The RASTRA wall
building system is the ultimate answer for economical and environment-
construction. A stay-in-place insulated
concrete form (ICS’s) system made of a lightweight composition
with a higher than 80% content of recycled material. Rastra is made
from a lightweight honeycomb like mixture of small foam beads, like
recycled packing material, food containers and modified concrete.
It has a high insulation value and is resistant against fire, frost
and other climate influence. It takes stucco or other types of wall
covering very well. Installation of the Rastra elements is very simple
and does not require special skills or tools, making it well suited
for the owner/builder. Rastra walls go up much faster then conventional
methods of building and unlike framed walls, are ready for finishing
once the cells are filled. The blocks are basically stacked one on
top of another and glued together with a foam adhesive. Once the walls
are constructed, the cells are filled with concrete, reinforced with
rebar, and very little bracing is needed. You can cut and shape the
blocks with just about anything; an electric chainsaw works great
can cut they by hand.
The most popular
blocks used in this area are 12 inches thick by
15 inches high by 7 1/2ft long. The 12 inch block has an
about 35 and weights 148 lbs. Two people can easily lift the blocks
into place, or a lift can be used. We have built walls up to 12
ft. high working off scaffolding. Any type of roof structure
can be used
with the Rastra system, and walls up to 6 stories high are possible.
The interior grid of horizontal and vertical reinforced concrete
cells, as shown in the picture to the left, makes
for walls with strengths 700% higher than traditionally used framed
shear walls. Because
Rastra is frost-proof and insensitive to temperature or moisture,
it is well suited for below grade construction. Unlike conventional-frame
construction, you can start a Rastra wall right on top of the footer
and continue up to the roof, a great time and money
saver. You can easily create curved walls, cut out arched doors
and windows and even use rastra for the roof. The plumbing and
electrical lines can be placed in the cells prier to grouting
or can be cut into the elements and foamed over. For more detailed
information on building with Rastra you can request a copy of
the Rastra Installation Guide from my contact page or go to www.rastra.com.
AND COMPARISIONS AT A GLANCE
Insulation is rated in terms of thermal resistance, called R-values.
The higher the R-value, the greater the insulating effectiveness.
You also need to factor in the performance of the whole wall, such
as thermal mass, air tightness, and moisture tolerance.
The whole wall R-value of Rastra elements for this climate zone are
10 inch = R 24
12 inch = R 35
14 inch = R 48
It should be noted that these values do not include the other benefits such as
tightness or stucco and plaster wall finishes. Most building systems base R-values
on a section of wall do not include design details that interfere with the insulating
envelope, such as studs, headers, and corner details. Therefore the standard
2x6 framed wall with R-19 infill insulation between the studs and 1 inch ridge
exterior insulation, rated at R-21 is more then likely over rated. Washington
energy code requires exterior walls to be a minimum of R-21 for this climate
Comparing a Rastra
wall to a standard wood framed wall is somewhat problematic, because
it would difficult and very costly to build a
wood wall with all the properties of a Rastra wall, such as 4-hour
fire rating, mold and rot resistance, and thermal mass effect. So
it is important to remember that you are not comparing apples to
when you look at these two wall systems. Also keep in mind that the
walls of most residential buildings only account for about 15% of
the total cost of the structure. To get a true comparisons of the
shell price of the two wall systems you need to compare the framed
wall completed from sheet rock on the inside to being ready for stucco
on the outside. Depending on your location and the nature of your
building project, a Rastra wall will cost about 10 to 15% more then
a wood framed wall. The cost of the 12 inch thick Rastra material
delivered to eastern Washington is about $4.50 per sq ft of wall.
Call or e-mail for current pricing and estimating for your project.