My band stretches if necessary with the following conditions, I do not know yours. I have started with the ireport 1.0 netbeans plug-in and jasper 3.5.2. The Split type for the band has been set to Stretch.
<band height="108" splitType="Stretch"></band>The Stretch with overflow for the field has been checked, e.g.:
<textField isStretchWithOverflow="true"><reportElement positionType="Float" x="70" y="28" width="485" height="14"/><textElement><font size="10"/></textElement><textFieldExpression class="java.lang.String"><![CDATA[($F{EQUIPMENTS}==null?"-": $F{EQUIPMENTS})]]></textFieldExpression></textField>