diff --git a/.idea/phpspec.xml b/.idea/phpspec.xml
index ec7e1d4..c7cfbc2 100644
--- a/.idea/phpspec.xml
+++ b/.idea/phpspec.xml
@@ -8,6 +8,9 @@
       <PhpSpecSuiteConfiguration>
         <option name="myPath" value="$PROJECT_DIR$" />
       </PhpSpecSuiteConfiguration>
+      <PhpSpecSuiteConfiguration>
+        <option name="myPath" value="$PROJECT_DIR$" />
+      </PhpSpecSuiteConfiguration>
     </suites>
   </component>
 </project>
\ No newline at end of file
diff --git a/src/ext/spreadsheet/wsutils.php b/src/ext/spreadsheet/wsutils.php
index dad2dd9..0f83442 100644
--- a/src/ext/spreadsheet/wsutils.php
+++ b/src/ext/spreadsheet/wsutils.php
@@ -6,10 +6,10 @@ use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
 
 class wsutils {
   static function get_highest_coords(Worksheet $ws): array {
-    $highestRow = $ws->getHighestRow();
     $highestColumnA = $ws->getHighestColumn();
     $highestCol = Coordinate::columnIndexFromString($highestColumnA);
-    return [$highestRow, $highestCol];
+    $highestRow = $ws->getHighestRow();
+    return [$highestCol, $highestRow];
   }
 
   /**
@@ -24,18 +24,18 @@ class wsutils {
   const MAX_EMPTY_THRESHOLD = 150;
 
   static function compute_max_coords(Worksheet $ws): array {
-    [$highestRow, $highestCol] = self::get_highest_coords($ws);
+    [$highestCol, $highestRow] = self::get_highest_coords($ws);
 
-    $maxRow = 1;
     $maxCol = 1;
+    $maxRow = 1;
     $maxEmptyRows = self::MAX_EMPTY_THRESHOLD;
     for ($row = 1; $row <= $highestRow; $row++) {
       $emptyRow = true;
       $maxEmptyCols = self::MAX_EMPTY_THRESHOLD;
       for ($col = 1; $col <= $highestCol; $col++) {
         $value = null;
-        if ($ws->cellExists([$col, $row])) {
-          $value = $ws->getCell([$col, $row])->getValue();
+        if ($ws->cellExistsByColumnAndRow($col, $row)) {
+          $value = $ws->getCellByColumnAndRow($col, $row)->getValue();
         }
         if ($value === null) {
           $maxEmptyCols--;
@@ -54,6 +54,6 @@ class wsutils {
         $maxEmptyRows = self::MAX_EMPTY_THRESHOLD;
       }
     }
-    return [$maxRow, $maxCol];
+    return [$maxCol, $maxRow];
   }
 }
diff --git a/src/file/csv/CsvBuilder.php b/src/file/csv/CsvBuilder.php
index cef42bd..07f0df6 100644
--- a/src/file/csv/CsvBuilder.php
+++ b/src/file/csv/CsvBuilder.php
@@ -8,12 +8,7 @@ use nur\sery\web\http;
  * Class CsvBuilder: construction d'un fichier CSV, pour envoi à l'utilisateur
  */
 class CsvBuilder extends AbstractBuilder {
-  static function with($builder): self {
-    if ($builder instanceof self) return $builder;
-    elseif (is_string($builder)) return new static($builder);
-    elseif (is_array($builder)) return new static(null, $builder);
-    else throw ValueException::invalid_type($builder, self::class);
-  }
+  use TAbstractBuilder;
 
   function __construct(?string $output, ?array $params=null) {
     $csvFlavour = $params["csv_flavour"] ?? null;
diff --git a/src/file/csv/SpreadsheetBuilder.php b/src/file/csv/SsBuilder.php
similarity index 62%
rename from src/file/csv/SpreadsheetBuilder.php
rename to src/file/csv/SsBuilder.php
index 5cffa1b..d23740d 100644
--- a/src/file/csv/SpreadsheetBuilder.php
+++ b/src/file/csv/SsBuilder.php
@@ -1,6 +1,7 @@
 <?php
 namespace nur\sery\file\csv;
 
