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Carnation Walling - Wall Rebar

Star Fit the horizontal and vertical rebar to the walls in all the right locations as per structural engineering.

Fitting rebar supporting wall tie pipes

Wall tie rods already present

There should already be 3/8" threaded rod wall ties in all the significant positions through the outer wall EPS.  The significant positions were chosen to provide the required support for the rebar at all the required distances up the wall.

Remove internal vertical 2x4 batons in the concrete cavity

The EPS wall round the outside of the building is all glued together and so it is ok to remove the internal vertical 2x4 batons for a wall section that you are about to work on.  Leave the external vertical 2x4 batons in place, together with the wall tie threaded rods.  In areas that you are not yet working then leave the internal vertical 2x4 batons in place (where the concrete will go) just in case of high winds.  The section cleared of batons needs to be wide enough to accept the 19' lengths of horizontal rebar.

To remove the batons you need to remove the steel nuts and washers, but leave the steel threaded studs in place.  For an 8" cavity they should protrude 1' 0-3/8" beyond the inside surface of the EPS.

Rebar placement CAD drawings

Rebar placement should be specified on your CAD drawings and should have been added to your drawings to meet the requirements of the structural engineering process.

Make rebar supporting plastic pipes

Electrical conduit plastic pipe is used because it is low cost.  It is 1/2" diameter.

Electrical conduit half inch   PVC pipe half inch

Getting the length of the plastic tube right is important.  The calculation is...

Cavity width - 1/16" for washer + Expected compression of EPS (1/8") + expected compression of plywood (1/16") + How much less thin ply is from 1/4" (1/16") + How much less thick ply is from 1/2" (1/16").

For an 8" cavity that means 8 - 1/16 + 1/8 + 1/16 + 1/16 + 1/16 = 8-1/4".

Use a length stop jig on a chop saw to cut the conduit.

Conduit Spacer Cutting Jig 

Rebar positioning within the concrete cavity width is important.
Relative to 8" thick concrete, the center of the horizontal rebar will be at 1-3/4",  4",  and/or 6-1/4".

Horizontal Rebar Positions 8in
Relative to 12" cavity concrete, the center of the horizontal rebar will be at 1-3/4",  4",  6-1/4",  8-1/2",  and/or 10-1/4".

Horizontal Rebar Positions 12in
(Relative to 6" cavity concrete, the center of the rebar will be at 1-3/4",  3",  and/or 4-1/4".)

Note that the locations given are for the horizontal rebar.  The vertical rebar positions are typically offset by half an inch relative to these locations.

The horizontal rebar is kept at the right position within the width of the cavity using small snap-on pieces of 3/4" conduit.  The 3/4" conduit is cut on a chop saw or band saw to 3/8" lengths and then the edge is cut open in one place on a band saw.  They can be added after the 1/2" conduit is fitted, but it is best to add them on the bench assuming you know where you want the rebar positioned.  It is much better to know ahead of time where the rebar will be placed so you don't have to think about it when up a ladder building the wall.  Often it will be just in the center, but on a backfilled retaining wall you will most likely want just the inner position.  The 3/4" conduit collars slide over the end of the cut to length 1/2" conduit pipe and are glued in place with a dab of regular PVC pipe glue (applied after the collar is in the right place).  The collars are placed to provide a half inch gap between the two collars.  A collar pair is only needed where rebar is actually required.  Usually only one collar pair are needed per wall tie.  Typically it is only worth putting collars on the wall ties that use threaded stud because these are in strategic positions and will provide easily enough holding for the rebar.  It is worth making wooden jigs to help you quickly position the collars.  (In the diagrams below the dimensions do not reflect the 1/16" resolution needed so look at the actual CAD drawing when making the jigs.)

Wooden collar jig 8in cavity         Wooden collar jig 12in cavity 

Tie Rod Tube Spacer Jig

Wall Tie Pipe With Colar Pairs 

Fit washers and pipes

Onto the steel threaded rods fit a 1.5" nylon washer .  Then fit a plastic conduit wall tie pipe with the collars fitted in the right places for that particular section of wall.


Add rebar to cavity next to EPS

At this stage we are only putting the rebar into the cavity in its right sequence relative to each other in the cavity.  It is temporarily placed right up against the EPS so that it does not cause the unsupported threaded rod wall ties to bend down.

At the edges of openings there will be more vertical rebar and it will be constrained by rebar stirrups.  The stirrups need to be added as you add the vertical rebar.

There will also be extra vertical rebar at corners.

You need to make sure everything is as per the structural engineering rebar placement requirements.

At the corners it is best where possible to use horizontal rebar with 90 degree bend ends to bend into to the adjacent wall where it can be tied to the horizontal rebar of that wall.

Throughout the building of the walls, look for opportunities to add more rebar anywhere you think it will help.  Remember that the rebar placement spec in the structural engineering drawings is just the minimum required.

Do the following steps for the internal walls too.

Add horizontal rebar that's further out than vertical rebar

It is important to first add any horizontal rebar that needs to be closer to the outside of the wall than the vertical rebar.

In the case of a backfilled wall the vertical rebar will be close to the inside of the building, but then the horizontal rebar will be in the 6-1/4" position (from the outside of the concrete) closest to the inside of the wall so the vertical rebar (at 5-3/4" from the outside of the concrete) will still be nearer the wall outside than the horizontal rebar.  Even with a backfilled 8" wall there will however still be some occasional horizontal rebar in the center position and this is closer to the outside than the vertical rebar, so this needs to be added first.

Note that the vertical rebar positions do not correspond with the positions of the wall tie rods.  These are typically at the positions where the vertical rebar comes up through the slab.

