> For the complete documentation index, see [llms.txt](https://orbcity.gitbook.io/orbcity/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://orbcity.gitbook.io/orbcity/building/upgrading-system/tier-up-evolution.md).

# Tier Up(=evolution)

#### There are 5 tiers of buildings: common, rare, epic, unique, and legendary. To go to the next tier, you need level 1 lv building NFTs materials (= building demand) of the same tier. Since tier upgrades are based on chance, 1 lv building NFTs materials are consumed, and in addition to consumption, the 3 lv building NFTs you want to tier up can be destroyed (destructed building NFTs can be restored). To get to the next tier, $Lay 007 and $Orb for each building's level and tier are consumed. Tiering up also takes time.

#### If a building is successfully tiered up, building NFTs' Lay-Bours and Green Value will increase by 1 to a fixed value.

{% hint style="info" %}
**Rare Tier Building NFTs** = Level 3 Common + Level 1 Common (material), with a chance of failure. Failure may also result in the destruction of a level 3 Common. **If it succeeds or fails, the level 1 Common(material) is burned.**
{% endhint %}

{% hint style="info" %}
**Epic Tier Building NFTs** = Level 3 Rare + Level 1 Rare (material), with a chance of failure. Failure may also result in the destruction of a level 3 Rare. **If it succeeds or fails, the level 1 Rare(material) is burned.**
{% endhint %}

[Time](/orbcity/building/upgrading-system/tier-up-evolution/time.md)

[Chance of tier up](/orbcity/building/upgrading-system/tier-up-evolution/chance-of-tier-up.md)

[Cost](/orbcity/building/upgrading-system/tier-up-evolution/cost.md)

[Restoration cost](/orbcity/building/upgrading-system/tier-up-evolution/restoration-cost.md)

{% hint style="danger" %} <mark style="color:red;">**Note: Keep in mind that all tokens and NFTs spent on the upgrade are irrevocable and non-refundable.**</mark>
{% endhint %}