diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/DayAssignment.java b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/DayAssignment.java
index 234396def..11230d189 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/DayAssignment.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/DayAssignment.java
@@ -173,12 +173,13 @@ public abstract class DayAssignment extends BaseEntity {
 
     }
 
-    protected DayAssignment(LocalDate day, int hours, Resource resource) {
+    protected DayAssignment(LocalDate day, EffortDuration duration,
+            Resource resource) {
         Validate.notNull(day);
-        Validate.isTrue(hours >= 0);
+        Validate.notNull(duration);
         Validate.notNull(resource);
         this.day = day;
-        this.duration = EffortDuration.hours(hours);
+        this.duration = duration;
         this.resource = resource;
     }
 
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/DerivedDayAssignment.java b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/DerivedDayAssignment.java
index a06d757b1..27b9a32b5 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/DerivedDayAssignment.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/DerivedDayAssignment.java
@@ -19,6 +19,8 @@
  */
 package org.navalplanner.business.planner.entities;
 
+import static org.navalplanner.business.workingday.EffortDuration.hours;
+
 import org.apache.commons.lang.Validate;
 import org.hibernate.validator.NotNull;
 import org.joda.time.LocalDate;
@@ -27,6 +29,7 @@ import org.navalplanner.business.resources.entities.Worker;
 import org.navalplanner.business.scenarios.entities.Scenario;
 import org.navalplanner.business.util.deepcopy.OnCopy;
 import org.navalplanner.business.util.deepcopy.Strategy;
+import org.navalplanner.business.workingday.EffortDuration;
 
 
 /**
@@ -35,9 +38,17 @@ import org.navalplanner.business.util.deepcopy.Strategy;
  */
 public class DerivedDayAssignment extends DayAssignment {
 
+    @Deprecated
     public static DerivedDayAssignment create(LocalDate day, int hours,
             Resource resource, DerivedAllocation derivedAllocation) {
-        return create(new DerivedDayAssignment(day, hours, resource,
+        return create(new DerivedDayAssignment(day, hours(hours), resource,
+                derivedAllocation));
+    }
+
+    public static DerivedDayAssignment create(LocalDate day,
+            EffortDuration duration, Resource resource,
+            DerivedAllocation derivedAllocation) {
+        return create(new DerivedDayAssignment(day, duration, resource,
                 derivedAllocation));
     }
 
@@ -110,18 +121,21 @@ public class DerivedDayAssignment extends DayAssignment {
     @OnCopy(Strategy.IGNORE)
     private ParentState parentState;
 
-    private DerivedDayAssignment(LocalDate day, int hours, Resource resource) {
+    private DerivedDayAssignment(LocalDate day, EffortDuration hours,
+            Resource resource) {
         super(day, hours, resource);
         Validate.isTrue(resource instanceof Worker);
     }
 
-    private DerivedDayAssignment(LocalDate day, int hours, Resource resource,
+    private DerivedDayAssignment(LocalDate day, EffortDuration hours,
+            Resource resource,
             DerivedAllocation derivedAllocation) {
         this(day, hours, resource);
         this.parentState = new TransientParentState(derivedAllocation);
     }
 
-    private DerivedDayAssignment(LocalDate day, int hours, Resource resource,
+    private DerivedDayAssignment(LocalDate day, EffortDuration hours,
+            Resource resource,
             DerivedDayAssignmentsContainer container) {
         this(day, hours, resource);
         Validate.notNull(container);
@@ -140,7 +154,8 @@ public class DerivedDayAssignment extends DayAssignment {
 
     private static DerivedDayAssignment create(LocalDate day, int hours,
             Resource resource, DerivedDayAssignmentsContainer container) {
-        return create(new DerivedDayAssignment(day, hours, resource, container));
+        return create(new DerivedDayAssignment(day,
+                EffortDuration.hours(hours), resource, container));
     }
 
