diff --git a/src/sorobandata_builder.js b/src/sorobandata_builder.js
index 8beea47b..e4e0d6da 100644
--- a/src/sorobandata_builder.js
+++ b/src/sorobandata_builder.js
@@ -35,10 +35,8 @@ export class SorobanDataBuilder {
   constructor(sorobanData) {
     let data;
 
-    if (typeof sorobanData === 'string') {
-      data = SorobanDataBuilder.fromXDR(sorobanData, 'base64');
-    } else if (ArrayBuffer.isView(sorobanData)) {
-      data = SorobanDataBuilder.fromXDR(sorobanData, 'raw');
+    if (typeof sorobanData === 'string' || ArrayBuffer.isView(sorobanData)) {
+      data = SorobanDataBuilder.fromXDR(sorobanData);
     } else if (!sorobanData) {
       data = new xdr.SorobanTransactionData({
         resources: new xdr.SorobanResources({
@@ -102,22 +100,37 @@ export class SorobanDataBuilder {
     return this;
   }
 
+  /**
+   * Appends the given ledger keys to the existing storage access footprint.
+   * @param {xdr.LedgerKey[]} readOnly   read-only keys to add
+   * @param {xdr.LedgerKey[]} readWrite  read-write keys to add
+   * @returns {SorobanDataBuilder} this builder instance
+   */
+  appendFootprint(readOnly, readWrite) {
+    return this.setFootprint(
+      this.getReadOnly().concat(readOnly),
+      this.getReadWrite().concat(readWrite)
+    );
+  }
+
   /**
    * Sets the storage access footprint to be a certain set of ledger keys.
    *
    * You can also set each field explicitly via
    * {@link SorobanDataBuilder.setReadOnly} and
-   * {@link SorobanDataBuilder.setReadWrite}.
+   * {@link SorobanDataBuilder.setReadWrite} or add to the existing footprint
+   * via {@link SorobanDataBuilder.appendFootprint}.
    *
    * Passing `null|undefined` to either parameter will IGNORE the existing
    * values. If you want to clear them, pass `[]`, instead.
    *
    * @param {xdr.LedgerKey[]|null} [readOnly]   the set of ledger keys to set in
-   *    the read-only portion of the transaction's `sorobanData`
+   *    the read-only portion of the transaction's `sorobanData`, or `null |
+   *    undefined` to keep the existing keys
    * @param {xdr.LedgerKey[]|null} [readWrite]  the set of ledger keys to set in
-   *    the read-write portion of the transaction's `sorobanData`
-   *
-   * @returns {SorobanDataBuilder}
+   *    the read-write portion of the transaction's `sorobanData`, or `null |
+   *    undefined` to keep the existing keys
+   * @returns {SorobanDataBuilder} this builder instance
    */
   setFootprint(readOnly, readWrite) {
     if (readOnly !== null) {
@@ -160,4 +173,18 @@ export class SorobanDataBuilder {
   build() {
     return xdr.SorobanTransactionData.fromXDR(this._data.toXDR()); // clone
   }
+
+  //
+  // getters follow
+  //
+
+  /** @returns {xdr.LedgerKey[]} the read-only storage access pattern */
+  getReadOnly() {
+    return this._data.resources().footprint().readOnly();
+  }
+
+  /** @returns {xdr.LedgerKey[]} the read-write storage access pattern */
+  getReadWrite() {
+    return this._data.resources().footprint().readWrite();
+  }
 }
diff --git a/test/unit/sorobandata_builder_test.js b/test/unit/sorobandata_builder_test.js
index cae369ef..623087c5 100644
--- a/test/unit/sorobandata_builder_test.js
+++ b/test/unit/sorobandata_builder_test.js
@@ -59,6 +59,20 @@ describe('SorobanTransactionData can be built', function () {
     expect(data2.resources().footprint().readWrite()).to.eql([]);
   });
 
+  it('appends footprints', function () {
+    const builder = new dataBuilder();
+
+    const data = builder
+      .setFootprint([key], [key])
+      .appendFootprint([key, key], []);
+    const built = data.build();
+
+    expect(data.getReadOnly()).to.eql([key, key, key]);
+    expect(data.getReadWrite()).to.eql([key]);
+    expect(built.resources().footprint().readOnly()).to.eql([key, key, key]);
+    expect(built.resources().footprint().readWrite()).to.eql([key]);
+  });
+
   it('makes copies on build()', function () {
     const builder = new dataBuilder();
     const first = builder.build();
diff --git a/types/index.d.ts b/types/index.d.ts
index 8bb10139..7287d6d7 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1139,7 +1139,8 @@ export function humanizeEvents(
 ): SorobanEvent[];
 
 export class SorobanDataBuilder {
-  constructor(data?: string | xdr.SorobanTransactionData);
+  constructor(data?: string | Uint8Array | Buffer | xdr.SorobanTransactionData);
+  static fromXDR(data: Uint8Array | Buffer | string): SorobanDataBuilder;
 
   setRefundableFee(fee: IntLike): SorobanDataBuilder;
   setResources(
@@ -1153,9 +1154,16 @@ export class SorobanDataBuilder {
     readOnly?: xdr.LedgerKey[] | null,
     readWrite?: xdr.LedgerKey[] | null
   ): SorobanDataBuilder;
+  appendFootprint(
+    readOnly: xdr.LedgerKey[],
+    readWrite: xdr.LedgerKey[]
+  ): SorobanDataBuilder;
+
+  setReadOnly(keys: xdr.LedgerKey[]): SorobanDataBuilder;
+  setReadWrite(keys: xdr.LedgerKey[]): SorobanDataBuilder;
 
-  setReadOnly(keys?: xdr.LedgerKey[]): SorobanDataBuilder;
-  setReadWrite(keys?: xdr.LedgerKey[]): SorobanDataBuilder;
+  getReadOnly(): xdr.LedgerKey[];
+  getReadWrite(): xdr.LedgerKey[];
 
   build(): xdr.SorobanTransactionData;
 }