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Foundation Rebar

Rebar implementation

Tying rebar

There are two options for tying the rebar.  Either plastic cable ties or wire.  I use cable ties.  The argument for cable ties is that they will not rust, but in practice the wire is thin so if it rusts will not expand enough to crack the concrete, and anyway my concrete is kept dry.  For horizontal rebar and simple joins in vertical rebar, I find cable ties are quicker to use than wire.  You cannot undo cable ties so they are not good when you initially have two pieces of rebar and then you need to add a third.  If using cable ties then it is sensible to use strong ones.  Regular tie wraps are rated at 18 - 50 pounds, but for rebar tying I recommend using at least 60 pound rated.  For really critical joins you can even use 120 or 175 pound rated, but that's overkill.

Details on where to get cable ties can be found here .

Tie wraps  

Chairs to support rebar

To support the rebar the right distance from the bottom of the footing trench and over the slab, it is necessary to use what are called "chairs".  The easiest chair to use is a thin plastic one such as these plastic rebar chairs .  You want ones with a wide base so that the force is better taken by the EPS polystyrene sheet underneath.

Rebar Chair Unmodified  Rebar Chair Drawing

When necessary I modify the plastic chairs to the height I want using a small band saw.

Spacing rebar off the walls

It is necessary for the rebar assembly to not move about in the footing trench.  It would be particularly bad if a sharp end of rebar were to puncture the waterproof membrane.  The solution is to use rebar chairs horizontally to the wall of the footing trench.  On a stirrup they are attached using a cross formed by two cable ties and then some PL-Premium adhesive to stop the position rotating.  A chair can also be tied onto the end of a rebar straight using a cable tie through a drilled hole.

Safety first

Cut rebar is very sharp and also will impale you if you fall on it, so OSHA (Occupational Safety and Health Administration ) requires safety caps.  They are made of high impact plastic with a metal plate embedded in them.  They need to be OSHA compliant to guard against impalement.  Detail on purchasing is here .  Put them on any pieces of vertical rebar as soon as they are placed.

Rebar safety caps

Also put safety caps on any horizontal rebar that might poke you in the eye.  On horizontal rebar some people use the lower cost non-OSHA rebar safety caps.  These are available from here .

Horizontal rebar safety cap

Even when using safety caps, it is important to also wear protective eye goggles or glasses because the ends of the wire used to secure the rebar can also do you a lot of damage.

Safety goggles when working on rebar 


Foundation Design

It is worth looking closely at the AutoCAD drawing of the overall foundation design to see where all the rebar goes.

Foundation Exterior Foundation Exterior (Cropped)

Here is the drawing version for the internal concrete walls...

Foundation Interiorwalls 

Foundation Interior Wall Cropped) 


Set batterboard strings at vertical rebar positions

Currently there are screws in the top of the batterboards to indicate the outer edges of the Form-a-drain.  What is now needed is a batterboard string between the two current strings that indicates the position of the vertical rebar.

For external walls, add a batterboard screw that is 1' 9-3/4" from the outer form-a-drain edge screw and add strings along all the footing trenches.

The positions of the internal wall vertical rebar are slightly offset compared with external walls, but again the positions will be as per your AutoCAD drawing.  The following drawing shows the internal wall vertical rebar positions relative to the existing batterboard strings...

Vertical Rebar Positions Internal Walls 

To summarize the above drawing for internal walls, the vertical rebar string needs to be 2' 4-1/2" from the internal wall outside form-a-drain.

Where the strings cross at a corner, is the exact position of the corner vertical rebar.  Other vertical positions along the trench can be found by measuring in 1 foot increments from the corner position. 

Mark rebar grid positions

Measuring in from the string in the perpendicular footing allows marks to be put on the slab protection EPS and on the outer form-a-drain.  To do this, use a plumb-bob and a wooden stick marked with 1' marks.

Put marks on slab edge

Setting Rebar Vertical Marking Plumb Bob 

Use half inch colored tape to show the positions.

Marking Tape Colored Half Inch

One edge of the half inch tape indicates the vertical rebar position and the other edge is the horizontal rebar position that is offset by half an inch towards the building center.

Setting Rebar Vertical Marking Stick Tape 

To avoid getting confused, mark with a circle the edge of the tape that is the vertical rebar position.  Mark the other tape edge with a line to represent the horizontal rebar position.  It is also worth numbering the marks starting from 0 and working towards the center.

