diff --git a/Source/ccib.f90 b/Source/ccib.f90
index ece31a7a56a..71388936eec 100644
--- a/Source/ccib.f90
+++ b/Source/ccib.f90
@@ -1673,6 +1673,7 @@ SUBROUTINE GET_FH_FROM_PRHS_AND_BCS(NM,DT,CYL_FCT,UNKH,NUNKH,IPZ,F_H)
 ! Local variables:
 INTEGER :: I,J,K,IROW,IW,IIG,JJG,KKG,IOR,ICFACE,IFACE,JFACE,ILH,JLH,KLH,IRC
 TYPE (WALL_TYPE), POINTER :: WC=>NULL()
+TYPE (EXTERNAL_WALL_TYPE), POINTER :: EWC=>NULL()
 TYPE(CFACE_TYPE), POINTER :: CFA=>NULL()
 REAL(EB) :: IDX, AF, VAL, BCV
 
@@ -1708,9 +1709,10 @@ SUBROUTINE GET_FH_FROM_PRHS_AND_BCS(NM,DT,CYL_FCT,UNKH,NUNKH,IPZ,F_H)
    IFACE= CFA%CUT_FACE_IND1
    JFACE= CFA%CUT_FACE_IND2
    WC  => WALL(CUT_FACE(IFACE)%IWC)
+   EWC => EXTERNAL_WALL(CUT_FACE(IFACE)%IWC)
 
    ! DIRICHLET boundaries:
-   IF_CFACE_DIRICHLET: IF (WC%PRESSURE_BC_INDEX==DIRICHLET) THEN
+   IF_CFACE_DIRICHLET: IF (EWC%PRESSURE_BC_TYPE==DIRICHLET) THEN
 
       ! Gasphase cell indexes:
       BC => BOUNDARY_COORD(WC%BC_INDEX); IF(ZONE_SOLVE(PRESSURE_ZONE(BC%IIG,BC%JJG,BC%KKG))%CONNECTED_ZONE_PARENT/=IPZ) CYCLE
@@ -1747,6 +1749,7 @@ SUBROUTINE GET_FH_FROM_PRHS_AND_BCS(NM,DT,CYL_FCT,UNKH,NUNKH,IPZ,F_H)
 WALL_CELL_LOOP_1: DO IW=1,N_EXTERNAL_WALL_CELLS
 
    WC => WALL(IW)
+   EWC => EXTERNAL_WALL(IW)
    ! Drop if this is a cut-face or NULL Boundary. Dealt with external CFACE.
    IF (WC%CUT_FACE_INDEX>0 .OR. WC%BOUNDARY_TYPE==NULL_BOUNDARY) CYCLE
    ! Gasphase cell indexes:
@@ -1754,7 +1757,7 @@ SUBROUTINE GET_FH_FROM_PRHS_AND_BCS(NM,DT,CYL_FCT,UNKH,NUNKH,IPZ,F_H)
    IIG = BC%IIG; JJG = BC%JJG; KKG = BC%KKG; IOR = BC%IOR
 
    ! NEUMANN boundaries:
-   IF_NEUMANN: IF (WC%PRESSURE_BC_INDEX==NEUMANN) THEN
+   IF_NEUMANN: IF (EWC%PRESSURE_BC_TYPE==NEUMANN) THEN
       ! Define cell size, normal to WC:
       SELECT CASE (IOR)
       CASE(-1) ! -IAXIS oriented, high face of IIG cell.
@@ -1790,7 +1793,7 @@ SUBROUTINE GET_FH_FROM_PRHS_AND_BCS(NM,DT,CYL_FCT,UNKH,NUNKH,IPZ,F_H)
    ENDIF IF_NEUMANN
 
