| Document and Entity Information | Oct. 13, 2021 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001839839 |
| Document Type | 8-K |
| Document Period End Date | Oct. 13, 2021 |
| Entity Registrant Name | Janus International Group, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-40456 |
| Entity Tax Identification Number | 86-1476200 |
| Entity Address, Address Line One | 135 Janus International Blvd. |
| Entity Address, City or Town | Temple |
| Entity Address, State or Province | GA |
| Entity Address, Postal Zip Code | 30179 |
| City Area Code | (866) |
| Local Phone Number | 562-2580 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Common Stock Par Value 0.0001 Per Share [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, par value $0.0001 per share |
| Trading Symbol | JBI |
| Security Exchange Name | NYSE |
| Warrants Each To Purchase One Share Of Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Warrants, each to purchase one share of Common Stock |
| Trading Symbol | JBI WS |
| Security Exchange Name | NYSE |
