diff --git a/civpy/math/linalg.py b/civpy/math/linalg.py
index baba4a1..1ccd4ea 100644
--- a/civpy/math/linalg.py
+++ b/civpy/math/linalg.py
@@ -1,3 +1,7 @@
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
 import numpy as np
 from math import cos, sin
 
diff --git a/civpy/math/optimize.py b/civpy/math/optimize.py
index a53833b..d7934d4 100644
--- a/civpy/math/optimize.py
+++ b/civpy/math/optimize.py
@@ -1,3 +1,7 @@
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
 import scipy.optimize
 
 __all__ = ['fsolve']
diff --git a/civpy/structures/element.py b/civpy/structures/element.py
index 04ca36e..176c68a 100644
--- a/civpy/structures/element.py
+++ b/civpy/structures/element.py
@@ -1,5 +1,10 @@
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
 import copy
-import propy
+import attr
+import weakref
 import numpy as np
 from math import cos, sin
 from functools import lru_cache
@@ -153,6 +158,7 @@ def clear_element_cache():
     transformation_matrix.cache_clear()
 
 
+@attr.s(hash=False)
 class Element(object):
     """
     A class representing a structural element.
@@ -174,57 +180,62 @@ class Element(object):
     jmx_free, jmy_free, jmz_free : bool
         The rotational fixities at the j-node about the local x, y, and z axes.
     """
-    SYMMETRIES = (None, 'x', 'y', 'xy')
+    P = 'p'
+    X = 'x'
+    Y = 'y'
+    XY = 'xy'
+    SYMMETRIES = (None, X, Y, XY)
 
     TRANSFORMS = {
-        'x': {'p': 'x', 'x': 'p', 'y': 'xy', 'xy': 'y'},
-        'y': {'p': 'y', 'x': 'xy', 'y': 'p', 'xy': 'x'},
+        X: {P: X, X: P, Y: XY, XY: Y},
+        Y: {P: Y, X: XY, Y: P, XY: X},
     }
 
-    # Custom properties
-    name = propy.str_property('name')
-    inode = propy.str_property('inode_name')
-    jnode = propy.str_property('jnode_name')
-    symmetry = propy.enum_property('symmetry', set(SYMMETRIES))
-
-    imx_free = propy.bool_property('imx_free')
-    imy_free = propy.bool_property('imy_free')
-    imz_free = propy.bool_property('imz_free')
-
-    jmx_free = propy.bool_property('jmx_free')
-    jmy_free = propy.bool_property('jmy_free')
-    jmz_free = propy.bool_property('jmz_free')
-
-    inode_ref = propy.weakref_property('inode_ref')
-    jnode_ref = propy.weakref_property('jnode_ref')
-
-    def __init__(self, name, inode, jnode, group,
-                 symmetry=None, roll=0, unstr_length=None,
-                 imx_free=False, imy_free=False, imz_free=False,
-                 jmx_free=False, jmy_free=False, jmz_free=False):
-        self.name = name
-        self.inode = inode
-        self.jnode = jnode
-        self.group = group
-        self.symmetry = symmetry
-        self.roll = roll
-        self.unstr_length = unstr_length
-
-        self.imx_free = imx_free
-        self.imy_free = imy_free
-        self.imz_free = imz_free
-
-        self.jmx_free = jmx_free
-        self.jmy_free = jmy_free
-        self.jmz_free = jmz_free
-
-        self.inode_ref = None
-        self.jnode_ref = None
-
-    __repr__ = propy.repr_method(
-        'name', 'inode', 'jnode', 'group', 'symmetry', 'roll',
-        'imx_free', 'imy_free', 'imz_free', 'jmx_free', 'jmy_free', 'jmz_free'
-    )
+    name = attr.ib(converter=str)
+    inode = attr.ib()
+    jnode = attr.ib()
+    group = attr.ib()
+    symmetry = attr.ib(default=None, validator=attr.validators.in_(SYMMETRIES))
+    roll = attr.ib(default=0)
+    unstr_length = attr.ib(default=None)
+    imx_free = attr.ib(default=False)
+    imy_free = attr.ib(default=False)
+    imz_free = attr.ib(default=False)
+    jmx_free = attr.ib(default=False)
+    jmy_free = attr.ib(default=False)
+    jmz_free = attr.ib(default=False)
+    _inode_ref = attr.ib(default=None, init=False, repr=False)
+    _jnode_ref = attr.ib(default=None, init=False, repr=False)
+
+    def inode_ref():
+        def fget(self):
+            value = self._inode_ref
+            if value is None:
+                return value
+            return value()
+        def fset(self, value):
+            if value is not None:
+                value = weakref.ref(value)
+            self._inode_ref = value
+        def fdel(self):
+            del self._inode_ref
+        return locals()
+    inode_ref = property(**inode_ref())
+
+    def jnode_ref():
+        def fget(self):
+            value = self._jnode_ref
+            if value is None:
+                return value
+            return value()
+        def fset(self, value):
+            if value is not None:
+                value = weakref.ref(value)
+            self._jnode_ref = value
+        def fdel(self):
+            del self._jnode_ref
+        return locals()
+    jnode_ref = property(**jnode_ref())
 
     def __str__(self):
         return self.name
diff --git a/civpy/structures/element_group.py b/civpy/structures/element_group.py
index f1f6a0f..c81f465 100644
--- a/civpy/structures/element_group.py
+++ b/civpy/structures/element_group.py
@@ -1,8 +1,13 @@
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
+import attr
 