    ! DIRICHLET boundaries:
-   IF_DIRICHLET: IF (WC%PRESSURE_BC_INDEX==DIRICHLET) THEN
+   IF_DIRICHLET: IF (EWC%PRESSURE_BC_TYPE==DIRICHLET) THEN
       ! Global matrix solve, skip INTERPOLATED boundaries.
       IF (PRES_FLAG/=ULMAT_FLAG .AND. WC%BOUNDARY_TYPE==INTERPOLATED_BOUNDARY) CYCLE
       ! Here case where SOLID and OPEN or interpolated are mixed on a boundary:
diff --git a/Source/func.f90 b/Source/func.f90
index c3597d9923d..00f6e37e081 100644
--- a/Source/func.f90
+++ b/Source/func.f90
@@ -1580,9 +1580,7 @@ SUBROUTINE PACK_WALL(NM,OS,WC,SURF_INDEX,RC,IC,LC,UNPACK_IT,COUNT_ONLY)
 IC=IC+1 ; IF (.NOT.COUNT_ONLY) CALL EQUATE(OS%INTEGERS(IC),WC%BACK_MESH,UNPACK_IT)
 IC=IC+1 ; IF (.NOT.COUNT_ONLY) CALL EQUATE(OS%INTEGERS(IC),WC%BACK_SURF,UNPACK_IT)
 IC=IC+1 ; IF (.NOT.COUNT_ONLY) CALL EQUATE(OS%INTEGERS(IC),WC%BOUNDARY_TYPE,UNPACK_IT)
-IC=IC+1 ; IF (.NOT.COUNT_ONLY) CALL EQUATE(OS%INTEGERS(IC),WC%SURF_INDEX_ORIG,UNPACK_IT)
 IC=IC+1 ; IF (.NOT.COUNT_ONLY) CALL EQUATE(OS%INTEGERS(IC),WC%OBST_INDEX,UNPACK_IT)
-IC=IC+1 ; IF (.NOT.COUNT_ONLY) CALL EQUATE(OS%INTEGERS(IC),WC%PRESSURE_BC_INDEX,UNPACK_IT)
 IC=IC+1 ; IF (.NOT.COUNT_ONLY) CALL EQUATE(OS%INTEGERS(IC),WC%VENT_INDEX,UNPACK_IT)
 IC=IC+1 ; IF (.NOT.COUNT_ONLY) CALL EQUATE(OS%INTEGERS(IC),WC%JD11_INDEX,UNPACK_IT)
 IC=IC+1 ; IF (.NOT.COUNT_ONLY) CALL EQUATE(OS%INTEGERS(IC),WC%JD12_INDEX,UNPACK_IT)
diff --git a/Source/init.f90 b/Source/init.f90
index be3afc3cdd5..96c18f4fcfb 100644
--- a/Source/init.f90
+++ b/Source/init.f90
@@ -2296,6 +2296,7 @@ SUBROUTINE INITIALIZE_POISSON_SOLVER(NM)
 INTEGER, POINTER, DIMENSION(:) :: NOC
 TYPE (VENTS_TYPE), POINTER :: VT
 TYPE (WALL_TYPE), POINTER :: WC
+TYPE (EXTERNAL_WALL_TYPE), POINTER :: EWC
 TYPE (MESH_TYPE), POINTER :: M
 TYPE (BOUNDARY_COORD_TYPE), POINTER :: BC
 
@@ -2570,31 +2571,32 @@ SUBROUTINE INITIALIZE_POISSON_SOLVER(NM)
 
