A feed mill is rarely treated as a serious construction project. Yet the building has to do three conflicting things at once: keep moisture away from grain, keep explosive organic dust under control, and stay cheap, because margins in feed manufacturing are thin. Miss any one of them and the loss does not show up in the wall, it shows up in the inventory. This guide covers how to specify sandwich panels for feed production halls and their raw material warehouses.
Why a Feed Warehouse Is Not an Ordinary Warehouse
An ordinary warehouse only needs to be dry and secure. A feed raw material store holds biologically active cargo: maize, soybean meal, rice bran, fish meal. All of it absorbs moisture from the air and releases it again. Indonesia's SNI 8173-1:2022 through SNI 8173-3:2022 for broiler feed cap moisture content at 14.0 percent. That figure is not just a quality parameter; above it, mould has room to grow.
Indonesia's Good Feed Manufacturing Practice guidance, rooted in Ministry of Agriculture Decree 240/Kpts/OT.210/4/2003 and now a certification requirement for registered feed producers, scores buildings as a parameter in its own right, alongside raw materials, hygiene and quality control. Wall and roof quality is therefore part of the audit file, not a matter of appearance.
There is also a dimension that gets ignored: pests. Rodents and birds enter through structural gaps, and droppings on raw material is a recurring audit finding. Panel construction with tight joints and correctly fitted flashing closes the entry paths that conventional buildings always leave at the wall-to-roof junction. The same principle has long been applied in closed house poultry sheds.
Moisture: The Loss You Cannot See
Aspergillus flavus, the mould behind aflatoxin, does not need standing water. It needs sufficient water activity in the grain. Storage research shows aflatoxin B1 accumulation can be avoided by holding sorghum at a water activity of 0.91 or below, while the optimum temperature for toxin production sits around 24 to 35 degrees Celsius. That is exactly the daily range inside an Indonesian warehouse.
This is where the envelope matters. Uninsulated masonry absorbs heat during the day and releases it at night, so the inner surface can fall toward dew point and condense moisture onto the outermost stacked sacks. A sandwich panel breaks that thermal path. Core conductivity across products on the market runs 0.033-0.038 W/mK for EPS, 0.022-0.026 W/mK for PU/PIR and 0.038-0.042 W/mK for rockwool.
The logic is simple: the lower the conductivity, the more stable the internal surface temperature and the smaller the chance of local condensation. For an unrefrigerated raw material store, PIR delivers the best thermal performance per millimetre. Rockwool, however, wins on the thing that matters more in a feed mill, which is behaviour in fire.
Combustible Dust and Rules That Just Changed
Feed dust is combustible dust. A dust cloud in an enclosed space can ignite and produce a secondary explosion far more destructive than the initial fire. The numbers are consistent: Dust Safety Science recorded seven grain dust explosions in the United States during 2025, with ten injuries and four fatalities, above the ten-year average of 8.5 events per year.
The reference has moved too. On 6 December 2024 the NFPA issued NFPA 660, consolidating the separate combustible dust standards, including NFPA 61 for agricultural and food processing facilities plus NFPA 652, 654, 655 and 664, into a single document. Any consultant still citing NFPA 61 as a standalone standard is working from an old map.
For an owner there are two practical consequences. First, a dust hazard analysis requires test data for your own material: Kst, Pmax, MEC, MIE and MIT. Second, the building must support that strategy rather than fight it. Walls offering few horizontal ledges for dust to settle on are easier to clean, and an easily cleaned surface is the cheapest explosion control available.
On site this means choosing flat-faced wall profiles and cutting down on open racks, beams and exposed pipe runs that give dust somewhere to sit. Hidden screw wall panels help, since they leave no protruding screw heads on the inside face. Scheduled cleaning is still mandatory, but the building should not add to that workload.
A Sensible Panel Specification
The combinations below are common, and each has a reason:
- Process areas and machinery zones (hammer mill, mixer, pellet mill): rockwool core, 75-100 mm. Rockwool is mineral, which makes it the reasonable choice where heat sources and dust concentration are highest.
- Raw material and finished goods stores: EPS or PIR at 50-75 mm is normally enough, because the load here is thermal rather than direct fire exposure.
- Steel facings: 0.3-0.5 mm is the Indonesian market range; take the upper end for walls exposed to forklifts and sack traffic.
- Joints and corners: minimise open gaps, since every gap is a nesting site for dust and pests.
- Roof: design for wind loads under SNI 1727:2020, which sets minimum design loads of 0.38 kN/m2 on roof surfaces and 0.77 kN/m2 on walls.
For reaction-to-fire classification, ask the manufacturer for test results under EN 13501-1, and for load-deflection tables derived by the EN 14509 method. Thickness selection is covered further in our guide to standard wall panel thicknesses, while what EI60 and EI120 actually mean is explained in our article on fire rated sandwich panels.
2026 Cost Estimates
A survey of public price lists from panel suppliers and contractors in mid-2026 gives the following rough picture. EPS roof panel with a 1,050 mm cover width runs about Rp371,000 per linear metre at 50 mm and Rp455,000 at 100 mm; rockwool at 75 mm sits near Rp485,000 per linear metre. Installed PU panel at 50-75 mm generally costs Rp350,000-550,000 per square metre, and installation labour alone Rp150,000-230,000 per square metre.
One trap regularly wrecks budgets: roof panel is quoted per linear metre, not per square metre. At a 1,050 mm cover width one linear metre equals 1.05 m2, so Rp371,000 per linear metre is about Rp353,000 per m2. The difference is small per sheet and large across a 3,000 m2 warehouse.
In short, a good feed mill building solves three problems at once: it holds internal surface temperature high enough to avoid condensation, it presents surfaces that are easy to clean so dust never accumulates, and it closes the gaps that let pests in. Sandwich panel construction addresses all three in a single layer, provided the core and thickness are chosen zone by zone rather than standardised to simplify procurement.
FAQ
What panel thickness suits a feed raw material warehouse?
For an unrefrigerated store in the Indonesian climate, 50-75 mm is usually adequate, because the goal is to damp daily temperature swings rather than hold a setpoint. Move to 100 mm when the store holds high-value inputs such as fish meal or premix, or when the roof span is wide enough that daytime radiation dominates. The final call should rest on the manufacturer's load-deflection table, not a general figure.
Is an EPS core safe to use in a feed mill?
EPS is appropriate for storage areas away from heat sources and ignition points, and it is the most economical option for large-span warehouses. What is not advisable is using EPS in process rooms housing hammer mills, pellet mills and electrical panels. In those zones a mineral core such as rockwool provides a safety margin that material savings cannot buy back.