     DerivedDayAssignment copyAsChildOf(DerivedAllocation derivedAllocation) {
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/GenericDayAssignment.java b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/GenericDayAssignment.java
index d1edd1381..9eded3247 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/GenericDayAssignment.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/GenericDayAssignment.java
@@ -20,6 +20,8 @@
 
 package org.navalplanner.business.planner.entities;
 
+import static org.navalplanner.business.workingday.EffortDuration.hours;
+
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
@@ -33,6 +35,7 @@ import org.navalplanner.business.resources.entities.Resource;
 import org.navalplanner.business.scenarios.entities.Scenario;
 import org.navalplanner.business.util.deepcopy.OnCopy;
 import org.navalplanner.business.util.deepcopy.Strategy;
+import org.navalplanner.business.workingday.EffortDuration;
 
 /**
  *
@@ -117,11 +120,15 @@ public class GenericDayAssignment extends DayAssignment {
     }
 
 
+    @Deprecated
     public static GenericDayAssignment create(LocalDate day, int hours,
             Resource resource) {
-        GenericDayAssignment result = new GenericDayAssignment(day, hours,
-                        resource);
-        return create(result);
+        return create(new GenericDayAssignment(day, hours(hours), resource));
+    }
+
+    public static GenericDayAssignment create(LocalDate day,
+            EffortDuration duration, Resource resource) {
+        return create(new GenericDayAssignment(day, duration, resource));
     }
 
     public static Set<GenericDayAssignment> copy(
@@ -163,8 +170,9 @@ public class GenericDayAssignment extends DayAssignment {
         return result;
     }
 
-    private GenericDayAssignment(LocalDate day, int hours, Resource resource) {
-        super(day, hours, resource);
+    private GenericDayAssignment(LocalDate day, EffortDuration duration,
+            Resource resource) {
+        super(day, duration, resource);
         parentState = new ContainerNotSpecified();
     }
 
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/SpecificDayAssignment.java b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/SpecificDayAssignment.java
index e8be46ee8..c8159921f 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/SpecificDayAssignment.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/SpecificDayAssignment.java
@@ -20,6 +20,8 @@
 
 package org.navalplanner.business.planner.entities;
 
+import static org.navalplanner.business.workingday.EffortDuration.hours;
+
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
@@ -33,6 +35,7 @@ import org.navalplanner.business.resources.entities.Resource;
 import org.navalplanner.business.scenarios.entities.Scenario;
 import org.navalplanner.business.util.deepcopy.OnCopy;
 import org.navalplanner.business.util.deepcopy.Strategy;
+import org.navalplanner.business.workingday.EffortDuration;
 
 
 /**
@@ -156,14 +159,20 @@ public class SpecificDayAssignment extends DayAssignment {
     @NotNull
     private SpecificDayAssignmentsContainer container;
 
+    @Deprecated
     public static SpecificDayAssignment create(LocalDate day, int hours,
             Resource resource) {
-        return create(new SpecificDayAssignment(day,
-                hours, resource));
+        return create(new SpecificDayAssignment(day, hours(hours), resource));
     }
 
-    public SpecificDayAssignment(LocalDate day, int hours, Resource resource) {
-        super(day, hours, resource);
+    public static SpecificDayAssignment create(LocalDate day,
+            EffortDuration duration, Resource resource) {
+        return create(new SpecificDayAssignment(day, duration, resource));
+    }
+
+    public SpecificDayAssignment(LocalDate day, EffortDuration duration,
+            Resource resource) {
+        super(day, duration, resource);
         this.parentState = new ContainerNotSpecified();
     }
 
diff --git a/navalplanner-business/src/test/java/org/navalplanner/business/test/resources/entities/ResourceTest.java b/navalplanner-business/src/test/java/org/navalplanner/business/test/resources/entities/ResourceTest.java
index aefe10eff..e339a7dc3 100644
--- a/navalplanner-business/src/test/java/org/navalplanner/business/test/resources/entities/ResourceTest.java
+++ b/navalplanner-business/src/test/java/org/navalplanner/business/test/resources/entities/ResourceTest.java
@@ -19,6 +19,7 @@
  */
 