 WALL_CELL_LOOP: DO IW=1,M%N_EXTERNAL_WALL_CELLS
    WC => M%WALL(IW)
+   EWC => M%EXTERNAL_WALL(IW)
    BC => M%BOUNDARY_COORD(WC%BC_INDEX)
    IOR = BC%IOR
    SELECT CASE(IOR)
       CASE( 1)
          IF (LBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. &
-             LBC==FISHPAK_BC_NEUMANN_DIRICHLET   .OR. LBC==6) WC%PRESSURE_BC_INDEX = NEUMANN
+             LBC==FISHPAK_BC_NEUMANN_DIRICHLET   .OR. LBC==6) EWC%PRESSURE_BC_TYPE = NEUMANN
          IF (LBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. &
-             LBC==FISHPAK_BC_DIRICHLET_NEUMANN   .OR. LBC==5) WC%PRESSURE_BC_INDEX = DIRICHLET
+             LBC==FISHPAK_BC_DIRICHLET_NEUMANN   .OR. LBC==5) EWC%PRESSURE_BC_TYPE = DIRICHLET
       CASE(-1)
          IF (LBC==FISHPAK_BC_DIRICHLET_NEUMANN   .OR. &
-             LBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. LBC==6) WC%PRESSURE_BC_INDEX = NEUMANN
+             LBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. LBC==6) EWC%PRESSURE_BC_TYPE = NEUMANN
          IF (LBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. &
-             LBC==FISHPAK_BC_NEUMANN_DIRICHLET   .OR. LBC==5) WC%PRESSURE_BC_INDEX = DIRICHLET
+             LBC==FISHPAK_BC_NEUMANN_DIRICHLET   .OR. LBC==5) EWC%PRESSURE_BC_TYPE = DIRICHLET
       CASE( 2)
-         IF (MBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. MBC==FISHPAK_BC_NEUMANN_DIRICHLET) WC%PRESSURE_BC_INDEX = NEUMANN
-         IF (MBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. MBC==FISHPAK_BC_DIRICHLET_NEUMANN) WC%PRESSURE_BC_INDEX = DIRICHLET
+         IF (MBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. MBC==FISHPAK_BC_NEUMANN_DIRICHLET) EWC%PRESSURE_BC_TYPE = NEUMANN
+         IF (MBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. MBC==FISHPAK_BC_DIRICHLET_NEUMANN) EWC%PRESSURE_BC_TYPE = DIRICHLET
       CASE(-2)
-         IF (MBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. MBC==FISHPAK_BC_DIRICHLET_NEUMANN) WC%PRESSURE_BC_INDEX = NEUMANN
-         IF (MBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. MBC==FISHPAK_BC_NEUMANN_DIRICHLET) WC%PRESSURE_BC_INDEX = DIRICHLET
+         IF (MBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. MBC==FISHPAK_BC_DIRICHLET_NEUMANN) EWC%PRESSURE_BC_TYPE = NEUMANN
+         IF (MBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. MBC==FISHPAK_BC_NEUMANN_DIRICHLET) EWC%PRESSURE_BC_TYPE = DIRICHLET
       CASE( 3)
-         IF (NBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. NBC==FISHPAK_BC_NEUMANN_DIRICHLET) WC%PRESSURE_BC_INDEX = NEUMANN
-         IF (NBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. NBC==FISHPAK_BC_DIRICHLET_NEUMANN) WC%PRESSURE_BC_INDEX = DIRICHLET
+         IF (NBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. NBC==FISHPAK_BC_NEUMANN_DIRICHLET) EWC%PRESSURE_BC_TYPE = NEUMANN
+         IF (NBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. NBC==FISHPAK_BC_DIRICHLET_NEUMANN) EWC%PRESSURE_BC_TYPE = DIRICHLET
       CASE(-3)
-         IF (NBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. NBC==FISHPAK_BC_DIRICHLET_NEUMANN) WC%PRESSURE_BC_INDEX = NEUMANN
-         IF (NBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. NBC==FISHPAK_BC_NEUMANN_DIRICHLET) WC%PRESSURE_BC_INDEX = DIRICHLET
+         IF (NBC==FISHPAK_BC_NEUMANN_NEUMANN     .OR. NBC==FISHPAK_BC_DIRICHLET_NEUMANN) EWC%PRESSURE_BC_TYPE = NEUMANN
+         IF (NBC==FISHPAK_BC_DIRICHLET_DIRICHLET .OR. NBC==FISHPAK_BC_NEUMANN_DIRICHLET) EWC%PRESSURE_BC_TYPE = DIRICHLET
    END SELECT
 ENDDO WALL_CELL_LOOP
 
@@ -3543,7 +3545,7 @@ SUBROUTINE INIT_WALL_CELL(NM,I,J,K,OBST_INDEX,IW,IOR,SURF_INDEX,IERR,TT)
 
 ! Record original boundary condition index for exterior wall cells that might get covered up
 
-IF (OBST_INDEX==0) WC%SURF_INDEX_ORIG = SURF_INDEX_NEW
+IF (OBST_INDEX==0 .AND. IW<=M%N_EXTERNAL_WALL_CELLS) EWC%SURF_INDEX_ORIG = SURF_INDEX_NEW
 
