diff --git a/docs/concept.md b/docs/concept.md
index 0d8a7d3..3aa8f45 100644
--- a/docs/concept.md
+++ b/docs/concept.md
@@ -21,8 +21,10 @@ A single-player asymmetric game inspired by DOTA's wave/tower structure, combine
 ## Factory & Belts
 
 - Factory buildings are placed from a queue and constructed one at a time, each taking some time to complete.
-- Materials are transported between buildings manually using belts.
 - The crafting/production tree is defined in a config file so it can be extended without code changes.
+- Materials are transported between buildings using belts (straight, curved) and splitters.
+- Buildings accept any material delivered by belts feeding into them; there are no labeled input ports. Each building has one fixed output port.
+- A building's input buffer holds up to twice the amount needed for one production cycle of the selected recipe.
 
 ## Resources & Building Blocks
 
@@ -33,6 +35,19 @@ Two sources feed the same production tree:
 
 **Building blocks** are the only globally shared resource. An assembler recipe produces them from materials; they are transported via belts into the HQ, which adds them to the global stock. Building blocks are spent to place factory buildings and to unlock additional asteroid columns.
 
+## Buildings
+
+| Building | Size | Description |
+|---|---|---|
+| **HQ** | 4×3 | Pre-placed. Accepts building blocks via belt and adds them to the global stock. |
+| **Miner** | 2×2 | Player selects which ore type to extract. Ore never depletes. |
+| **Smelter** | 2×2 | Converts ore or scrap into basic materials. No recipe selection needed. |
+| **Assembler** | 3×3 | Player selects a recipe. Produces building blocks or intermediate/advanced products. |
+| **Reprocessing Plant** | 3×3 | Converts scrap into higher-level products with fixed probabilities per product type. |
+| **Shipyard** | 4×2 | Player selects a blueprint. Produces that ship type when required materials are available. |
+| **Belt** | 1×1 | Transports materials. Comes in straight and curved variants. |
+| **Splitter** | 1×1 | Splits a belt's flow into two outputs. |
+
 ## Ships & Shipyards
 
 - Shipyards are built at the asteroid's right edge.
@@ -45,6 +60,7 @@ Two sources feed the same production tree:
 
 ## Enemy Waves & Difficulty Scaling
 
+- Waves consist of a single enemy ship type whose stats scale with difficulty.
 - Waves spawn over several seconds; a gap follows before the next wave begins spawning. The previous wave may still be approaching or fighting during the gap.
 - Difficulty scales multiplicatively from two sources:
   - **Time scaling** — enemy strength increases gradually over elapsed time.
@@ -58,7 +74,7 @@ Two sources feed the same production tree:
 
 ## Starting Conditions & Game Over
 
-- The player starts with the HQ pre-placed and a stock of building blocks; no other buildings are pre-placed.
+- The player starts with the HQ and player defence stations pre-placed and a stock of building blocks; no other buildings are pre-placed.
 - There is a grace period before the first wave to allow initial setup.
 - If all ships and player defence stations are destroyed, enemies attack the HQ. The game is lost when the HQ is destroyed. Factory buildings are never targeted.