 __all__ = ['ElementGroup']
 
 
+@attr.s(hash=False)
 class ElementGroup(object):
     """
     A class representing a group of element properties.
@@ -16,12 +21,6 @@ class ElementGroup(object):
     material : :class:`.Material`
         The group material.
     """
-    # Custom properties
-    name = propy.str_property('name')
-
-    def __init__(self, name, section, material):
-        self.name = name
-        self.section = section
-        self.material = material
-
-    __repr__ = propy.repr_method('name', 'section', 'material')
+    name = attr.ib()
+    section = attr.ib()
+    material = attr.ib()
diff --git a/civpy/structures/element_load.py b/civpy/structures/element_load.py
index 3fae3cb..ed0336a 100644
--- a/civpy/structures/element_load.py
+++ b/civpy/structures/element_load.py
@@ -1,4 +1,8 @@
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
+import weakref
 import numpy as np
 from functools import lru_cache
 from .element import transformation_matrix
@@ -248,16 +252,6 @@ class ElementLoad(np.ndarray):
         The distance from the ix position toward the j node over which
         the loads are applied.
     """
-    # Custom properties
-    element = propy.str_property('element')
-    fx = propy.index_property(0)
-    fy = propy.index_property(1)
-    fz = propy.index_property(2)
-    mx = propy.index_property(3)
-    my = propy.index_property(4)
-    mz = propy.index_property(5)
-    _element_ref = propy.weakref_property('_element_ref')
-
     def __new__(cls, element, fx=0, fy=0, fz=0, mx=0, my=0, mz=0, ix=0, dx=-1):
         obj = np.array([fx, fy, fz, mx, my, mz], dtype='float').view(cls)
         obj.element = element
@@ -270,7 +264,82 @@ def __array_finalize__(self, obj):
         self.element = getattr(obj, 'element', '')
         self.ix = getattr(obj, 'ix', 0)
         self.dx = getattr(obj, 'dx', 0)
-        self._element_ref = None
+        self.element_ref = None
+
+    def element():
+        def fget(self):
+            return self._element
+        def fset(self, value):
+            if not isinstance(value, str):
+                value = str(value)
+            self._element = value
+        def fdel(self):
+            del self._element
+        return locals()
+    element = property(**element())
+
+    def element_ref():
+        def fget(self):
+            value = self._element_ref
+            if value is None:
+                return value
+            return value()
+        def fset(self, value):
+            if value is not None:
+                value = weakref.ref(value)
+            self._element_ref = value
+        def fdel(self):
+            del self._element_ref
+        return locals()
+    element_ref = property(**element_ref())
+
+    def fx():
+        def fget(self):
+            return self[0]
+        def fset(self, value):
+            self[0] = value
+        return locals()
+    fx = property(**fx())
+
+    def fy():
+        def fget(self):
+            return self[1]
+        def fset(self, value):
+            self[1] = value
+        return locals()
+    fy = property(**fy())
+
+    def fz():
+        def fget(self):
+            return self[2]
+        def fset(self, value):
+            self[2] = value
+        return locals()
+    fz = property(**fz())
+
+    def mx():
+        def fget(self):
+            return self[3]
+        def fset(self, value):
+            self[3] = value
+        return locals()
+    mx = property(**mx())
+
+    def my():
+        def fget(self):
+            return self[4]
+        def fset(self, value):
+            self[4] = value
+        return locals()
+    my = property(**my())
+
+    def mz():
+        def fget(self):
+            return self[5]
+        def fset(self, value):
+            self[5] = value
+        return locals()
+    mz = property(**mz())
 
     def __repr__(self):
         s = [
@@ -278,7 +347,7 @@ def __repr__(self):
             'forces={!r}'.format((self.fx, self.fy, self.fz)),
             'moments={!r}'.format((self.mx, self.my, self.mz)),
             'ix={!r}'.format(self.ix),
-            'dx={!r}'.format(self.dx)
+            'dx={!r}'.format(self.dx),
         ]
 
         return '{}({})'.format(type(self).__name__, ', '.join(s))
diff --git a/civpy/structures/load_case.py b/civpy/structures/load_case.py
index 3566c3b..3e4f97c 100644
--- a/civpy/structures/load_case.py
+++ b/civpy/structures/load_case.py
@@ -1,8 +1,13 @@
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
+import attr
 
 __all__ = ['LoadCase']
 
 
+@attr.s(hash=False)
 class LoadCase(object):
     """
     A class representing a structural load case.
@@ -17,14 +22,9 @@ class LoadCase(object):
         A list of :class:`.ElementLoad` to apply with the load case.
     """
     # Custom properties
-    name = propy.str_property('name')
-
-    def __init__(self, name, node_loads=[], elem_loads=[]):
-        self.name = name
-        self.node_loads = node_loads
-        self.elem_loads = elem_loads
-
-    __repr__ = propy.repr_method('name', 'node_loads', 'elem_loads')
+    name = attr.ib()
+    node_loads = attr.ib(default=[])
+    elem_loads = attr.ib(default=[])
 
     def set_nodes(self, ndict):
         """
diff --git a/civpy/structures/material.py b/civpy/structures/material.py
index 3a8dc3a..906e5e8 100644
--- a/civpy/structures/material.py
+++ b/civpy/structures/material.py
@@ -1,8 +1,13 @@
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
+import attr
 
