a clear gap remains between them. The peak lets rain run off and the hot air rise to the vents.
Step 3: Extend the overhang. Let the roof project at least 60 cm beyond the walls on every side. It sheds rain away from the walls and shades them.
Step 4: Cut the vents. Open vents at the high end of the gap and low ones at the sides, so air enters low and leaves high. Screen them.
Step 5: Cover and finish. Lay the roofing, then pale-coat it if you can.
Step 6: Insulate the ceiling. When the ice is stacked, cover the top with 20-30 cm of sawdust or straw. See Ice Stacking.
Worked Example: How Much Vent Area
A common building-code rule of thumb for roof spaces, recalled from residential building codes rather than checked, is a net vent area of about 1/150 of the area of the space beneath the roof. For a 3 m pit with a 60 cm overhang, the roof diameter is 3.0 + 2 x 0.6 = 4.2 m.
- Roof footprint: pi x (4.2 / 2)^2 = 3.1416 x 4.41 = 13.9 m2.
- Vent area at 1/150: 13.9 / 150 = 0.092 m2, which is 920 cm2.
- Split between high and low vents: about 460 cm2 each, for example four openings of about 115 cm2 high and four low, giving 8 x 115 = 920 cm2.
Use this as a starting size and watch whether the gap runs hot on summer afternoons; if it does, open more.
Common Mistakes
- A single roof directly over the ice — the sun’s heat lands on the insulation. Use two layers.
- No overhang — rain reaches the walls and the sun heats them.
- Closing the vents against animals with a tight seal — the gap fills with hot air. Screen them, do not seal them.
- Dark roofing in full sun — it absorbs the most heat. Shade it with trees or pale-coat it.
- Leaking roofing — wet insulation conducts heat and rots. Check for leaks every season.
Safety
Falls from the roof and into the pit
A pit 2-3 m deep sits directly beneath the roof frame while you build. A fall from the rafters can end in the pit, and an unfinished ceiling is a hole. Cover the pit with boards before working above it, work with a second person, and do not climb wet or frosty roofing.
What’s Next
- Learn next: Insulation Methods — what goes under the roof
- Combine with: Ice House Construction — the whole sequence