It is necessary to brace an ICF wall to hold it straight and true while the concrete is being poured and is setting. If you don't brace enough then there is the danger of blowouts, particularly when pouring high walls in one pour. There are various manufacturers of bracing systems, but they are very expensive to buy and expensive to rent. The other problem with renting is that you are working against the clock whereas I prefer to take my time to get the ICF walling exactly right and so that I have time to make all the conduit openings etc.
My solution was to design my own low cost ICF bracing system using 2x4s. It is described here.
Vertical 2x4s are actually two 8 foot long 2x4s, one face-on to the ICF and one edge-on that is screwed to the first 2x4. The edge-on one is positioned 2" higher than the face-on one because the face-on one needs to tuck into the grove at the bottom of the wall.
It is important to select only very straight pieces of 2x4 for use as the edge-on verticals. Use your eye down the length of the 2x4 to select the straightest pieces. The holes in the edge-on 2x4 are clearance drilled (2" of wood left) so that they can be screwed to the face-on 2x4. Don't screw from the other side or you will not be able to easily remove the edge-on pieces later.
The face on 2x4s have holes for screwing to the ICF webbing. These are best positioned either 3.5" from the bottom of the block or 3" from the top of the block. It is important to keep track of there the block joins are up the bracing 2x4. Put them 1.5" from the edge.
Near the top of the edge-on vertical 2x4, a 45 degree 2x4 is attached using a bolt in a slot arrangement. The hole is X'X" from the bottom and X.X" from the edge. The slot is what allows the vertical-ness of the wall to be adjusted. Half inch screw thread studding (6" long) is used on both ends of the slot moving parts. Turnbuckles can be fitted between these and are used to set the vertical-ness of the wall. The nuts on the half inch studding can then be tightened in position and the turnbuckles are no longer required (saves the cost of lots of turnbuckles).
The bracing with the 45 degree 2x4s is used on the inside of the building. The bracing assembly is screwed into the plastic webbing of the ICF blocks using long (5") screws. On the outside it is also necessary to screw on vertical face-on 2x4s so that the wall is supported equally on both sides so it doesn't bow. In the case of the outside vertical 2x4s they do not need any 45 degree 2x4s because they are screwed into the web that is held vertical by the inside 45 degree 2x4s.
The bottom of the 45 degree 2x4s are bolted to short horizontal pieces of 2x4. These are screwed to long lengths of 2x4 that are nailed to the concrete slab using a concrete nail gun.
The vertical bracing is installed about every 2 feet, but that spacing will vary to accommodate where the window and door openings are. You need bracing directly next to both sides of a window/door opening.
It is necessary to keep the inside 2x4 bracing dry. This is partly because the inside vertical 2x4s will stay in place behind the drywall so you don't want any rot, and partly because wet lumber expands so you would have to keep adjusting the vertical-ness of the wall. The polyethylene sheeting over the window bucking will stop some rain getting into the building, but you will also need a temporary tarpaulin or polyethylene sheeting over the whole building (supported by the polystyrene walls).
Some people use slotted holes in the vertical bracing when attaching it to the ICF blocks so that the blocks can settle under the weight of the concrete etc. I do not do this. Instead I rely on the vertical 2x4s on each side of the wall to hold the ICF blocks in a fixed position. The weight of the concrete etc is transmitted down the 2x4s to the concrete slab.
Prior to pumping the concrete into the ICF wall, the turnbuckles are used to get the wall vertical and the bolts are tightened to fix everything in place. Immediately after the concrete has been poured (before it sets) you then go round and re-adjust whatever bracing is necessary to ensure that the wall sets perfectly vertically.
If there is a concrete ledge to support a wooden floor or thermally isolated balcony or decking then the vertical bracing will need to be cut to a length such that it comes up to (and supports) the bottom of the box that forms the concrete ledge. Lumber is table sawn to 9" wide, which with the 2-by top and bottom makes it 1 foot high which is the same as an ICF block. The top and bottom lumber is table sawn to be 8-1/8" wide, which means the lip sticks out 5-1/2" beyond the outside edge of the ICF EPS. Bits of 2x4 are attached top and bottom to keep it in line with the ICF blocks that are under and over "wooden block" assembly.
The vertical part of the bracing is screwed onto the ICF webbing using 5" long wood screws.
Before screwing, choose a spacer shim for under the leg that gets it to the right height (eg for supporting a concrete lip). Cut the shims from some spare 2-by lumber. Just cut random widths and then you can pick the width that works.
As with the internal ICF bracing, it is important to include the appropriate spacer shims to start the 2x4 bracing at the exact height that the ICF bricks start at. The ICF blocks may have EPS shims between them and the concrete, and the 2x4 batons need to have the same width of wooden spacer shim under them. This arrangement will ensure that the weight taken by the batons is properly transferred into the concrete slab.
Where there is a concrete lip on just one side of the wall, the vertical batons on the other side should be made longer (eg 8' instead of 7') in order to take the other end of the horizontal 1/2"studding.
At the bottom of the wall it is necessary to use very good bracing on both sides because the pressure is greatest at the bottom.
The floor above
The forming for the floor near the top of the walls is an important aspect of bracing strategy for the walls. The floor will hold the walls in a nice accurate rectangle and will also stop the walls bowing outwards or inwards. Prior to the concrete pour, the floor will just be supported by the internal vertical bracing 2x4s (and an additional forest of 2x4s to stop the floor bowing down). The floor bracing needs to be strong enough such that the floor can be used as a walkway when pouring the concrete into the ICF walls.
Bracing around windows
On each side of a window (or door) opening it is necessary to have a vertical bracing assembly. The cut ICF polystyrene will be weak in this area so needs good bracing. The bracing also is used to help support the weight of the window bucking. Short lengths of 2x4 attach to the inner sides of the bucking and screw to the vertical bracing (via a 2x4 spacer).
For the opposite side of the window it is necessary to make a mirror image of what's shown in the bracing design diagram.
Where there are window and door openings you need to ensure that the ICF blocks on each side do not splay outwards away from the opening (they will naturally try to slay out). Bracing batons should be screwed to the ICF webbing on either side of the opening and then another piece of 2x4 can be screwed between the vertical batons to keep the distance above the window the same as the distance below the window. Use a twisted pull wire between screws to pull the vertical batons (and the associated ICF blocks) to the right distance apart at the top.
Once the wire has pulled the top in to be the same as the bottom, fix a piece of 2x4 across the top to hold it at the right dimension.
You may also want to use other techniques to pull everything into the correct alignment (eliminating the splay of the ICF blocks). Sometimes it will be a wooden floor that sets the required dimensions. You can attach temporary blocks to the wooden floor and use an adjustable clamp to pull the ICF block wall inwards.
Bracing pipes through ICF walls
Where there are holes to allow electrical, plumbing, utilities, and vents through the ICF wall, it is best to use 4" ABS pipe cut to a length of 16-1/4". This is the right length for the 13-1/4" ICF block width plus two pieces of 2-by either side to brace it.
(The pictures show bits of 2x4 to sometimes attach to the vertical bracing, but it is better to just always toenail them to the batons using 3" screws (in lots of places you need this anyway, so you may as well do it everywhere). Drill angled screw holes 1-5/8" in from the edge so the holes come out about half way on the edge.)
Wherever you think there might be a weak area in the polystyrene ICF wall it is good to add some extra bracing. Typically this means some horizontal pieces of 2x4 that are screwed between the vertical bracing assemblies.
Sometimes a long horizontal plank is useful to keep two windows in line. It also forms a useful shelf for tools and lights.
Any cut joins in the ICF should be braced.