 __all__ = ['Material']
 
 
+@attr.s(hash=False)
 class Material(object):
     """
     A class representing an engineered material.
@@ -16,12 +21,6 @@ class Material(object):
     rigidity : float
         The modulus of rigidity.
     """
-    # Custom properties
-    name = propy.str_property('name')
-
-    def __init__(self, name, elasticity, rigidity=0):
-        self.name = name
-        self.elasticity = elasticity
-        self.rigidity = rigidity
-
-    __repr__ = propy.repr_method('name', 'elasticity', 'rigidity')
+    name = attr.ib()
+    elasticity = attr.ib()
+    rigidity = attr.ib(default=0)
diff --git a/civpy/structures/node.py b/civpy/structures/node.py
index dee5ff9..5e436ab 100644
--- a/civpy/structures/node.py
+++ b/civpy/structures/node.py
@@ -1,5 +1,8 @@
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
 import copy
-import propy
 import numpy as np
 
 __all__ = ['Node']
@@ -22,22 +25,10 @@ class Node(np.ndarray):
     mx_free, my_free, mz_free : bool
         The moment fixities of the node about the x, y, and z axes.
     """
-    SYMMETRIES = (None, 'x', 'y', 'xy')
-
-    # Custom properties
-    name = propy.str_property('name')
-    x = propy.index_property(0)
-    y = propy.index_property(1)
-    z = propy.index_property(2)
-    symmetry = propy.enum_property('symmetry', set(SYMMETRIES))
-
-    fx_free = propy.bool_property('fx_free')
-    fy_free = propy.bool_property('fy_free')
-    fz_free = propy.bool_property('fz_free')
-
-    mx_free = propy.bool_property('mx_free')
-    my_free = propy.bool_property('my_free')
-    mz_free = propy.bool_property('mz_free')
+    X = 'x'
+    Y = 'y'
+    XY = 'xy'
+    SYMMETRIES = (None, X, Y, XY)
 
     def __new__(cls, name, x=0, y=0, z=0, symmetry=None,
                 fx_free=True, fy_free=True, fz_free=True,
@@ -71,8 +62,59 @@ def __array_finalize__(self, obj):
         self.my_free = getattr(obj, 'my_free', True)
         self.mz_free = getattr(obj, 'mz_free', True)
 
-    __repr__ = propy.repr_method('name', 'x', 'y', 'z', 'symmetry',
-        'fx_free', 'fy_free', 'fz_free', 'mx_free', 'my_free', 'mz_free')
+    def x():
+        def fget(self):
+            return self[0]
+        def fset(self, value):
+            self[0] = value
+        return locals()
+    x = property(**x())
+
+    def y():
+        def fget(self):
+            return self[1]
+        def fset(self, value):
+            self[1] = value
+        return locals()
+    y = property(**y())
+
+    def z():
+        def fget(self):
+            return self[2]
+        def fset(self, value):
+            self[2] = value
+        return locals()
+    z = property(**z())
+
+    def symmetry():
+        def fget(self):
+            return self._symmetry
+        def fset(self, value):
+            if value not in self.SYMMETRIES:
+                raise ValueError('Type {!r} must be in {!r}.'.format(value, self.SYMMETRIES))
+            self._symmetry = value
+        def fdel(self):
+            del self._symmetry
+        return locals()
+    symmetry = property(**symmetry())
+
+    def __repr__(self):
+        s = [
+            ('name', self.name),
+            ('x', self.x),
+            ('y', self.y),
+            ('z', self.z),
+            ('symmetry', self.symmetry),
+            ('fx_free', self.fx_free),
+            ('fy_free', self.fy_free),
+            ('fz_free', self.fz_free),
+            ('mx_free', self.mx_free),
+            ('my_free', self.my_free),
+            ('mz_free', self.mz_free),
+        ]
+
+        s = ', '.join('{}={!r}'.format(x, y) for x, y in s)
+        return '{}({})'.format(type(self).__name__, s)
 
     def __str__(self):
         return self.name
diff --git a/civpy/structures/node_load.py b/civpy/structures/node_load.py
index 685c99d..f1c958a 100644
--- a/civpy/structures/node_load.py
+++ b/civpy/structures/node_load.py
@@ -1,4 +1,8 @@
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
+import weakref
 import numpy as np
 
