<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><Version>2.2.0.25</Version><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><ReportLongName>10401 - Disclosure - Timber Notes/Non-Recourse Debt</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelColumn>false</LabelColumn><CurrencyCode>USD</CurrencyCode><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName>12/26/2010 - 3/26/2011
USD ($)

USD ($) / shares
</KeyName><CurrencySymbol>$</CurrencySymbol><contextRef><ContextID>Duration_12_26_2010_To_3_26_2011</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0000012978</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2010-12-26T00:00:00</PeriodStartDate><PeriodEndDate>2011-03-26T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS><UnitProperty><UnitID>Unit12</UnitID><UnitType>Standard</UnitType><StandardMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></StandardMeasure><Scale>0</Scale></UnitProperty><UnitProperty><UnitID>Unit13</UnitID><UnitType>Divide</UnitType><NumeratorMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></NumeratorMeasure><DenominatorMeasure><MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema><MeasureValue>shares</MeasureValue><MeasureNamespace>xbrli</MeasureNamespace></DenominatorMeasure><Scale>0</Scale></UnitProperty></UPS><CurrencyCode>USD</CurrencyCode><OriginalCurrencyCode>USD</OriginalCurrencyCode></MCU><CurrencySymbol>$</CurrencySymbol><Labels><Label Id="1" Label="3 Months Ended" /><Label Id="2" Label="Mar. 26, 2011" /></Labels></Column></Columns><Rows><Row><Id>2</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><Level>0</Level><ElementName>omx_TimberNotesAbstract</ElementName><ElementPrefix>omx</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><ShortDefinition>Timber Notes [Abstract]</ShortDefinition><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsSubReportEnd>false</IsSubReportEnd><IsCalendarTitle>false</IsCalendarTitle><IsTuple>false</IsTuple><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole /><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><NonNumericTextHeader /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>Timber Notes [Abstract]</ElementDefenition><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>Timber Notes/Non-Recourse Debt</Label></Row><Row><Id>3</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><Level>0</Level><ElementName>omx_TimberNotesReceivableNonRecourseDebtTextBlock</ElementName><ElementPrefix>omx</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><ShortDefinition>Timber Notes Receivable / Non-Recourse Debt [Text Block]</ShortDefinition><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsSubReportEnd>false</IsSubReportEnd><IsCalendarTitle>false</IsCalendarTitle><IsTuple>false</IsTuple><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>terselabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div&gt;

&lt;p style="margin-top: 0px; margin-bottom: 0px;"&gt;&lt;font style="font-family: Times New Roman;" class="_mt" size="2"&gt;&lt;b&gt;4. Timber Notes/Non-Recourse Debt &lt;/b&gt;&lt;/font&gt;&lt;/p&gt;

&lt;p style="margin-top: 6px; text-indent: 32px; margin-bottom: 0px;"&gt;&lt;font style="font-family: Times New Roman;" class="_mt" size="2"&gt;In October 2004, we sold our timberland assets in exchange for $15&amp;nbsp;million in cash plus credit-enhanced timber installment notes in the amount of $1,635&amp;nbsp;million (the "Installment Notes"). The Installment Notes were issued by single-member limited liability companies formed by affiliates of Boise Cascade, L.L.C. (the "Note Issuers"). The Installment Notes are 15-year non-amortizing obligations and were issued in two equal $817.5&amp;nbsp;million tranches bearing interest at 5.11% and 4.98%, respectively. In order to support the issuance of the Installment Notes, the Note Issuers transferred a total of $1,635&amp;nbsp;million in cash to Lehman Brothers Holdings&amp;nbsp;Inc. ("Lehman") and Wachovia Corporation ("Wachovia") (which was later purchased by Wells Fargo&amp;nbsp;&amp;amp; Company) ($817.5&amp;nbsp;million to each of Lehman and Wachovia). Lehman and Wachovia issued collateral notes (the "Collateral Notes") to the Note Issuers. Concurrently with the issuance of the Installment and Collateral Notes, Lehman and Wachovia guaranteed the respective Installment Notes and the Note Issuers pledged the Collateral Notes as security for the performance of the Installment Note obligations. The Installment Notes are reported as timber notes receivable in our Consolidated Balance Sheets. &lt;/font&gt;&lt;/p&gt;

