The IronStraw Group pages (2)
This is the second of three 'mirrored' pages of sections of the Web
Site of the USA based IronStraw Group (Cashmere, Washington).
Permission was received to copy the information on the pages.
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More information about The IronStraw Group is provided at the
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The IronStraw Group
Building Technical Info
Section 4
This is the fourth section in this series about building strawbale
homes. Many times we focus on the technical aspect of building and
forget about why we build this way.
We will try to include photographs of finished strawbale homes or
details within homes so you can see the beauty in these strong
buildings.
Because the walls are two feet thick, it is possible to make
wonderful window seats built right into the walls that look very
natural as in the photograph on the left. Just add pillows or cushions,
coffee and a good book. We loved sitting and looking out this window
to the forest behind our house. Nature and all the wildlife can be
observed if we take the time to slow down and look. This is part of
strawbale building also, don't forget to nourish the soul.
Raising the Walls - continued
In the previous section we showed several photographs of the wall
going up during a workshop and how hectic it can get. Pinning bales
is an integral part of your home's stability and can easily be
overlooked. Someone needs to check this - that's why we recommend
wall captains for each wall. Starting with the first course,
all corners must be pinned together. One method is to use rebar bent
into a "U" shape approximately 2' along the base
with 6"-10" legs. We recommend #3 rebar because it is
easier to make the tight bends of the "U".
This pin can easily be pushed into the tops of the two corner bales
to secure them together.
It is advisable to have all window and door frames complete and
ready to install on the work site before you have your workshop.
This will make your wall raising go much smoother and faster.
Preparation of the frames also includes corner braces so everything
stays square during installation and further bale stacking.
Corner braces can be made from any kind of scrap wood on your site,
or salvaged from past projects as long as it is strong enough to
keep everything in place. We like to brace as many corners as
possible, with some on the inside and some on the outside. We think
that two is a minimum if they are fairly large.
This photograph shows a window/door frame combination installed
with several courses of bales stacked in place. Keep in mind that
stacking the bales should start at your door and window openings as
well as your corners. Always stack towards the center away from your
openings and don't force bales into your walls. A nice snug fit will
help keep your frames in place and square. Too much cramming and
jamming of bales in the wall can cause your corner posts to move or
your window/door frames to go out of square. The wall raising will
go quickly, make sure your wall captains know how snug the bales
should be and that they check each course.
When the 4th course is complete it's time to pin
everything together. This is the time to inspect the wall to insure
it is straight and that there are no bales sticking out where they
shouldn't. Line up all bales - use a large sledge hammer to move
stubborn bales. Some people have made "bale whackers"
using a sledge hammer size handle and a large block of wood
(4"x8"x12"). This can be great fun! Run a string
between your corner posts at each course to be a guide.
Each course of bales should have been inspected and aligned before
the next course went on top, this is an extra check.
Once you are happy that all the bales are ready to be pinned it's
time to pound rebar. We recommend using #4 rebar to pin the bales.
Some people have used bamboo and wood stakes and they work well;
however, if you have had to convince your building official that
the strawbale walls are really safe, then they will usually prefer
rebar. As long as your building official is satisfied with your
choice, use the material you prefer. We will talk about using rebar
since it is widely available at local lumber yards and inexpensive.
The added stiffness of #4 rebar is suggested here rather than the
flexibilty of the #3 used for the corner "U" pins.
Tools to aid in pounding rebar are illustrated in Build
It With Bales (Buy this book at the beginning of your planning and
read it - see details below.) During the wall raising assign two people to cut rebar
in 5' lengths. You will need 2 pieces for each full bale
(if you have 30 bales around the house, you need 60 pieces.) This
rebar gets pounded down through all 4 courses tying every bale to
the ones above and below.
This procedure will be repeated for every course upward. If your
walls are 6 bales high, you will need another 120 pieces of rebar.
the photograph above shows a 7 bale high wall ready to be covered in
plastic at the end of a day. This wall has a 30 degree bend in the
middle of it.
The IronStraw Group
Building Technical Info
Section 5
This is the fifth section in this series about building strawbale
homes.