 END SUBROUTINE INIT_WALL_CELL
 
@@ -4555,9 +4557,10 @@ SUBROUTINE REASSIGN_WALL_CELLS(T,NM)
 
 SUBROUTINE GET_BOUNDARY_TYPE
 
-INTEGER :: IOR,IIG,JJG,KKG,IW_OLD,IERR,PRESSURE_BC_INDEX,ICG_OLD,II
+INTEGER :: IOR,IIG,JJG,KKG,IW_OLD,IERR,PRESSURE_BC_TYPE,ICG_OLD,II
 TYPE (BOUNDARY_PROP1_TYPE), POINTER :: B1,B1_OLD
 TYPE (WALL_TYPE), POINTER :: WC_OLD
+TYPE (EXTERNAL_WALL_TYPE), POINTER :: EWC
 TYPE (STORAGE_TYPE), POINTER :: OS
 TYPE (SURFACE_TYPE), POINTER :: SF
 
@@ -4565,20 +4568,21 @@ SUBROUTINE GET_BOUNDARY_TYPE
 BC => MESHES(NM)%BOUNDARY_COORD(WC%BC_INDEX)
 
 IF (IW<=N_EXTERNAL_WALL_CELLS .AND. REMOVE) THEN
+   EWC => MESHES(NM)%EXTERNAL_WALL(IW)
    WC%BOUNDARY_TYPE = SOLID_BOUNDARY
    CELL(IC)%SOLID       = .TRUE.
-   IF (WC%SURF_INDEX_ORIG==MIRROR_SURF_INDEX) THEN
+   IF (EWC%SURF_INDEX_ORIG==MIRROR_SURF_INDEX) THEN
       WC%BOUNDARY_TYPE = MIRROR_BOUNDARY
       WC%SURF_INDEX    = MIRROR_SURF_INDEX
       CELL(IC)%SOLID   = .TRUE.
       RETURN
    ENDIF
-   IF (WC%SURF_INDEX_ORIG==OPEN_SURF_INDEX) THEN
+   IF (EWC%SURF_INDEX_ORIG==OPEN_SURF_INDEX) THEN
       WC%BOUNDARY_TYPE = OPEN_BOUNDARY
       WC%SURF_INDEX    = OPEN_SURF_INDEX
       CELL(IC)%SOLID   = .FALSE.
    ENDIF
-   IF (WC%SURF_INDEX_ORIG==INTERPOLATED_SURF_INDEX) THEN
+   IF (EWC%SURF_INDEX_ORIG==INTERPOLATED_SURF_INDEX) THEN
       WC%BOUNDARY_TYPE = INTERPOLATED_BOUNDARY
       WC%SURF_INDEX    = INTERPOLATED_SURF_INDEX
       CELL(IC)%SOLID   = .FALSE.
@@ -4607,7 +4611,9 @@ SUBROUTINE GET_BOUNDARY_TYPE
 IF (WC%BOUNDARY_TYPE/=NULL_BOUNDARY) THEN
    IF (IW<=N_EXTERNAL_WALL_CELLS) THEN
       WC%OBST_INDEX = 0
-      WC%SURF_INDEX = WC%SURF_INDEX_ORIG
+      EWC => EXTERNAL_WALL(IW)
+      WC%SURF_INDEX = EWC%SURF_INDEX_ORIG
+      PRESSURE_BC_TYPE = EWC%PRESSURE_BC_TYPE  ! Save this parameter and restore it after the call to INIT_WALL_CELL
    ENDIF
    IF (CELL(IC)%OBST_INDEX>0) THEN
       WC%OBST_INDEX = CELL(IC)%OBST_INDEX
@@ -4617,10 +4623,9 @@ SUBROUTINE GET_BOUNDARY_TYPE
       WC%SURF_INDEX = OBSTRUCTION(WC%OBST_INDEX)%SURF_INDEX(BC%IOR)
    ENDIF
    IF (OBSTRUCTION(WC%OBST_INDEX)%SURF_INDEX_INTERIOR>0) WC%SURF_INDEX = OBSTRUCTION(WC%OBST_INDEX)%SURF_INDEX_INTERIOR
-   PRESSURE_BC_INDEX = WC%PRESSURE_BC_INDEX  ! Save this parameter and restore it after the call to INIT_WALL_CELL
    CALL INIT_WALL_CELL(NM,BC%II,BC%JJ,BC%KK,WC%OBST_INDEX,IW,BC%IOR,WC%SURF_INDEX,IERR,T)
    WC => MESHES(NM)%WALL(IW)
-   WC%PRESSURE_BC_INDEX = PRESSURE_BC_INDEX
+   IF (IW<=N_EXTERNAL_WALL_CELLS) EWC%PRESSURE_BC_TYPE = PRESSURE_BC_TYPE
 ENDIF
 