 __all__ = ['NodeLoad']
@@ -21,22 +25,6 @@ class NodeLoad(np.ndarray):
     rx, ry, rz : float
         The applied node rotations.
     """
-    # Custom properties
-    node = propy.str_property('node')
-    _node_ref = propy.weakref_property('_node_ref')
-    fx = propy.index_property(0)
-    fy = propy.index_property(1)
-    fz = propy.index_property(2)
-    mx = propy.index_property(3)
-    my = propy.index_property(4)
-    mz = propy.index_property(5)
-    dx = propy.index_property(6)
-    dy = propy.index_property(7)
-    dz = propy.index_property(8)
-    rx = propy.index_property(9)
-    ry = propy.index_property(10)
-    rz = propy.index_property(11)
-
     def __new__(cls, node, fx=0, fy=0, fz=0, mx=0, my=0, mz=0,
                 dx=0, dy=0, dz=0, rx=0, ry=0, rz=0):
         obj = np.array([fx, fy, fz, mx, my, mz,
@@ -47,7 +35,142 @@ def __new__(cls, node, fx=0, fy=0, fz=0, mx=0, my=0, mz=0,
     def __array_finalize__(self, obj):
         if obj is None: return
         self.node = getattr(obj, 'node', '')
-        self._node_ref = None
+        self.node_ref = None
+
+    def node():
+        def fget(self):
+            return self._node
+        def fset(self, value):
+            if not isinstance(value, str):
+                value = str(value)
+            self._node = value
+        def fdel(self):
+            del self._node
+        return locals()
+    node = property(**node())
+
+    def node_ref():
+        def fget(self):
+            value = self._node_ref
+            if value is None:
+                return value
+            return value()
+        def fset(self, value):
+            if value is not None:
+                value = weakref.ref(value)
+            self._node_ref = value
+        def fdel(self):
+            del self._node_ref
+        return locals()
+    node_ref = property(**node_ref())
+
+    def fx():
+        def fget(self):
+            return self[0]
+        def fset(self, value):
+            self[0] = value
+        return locals()
+    fx = property(**fx())
+
+    def fy():
+        def fget(self):
+            return self[1]
+        def fset(self, value):
+            self[1] = value
+        return locals()
+    fy = property(**fy())
+
+    def fz():
+        def fget(self):
+            return self[2]
+        def fset(self, value):
+            self[2] = value
+        return locals()
+    fz = property(**fz())
+
+    def mx():
+        def fget(self):
+            return self[3]
+        def fset(self, value):
+            self[3] = value
+        return locals()
+    mx = property(**mx())
+
+    def my():
+        def fget(self):
+            return self[4]
+        def fset(self, value):
+            self[4] = value
+        return locals()
+    my = property(**my())
+
+    def mz():
+        def fget(self):
+            return self[5]
+        def fset(self, value):
+            self[5] = value
+        return locals()
+    mz = property(**mz())
+
+    def dx():
+        def fget(self):
+            return self[6]
+        def fset(self, value):
+            self[6] = value
+        def fdel(self):
+            del self._dx
+        return locals()
+    dx = property(**dx())
+
+    def dy():
+        def fget(self):
+            return self[7]
+        def fset(self, value):
+            self[7] = value
+        def fdel(self):
+            del self._dy
+        return locals()
+    dy = property(**dy())
+
+    def dz():
+        def fget(self):
+            return self[8]
+        def fset(self, value):
+            self[8] = value
+        def fdel(self):
+            del self._dz
+        return locals()
+    dz = property(**dz())
+
+    def rx():
+        def fget(self):
+            return self[9]
+        def fset(self, value):
+            self[9] = value
+        def fdel(self):
+            del self._rx
+        return locals()
+    rx = property(**rx())
+
+    def ry():
+        def fget(self):
+            return self[10]
+        def fset(self, value):
+            self[10] = value
+        def fdel(self):
+            del self._ry
+        return locals()
+    ry = property(**ry())
+
+    def rz():
+        def fget(self):
+            return self[11]
+        def fset(self, value):
+            self[11] = value
+        def fdel(self):
+            del self._rz
+        return locals()
+    rz = property(**rz())
 
     def __repr__(self):
         s = [
@@ -70,9 +193,9 @@ def deflections(self):
 
     def get_node(self):
         """Gets the referenced node."""
-        if self._node_ref is None:
+        if self.node_ref is None:
             raise ValueError('Node has not been set.')
-        return self._node_ref
+        return self.node_ref
 
     def set_node(self, ndict):
         """
@@ -83,4 +206,4 @@ def set_node(self, ndict):
         ndict : dict
             A dictionary mapping node names to node objects.
         """
-        self._node_ref = ndict[self.node]
+        self.node_ref = ndict[self.node]
diff --git a/civpy/structures/structure.py b/civpy/structures/structure.py
index db9441d..cad2d22 100644
--- a/civpy/structures/structure.py
+++ b/civpy/structures/structure.py
@@ -1,4 +1,8 @@
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
+import attr
 import inspect
 import numpy as np
 import pandas as pd
@@ -25,7 +29,7 @@ def index(lst, s):
     @wraps(func)
     def wrapper(obj, *args, **kwargs):
         # If already built, perform the operation
-        if obj.build:
+        if obj._build:
             return func(obj, *args, **kwargs)
 
         # If not built, build it, perform the operation, and destroy the build
@@ -41,7 +45,7 @@ def wrapper(obj, *args, **kwargs):
 
         obj._create_build(lc)
         result = func(obj, *args, **kwargs)
-        obj.build.clear()
+        obj._build.clear()
         clear_element_cache()
         clear_element_load_cache()
 
@@ -53,6 +57,7 @@ def wrapper(obj, *args, **kwargs):
     return wrapper
 
 
+@attr.s(hash=False)
 class Structure(object):
     """
     A class representing a structure.
@@ -76,16 +81,11 @@ class Structure(object):
     .. plot:: ../examples/structures/structure_ex1.py
         :include-source:
     """
-    # Custom properties
-    name = propy.str_property('name')
-    symmetry = propy.bool_property('symmetry')
-
-    def __init__(self, name, nodes, elements, symmetry=False):
-        self.name = name
-        self.nodes = nodes
-        self.elements = elements
-        self.symmetry = symmetry
-        self.build = {}
+    name = attr.ib()
+    nodes = attr.ib()
+    elements = attr.ib()
+    symmetry = attr.ib(default=False)
+    _build = attr.ib(default={}, init=False, repr=False)
 
     def _create_build(self, load_cases=[]):
         """
@@ -125,7 +125,7 @@ def _create_build(self, load_cases=[]):
         ndict = {n.name: 6*i for i, n in enumerate(nodes)}
         edict = {e.name: i for i, e in enumerate(elements)}
 