Wall raising continued -
We emphasised the importance of pinning bales and making sure the
bales are stacked straight in the last article. This is really
important at this stage - it will make your job much easier later on.
Wall captains, or someone should be diligent about checking the
straightness of your walls. Make sure the corner guides have not
moved and the door/window frames have not been pushed out of square.
Be patient and check this and fix any problems as the walls go up.
We recommend that the owner builder not have any assigned tasks except
to oversee this part of the wall construction.
This will payoff (and it's so much easier now) making box beam
placement and eventually stucco-ing much easier. Don't pin a course
of bales until you are satisfied that it is straight and just the way
it should be.
Which brings us to box beams, or as described in Build
It With Bales, rigid beam assemblies. No matter what you
call them, for load-bearing walls, something has to be on top of the
wall for your roof structure to sit on. We have used many of the
variations in Build
It With Bales and prefer a box beam made of 2x4, 2x6, or TJI
(in order of least to most rigid) all combined with plywood tops
and bottoms and stuffed with straw. Assemblies are made to various
lengths to fit your walls.
*NOTE: This drawing is not meant to be a substitute
for your drawings to be submitted to your building official, it is a
general drawing to give you an idea of how a box beam is constructed.
Depending on each individual building design, one of these beam
assemblies is usually a good choice. Now is a good time to mention
structural engineers who will remind us about the length of the span
for openings, or the distance between trusses and the roof dead load
and the snow load, etc., to determine the appropriate beam assembly.
If you have not had any building experience it is a good idea to have
your plans reviewed by someone who can calculate or verify that your
structure is safe. This does not mean you need to spend thousands of
dollars hiring architects and structural engineers. (Although they are
highly trained professionals that will ensure your building is safe.)
During our last workshop, one of the volunteers told us about a
very reasonably priced engineer familiar with strawbale buildings
that he highly recommended. Contact us if you want to hire an engineer
and we'll pass along his information.
Here's an example of a wall during construction showing many of the
things discussed here and in previous articles. So take a look.
This is a load bearing wall with a load bearing door frame.
The door frame will support all the weight of any bales and the roof
loads above it. This type door frame does not require a separate
lintel (as long as you have calculated the wood needed to support
across the distance of the door opening.)
Also note the temporary support to keep the wall straight.
Here the "box beam" is in place but not connected down to
the foundation yet. The hole between the bales just above the door
to the right will be stuffed with straw after the wall is secured.
This is a 6 bale high wall using 3 string bales. The resulting
ceiling height is about 8'-6". Also note the sill plates under the
bales, two 2x4's to give a 3" step up for the bales to sit on. It is
inexpensive insurance against future water damage from flooded
floors.
Which brings us to wall tie down systems, or strapping. We have
favored high strength poly strapping rather than metal strapping
because it is much easier to work with and less likely to cut hands.
Another alternative is wire fence material and
Gripple™ wire rope connectors. This is really a personal
choice so we suggest you participate in some building projects,
either through workshops or volunteer on a site. You will want to
do this anyway before you tackle your project, so it would be a good
time to check the method used on the work sites you visit.
This photo shows the green poly strapping on the far wall (if you can see it...). This
runs under the sill plate (anchor bolted to the footing) and up over
the top of the box beams on top of the walls. You can also see the
radiant infloor heating tubes (red) and the rough plumbing. All this
ready for the concrete floor to be poured. We used rigid 2"
insulation under the entire floor.
In the next section we'll show you some trusses and talk about
getting the roof on your walls as quickly as possible to protect your
straw. Post and beam construction gets your roof built before the
walls, so protecting your straw is not as much of an issue.
If you are planning to build where it is rainy all the time you
might want to consider post and beam. We have always built in
climates that have some time of year that you can count on it being
sunny and dry to build.
Recommended
Reading:
Matts Myhrman and Steve MacDonald,
Build It With Bales,
Version 2. Out On Bale, 1037 E. Linden Street, Tucson,
AZ 87519 USA. [Price US$29.95 plus S&H]
If you are interested in building, see
our consulting page to see how we can help
you. You can e-mail Michael Thomas, Co-Founder of
IronStraw Group in the USA at: thomas@ironstraw.org
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