private function _writeDefaultRowHeight()
	{
		$defaultRowHeight = $this->_phpSheet->getDefaultRowDimension()->getRowHeight();

		if ($defaultRowHeight < 0) {
			return;
		}

		// convert to twips
		$defaultRowHeight = (int) 20 * $defaultRowHeight;

		$record   = 0x0225;	  // Record identifier
		$length   = 0x0004;	  // Number of bytes to follow

		$header   = pack("vv", $record, $length);
		$data	 = pack("vv",  1, $defaultRowHeight);
		$this->_append($header . $data);
	}