DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Policies)	6 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“US GAAP”) for interim financial information, and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, these financial statements do not include all the information and footnotes required by US GAAP for complete financial statements. As such, they should be read together with Griffon’s Annual Report on Form 10-K for the fiscal year ended September 30, 2025, which provides a more complete explanation of Griffon’s accounting policies, financial position, operating results, business, properties and other matters. In the opinion of management, these financial statements reflect all adjustments considered necessary for a fair statement of interim results. Griffon’s businesses are seasonal; for this and other reasons, the financial results of the Company for any interim period are not necessarily indicative of the results for the full year. The Condensed Consolidated Balance Sheet information at September 30, 2025 was derived from the audited financial statements included in Griffon’s Annual Report on Form 10-K for the year ended September 30, 2025. The condensed consolidated financial statements include the accounts of Griffon and all subsidiaries. Intercompany accounts and transactions have been eliminated in consolidation. Certain amounts in prior years may have been reclassified to conform to the current year presentation. The preparation of financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting periods. These estimates may be adjusted due to changes in economic, industry or customer financial conditions, as well as changes in technology or demand. Significant estimates include expected loss allowances for credit losses and returns, net realizable value of inventories, restructuring reserves, valuation of goodwill and intangible assets, assumptions associated with pension benefit obligations and income or expenses, useful lives associated with depreciation and amortization of intangible and fixed assets, warranty reserves, sales incentive accruals, assumptions associated with stock based compensation valuation, income taxes and tax valuation reserves, environmental reserves, legal reserves, insurance reserves, the valuation of assets and liabilities of discontinued operations and the accompanying disclosures. These estimates are based on management’s best knowledge of current events and actions Griffon may undertake in the future. Actual results may ultimately differ from these estimates.
Fair Value Measurements	The carrying values of cash and equivalents, accounts receivable, accounts and notes payable, and revolving credit and variable interest rate debt approximate fair value due to either the short-term nature of such instruments or the fact that the interest rate of the revolving credit and variable rate debt is based upon current market rates. Applicable accounting guidance establishes a fair value hierarchy requiring the Company to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. A financial instrument’s categorization within the hierarchy is based on the lowest level of input that is significant to the fair value measurement. The accounting guidance establishes three levels of inputs that may be used to measure fair value, as follows: •Level 1 inputs are measured and recorded at fair value based upon quoted prices in active markets for identical assets. •Level 2 inputs include inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices in active markets for similar assets and liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of assets or liabilities. •Level 3 inputs are unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions.
Inventories	Inventories are stated at the lower of cost (first-in, first-out or average cost) or net realizable value.
Issued but not yet effective accounting pronouncements	Issued but not yet effective accounting pronouncements In December 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. The new standard was issued to improve transparency and decision usefulness of income tax disclosures by providing information that helps investors better understand how an entity's operations, tax risks, tax planning and operational opportunities affect its tax rate and future cash flows. The standard requires significant additional disclosures focused on income taxes paid and the rate reconciliation table. Specifically, the amendments in the standard require the Company to disclose disaggregated: (1) income taxes paid by federal, state, and foreign, (2) continuing operations pre-tax income between domestic and foreign, and (3) continuing operations income tax expense by federal, state and foreign. The standard also requires the Company to disclose specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This standard is effective for the Company beginning with our fiscal year 2026 annual reporting period, and can be applied prospectively or retrospectively. While the Company is currently evaluating the guidance to determine the impact it may have on its condensed consolidated financial statements, the Company does not expect the adoption of this standard to have a material impact on its financial position, results of operations, or cash flows. In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. The amendments in this update require disclosures and further disaggregation, in the notes to financial statements, of specified information regarding certain costs and expenses. The required disclosures include the amounts of purchases of inventory, employee compensation, depreciation, intangible asset amortization, and depreciation, depletion, and amortization recognized as part of oil and gas producing activities included in each relevant expense caption. Additionally, further disclosures are required for certain amounts already required to be disclosed under current GAAP, a qualitative description of amounts remaining in relevant expense captions that are not separately disaggregated quantitatively, and the total amount of selling expenses, and on an annual basis, the definition of selling expenses. The ASU is effective for the Company beginning with the Company's fiscal year 2028 and interim reporting periods beginning with the Company's 2029 fiscal year. Implementation of this standard may be applied prospectively or retrospectively. The Company is currently evaluating this guidance to determine the impact it may have on its condensed consolidated financial statements.
Consolidation, Policy	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“US GAAP”) for interim financial information, and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, these financial statements do not include all the information and footnotes required by US GAAP for complete financial statements. As such, they should be read together with Griffon’s Annual Report on Form 10-K for the fiscal year ended September 30, 2025, which provides a more complete explanation of Griffon’s accounting policies, financial position, operating results, business, properties and other matters. In the opinion of management, these financial statements reflect all adjustments considered necessary for a fair statement of interim results. Griffon’s businesses are seasonal; for this and other reasons, the financial results of the Company for any interim period are not necessarily indicative of the results for the full year. The Condensed Consolidated Balance Sheet information at September 30, 2025 was derived from the audited financial statements included in Griffon’s Annual Report on Form 10-K for the year ended September 30, 2025. The condensed consolidated financial statements include the accounts of Griffon and all subsidiaries. Intercompany accounts and transactions have been eliminated in consolidation. Certain amounts in prior years may have been reclassified to conform to the current year presentation.

