Production upgrades do not increase your yield multiplier, but rather have unique benefits.
The Toolsheds are upgrades that allow you to decrease repair costs for a given resource type. All 4 can be owned at once, but only one can be active at a time. Each Toolshed reduces repair costs for its respective resource by 30% and all 4 Toolsheds reduce power repair cost by 20%.
The Firepit allows you to burn lumber for power. Each lumber generates 10 power.
The Concrete Foundation upgrade reduces the rate of durability decline from 10% daily to 8% daily.
Fortifications can increase the max durability of your property beyond 100%, introducing a positive yield multiplier. Fortifications can stack on each other. For example:
110% Durability (1 Fortification): 1.1x Multiplier120% Durability (2 Fortifications): 1.2x Multiplier130% Durability (3 Fortifications): 1.3x Multiplier
Fortifications are also dependencies for certain yield upgrades. Please see the section below for more details on dependencies:
The Hire Handyman consumable allows you to restore your property to 100% once per week for a flat rate of 1 LAND. This upgrade is very useful for situations where you may have let your property's durability decline. The gas and resource costs of repairs at this point are much higher at this stage, so it is advisable to use this upgrade in those cases.