Hi infinitanet,
I am not sure that I understand what you mean.
<?php if ($this->countModules('module-position')) : ?>
<div class="class-name <?php $this->_c('module-position', array('default' => 'span6', 'xtablet' => 'span9', 'tablet' => 'span12', 'mobile' => 'span12'))?>">
<jdoc:include type="modules" name="<?php $this->_p('module-position') ?>" style="raw" />
</div>
<?php endif ?>
You just need some condition to check if any module is exist for that position.
Regards