&lt;p style="margin-top: 12px; text-indent: 32px; margin-bottom: 0px;"&gt;&lt;font style="font-family: Times New Roman;" class="_mt" size="2"&gt;In December 2004, we completed a securitization transaction in which the Company's interests in the Installment Notes and related guarantees were transferred to wholly-owned bankruptcy remote subsidiaries. The subsidiaries pledged the Installment Notes and related guarantees and issued securitized notes (the "Securitization Notes") in the amount of $1,470&amp;nbsp;million ($735&amp;nbsp;million through the structure supported by the Lehman guaranty and $735&amp;nbsp;million through the structure supported by the Wachovia guaranty). As a result of these transactions, we received $1,470&amp;nbsp;million in cash. Recourse on the Securitization Notes is limited to the proceeds of the applicable pledged Installment Notes and underlying Lehman or Wachovia guaranty, and therefore there is no recourse against OfficeMax. The Securitization Notes are 15-year non-amortizing, and were issued in two equal $735&amp;nbsp;million tranches paying interest of 5.54% and 5.42%, respectively. The Securitization Notes are reported as non-recourse debt in the Company's Consolidated Balance Sheets. &lt;/font&gt;&lt;/p&gt;

&lt;p style="margin-top: 12px; text-indent: 32px; margin-bottom: 0px;"&gt;&lt;font style="font-family: Times New Roman;" class="_mt" size="2"&gt;On September&amp;nbsp;15, 2008, Lehman, the guarantor of half of the Installment Notes and the Securitization Notes, filed a petition in the United States Bankruptcy Court for the Southern District of New York seeking relief under chapter&amp;nbsp;11 of the United States Bankruptcy Code. Lehman's bankruptcy filing constituted an event of default under the $817.5&amp;nbsp;million Installment Note guaranteed by Lehman (the "Lehman Guaranteed Installment Note"). &lt;/font&gt;&lt;/p&gt;

&lt;p style="margin-top: 12px; text-indent: 32px; margin-bottom: 0px;"&gt;&lt;font style="font-family: Times New Roman;" class="_mt" size="2"&gt;We are required for accounting purposes to assess the carrying value of assets whenever circumstances indicate that a decline in value may have occurred. In 2008, we evaluated the carrying value of the Lehman Guaranteed Installment Note and reduced it to the estimated amount we expect to collect ($81.8&amp;nbsp;million) by recording a non-cash impairment charge of $735.8&amp;nbsp;million, pre-tax. The ultimate amount to be realized on the Lehman Guaranteed Installment Note depends entirely on the proceeds from the Lehman bankruptcy estate, which may not be finally determined for several years. Our estimate of the expected proceeds has not changed, and at March&amp;nbsp;26, 2011, the carrying value of the Lehman Guaranteed Installment Note remained at $81.8&amp;nbsp;million. On April&amp;nbsp;14, 2010, Lehman filed its Debtors' Disclosure Statement with the United States Bankruptcy Court for the Southern District of New York. The Disclosure Statement indicated a range of estimated recoveries for general unsecured creditors of Lehman. As our estimate is similar to the estimate included in the Disclosure Statement, we have not adjusted our estimated carrying value for the Lehman Guaranteed Installment Note. Going forward, we intend to adjust the carrying value of the Lehman Guaranteed Installment Note as further information regarding our share of the proceeds, if any, from the Lehman bankruptcy estate becomes available. &lt;/font&gt;&lt;/p&gt;