Setting Rebar Vertical Marking Tape 

At the center of the wall the spacing will be less than 1 foot because the 1' grid is from the corners working towards the center.  The actual dimension in my case is 7-1/4".

Mark on outside of trench

Also put tape pieces around the outside of the footing trench to show the 12" grid positions.  Again mark one tape edge with a 0 to represent the vertical rebar position and the other edge with a line to represent the offset horizontal rebar position.  Obviously the markings need to be as per your AutoCAD drawing that details the positions of the vertical wall rebar.  Use a plumb bob off your batterboard strings to find the positions to mark.

Setting Rebar Vertical Marking Outside Stick

Setting Rebar Vertical Marking Outside Tape 

At the center of the wall the spacing will be less than 1 foot because the 1' grid is from the corners working towards the center.  The actual dimension in my case is 7-1/4".

Mark cube positions

Eight inch wooden cubes are used later to support the groove planks and the walkway.  It is good to mark out early the places where the cubes will go.  The cubes are in the spaces between the crosshatch grid of rebar that will go over the slab.  The positions of the cubes are as per your AutoCAD drawing.  It is worth doing it in CAD because on a large foundation it can get a bit complicated figuring out how to avoid the rebar grid.  Mark the cube positions on the slab protection EPS using tape.

Cube Position Marking Tape 

Cube Position Marking Tape Corner 


Stirrup assembly - External wall footings

The structural engineering for the foundation calls for stirrups manufactured from half inch basalt rebar.


The bottom of the stirrup is supported off the bottom of the footing trench by 3.25" plastic rebar chairs to the bottom of their U.

Two of the following are also used...


Finally this piece goes horizontally half way up the footing...


It is good to do as much rebar tying work as possible before going down into the footing trench.  Use a jig to form an assembly from the different rebar stirrups.  You need to make a few hundred of the foundation stirrup assemblies.  Tie them together using cable ties

Foundation stirrup assembly jig

Add small wood blocks on a plywood base to form the jig.  Where there are going to be cable ties it is good to cut an access hole.  The dimensions for fixing the wood blocks will come from your foundation AutoCAD drawings.

External wall stirrup assembly...

Measurements Foundation Stirrup Jig 

Internal wall stirrup assembly...

Measurements Foundation Stirrup Jig Internal 

Here is the finished external wall jig that also has cable tie access holes.  It also has cut slots in the edges where the rebar chairs will go...

Foundation Rebar Stirrup Form Board 

The internal wall stirrup assembly is different from the external wall case.  Here is the internal wall jig (sitting on the external wall jig)...

Internal Wall Stirrup Assembly Jig 

Make foundation stirrup assemblies

Lay the various stirrups into the jig.  For both external wall and internal wall cases there are two versions of the sequence of adding rebar stirrups.  This makes two variants of the stirrup assemblies.

The sequence for the Green variant (and Cyan variant) is...
    Big U
    Middle Big L
    Inner Big L

For the Red variant (and Magenta variant), reverse the sequence.

For my house I need the following number of pre-made stirrup assemblies...
    External wall Green variant     90
    External wall Red variant         90
    Internal wall Cyan variant       48
    Internal wall Magenta variant     48

At the corners, individual stirrups are used rather than stirrup assemblies.

On the stirrup assembly jig tie the stirrups together with cable ties at the places where there is a jig hole.  If a stirrup is a bit warped then you may occasionally decide to add an additional cable tie.

Also add rebar chairs to the assembly, both at the bottom and the sides.  At the bottom use 3.25" chairs and at the sides 2.25" chairs.  Put the rebar in the chair U and then add two cable ties in a cross.  Then once the assembly is off the jig spread PL-Premium adhesive on the joint to stop the chair position rotating.

Foundation Stirrups Tied Cross Cable Ties 

Tied And Glued Bottom Chair 

Here is the built assembly on the jig (complete with rebar chairs)...

Foundation Stirrups On Jig 

Remove the assembly from the jig.

Foundation Stirrups Tied Assembly 

Here is the internal wall version...

Internal Wall Stirrup Assembly 

The assemblies go every 1 foot along the external wall footings.  They should all be shown on your CAD foundation drawings.