 package org.navalplanner.business.test.resources.entities;
+
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -29,6 +30,7 @@ import static org.navalplanner.business.BusinessGlobalNames.BUSINESS_SPRING_CONF
 import static org.navalplanner.business.test.BusinessGlobalNames.BUSINESS_SPRING_CONFIG_TEST_FILE;
 import static org.navalplanner.business.test.resources.daos.CriterionSatisfactionDAOTest.date;
 import static org.navalplanner.business.test.resources.daos.CriterionSatisfactionDAOTest.year;
+import static org.navalplanner.business.workingday.EffortDuration.hours;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -516,8 +518,9 @@ public class ResourceTest {
         LocalDate today = new LocalDate();
         LocalDate tomorrow = today.plus(Days.days(1));
         SpecificDayAssignment specificDayAssignment = new SpecificDayAssignment(
-                today, 10, worker);
-        SpecificDayAssignment another = new SpecificDayAssignment(tomorrow, 10,
+                today, hours(10), worker);
+        SpecificDayAssignment another = new SpecificDayAssignment(tomorrow,
+                hours(10),
                 worker);
         givenWorkerWithAssignments(specificDayAssignment, another);
 
@@ -532,12 +535,13 @@ public class ResourceTest {
         LocalDate today = new LocalDate();
         LocalDate tomorrow = today.plus(Days.days(1));
         SpecificDayAssignment specificDayAssignment = new SpecificDayAssignment(
-                today, 10, worker);
-        SpecificDayAssignment another = new SpecificDayAssignment(tomorrow, 10,
+                today, hours(10), worker);
+        SpecificDayAssignment another = new SpecificDayAssignment(tomorrow,
+                hours(10),
                 worker);
         givenWorkerWithAssignments(specificDayAssignment, another);
 
-        DayAssignment other = new SpecificDayAssignment(today, 3, worker);
+        DayAssignment other = new SpecificDayAssignment(today, hours(3), worker);
         worker.addNewAssignments(Arrays.asList(other));
         assertTrue(worker.getAssignments().size() == assignments.size() + 1);
     }
@@ -554,12 +558,11 @@ public class ResourceTest {
         givenWorker();
         LocalDate today = new LocalDate();
         SpecificDayAssignment specificDayAssignment = new SpecificDayAssignment(
-                today, 10, worker);
-        SpecificDayAssignment another = new SpecificDayAssignment(today, 3,
-                worker);
-        SpecificDayAssignment atAnotherDay = new SpecificDayAssignment(today
-                .plusDays(1), 1,
-                worker);
+                today, hours(10), worker);
+        SpecificDayAssignment another = new SpecificDayAssignment(today,
+                hours(3), worker);
+        SpecificDayAssignment atAnotherDay = new SpecificDayAssignment(
+                today.plusDays(1), hours(1), worker);
         givenWorkerWithAssignments(specificDayAssignment, another, atAnotherDay);
 
         assertThat(worker.getAssignedHours(today), equalTo(13));
@@ -570,11 +573,11 @@ public class ResourceTest {
         givenWorker();
         LocalDate today = new LocalDate();
         SpecificDayAssignment specificDayAssignment = new SpecificDayAssignment(
-                today, 10, worker);
+                today, hours(10), worker);
         givenWorkerWithAssignments(specificDayAssignment);
         worker.getAssignedHours(today);
-        SpecificDayAssignment another = new SpecificDayAssignment(today, 3,
-                worker);
+        SpecificDayAssignment another = new SpecificDayAssignment(today,
+                hours(3), worker);
         worker.addNewAssignments(Arrays.asList(another));
 
         assertThat(worker.getAssignedHours(today), equalTo(13));