 ! Special case: A BURNed_AWAY obstruction exposes a surface that also burns, in which case the surface is to ignite immediately.
diff --git a/Source/pres.f90 b/Source/pres.f90
index f9f5bc351fc..e8c010a71b3 100644
--- a/Source/pres.f90
+++ b/Source/pres.f90
@@ -76,7 +76,7 @@ SUBROUTINE PRESSURE_SOLVER_COMPUTE_RHS(T,DT,NM)
 
    ! Apply pressure gradients at NEUMANN boundaries: dH/dn = -F_n - d(u_n)/dt
 
-   IF_NEUMANN: IF (WC%PRESSURE_BC_INDEX==NEUMANN) THEN
+   IF_NEUMANN: IF (EWC%PRESSURE_BC_TYPE==NEUMANN) THEN
 
       SELECT CASE(IOR)
          CASE( 1)
@@ -96,7 +96,7 @@ SUBROUTINE PRESSURE_SOLVER_COMPUTE_RHS(T,DT,NM)
 
    ! Apply pressures at DIRICHLET boundaries, depending on the specific type
 
-   IF_DIRICHLET: IF (WC%PRESSURE_BC_INDEX==DIRICHLET) THEN
+   IF_DIRICHLET: IF (EWC%PRESSURE_BC_TYPE==DIRICHLET) THEN
 
       NOT_OPEN: IF (WC%BOUNDARY_TYPE/=OPEN_BOUNDARY .AND. WC%BOUNDARY_TYPE/=INTERPOLATED_BOUNDARY) THEN
 
@@ -1126,6 +1126,7 @@ SUBROUTINE ULMAT_SOLVER_SETUP(NM)
 TYPE(ZONE_MESH_TYPE), POINTER :: ZM
 TYPE (MESH_TYPE), POINTER :: M=>NULL()
 TYPE (WALL_TYPE), POINTER :: WC=>NULL()
+TYPE (EXTERNAL_WALL_TYPE), POINTER :: EWC=>NULL()
 TYPE (BOUNDARY_COORD_TYPE), POINTER :: BC
 INTEGER, PARAMETER :: NULL_BTYPE=0,DIRICHLET_BTYPE=1,NEUMANN_BTYPE=2,PERIODIC_BTYPE=3
 
@@ -1207,6 +1208,7 @@ SUBROUTINE ULMAT_SOLVER_SETUP(NM)
       ZBTYPE_LAST=NULL_BTYPE
       WALL_LOOP: DO IW=1,M%N_EXTERNAL_WALL_CELLS
          WC=>M%WALL(IW)
+         EWC=>M%EXTERNAL_WALL(IW)
          BC=>M%BOUNDARY_COORD(WC%BC_INDEX)
          IOR = BC%IOR
          WALL_BTYPE=NULL_BTYPE
@@ -1224,7 +1226,7 @@ SUBROUTINE ULMAT_SOLVER_SETUP(NM)
 
