diff --git a/app/models/derived_variables/sales_log_variables.rb b/app/models/derived_variables/sales_log_variables.rb
index 1edb6b0a8..1e092a26a 100644
--- a/app/models/derived_variables/sales_log_variables.rb
+++ b/app/models/derived_variables/sales_log_variables.rb
@@ -75,7 +75,7 @@ module DerivedVariables::SalesLogVariables
     self.nationality_all = nationality_all_group if nationality_uk_or_prefers_not_to_say?
     self.nationality_all_buyer2 = nationality_all_buyer2_group if nationality2_uk_or_prefers_not_to_say?
 
-    self.numstair = 1 if is_firststair?
+    self.numstair = is_firststair? ? 1 : nil if numstair == 1 && firststair_changed?
     self.mrent = 0 if stairowned_100?
 
     set_encoded_derived_values!(DEPENDENCIES)
diff --git a/app/models/form/sales/questions/staircase_count.rb b/app/models/form/sales/questions/staircase_count.rb
index bad35be2e..07095cd6a 100644
--- a/app/models/form/sales/questions/staircase_count.rb
+++ b/app/models/form/sales/questions/staircase_count.rb
@@ -6,6 +6,7 @@ class Form::Sales::Questions::StaircaseCount < ::Form::Question
     @type = "numeric"
     @width = 2
     @min = 2
+    @max = 10
     @step = 1
     @question_number = QUESTION_NUMBER_FROM_YEAR[form.start_date.year] || QUESTION_NUMBER_FROM_YEAR[QUESTION_NUMBER_FROM_YEAR.keys.max]
   end
diff --git a/app/models/validations/sales/sale_information_validations.rb b/app/models/validations/sales/sale_information_validations.rb
index 3c5e3f2b9..1ce9bf0ca 100644
--- a/app/models/validations/sales/sale_information_validations.rb
+++ b/app/models/validations/sales/sale_information_validations.rb
@@ -32,6 +32,14 @@ module Validations::Sales::SaleInformationValidations
     end
   end
 
+  def validate_staircasing_initial_purchase_date(record)
+    return unless record.initialpurchase
+
+    if record.initialpurchase < Time.zone.local(1980, 1, 1)
+      record.errors.add :initialpurchase, I18n.t("validations.sales.sale_information.initialpurchase.must_be_after_1980")
+    end
+  end
+
   def validate_previous_property_unit_type(record)
     return unless record.fromprop && record.frombeds
 
@@ -348,6 +356,15 @@ module Validations::Sales::SaleInformationValidations
     end
   end
 
+  def validate_number_of_staircase_transactions(record)
+    return unless record.numstair
+
+    if record.firststair == 2 && record.numstair < 2
+      record.errors.add :numstair, I18n.t("validations.sales.sale_information.numstair.must_be_greater_than_one")
+      record.errors.add :firststair, I18n.t("validations.sales.sale_information.firststair.cannot_be_no")
+    end
+  end
+
   def over_tolerance?(expected, actual, tolerance, strict: false)
     if strict
       (expected - actual).abs > tolerance
diff --git a/config/locales/validations/sales/sale_information.en.yml b/config/locales/validations/sales/sale_information.en.yml
index 20aca17d2..55b9cfede 100644
--- a/config/locales/validations/sales/sale_information.en.yml
+++ b/config/locales/validations/sales/sale_information.en.yml
@@ -17,6 +17,8 @@ en:
         exdate:
           must_be_before_saledate: "Contract exchange date must be before sale completion date."
           must_be_less_than_1_year_from_saledate: "Contract exchange date must be less than 1 year before sale completion date."
+        initialpurchase:
+          must_be_after_1980: "The initial purchase date must be after January 1, 1980."
         fromprop:
           previous_property_type_bedsit: "A bedsit cannot have more than 1 bedroom."
         frombeds:
@@ -123,3 +125,7 @@ en:
         postcode_full:
           value_over_discounted_london_max: "The percentage discount multiplied by the purchase price is %{discount_value}. This figure should not be more than £136,400 for properties in London."
           value_over_discounted_max: "The percentage discount multiplied by the purchase price is %{discount_value}. This figure should not be more than £102,400 for properties outside of London."
+        numstair:
+          must_be_greater_than_one: "The number of staircasing transactions must be greater than 1 when this is not the first staircasing transaction."
+        firststair:
+          cannot_be_no: "The answer to 'Is this the first staircasing transaction?' cannot be 'no' if the number of staircasing transactions is 1."
diff --git a/spec/models/validations/sales/sale_information_validations_spec.rb b/spec/models/validations/sales/sale_information_validations_spec.rb
index 36dadc345..e7b1d53d5 100644
--- a/spec/models/validations/sales/sale_information_validations_spec.rb
+++ b/spec/models/validations/sales/sale_information_validations_spec.rb
@@ -1406,4 +1406,44 @@ RSpec.describe Validations::Sales::SaleInformationValidations do
       end
     end
   end
+
+  describe "#validate_number_of_staircase_transactions" do
+    let(:record) { build(:sales_log, numstair:, firststair:) }
+
+    before do
+      sale_information_validator.validate_number_of_staircase_transactions(record)
+    end
+
+    context "when it is not the first staircasing transaction" do
+      context "and the number of staircasing transactions is between 2 and 10" do
+        let(:numstair) { 6 }
+        let(:firststair) { 2 }
+
+        it "does not add an error" do
+          expect(record.errors).to be_empty
+        end
+      end
+
+      context "and the number of staircasing transactions is less than 2" do
+        let(:numstair) { 1 }
+        let(:firststair) { 2 }
+
+        it "adds an error" do
+          expect(record.errors[:numstair]).to include(I18n.t("validations.sales.sale_information.numstair.must_be_greater_than_one"))
+          expect(record.errors[:firststair]).to include(I18n.t("validations.sales.sale_information.firststair.cannot_be_no"))
+        end
+      end
+    end
+
+    context "when it is the first staircasing transaction" do
+      context "and numstair is also 1" do
+        let(:numstair) { 1 }
+        let(:firststair) { 1 }
+
+        it "does not add an error" do
+          expect(record.errors).to be_empty
+        end
+      end
+    end
+  end
 end