Stirrup Assemblies Stacked On Slab

Site Rebar Stirrup Assemblies Built Stacked 


Install assemblies in footings

Adjust liners

Make sure the ToughLiner and underlying waterproof membrane are in the right position.  You want the slack to be at the sides of the trench and you want to ensure that there is slack both above and below where the horizontal side chairs will be.

Marker tape in trench

Using a self leveling laser with a vertical beam, add two bits of marker tape at the bottom of the trenches to correspond to the marker tape on the slab and outer form-a-drain.  The "horizontal" edge of the marker tape shows the center of the chairs at the bottom of the assembly.  Also put marker tape on the sides where the side chairs will be.  The reason this tape is not added earlier is that the ToughLiner in the trench may move around a bit.

Add assemblies either side of corners

Either side of the corners, add one completely orthogonal stirrup assembly and one very slightly angled.  This is enough to be tied to the three inner corner pieces and a few more of the further in corner pieces.

Cut to make horizontal #4 corner pieces

At the corners use #4 angle pieces.  They will overlap by at least 22.5" (ie at least 30 times the #6 rebar diameter).  In practice the legs of my corner pieces are 2'6" (30") as they are the corners cut from my rebar straights that have a bend in the end.

The bend pieces are made by cutting off the corners from the straights that have a bend in the end.  Each leg is 2'6" so it leaves a straight offcut piece that is 16 foot long.

Even though it is not a requirement of the structural engineering, it is good to provide continuity between the horizontal rebar in the footings round the corner.  As there are 13 pieces of horizontal rebar that means each convex corner needs 13 corner pieces.  It is not a concern that you will be joining #6 and #5 rebar straights using #4 diameter corner pieces (given that it is not a structural engineering requirement even to have corner pieces).

My main house has 8 convex corners so that means I need 104 corner pieces.

The bend pieces will not all be within the stirrup assemblies and even the ones that are will be in different places inside the stirrup assembly.

Internal wall footing corners do not require corner pieces because these are all crosses and the horizontal rebar can be continued across the cross, all be it with a slight joggle of their position between an internal wall footing and an external wall footing.

Horizontal straight rebar at corners

When at 45 degrees the Big U stirrups are not wide enough to go to the corner of the trench.  A horizontal rebar straight with a chair on each end will work ok in the corners to hold the stirrup assembly in the right place laterally.  In practice there is lots of bunched up polyethylene sheet in the corners to make a relatively flat surface for the chair to rest on.  This also keeps the liners properly fitted into the corners.

Corner rebar 

Add angled stirrups at corners

These are the same stirrups but placed at an angle in the corners.  They cannot be pre-formed into stirrup assemblies because the dimensions of the assembly need to be different at the corners.  You need to form modified stirrup assemblies in situ at the corners.  Do not yet tie the assemblies together too much (especially at the top) or it will be hard to get the horizontal corner pieces in place.

Foundation Stirrups At Corners 

At the corners, tie the stirrups to the 45 degree horizontal rebar using cable ties.

Note that even at the corners it is the position of the vertical rebar (that will go up into the walls) that determines the position of the stirrup assemblies.

Put in place corner pieces

Thread the corner pieces through the variants of the stirrup assemblies used at the corners.

On the inside of the curve use cable ties to attach them such that they are in the right places to mate up with the horizontal rebar that is not yet added.  This uses a few extra cable ties but it is worth it to hold the corners together.  The positions for the horizontal rebar can be found from the orthogonal stirrup assemblies on each side of the corner.

Also tie in place the corner pieces on the outside of the curve but in practice these will not span the full complement of angled stirrup assemblies.

Add temporary wooden sticks

To make up for the corner pieces being too short, on the outside of the curve, 6 foot wooden sticks are used to temporarily hold the angled stirrup assemblies in place.  You can use garden wire to temporarily hold them.  Wire is better than cable ties for temporarily holding things as it can be adjusted as needed, but cable ties will also work.

The corner assemblies should now form a stable "corner-stone" that can help hold everything in place.


Put other stirrup assemblies bunched up in the trench

The rebar stirrup assemblies go at 12" on center as shown in your AutoCAD drawings.

Note that you can not yet put the stirrup assemblies in their proper 1 foot locations as the horizontal straight rebar is not yet threaded through.  Instead, put the required number of assemblies in the trench all bunched up together in the corners.  There are two versions of the stirrup assemblies, so put one one variant at one end and the other variant at the other end.