-        self.build = {
+        self._build = {
             'nodes': nodes,
             'elements': elements,
             'ndict': ndict,
@@ -150,7 +150,7 @@ def plot_3d(self, ax=None, symbols={}):
                 * 'elements': The element lines, default is 'b--'.
         """
         # Build the structure
-        x = np.array(self.build['nodes'])
+        x = np.array(self._build['nodes'])
 
         # Create figure is one not provided
         if ax is None:
@@ -182,13 +182,13 @@ def plot_3d(self, ax=None, symbols={}):
 
         # Plot elements
         if sym['elements'] is not None:
-            for e in self.build['elements']:
+            for e in self._build['elements']:
                 e = np.array(e.get_nodes())
                 ax.plot(e[:,0], e[:,1], e[:,2], sym['elements'])
 
         # Plot element text
         if sym['etext'] is not None:
-            for e in self.build['elements']:
+            for e in self._build['elements']:
                 p, q = e.get_nodes()
                 p = (q - p) / 3 + p
                 ax.text(p[0], p[1], p[2], e.name, ha='center',
@@ -200,7 +200,7 @@ def plot_3d(self, ax=None, symbols={}):
 
         # Plot node text
         if sym['ntext'] is not None:
-            for n in self.build['nodes']:
+            for n in self._build['nodes']:
                 ax.text(n[0], n[1], n[2], n.name, color=sym['ntext'])
 
         return ax
@@ -226,7 +226,7 @@ def plot_2d(self, ax=None, angle_x=0, angle_y=0,
         """
         # Build the structure
         r = rotation_matrix3(angle_x, angle_y, angle_z).T
-        x = np.array(self.build['nodes']).dot(r)
+        x = np.array(self._build['nodes']).dot(r)
 
         # Create figure is one not provided
         if ax is None:
@@ -255,13 +255,13 @@ def plot_2d(self, ax=None, angle_x=0, angle_y=0,
 
         # Plot elements
         if sym['elements'] is not None:
-            for e in self.build['elements']:
+            for e in self._build['elements']:
                 e = np.array(e.get_nodes()).dot(r)
                 ax.plot(e[:,0], e[:,1], sym['elements'])
 
         # Plot element text
         if sym['etext'] is not None:
-            for e in self.build['elements']:
+            for e in self._build['elements']:
                 p = np.array(e.get_nodes()).dot(r)
                 p = (p[1] - p[0]) / 3 + p[0]
                 ax.text(p[0], p[1], e.name, ha='center',
@@ -273,7 +273,7 @@ def plot_2d(self, ax=None, angle_x=0, angle_y=0,
 
         # Plot node text
         if sym['ntext'] is not None:
-            for n in self.build['nodes']:
+            for n in self._build['nodes']:
                 p = n.dot(r)
                 ax.text(p[0], p[1], n.name, color=sym['ntext'])
 
@@ -290,9 +290,9 @@ def global_stiffness(self, defl=None):
             The deflection matrix. If None, all deflections will be
             assumed to be zero.
         """
-        n = len(self.build['nodes'])
+        n = len(self._build['nodes'])
         k = np.zeros((6*n, 6*n), dtype='float')
-        ndict = self.build['ndict']
+        ndict = self._build['ndict']
 
         if defl is None:
             defl = np.zeros(6*n)
@@ -319,9 +319,9 @@ def global_node_loads(self, lc):
         lc : :class:`.LoadCase`
             The applied load case.
         """
-        n = len(self.build['nodes'])
+        n = len(self._build['nodes'])
         q = np.zeros(6*n, dtype='float')
-        ndict = self.build['ndict']
+        ndict = self._build['ndict']
 
         for n in lc.node_loads:
             i = ndict[n.node]
@@ -341,11 +341,11 @@ def local_elem_loads(self, lc, defl=None):
         defl : array
             The global node deflections.
         """
-        n = len(self.build['nodes'])
-        m = len(self.build['elements'])
+        n = len(self._build['nodes'])
+        m = len(self._build['elements'])
         q = np.zeros((m, 12), dtype='float')
-        ndict = self.build['ndict']
-        edict = self.build['edict']
+        ndict = self._build['ndict']
+        edict = self._build['edict']
 
         if defl is None:
             defl = np.zeros(6*n)
@@ -370,9 +370,9 @@ def global_elem_loads(self, lc, defl=None):
         defl : array
             The global node deflections.
         """
-        n = len(self.build['nodes'])
+        n = len(self._build['nodes'])
         q = np.zeros(6*n, dtype='float')
-        ndict = self.build['ndict']
+        ndict = self._build['ndict']
 
         if defl is None:
             defl = np.zeros(6*n)
@@ -398,9 +398,9 @@ def global_defl(self, lc):
         lc : :class:`.LoadCase`
             The applied load case.
         """
-        n = len(self.build['nodes'])
+        n = len(self._build['nodes'])
         d = np.zeros(6*n, dtype='float')
-        ndict = self.build['ndict']
+        ndict = self._build['ndict']
 
         for n in lc.node_loads:
             i = ndict[n.node]
@@ -417,16 +417,16 @@ def _create_summary(self, r):
         r : dict
             A dictionary of result arrays.
         """
-        n = len(self.build['nodes'])
-        m = len(self.build['elements'])
-        lc = self.build['load_cases']
+        n = len(self._build['nodes'])
+        m = len(self._build['elements'])
+        lc = self._build['load_cases']
         u = [x.fixities() for x in self.nodes] * len(lc)
         u = np.array(u, dtype='bool')
 