          ! Test for obstructions on an open boundary or mirror set to dirichlet
          IF ( (WC%BOUNDARY_TYPE==SOLID_BOUNDARY .OR. WC%BOUNDARY_TYPE==MIRROR_BOUNDARY) &
-            .AND. WC%PRESSURE_BC_INDEX==DIRICHLET) THEN
+            .AND. EWC%PRESSURE_BC_TYPE==DIRICHLET) THEN
             ZM%USE_FFT=.FALSE.
             EXIT WALL_LOOP
          ENDIF
@@ -1439,6 +1441,7 @@ SUBROUTINE ULMAT_SOLVE_ZONE(NM,IPZ)
 REAL(EB):: SUM_FH(1:2),MEAN_FH,SUM_XH(1:2),MEAN_XH,DIV_FN_VOL,DIV_FN,IDX,AF,VAL,BCV
 TYPE(ZONE_MESH_TYPE), POINTER :: ZM
 TYPE (WALL_TYPE),  POINTER :: WC
+TYPE (EXTERNAL_WALL_TYPE),  POINTER :: EWC
 TYPE (CFACE_TYPE), POINTER :: CFA
 TYPE (BOUNDARY_COORD_TYPE), POINTER :: BC
 REAL(EB), POINTER, DIMENSION(:,:,:) :: HP=>NULL()
@@ -1498,9 +1501,10 @@ SUBROUTINE ULMAT_SOLVE_ZONE(NM,IPZ)
    IFACE= CFA%CUT_FACE_IND1
    JFACE= CFA%CUT_FACE_IND2
    WC  => WALL(CUT_FACE(IFACE)%IWC)
+   EWC  => EXTERNAL_WALL(CUT_FACE(IFACE)%IWC)
    BC  => BOUNDARY_COORD(WC%BC_INDEX)
    ! DIRICHLET boundaries:
-   IF_CFACE_DIRICHLET: IF (WC%PRESSURE_BC_INDEX==DIRICHLET) THEN
+   IF_CFACE_DIRICHLET: IF (EWC%PRESSURE_BC_TYPE==DIRICHLET) THEN
       ! Gasphase cell indexes:
       IIG = BC%IIG; JJG = BC%JJG; KKG = BC%KKG
       IF(ZONE_MESH(PRESSURE_ZONE(IIG,JJG,KKG))%CONNECTED_ZONE_PARENT/=IPZ) CYCLE CFACE_LOOP
@@ -1534,6 +1538,7 @@ SUBROUTINE ULMAT_SOLVE_ZONE(NM,IPZ)
 ! Finally add External Wall cell BCs:
 WALL_CELL_LOOP_1 : DO IW=1,N_EXTERNAL_WALL_CELLS
    WC => WALL(IW)
+   EWC => EXTERNAL_WALL(IW)
    ! Drop if NULL or this is a cut-face. Dealt with external CFACE.
    IF (WC%BOUNDARY_TYPE==NULL_BOUNDARY .OR. WC%CUT_FACE_INDEX>0) CYCLE WALL_CELL_LOOP_1
    BC  => BOUNDARY_COORD(WC%BC_INDEX)
@@ -1541,7 +1546,7 @@ SUBROUTINE ULMAT_SOLVE_ZONE(NM,IPZ)
    IIG = BC%IIG; JJG = BC%JJG; KKG = BC%KKG; IOR = BC%IOR
    IF(ZONE_MESH(PRESSURE_ZONE(IIG,JJG,KKG))%CONNECTED_ZONE_PARENT/=IPZ) CYCLE WALL_CELL_LOOP_1
    ! NEUMANN boundaries:
-   IF_NEUMANN_1: IF (WC%PRESSURE_BC_INDEX==NEUMANN) THEN
+   IF_NEUMANN_1: IF (EWC%PRESSURE_BC_TYPE==NEUMANN) THEN
 
       IROW = MUNKH(IIG,JJG,KKG)
       IF(CC_IBM) THEN
@@ -1577,7 +1582,7 @@ SUBROUTINE ULMAT_SOLVE_ZONE(NM,IPZ)
    ENDIF IF_NEUMANN_1
 