+use nur\sery\ext\spreadsheet\wsutils;
 use nur\sery\os\path;
 use nur\sery\ValueException;
 use nur\sery\web\http;
@@ -16,73 +17,64 @@ use PhpOffice\PhpSpreadsheet\Writer\Xlsx;
  * Class SpreadsheetBuilder: construction d'une feuille de calcul, pour envoi
  * à l'utilisateur
  */
-class SpreadsheetBuilder extends AbstractBuilder {
-  static function with($builder): self {
-    if ($builder instanceof self) return $builder;
-    elseif (is_string($builder)) return new static($builder);
-    elseif (is_array($builder)) return new static(null, $builder);
-    else throw ValueException::invalid_type($builder, self::class);
-  }
+class SsBuilder extends AbstractBuilder {
+  use TAbstractBuilder;
 
   function __construct(?string $output, ?array $params=null) {
+    parent::__construct($output, $params);
     $this->ss = new Spreadsheet();
     $this->valueBinder = new StringValueBinder();
-    $this->wsname = $params["wsname"] ?? null;
-    parent::__construct($output, $params);
+    $this->setWsname($params["wsname"] ?? null);
   }
 
   protected Spreadsheet $ss;
 
   protected IValueBinder $valueBinder;
 
-  protected ?string $wsname;
+  protected ?Worksheet $ws;
 
-  protected ?Worksheet $ws = null;
+  protected int $nrow;
 
-  protected function ws(): Worksheet {
-    $ws = $this->ws;
-    if ($ws !== null) return $ws;
+  const STYLE_ROW = 0, STYLE_HEADER = 1;
+
+  protected int $rowStyle;
+
+  function setWsname(?string $wsname): void {
     $ss = $this->ss;
-    $wsname = $this->wsname;
+    $this->ws = null;
+    $this->nrow = 0;
+    $this->rowStyle = self::STYLE_ROW;
     if ($wsname === null) {
       $ws = $ss->getActiveSheet();
     } else {
       $ws = $ss->getSheetByName($wsname);
-      if ($ws === null) {
-        $ws = $ss->createSheet()->setTitle($wsname);
-      }
     }
-    return $this->ws = $ws;
+    if ($ws === null) {
+      $ws = $ss->createSheet()->setTitle($wsname);
+    } else {
+      $maxRow = wsutils::compute_max_coords($ws)[1];
+      $this->nrow = $maxRow - 1;
+    }
+    $this->ws = $ws;
   }
 
-  protected int $nrow = 0;
-
-  const STYLE_HEADER = 0, STYLE_ROW = 1;
-
-  protected int $style = self::STYLE_ROW;
-
   function _write(array $row): void {
-    $ws = $this->ws();
+    $ws = $this->ws;
+    $styleHeader = $this->rowStyle === self::STYLE_HEADER;
     $nrow = ++$this->nrow;
     $ncol = 1;
     foreach ($row as $col) {
-      //$cell = $ws->getCell([$ncol++, $nrow]);
-      $cell = $ws->getCellByColumnAndRow($ncol++, $nrow);
-      $cell->setValue($col, $this->valueBinder);
-      switch ($this->style) {
-      case self::STYLE_HEADER:
-        $cell->getStyle()->getFont()->setBold(true);
-        break;
-      case self::STYLE_ROW:
-          break;
-      }
+      $ws->getCellByColumnAndRow($ncol++, $nrow)->setValue($col, $this->valueBinder);
+    }
+    if ($styleHeader) {
+      $ws->getStyle("$nrow:$nrow")->getFont()->setBold(true);
     }
   }
 
   function writeHeaders(?array $headers=null): void {
-    $this->style = self::STYLE_HEADER;
+    $this->rowStyle = self::STYLE_HEADER;
     parent::writeHeaders($headers);
-    $this->style = self::STYLE_ROW;
+    $this->rowStyle = self::STYLE_ROW;
   }
 
   function _sendContentType(): void {
diff --git a/src/file/csv/TAbstractBuilder.php b/src/file/csv/TAbstractBuilder.php
new file mode 100644
index 0000000..8e2db7a
--- /dev/null
+++ b/src/file/csv/TAbstractBuilder.php
@@ -0,0 +1,13 @@
+<?php
+namespace nur\sery\file\csv;
+
+use nur\sery\ValueException;
+
+trait TAbstractBuilder {
+  static function with($builder): self {
+    if ($builder instanceof self) return $builder;
+    elseif (is_string($builder)) return new static($builder);
+    elseif (is_array($builder)) return new static(null, $builder);
+    else throw ValueException::invalid_type($builder, self::class);
+  }
+}