The horizontal rebar is 19'2" (or cut shorter for smaller wall sections).  You need to ensure there is enough bare trench available to get the horizontal rebar in.  The hardest horizontal rebar access case is the northern edge of the north portico and the southern edge of the south portico.


Thread horizontal rebar through stirrup assemblies

Wooden support jigs

Note that only the ends of the horizontal rebar will be threaded through the bunched up stirrup assemblies.  To support the rest of the rebar length it is good to use wooden jigs to get them to the right heights and stop them rubbing against the lining at the bottom of the trench.  The jigs have 2x4 feet to stop them tipping over.

Support Jigs For Horiz Rebar 

Cut horizontal rebar

Typically in a trench for each horizontal position will be one uncut length and one cut length.  It is good to work out the cut lengths in AutoCAD so they don't have to cut them in situ.

Opinion and code varies, but at absolute minimum they must overlap by at least 22.5" (ie at least 30 times the #6 rebar diameter).  I chose to make the overlap at least 3'2" (38") to be conservative.  In the calculation for how long the cut piece should be, assume the 19'2" rebar straight only provides 16'.

After calculation what the cut lengths need to be, use some judgment to increase the overlaps to avoid waste given that there is no point in having a bunch of little offcuts.  Sometimes increasing the cut length to 19'2 (and thus avoiding cutting) is the right thing to do.  Sometimes increasing the cut length to 9'7" (ie half of 19'2") is the right thing.  These rounding ups make particular sense where the extra can extend into internal wall areas.

For each footing trench make a drawing to show the lengths of horizontal rebar required in each trench.  The red figures give the figures that were decided on.

Furthest west (and the furthest east) north-south footing (2 off)

Footing Rebar Lengths Furthest West 

East-west corners (4 off)

Footing Rebar Lengths East West Corners 

Portico north-south short edges (4 off)

Footing Rebar Lengths Portico North South 

Portico east-west long edges (2 off)

Footing Rebar Lengths Portico East West 

Internal north-south long walls (2 off)

Footing Rebar Lengths Internal North South 

Internal east-west short portico walls (2 off)

Footing Rebar Lengths Internal East West

Overall cut list

So that you can do all the cutting in one go prior to moving the rebar to the appropriate places, it is worth doing an overall cut list.  It is also worth listing the uncut 19'2" lengths to help with moving logistics.

#6 rebar

19' 2"                    (2 x 13) + (4 x 0) + (4 x 9) + (2 x 9)   + (2 x 18) + (2 x 9) = 26 + 36 + 18 + 36 + 18 = 134

14' 2"                    (2 x 2) + (4 x 0) + (4 x 0) + (2 x 0)   + (2 x 0) + (2 x 0) = 4 = 4

13' 0"                    (2 x 1) + (4 x 0) + (4 x 0) + (2 x 0)   + (2 x 0) + (2 x 0) = 2 = 2

11' 0"                    (2 x 2) + (4 x 0) + (4 x 0) + (2 x 0)   + (2 x 0) + (2 x 0) = 4 = 4

9' 7"  (halving)     (2 x 0) + (4 x 9) + (4 x 0) + (2 x 4)   + (2 x 0) + (2 x 9) = 36 + 8 + 18 = 62

6' 2" (offcut)        (2 x 0) + (4 x 0) + (4 x 0) + (2 x 1)   + (2 x 0) + (2 x 0) = 2 = 2

5' 0" (offcut)        (2 x 0) + (4 x 0) + (4 x 0) + (2 x 2)   + (2 x 0) + (2 x 0) = 4 = 4

#5 rebar

19' 2"                     (2 x 5) + (4 x 0) + (4 x 4) + (2 x 4)   + (2 x 8) + (2 x 4) = 10 + 16 + 8 + 16 + 8 = 58

114' 2"                     (2 x 1) + (4 x 0) + (4 x 0) + (2 x 0)   + (2 x 0) + (2 x 0) = 2 = 2

13' 0"                     (2 x 1) + (4 x 0) + (4 x 0) + (2 x 0)   + (2 x 0) + (2 x 0) = 2 = 2

11' 0"                     (2 x 1) + (4 x 0) + (4 x 0) + (2 x 0)   + (2 x 0) + (2 x 0) = 2 = 2