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Policies)

6 Months Ended

Mar. 31, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“US GAAP”) for interim financial information, and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, these financial statements do not include all the information and footnotes required by US GAAP for complete financial statements. As such, they should be read together with Griffon’s Annual Report on Form 10-K for the fiscal year ended September 30, 2025, which provides a more complete explanation of Griffon’s accounting policies, financial position, operating results, business, properties and other matters. In the opinion of management, these financial statements reflect all adjustments considered necessary for a fair statement of interim results. Griffon’s businesses are seasonal; for this and other reasons, the financial results of the Company for any interim period are not necessarily indicative of the results for the full year.

The Condensed Consolidated Balance Sheet information at September 30, 2025 was derived from the audited financial statements included in Griffon’s Annual Report on Form 10-K for the year ended September 30, 2025.

The condensed consolidated financial statements include the accounts of Griffon and all subsidiaries. Intercompany accounts and transactions have been eliminated in consolidation. Certain amounts in prior years may have been reclassified to conform to the current year presentation.

The preparation of financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting periods. These estimates may be adjusted due to changes in economic, industry or customer financial conditions, as well as changes in technology or demand. Significant estimates include expected loss allowances for credit losses and returns, net realizable value of inventories, restructuring reserves, valuation of goodwill and intangible assets, assumptions associated with pension benefit obligations and income or expenses, useful lives associated with depreciation and amortization of intangible and fixed assets, warranty reserves, sales incentive accruals, assumptions associated with stock based compensation valuation, income taxes and tax valuation reserves, environmental reserves, legal reserves, insurance reserves, the valuation of assets and liabilities of discontinued operations and the accompanying disclosures. These estimates are based on management’s best knowledge of current events and actions Griffon may undertake in the future. Actual results may ultimately differ from these estimates.

Fair Value Measurements

The carrying values of cash and equivalents, accounts receivable, accounts and notes payable, and revolving credit and variable interest rate debt approximate fair value due to either the short-term nature of such instruments or the fact that the interest rate of the revolving credit and variable rate debt is based upon current market rates.

Applicable accounting guidance establishes a fair value hierarchy requiring the Company to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. A financial instrument’s categorization within the hierarchy is based on the lowest level of input that is significant to the fair value measurement. The accounting guidance establishes three levels of inputs that may be used to measure fair value, as follows:

•Level 1 inputs are measured and recorded at fair value based upon quoted prices in active markets for identical assets.

•Level 2 inputs include inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices in active markets for similar assets and liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of assets or liabilities.

•Level 3 inputs are unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions.

Inventories

Inventories are stated at the lower of cost (first-in, first-out or average cost) or net realizable value.

Issued but not yet effective accounting pronouncements

In December 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. The new standard was issued to improve transparency and decision usefulness of income tax disclosures by providing information that helps investors better understand how an entity's operations, tax risks, tax planning and operational opportunities affect its tax rate and future cash flows. The standard requires significant additional disclosures focused on income taxes paid and the rate reconciliation table. Specifically, the amendments in the standard require the Company to disclose disaggregated: (1) income taxes paid by federal, state, and foreign, (2) continuing operations pre-tax income between domestic and foreign, and (3) continuing operations income tax expense by federal, state and foreign. The standard also requires the Company to disclose specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. This standard is effective for the Company beginning with our fiscal year 2026 annual reporting period, and can be applied prospectively or retrospectively. While the Company is currently evaluating the guidance to determine the impact it may have on its condensed consolidated financial statements, the Company does not expect the adoption of this standard to have a material impact on its financial position, results of operations, or cash flows.

In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. The amendments in this update require disclosures and further disaggregation, in the notes to financial statements, of specified information regarding certain costs and expenses. The required disclosures include the amounts of purchases of inventory, employee compensation, depreciation, intangible asset amortization, and depreciation, depletion, and amortization recognized as part of oil and gas producing activities included in each relevant expense caption. Additionally, further disclosures are required for certain amounts already required to be disclosed under current GAAP, a qualitative description of amounts remaining in relevant expense captions that are not separately disaggregated quantitatively, and the total amount of selling expenses, and on an annual basis, the definition of selling expenses. The ASU is effective for the Company beginning with the Company's fiscal year 2028 and interim reporting periods beginning with the Company's 2029 fiscal year. Implementation of this standard may be applied prospectively or retrospectively. The Company is currently evaluating this guidance to determine the impact it may have on its condensed consolidated financial statements.

Consolidation, Policy