    ! DIRICHLET boundaries:
-   IF_DIRICHLET_1: IF (WC%PRESSURE_BC_INDEX==DIRICHLET) THEN
+   IF_DIRICHLET_1: IF (EWC%PRESSURE_BC_TYPE==DIRICHLET) THEN
       ! Here case where SOLID and OPEN or interpolated are mixed on a boundary:
       IF( WC%BOUNDARY_TYPE==SOLID_BOUNDARY .OR. WC%BOUNDARY_TYPE==MIRROR_BOUNDARY) CYCLE WALL_CELL_LOOP_1
       IROW = MUNKH(IIG,JJG,KKG)
@@ -1779,12 +1784,13 @@ SUBROUTINE ULMAT_SOLVE_ZONE(NM,IPZ)
 ! Fill external boundary conditions for Mesh, if necessary:
 WALL_CELL_LOOP_2 : DO IW=1,N_EXTERNAL_WALL_CELLS
    WC => WALL(IW)
+   EWC => EXTERNAL_WALL(IW)
    BC => BOUNDARY_COORD(WC%BC_INDEX)
    ! Gasphase cell indexes:
    IIG = BC%IIG; JJG = BC%JJG; KKG = BC%KKG; IOR = BC%IOR
-   IF(ZONE_MESH(PRESSURE_ZONE(IIG,JJG,KKG))%CONNECTED_ZONE_PARENT/=IPZ) CYCLE WALL_CELL_LOOP_2
+   IF (ZONE_MESH(PRESSURE_ZONE(IIG,JJG,KKG))%CONNECTED_ZONE_PARENT/=IPZ) CYCLE WALL_CELL_LOOP_2
    ! NEUMANN boundaries:
-   IF_NEUMANN_2 : IF (WC%PRESSURE_BC_INDEX==NEUMANN) THEN
+   IF_NEUMANN_2 : IF (EWC%PRESSURE_BC_TYPE==NEUMANN) THEN
       I   = BC%II;  J   = BC%JJ;  K   = BC%KK
       ! Define cell size, normal to WC:
       SELECT CASE (IOR)
@@ -1804,7 +1810,7 @@ SUBROUTINE ULMAT_SOLVE_ZONE(NM,IPZ)
    ENDIF IF_NEUMANN_2
 
    ! DIRICHLET boundaries:
-   IF_DIRICHLET_2 : IF (WC%PRESSURE_BC_INDEX==DIRICHLET) THEN
+   IF_DIRICHLET_2 : IF (EWC%PRESSURE_BC_TYPE==DIRICHLET) THEN
       I   = BC%II;  J   = BC%JJ;  K   = BC%KK
       ! Define cell size, normal to WC:
       IF (WC%BOUNDARY_TYPE==SOLID_BOUNDARY .OR. WC%BOUNDARY_TYPE==MIRROR_BOUNDARY) THEN
@@ -2933,6 +2939,7 @@ SUBROUTINE GLMAT_SOLVER(T,DT)
 #endif
 INTEGER :: NM, IW, IIG, JJG, KKG, IOR, IROW, I, J, K, ICC
 TYPE (WALL_TYPE), POINTER :: WC=>NULL()
+TYPE (EXTERNAL_WALL_TYPE), POINTER :: EWC=>NULL()
 TYPE (BOUNDARY_COORD_TYPE), POINTER :: BC
 REAL(EB), POINTER, DIMENSION(:,:,:)   :: HP
 REAL(EB) :: SUM_FH(2), SUM_XH(2), MEAN_FH, MEAN_XH
@@ -3105,6 +3112,7 @@ SUBROUTINE GLMAT_SOLVER(T,DT)
       ! Fill external boundary conditions for Mesh, if necesary:
       WALL_CELL_LOOP_2: DO IW=1,N_EXTERNAL_WALL_CELLS
          WC => WALL(IW)
+         EWC => EXTERNAL_WALL(IW)
          BC => BOUNDARY_COORD(WC%BC_INDEX)
 
          IIG = BC%IIG; JJG = BC%JJG; KKG = BC%KKG
@@ -3112,7 +3120,7 @@ SUBROUTINE GLMAT_SOLVER(T,DT)
          I = BC%II; J = BC%JJ; K = BC%KK; IOR = BC%IOR
 
          ! NEUMANN boundaries:
-         IF_NEUMANN2: IF (WC%PRESSURE_BC_INDEX==NEUMANN) THEN
+         IF_NEUMANN2: IF (EWC%PRESSURE_BC_TYPE==NEUMANN) THEN
             ! Define cell size, normal to WC:
             SELECT CASE (IOR)
                CASE(-1) ! -IAXIS oriented, high face of IIG cell.
@@ -3131,7 +3139,7 @@ SUBROUTINE GLMAT_SOLVER(T,DT)
          ENDIF IF_NEUMANN2
 