9' 7" (halving)      (2 x 0) + (4 x 4) + (4 x 0) + (2 x 1)   + (2 x 0) + (2 x 4) = 16 + 2 + 8 = 26

6' 2" (offcut)         (2 x 0) + (4 x 0) + (4 x 0) + (2 x 1)   + (2 x 0) + (2 x 0) = 2 = 2

5' 0" (offcut)         (2 x 0) + (4 x 0) + (4 x 0) + (2 x 1)   + (2 x 0) + (2 x 0) = 2 = 2


Lay 5 parallel longitudinal lengths of #6 rebar on bottom of stirrup assembly

These rebar lengths go all the way along the footing trench all the way round.  The specific positions are as per the AutoCAD drawing.  Four of the five positions are obvious on the stirrup assembly.  Use a wooden measuring stick to set the position of the fifth one.

Use three wooden jigs to support them about 6" from the bottom of the trench.

Wood Trench Rebar Support Lower 

Alternate which end of the trench gets the cut length of horizontal rebar.

Add four more pieces of #6 rebar at the middle

These will be later fixed to the underside of the horizontal "FootingBigHoriz" stirrup.

Use three wooden jigs to support them about 1' 7" from the bottom of the trench.

Wood Trench Rebar Support Middle 

Alternate which end of the trench gets the cut length of horizontal rebar.

Add four pieces of #5 rebar at the top of stirrup assembly

These will be later fixed to the underside of the horizontal legs of the "FootingBigL" stirrups.

Use three wooden jigs to support them about 3' from the bottom of the trench.

Wood Trench Rebar Support Upper 

Alternate which end of the trench gets the cut length of horizontal rebar.


Move stirrup assemblies to correct places and tie

Once all the horizontal rebar is threaded through the stirrup assemblies in the right places, move the stirrup assemblies to all their right places (as indicated by the marker tape).

Use cable ties to attach the horizontal rebar to all the right places on the stirrup assemblies.  Some of the rebar is resting on the stirrup assembly and some is hung from under the top. Initially tie the cable ties loosely so that accurate adjustment can be made later before final tightening.

Place the rebar assemblies such that the rebar center of the top edge of the assembly is on the "horizontal" edge of the 1/2" marker tape.  This is to make sure the vertical rebar added later will be in the correct position.  Use a straight wood stick between the marker tape on the slab and the marker tape on the outside form-a-drain to see where the vertical rebar will be.

You want some membrane slack above the side chairs and some below. 

If needed use a spreader tool to ensure there is enough width for the stirrup assembly and to get the ToughLiner and waterproof membrane in the right place. 

Rebar Measuring Spreader Tool

Position the spreader such that the chairs on the end of the spreader will be directly adjacent to where the side chairs of the stirrup assembly will be.  Center the spreader 2.25" from the "horizontal" edge of the marker tape.

Slide the rebar assemblies in at an angle with the horizontal rebar chairs held in the right place with your hands so they don't break.  Make sure you are not pulling the foundation linings out of their correct position and make sure there is equal slack in the linings on both sides of the trench (and above and below the horizontal chairs).

It is useful to use some 8' long wood sticks with half inch notches that hold the assemblies at 1' on center.

One Foot Rebar Spacer Sticks 


Install vertical footing rebar

This bent length of vertical rebar ties at the bottom to horizontal rebar and at the top of the stirrup assembly.  The connection at the bottom to all of the horizontal #6 rebar is done using a cable ties.  It must be securely tied in multiple places to avoid any danger of it breaking free and puncturing the waterproof membrane.

The verticals go 12" on center.

The bent legs are never shortened, ie they are always 2'6" long.  They are angled to fit them in.  Sometimes the bent leg goes inwards and sometimes outwards.  As there is more space inwards, use 3 legs inwards to one leg outwards.  The legs go outwards from the building center.

The length of the rebar above slab height is given in your AutoCAD drawings as it varies depending on the doors and windows.  There are some cases where the full length of the #4 rebar could be used, but it was decided that having this flopping around too far above slab height would be unmanageable.  Even when it could be longer, the maximum height above slab height will be 3' 6-1/2".

As you add each vertical piece of rebar, make sure you add safety caps on the top.