Check to make sure you really have added all the horizontal rebar that is nearer the outside compared with the vertical rebar.

Until the vertical rebar is in place and tied to the horizontal rebar, things are a bit fragile and there is a danger of the wall ties bending downwards.  The horizontal rebar that is on the outside of the wall relative to the vertical rebar needs to be rested in place right next to the EPS.  It will only get tied in its correct position after the vertical rebar has been installed and the internal vertical batons have been added.

Add stirrups where specified

These are actually added as you add the vertical rebar.  You will need to temporarily tie them in the right horizontal locations to stop them dropping down.  You can use electrical tape or tie wraps to the wall tie tubes to temporarily hold them.

Add vertical rebar

For external walls (both 8" and 12" cavity) the primary vertical rebar always has its center 5-3/4" from the outside edge of the wall concrete (ie 5-3/4" from the house outline reference line).  This corresponds to being just inside (nearer the center of the wall) compared with horizontal 1/2" rebar that is in the inner position on the 8" cavity plastic wall tie tube.

Vertical Rebar Positions 8in

Vertical Rebar Positions 12in

Secondary vertical rebar when required is at the following locations (also listed is the primary location of 5-3/4")...
        2-1/4"        (4-1/2")        5-3/4"        (8")        9-3/4"

For internal concrete walls the vertical rebar is near the center within the 8" cavity, but a half inch towards the building center tied to the horizontal rebar (at the 4" position) that is in the true center of the wall.  The vertical rebar is at the 4-1/2" position relative to the outside edge of the concrete of the internal wall.

For the moment, the vertical rebar is added right next to the horizontal rebar that is up against the EPS.

Do not yet tie the to the vertical foundation rebar.

The vertical rebar (using extension pieces if necessary) should be long enough to extend 3'6" beyond the top of the slab of the floor above.

The vertical rebar does not sit in a collar pair on the plastic pipe and is not even close to a tie rod, and anyway it cannot be tied until the adjacent horizontal rebar (that does sit in the collars) is added.  For the moment, the vertical rebar is as close to the EPS as you can get it.

The vertical rebar needs to be fitted through holes made in the 6mil polyethylene sheet that covers the floor above.  You want to for the moment keep the sheet over the wall cavity as it stops rain, leaves and pine needles getting into the wall cavity.

Add inner horizontal rebar

Add the rest of the horizontal rebar.  It should be pushed as close to the outer EPS as you can get it.  You do have to take care that the weight of the rebar does not bend the threaded rods down.  The more you can push the rebar over towards the EPS, the less likely it is for the threaded rods to bend down.  You might have to use some tape to temporarily hold the rebar close to the EPS.

Fit the vertical 2x4 batons in final position

As you gradually add horizontal rebar it becomes more necessary to support the threaded rod to stop it bending down.  Full height vertical 2x4 batons do this nicely but can get in the way of adding the horizontal rebar.  If there is a danger of the threaded rods bending down, you need to keep adding and removing the vertical 2x4 batons as you add horizontal rebar.  Sometimes you are able to thread the rebar in from the end and thus avoid temporarily removing a baton.

Certainly as soon as you have all the rebar added you need to add the vertical 2x4 batons in their final positions along the wall.  They sit against the nailed down kicker boards and on appropriate thickness wood shims.  Also horizontal bracing is added to hold them the right distance apart.  The net result is that all the threaded wall tie rods are held accurately in their right locations.


Tying the rebar to the plastic tubes

The story so far

All the rebar (both horizontal and vertical) has been added to the cavity in the right sequence relative to each other.  It is all pushed up against the EPS to avoid bending the tie rods.  The threaded rod wall ties with their plastic tubes are fully supported in their accurate right locations using the full height vertical 2x4 batons (with their horizontal batons).  There is no internal plywood on external walls so it is still possible to get your hands into the cavity to position rebar and tie it.  Internal concrete walls have plywood on the outside face (but not the inside face) and the internal wall rebar has also been added.

Tie all rebar in correct locations

Move the horizontal rebar to sit in the right locations relative to the collars.  Tie the horizontal rebar to the plastic tubes using strong cable ties.  Tie them very tight.  In the case of the vertical rebar it is typically rubbing next to a piece of horizontal rebar and the two are tied together (the tie point is not at the plastic tube).  You are relying on the friction between the horizontal rebar and the vertical rebar to hold the wall tie tube in the right vertical dimension.

The vertical rebar is tied using cable ties to the vertical rebar that comes up from the foundations every 12".  The 12" on center for the vertical rebar does not correspond to the 12" on center points for the wall ties.  For a backfilled wall with vertical rebar every 6" then only every other vertical wall rebar is tied to foundation rebar.  Note that this is much better than with traditional ICF where it is not practical to tie to the foundation rebar.  Tying to the foundation rebar also helps stop the forming rising up with the wet concrete pressure.

After tying, it is the rebar, particularly the vertical rebar, that is holding the tubes and therefore the threaded rods in the right locations.  Having them held in the right locations will be important later when it comes to fitting the plywood sheets.


Glue bucking studding in place

Make the studs

Use 8.5" lengths of 1/2" studding.  Fit two nuts and a washer on the protruding end and lock them together using a couple of spanners.

Fit the studs

Fit the studding assemblies that provide the anchor from the window and door cavity bucking into the concrete.  In the case of the top and bottom of the bucking you will choose which holes to use to avoid the wall ties.

The studs are glued into the cavity bucking using PL-Premium adhesive.  Squirt it into the hole and then push in the stud.

Any unused holes in the cavity bucking can be filled with foam gap filler, although this is not essential.