         # Global load data frame
         df1 = pd.DataFrame()
         df1['load_case'] = np.array([[l.name] * n for l in lc]).ravel()
-        df1['node'] = [x.name for x in self.build['nodes']] * len(lc)
+        df1['node'] = [x.name for x in self._build['nodes']] * len(lc)
 
         # Process global forces
         x = np.array(r.pop('glob_force')).reshape(-1, 6)
@@ -466,7 +466,7 @@ def _create_summary(self, r):
         # Local reaction data frame
         df3 = pd.DataFrame()
         df3['load_case'] = np.array([[l.name] * m for l in lc]).ravel()
-        df3['element'] = [x.name for x in self.build['elements']] * len(lc)
+        df3['element'] = [x.name for x in self._build['elements']] * len(lc)
 
         # Process local forces
         x = np.array(r.pop('loc_force')).reshape(-1, 12)
@@ -516,9 +516,9 @@ def linear_analysis(self, lc):
         lc : :class:`.LoadCase` or list
             A load case or list of load cases to perform analysis for.
         """
-        n = len(self.build['nodes'])
+        n = len(self._build['nodes'])
         k = self.global_stiffness()
-        ndict = self.build['ndict']
+        ndict = self._build['ndict']
 
         # Result dictionary
         r = dict(glob_force=[], glob_defl=[], loc_force=[], loc_defl=[])
@@ -536,7 +536,7 @@ def linear_analysis(self, lc):
         ki = np.linalg.inv(k[u][:,u])
         kuv = k[u][:,v]
 
-        for l in self.build['load_cases']:
+        for l in self._build['load_cases']:
             # Find unknown deflections and global forces
             d = self.global_defl(l)
             q = self.global_node_loads(l)
@@ -552,7 +552,7 @@ def linear_analysis(self, lc):
             # Find local forces
             q = self.local_elem_loads(l)
 
-            for m, e in enumerate(self.build['elements']):
+            for m, e in enumerate(self._build['elements']):
                 i, j = ndict[e.inode], ndict[e.jnode]
                 dl = np.array([d[i:i+6], d[j:j+6]]).ravel()
                 dl = e.transformation_matrix().dot(dl)
diff --git a/civpy/structures/structure_test.py b/civpy/structures/structure_test.py
index 585a6f6..ec735d3 100644
--- a/civpy/structures/structure_test.py
+++ b/civpy/structures/structure_test.py
@@ -37,7 +37,7 @@ def Structure1():
 def test_rotation_matrix():
     struct = Structure1()
     struct._create_build()
-    e1, e2, e3 = struct.build['elements']
+    e1, e2, e3 = struct._build['elements']
 
     a = e1.rotation_matrix().ravel()
     b = np.identity(3).ravel()
@@ -58,7 +58,7 @@ def test_rotation_matrix():
 def test_transformation_matrix():
     struct = Structure1()
     struct._create_build()
-    e1, e2, e3 = struct.build['elements']
+    e1, e2, e3 = struct._build['elements']
 
     a = e1.transformation_matrix().ravel()
     b = np.identity(12).ravel()
@@ -85,7 +85,7 @@ def test_transformation_matrix():
 def test_length():
     struct = Structure1()
     struct._create_build()
-    e1, e2, e3 = struct.build['elements']
+    e1, e2, e3 = struct._build['elements']
 
     a = e1.length()
     assert pytest.approx(a) == 240
@@ -100,7 +100,7 @@ def test_length():
 def test_local_stiffness():
     struct = Structure1()
     struct._create_build()
-    e1, _, _ = struct.build['elements']
+    e1, _, _ = struct._build['elements']
 
     a = e1.local_stiffness().ravel()
     b = np.array([
@@ -124,7 +124,7 @@ def test_local_stiffness():
 def test_global_stiffness():
     struct = Structure1()
     struct._create_build()
-    e1, e2, e3 = struct.build['elements']
+    e1, e2, e3 = struct._build['elements']
 
     a = e1.global_stiffness().ravel()
     b = np.array([
diff --git a/civpy/survey/alignment.py b/civpy/survey/alignment.py
index 9b324c0..f756dfd 100644
--- a/civpy/survey/alignment.py
+++ b/civpy/survey/alignment.py
@@ -1,5 +1,8 @@
-from __future__ import division
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
+import attr
 import numpy as np
 import matplotlib.pyplot as plt
 from .spatial_hash import SpatialHash
@@ -7,6 +10,7 @@
 __all__ = ['Alignment']
 
 
+@attr.s(hash=False)
 class Alignment(object):
     """
     A class representing a survey alignment.
@@ -34,22 +38,16 @@ class Alignment(object):
     .. plot:: ../examples/survey/alignment_ex1.py
         :include-source:
     """
+    # Global class variables
     BISC_TOL = 1e-4 # Bisector station tolerance
 
-    # Custom properties
-    name = propy.str_property('name')
-
-    def __init__(self, name, pis=[], stakes=[], grid=10, view_offset=15,
-                 view_margin=15):
-        self.name = name
-        self.pis = pis
-        self.stakes = stakes
-        self.grid = grid
-        self.view_offset = view_offset
-        self.view_margin = view_margin
-
-    __repr__ = propy.repr_method('name', 'grid', 'view_offset', 'view_margin',
-                                 'pis', 'stakes')
+    # Properties
+    name = attr.ib()
+    pis = attr.ib(default=[])
+    stakes = attr.ib(default=[])
+    grid = attr.ib(default=10)
+    view_offset = attr.ib(default=15)
+    view_margin = attr.ib(default=15)
 
     def set_stake_xy(self):
         """
diff --git a/civpy/survey/pi.py b/civpy/survey/pi.py
index 624933a..9d2f06a 100644
--- a/civpy/survey/pi.py
+++ b/civpy/survey/pi.py
@@ -1,4 +1,7 @@
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
 import numpy as np
 