&lt;p style="margin-top: 12px; text-indent: 32px; margin-bottom: 0px;"&gt;&lt;font style="font-family: Times New Roman;" class="_mt" size="2"&gt;Recourse on the Securitization Notes is limited to the proceeds from the applicable pledged Installment Notes and underlying Lehman or Wachovia guaranty. Accordingly, the Lehman Guaranteed Installment Note and underlying Lehman guaranty will be transferred to the holders of the Securitization Notes guaranteed by Lehman in order to settle and extinguish that liability. However, under current generally accepted accounting principles, we are required to continue to recognize the liability related to the Securitization Notes guaranteed by Lehman until such time as the liability has been extinguished. This will occur when the Lehman Guaranteed Installment Note and the related guaranty are transferred to and accepted by the Securitization Note holders. We expect that this will occur no later than the date when the assets of Lehman are distributed and the bankruptcy is finalized. Accordingly, we expect to recognize a non-cash gain equal to the difference between the carrying amount of the Securitization Notes guaranteed by Lehman ($735.0&amp;nbsp;million at March&amp;nbsp;26, 2011) and the carrying value of the Lehman Guaranteed Installment Note ($81.8&amp;nbsp;million at March&amp;nbsp;26, 2011) in a later period when the liability is legally extinguished. The actual gain to be recognized in the future will be measured based on the carrying amounts of the Lehman Guaranteed Installment Note and the Securitization Notes guaranteed by Lehman at the date of settlement. &lt;/font&gt;&lt;/p&gt;

&lt;p style="margin-top: 12px; text-indent: 32px; margin-bottom: 0px;"&gt;&lt;font style="font-family: Times New Roman;" class="_mt" size="2"&gt;Through March&amp;nbsp;26, 2011, we have received all payments due under the Installment Notes guaranteed by Wachovia (the "Wachovia Guaranteed Installment Notes"), which have consisted only of interest due on the notes, and have made all payments due on the related Securitization Notes guaranteed by Wachovia, again consisting only of interest due. As all amounts due on the Wachovia Guaranteed Installment Notes are current and we have no reason to believe that we will not be able to collect all amounts due according to the contractual terms of the Wachovia Guaranteed Installment Notes, the notes are stated in our Consolidated Balance Sheets at their original principal amount of $817.5&amp;nbsp;million. The Installment Notes and Securitization Notes are scheduled to mature in 2020 and 2019, respectively. The Securitization Notes have an initial term that is approximately three months shorter than the Installment Notes. &lt;/font&gt;&lt;/p&gt;

&lt;p style="margin-top: 12px; text-indent: 32px; margin-bottom: 0px;"&gt;&lt;font style="font-family: Times New Roman;" class="_mt" size="2"&gt;At the time of the sale of the timberlands in 2004, we generated a tax gain and recognized the related deferred tax liability. The timber installment notes structure allowed the Company to defer the resulting tax liability of $543&amp;nbsp;million until 2020, the maturity date for the Installment Notes. Due to the Lehman bankruptcy and note defaults, the recognition of the Lehman portion of the gain will be triggered when the Lehman Guaranteed Installment Note is transferred to the Securitization Note holders as payment and/or when the Lehman bankruptcy is resolved. At that time, we expect to reduce the estimated cash payment due by utilizing our available alternative minimum tax credits. &lt;/font&gt;&lt;/p&gt; &lt;/div&gt;</NonNumbericText><NonNumericTextHeader>4. Timber Notes/Non-Recourse Debt

In October 2004, we sold our timberland assets in exchange for $15&amp;nbsp;million in cash plus credit-enhanced timber</NonNumericTextHeader><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>us-types:textBlockItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>Timber Notes Receivable / Non-Recourse Debt [Text Block]</ElementDefenition><ElementReferences>No authoritative reference available.</ElementReferences><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>Timber Notes/Non-Recourse Debt</Label></Row></Rows><Footnotes /><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows><ReportName>Timber Notes/Non-Recourse Debt</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>false</HasCustomUnits><SharesShouldBeRounded>true</SharesShouldBeRounded></InstanceReport>