Vertical outer rebar 


Rebar over slab area

Lower layer on slab area

The over slab lower layer rebar alternates between straights with a bend and pure straights that go across the footing to a rebar chair on the outside (or right across in the case of an internal wall footing).  That means the bent ended rebar pieces are every 24".

The angled rebar has a bend radius of 6".  The bent leg does not need to be cut as 2'6" is fine.  The bent vertical leg goes down the inner edge of the footing trench.  The vertical leg must be tied in multiple places (4 places) with cable ties to ensure it cannot slip down and puncture the waterproof membrane.

On the slab area the angle pieces rest on short rebar chairs.  The regular chairs are modified on a band saw to support the bottom edge of the rebar 1.5" from the deck.  The concrete chairs can go directly onto the 1" EPS that covers the slab area.  Use cable ties to attach the rebar to the chair.

Rebar Chair Cut To 1.5 in

Use wood jigs to help you quickly and consistently cut the rebar chairs.


Upper layer on slab area

As with the lower layer, the upper layer alternates between a rebar piece with a bend in the end and a purely straight piece.  The leg of the bent piece goes vertically down near the center of the footing.  In the case of the purely straight rebar, it goes over the footing trench and terminates with a horizontal rebar chair tied on the end.

The center to center distance between the upper and lower slab rebar is 4".  That equates to 3.5" from the top surface of the lower rebar to the bottom surface of the upper rebar, or in practice 3-3/8" given that it will sit on a cable tie.  This spacing can be achieved with a 3.25" rebar chair and 1/8" of error (which can be ignored).

The bottom end of the rebar chair is attached to the lower rebar using a cable tie through a hole drilled near the bottom of the chair.  A cable tie is also used at the top round the U.

Glue everything in place

When you get to a natural point where you will not be moving things around for a day or two, it is worth going round with a glue gun loaded with PL Premium to make sure nothing can move.  You will also want to put glue around the base of the vertical bits of rebar to make sure they don't slip out of position.  Remember that wet concrete can exert quite a large force on the rebar and you don't want it to move.  You especially don't want the sharp end of a piece of vertical rebar to come free and possibly puncture the membranes that line the footing trench.

Also put PL Premium on the horizontal chairs on the ends of the over slab rebar.






Use angle pieces at the corners to strengthen the rectangle that constitutes the center of the wall.

Install angle pieces up the footing center

Even the short leg of the angled rebar is too long for the footing width, so rather than cutting the short leg, it is angled  to get it to fit.  Having more rebar is best so there is no sense in cutting off rebar and throwing away the offcuts.  Alternate left left and then right right at every 12" position.  The pattern repeats every 4 feet along the wall.  Tie the vertical long legs of the angled rebar to the center top ring of horizontal rebar that is the wall center,  At the bottom tie the short legs horizontally to the original cross trench pieces of rebar.

As you add each vertical piece of rebar, make sure you add safety caps on the top.

Angled rebar to wall center 

Vertical rebar that goes into walls

Because the angled rebar does not have long enough legs to form a proper overlap join above basement floor level, it is necessary to set pieces of straight rebar up from the footings. These rebar straights should protrude 3' 6-1/2" above the surface of the slab.  In the places where there are wall openings then the length can be reduced accordingly (as per your AutoCAD drawings).

The straight rebar lengths go down to where the original cross trench rebar bars are.  They attach to the cross rebar using galvanized wire through an 1/8" hole that is drilled 3/8" from the end.

Particularly at the top connection as they pass the center of wall horizontals, you may need to one at a time undo the galvanized wire and remake the join to now include the extra vertical rebar.

As you add each vertical piece of rebar, make sure you add safety caps on the top.

Vertical rebar that goes up into walls 

At the corners you also need the vertical rebar on 12" centers.

Vertical rebar at corners 

Install cross rebar that's half way up the footing

These go on 12" center across the footing trench half way up.   They tie to the vertical rebar in the middle and at the ends.  These pieces of rebar are 20" long (although if your trench walls are a bit bowed in then you might have to make then slightly less (possibly even 18") to avoid the possibility of them touching the waterproof membrane).  Drill a 1/8" hole about 3/8" from the end as this is used for the connection on the end nearest the slab.  They go 15" above the original cross pieces.  On the end without the wire hole, use a rubber thimble on the end of the rebar so there is no danger of a sharp end hurting the waterproof lining.

