COVER PAGE - shares	9 Months Ended
	Sep. 28, 2019	Oct. 25, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 28, 2019
Document Transition Report	false
Entity File Number	1-31429
Entity Registrant Name	Valmont Industries, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-0351813
Entity Address, Address Line One	One Valmont Plaza,
Entity Address, City or Town	Omaha,
Entity Address, State or Province	NE
Entity Address, Postal Zip Code	68154-5215
City Area Code	402
Local Phone Number	963-1000
Title of 12(b) Security	Common Stock $1.00 par value
Trading Symbol	VMI
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		21,525,585
Entity Central Index Key	0000102729
Amendment Flag	false
Current Fiscal Year End Date	--12-28
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3