 __all__ = ['PI']
@@ -16,11 +19,6 @@ class PI(np.ndarray):
         The radius of the horizontal curve. Use zero if a curve does not
         exist.
     """
-    # Custom properties
-    x = propy.index_property(0)
-    y = propy.index_property(1)
-    z = propy.index_property(2)
-
     def __new__(cls, x, y, z=0, radius=0):
         obj = np.array([x, y, z], dtype='float').view(cls)
         obj.radius = radius
@@ -30,4 +28,37 @@ def __array_finalize__(self, obj):
         if obj is None: return
         self.radius = getattr(obj, 'radius', 0)
 
-    __repr__ = propy.repr_method('x', 'y', 'z', 'radius')
+    def x():
+        def fget(self):
+            return self[0]
+        def fset(self, value):
+            self[0] = value
+        return locals()
+    x = property(**x())
+
+    def y():
+        def fget(self):
+            return self[1]
+        def fset(self, value):
+            self[1] = value
+        return locals()
+    y = property(**y())
+
+    def z():
+        def fget(self):
+            return self[2]
+        def fset(self, value):
+            self[2] = value
+        return locals()
+    z = property(**z())
+
+    def __repr__(self):
+        s = [
+            ('x', self.x),
+            ('y', self.y),
+            ('z', self.z),
+            ('radius', self.radius),
+        ]
+
+        s = ', '.join('{}={!r}'.format(x, y) for x, y in s)
+        return '{}({})'.format(type(self).__name__, s)
diff --git a/civpy/survey/spatial_hash.py b/civpy/survey/spatial_hash.py
index d37bc4d..1eb9eb4 100644
--- a/civpy/survey/spatial_hash.py
+++ b/civpy/survey/spatial_hash.py
@@ -1,4 +1,7 @@
-from __future__ import division
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
 import numpy as np
 import matplotlib.pyplot as plt
 from mpl_toolkits.mplot3d.art3d import Poly3DCollection
@@ -109,6 +112,8 @@ def _hash(self, point, norm):
 
     def multi_get(self, points, norm=True):
         """
+        Returns the point indices corresponding to the input array of points.
+
         Parameters
         ----------
         points : list
diff --git a/civpy/survey/survey_point.py b/civpy/survey/survey_point.py
index ce80c21..11eefbc 100644
--- a/civpy/survey/survey_point.py
+++ b/civpy/survey/survey_point.py
@@ -1,4 +1,7 @@
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
 import numpy as np
 
 __all__ = ['SurveyPoint']
@@ -13,11 +16,6 @@ class SurveyPoint(np.ndarray):
     x, y, z : float
         The x, y, and z coordinates.
     """
-    # Custom properties
-    x = propy.index_property(0)
-    y = propy.index_property(1)
-    z = propy.index_property(2)
-
     def __new__(cls, x, y, z, **kwargs):
         obj = np.array([x, y, z], dtype='float').view(cls)
         obj.meta = dict(**kwargs)
@@ -27,4 +25,37 @@ def __array_finalize__(self, obj):
         if obj is None: return
         self.meta = getattr(obj, 'meta', {})
 
-    __repr__ = propy.repr_method('x', 'y', 'z', 'meta')
+    def x():
+        def fget(self):
+            return self[0]
+        def fset(self, value):
+            self[0] = value
+        return locals()
+    x = property(**x())
+
+    def y():
+        def fget(self):
+            return self[1]
+        def fset(self, value):
+            self[1] = value
+        return locals()
+    y = property(**y())
+
+    def z():
+        def fget(self):
+            return self[2]
+        def fset(self, value):
+            self[2] = value
+        return locals()
+    z = property(**z())
+
+    def __repr__(self):
+        s = [
+            ('x', self.x),
+            ('y', self.y),
+            ('z', self.z),
+            ('meta', self.meta),
+        ]
+
+        s = ', '.join('{}={!r}'.format(x, y) for x, y in s)
+        return '{}({})'.format(type(self).__name__, s)
diff --git a/civpy/survey/survey_stake.py b/civpy/survey/survey_stake.py
index e9a2e3b..88db428 100644
--- a/civpy/survey/survey_stake.py
+++ b/civpy/survey/survey_stake.py
@@ -1,4 +1,7 @@
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
 import numpy as np
 
 __all__ = ['SurveyStake']
@@ -10,20 +13,15 @@ class SurveyStake(np.ndarray):
     using the :meth:`SurveyStake.init_xy` or :meth:`SurveyStake.init_station`
     class methods.
     """
-    TYPES = ('xy', 'station')
-
-    # Custom properties
-    x = propy.index_property(0)
-    y = propy.index_property(1)
-    z = propy.index_property(2)
-    lock_z = propy.bool_property('lock_z')
-    _type = propy.enum_property('_type', TYPES)
+    XY = 'xy'
+    STATION = 'station'
+    TYPES = (XY, STATION)
 
     def __new__(cls, x, y, z, station, offset, height, rotation, lock_z, _type,
                 _init=False, **kwargs):
         if not _init:
             raise ValueError('SurveyStake should be initialized using the '
-                '`SurveyStake.init_xy` or `SurveyStake.init_station` methods '
+                'SurveyStake.init_xy or SurveyStake.init_station methods '
                 'in lieu of the standard initializer.')
 