          ! DIRICHLET boundaries:
-         IF_DIRICHLET2: IF (WC%PRESSURE_BC_INDEX==DIRICHLET) THEN
+         IF_DIRICHLET2: IF (EWC%PRESSURE_BC_TYPE==DIRICHLET) THEN
             IF (WC%BOUNDARY_TYPE==INTERPOLATED_BOUNDARY .OR. &
                 WC%BOUNDARY_TYPE==        NULL_BOUNDARY ) CYCLE ! No need for these, that's the whole point of a
                                                                 ! global solve.
@@ -3296,6 +3304,7 @@ SUBROUTINE CHECK_UNSUPPORTED_MESH(SUPPORTED_MESH)
 LOGICAL, ALLOCATABLE, DIMENSION(:)   :: COUNTED
 INTEGER, ALLOCATABLE, DIMENSION(:)   :: DIRI_SET,MESH_LIST
 TYPE (WALL_TYPE), POINTER :: WC=>NULL()
+TYPE (EXTERNAL_WALL_TYPE), POINTER :: EWC=>NULL()
 
 INTEGER :: NOM,IW,NMLOC,NSETS,ISET,PIVOT,PIVOT_LOC,MESHES_LEFT,CTMSH_LO,CTMSH_HI
 
@@ -3447,7 +3456,8 @@ SUBROUTINE CHECK_UNSUPPORTED_MESH(SUPPORTED_MESH)
       ! OPEN_BOUNDARY condition.
       DO IW=1,N_EXTERNAL_WALL_CELLS
          WC => WALL(IW)
-         IF (WC%PRESSURE_BC_INDEX==DIRICHLET .AND. WC%BOUNDARY_TYPE==OPEN_BOUNDARY) DIRI_SET(ISET) = 1
+         EWC => EXTERNAL_WALL(IW)
+         IF (EWC%PRESSURE_BC_TYPE==DIRICHLET .AND. WC%BOUNDARY_TYPE==OPEN_BOUNDARY) DIRI_SET(ISET) = 1
       ENDDO
    ENDDO
 ENDDO SETS_LOOP
diff --git a/Source/type.f90 b/Source/type.f90
index 49435b353ad..da824976054 100644
--- a/Source/type.f90
+++ b/Source/type.f90
@@ -395,9 +395,7 @@ MODULE TYPES
    INTEGER :: BACK_MESH=0             !< Mesh number on back side of obstruction or exterior wall cell
    INTEGER :: BACK_SURF=0             !< SURF_INDEX on back side of obstruction or exterior wall cell
    INTEGER :: BOUNDARY_TYPE=0         !< Descriptor: SOLID, MIRROR, OPEN, INTERPOLATED, etc
-   INTEGER :: SURF_INDEX_ORIG=0       !< Original SURFace index for this cell
    INTEGER :: OBST_INDEX=0            !< Index of the OBSTruction
-   INTEGER :: PRESSURE_BC_INDEX       !< Poisson boundary condition, NEUMANN or DIRICHLET
    INTEGER :: VENT_INDEX=0            !< Index of the VENT containing this cell
    INTEGER :: JD11_INDEX=0
    INTEGER :: JD12_INDEX=0
@@ -424,6 +422,8 @@ MODULE TYPES
    INTEGER :: JJO_MAX                                 !< Maximum J index of adjacent cell in other mesh
    INTEGER :: KKO_MIN                                 !< Minimum K index of adjacent cell in other mesh
    INTEGER :: KKO_MAX                                 !< Maximum K index of adjacent cell in other mesh
+   INTEGER :: PRESSURE_BC_TYPE                        !< Poisson boundary condition, NEUMANN or DIRICHLET
+   INTEGER :: SURF_INDEX_ORIG=0                       !< Original SURFace index for this cell
    REAL(EB) :: AREA_RATIO                             !< Ratio of face areas of adjoining cells
    REAL(EB), ALLOCATABLE, DIMENSION(:) :: FVN         !< Flux-limited \f$ \int \rho Y_\alpha u_n \f$
    REAL(EB), ALLOCATABLE, DIMENSION(:) :: FVNS        !< Estimated value of FVN at next time step