         obj = np.array([x, y, z], dtype='float').view(cls)
@@ -46,8 +44,54 @@ def __array_finalize__(self, obj):
         self._type = getattr(obj, '_type', 'xy')
         self.meta = getattr(obj, 'meta', {})
 
-    __repr__ = propy.repr_method('_type', 'x', 'y', 'z', 'station', 'offset',
-                                 'lock_z', 'meta')
+    def x():
+        def fget(self):
+            return self[0]
+        def fset(self, value):
+            self[0] = value
+        return locals()
+    x = property(**x())
+
+    def y():
+        def fget(self):
+            return self[1]
+        def fset(self, value):
+            self[1] = value
+        return locals()
+    y = property(**y())
+
+    def z():
+        def fget(self):
+            return self[2]
+        def fset(self, value):
+            self[2] = value
+        return locals()
+    z = property(**z())
+
+    def _type():
+        def fget(self):
+            return self.__type
+        def fset(self, value):
+            if value not in self.TYPES:
+                raise ValueError('Type {!r} must be in {!r}.'.format(value, self.TYPES))
+            self.__type = value
+        return locals()
+    _type = property(**_type())
+
+    def __repr__(self):
+        s = [
+            ('_type', self._type),
+            ('x', self.x),
+            ('y', self.y),
+            ('z', self.z),
+            ('station', self.station),
+            ('offset', self.offset),
+            ('lock_z', self.lock_z),
+            ('meta', self.meta),
+        ]
+
+        s = ', '.join('{}={!r}'.format(x, y) for x, y in s)
+        return '{}({})'.format(type(self).__name__, s)
 
     @classmethod
     def init_xy(cls, x, y, z=0, height=0, rotation=0, lock_z=False, **kwargs):
diff --git a/civpy/survey/tin.py b/civpy/survey/tin.py
index b80f37b..bfc10b4 100644
--- a/civpy/survey/tin.py
+++ b/civpy/survey/tin.py
@@ -1,6 +1,10 @@
-from __future__ import division
-import propy
+"""
+Copyright (c) 2019, Matt Pewsey
+"""
+
+import attr
 import numpy as np
+from math import ceil
 import matplotlib.pyplot as plt
 from scipy.spatial import Delaunay
 from .spatial_hash import SpatialHash
@@ -8,6 +12,7 @@
 __all__ = ['TIN']
 
 
+@attr.s(hash=False)
 class TIN(object):
     """
     A class for creating triangulated irregular networks (TIN) models for
@@ -37,17 +42,17 @@ class TIN(object):
     .. plot:: ../examples/survey/tin_ex1.py
         :include-source:
     """
-    def __init__(self, name, points=[], breaklines=[], max_edge=None,
-                 step=0.1, grid=10):
-        self.name = name
-        self.breaklines = breaklines
-        self.max_edge = max_edge
-        self.step = step
-        self._create_triangulation(points, grid)
+    name = attr.ib()
+    points = attr.ib(default=[], converter=np.asarray)
+    breaklines = attr.ib(default=[])
+    max_edge = attr.ib(default=None)
+    step = attr.ib(default=0.1)
+    grid = attr.ib(default=10)
 
-    __repr__ = propy.repr_method('name')
+    def __attrs_post_init__(self):
+        self._create_triangulation()
 
-    def _create_triangulation(self, points, grid):
+    def _create_triangulation(self):
         """
         Creates the Delaunay trianguation and spatial hash.
 
@@ -58,7 +63,7 @@ def _create_triangulation(self, points, grid):
         grid : float
             The spatial hash grid spacing.
         """
-        points = np.asarray(points)
+        points = self.points
         b = self.breakpoints()
 
         if b.shape[0] > 0:
@@ -70,7 +75,7 @@ def _create_triangulation(self, points, grid):
 
         self.points = points
         self.tri = Delaunay(points[:,:2])
-        self.hash = SpatialHash(points[:,:2], grid)
+        self.hash = SpatialHash(points[:,:2], self.grid)
         self._remove_simplices()
 
     def _remove_simplices(self):
@@ -101,7 +106,7 @@ def breakpoints(self):
 
             for i, (a, b) in enumerate(zip(line[:-1], line[1:])):
                 m = a - b
-                n = int(np.ceil(np.linalg.norm(m) / self.step))
+                n = int(ceil(np.linalg.norm(m) / self.step))
                 if n < 2: n = 2 if i == 0 else 1
                 x = np.expand_dims(np.linspace(0, 1, n), 1)
                 y = m * x + b
diff --git a/pytest.ini b/pytest.ini
index 7c6da45..2ebd36a 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -1,2 +1,3 @@
 [pytest]
 python_files = tests.py test_*.py *_test.py
+addopts = --cov=. --cov-report=html
diff --git a/requirements.txt b/requirements.txt
index 1b4c904..361b4b2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,7 @@
 numpy>=1.14.5
 scipy>=1.1.0
 matplotlib>=2.2.2
-propy>=1.0.0
+attrs>=19.1.0
 pandas>=0.23.0
 xsect>=1.1.0
 
diff --git a/setup.cfg b/setup.cfg
index 1e1dc91..5b8d2fe 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -29,7 +29,7 @@ install_requires =
   numpy>=1.14.5
   scipy>=1.1.0
   matplotlib>=2.2.2
-  propy>=1.0.0
+  attrs>=19.1.0
   pandas>=0.23.0
   xsect>=1.1.0
 python_requires = >=3.5