Half way up cross bars 

Install the upper rebar over the slab area

This alternates with the lower rebar over the slab area.  The rebar is supported 6" off the EPS that covers the slab area by using rebar chairs that have rebar extension pieces.

Rebar chair wired 

Rebar chair wired and glued 

Alternatively these can be made by molding your own concrete block on the end of an appropriate length of rebar.

Extended concrete chair 

On the outside end on the horizontal over slab rebar, wire-on 1.5" rebar chairs horizontally and use 1/2" EPS pads to the outer side wall of the footing trench.  Note that the ends of the rebar droop down a bit (to the height of the outside verticals) in order to avoid the keyway for the wall.


Install angle pieces from footing to upper slab rebar

These angle pieces hang down into the footing.  The short leg goes into the footing.  The short legs tie to the cross rebar that is half way up the footing trench.

Upper over-slab rebar with chair on the end


Add two extra angle pieces at corners

Install two extra pieces of angled rebar at the corners as shown in the picture.

Angled corner rebar 


Install top two rings of horizontal rebar

These inner and outer rings of horizontal rebar use angle pieces at the corners. 

Horizontal upper rebar rings 



Jigs to form top groove

Cross trench jigs

There is 2" on the outside and 1.5" on the inside.  All this is shown on the foundation design drawings.

Groove At Corner Drawing 

About every about 6 feet there is a 2x4 assembly across the footing trench.  It hooks over the outer upper form-a-drain.  At the other end it is supported by an 8" wooden cube that sits within the rebar grid on the slab area.  The cross trench plank supports the groove notch plank that has 1 foot pitch holes for the vertical rebar.  Here's the drawing for the most common jig type that is used on the outer footings.  In my case I need 34 of these.

5' 4"    Outer footings    34 off

Jig For Vertical Rebar Drawing

Trial Groove Support Rig

Where possible it is good to stick to standard dimensions for the jigs that support the groove planks, but in some cases they need to be non standard to ensure they don't conflict with the rebar positions.  Also making some non-standard allows the number of 8" cube boxes to be minimized.  Plan it out on your AutoCAD drawings.

Foundation Walkway System 

Here are the other jig drawings.

5'9"   Internal footings    10 off

Groove Jig Internal Footing 

6'7"   East west at corners    4 off

Groove Jig Internal East West 

7'7"   North south at corners    4 off

Groove Jig North South 

Wooden cubes

On the slab area there are 8" wooden cubes to hold the assemblies at the right height.  The cubes are designed to be easy to remove after the concrete has set.  Screws are only used at the top and they are covered with tape to stop the heads being filled by concrete.  At the bottom, tape is used to stop the wood warping out.

Wood Block 8in Cube 

The cube edge is 3' 3-1/4" from the vertical rebar string in the case of outside walls.  For internal walls the distance is usually 2' 9-1/2", although it is a bit more at the corners.

Key notch plank

The 3.5" groove is formed by lumber cut to 2.5" x 1" with half inch EPS glued on the bottom and sides.  The EPS makes it easier to remove after the concrete has set.  The planks hold the vertical rebar in the right place.

Cut the 2.5"x1" wood from lumber that is 8' long.  You can get two pieces from a 2x6.  Join the planks together using a couple of 1/4" wood dowels in the end and some PL-Premium.  Arrange the bow of the planks such that the joins are the highest point and the bow is down in the middle.  The joins will be held lower by the straightening pieces that will be added later.

Groove Planks With Dowels 

Groove Plank Gluing Eps 

Start by making the corners (as these are the starting point for measuring the rebar hole positions).  Join by drilling holes for the dowels in the side of a second plank.  Glue the corners with PL-Premium.  Once the glue has set, drill 3/4" holes in the groove planks to correspond to the vertical rebar positions, which are 12" on center. 

Having the key notch lumber in place while pouring the concrete is useful as it will help show the required concrete level.  The top of the planks will be at the same height as the outer Form-a-drain.

 In order to take out bow in the groove planks it is necessary to attach on edge 2x4s to the middle of the top side.  These are attached with  just 2 screws so they can be removed for final screeding after the concrete is starting to harden.

Stiffening 2x4

This is a piece of 'on-edge' 2x4 screwed on top of the cross trench jig.  It stiffens the jig and provides height adjustment.

You can use a self leveling laser to get the key notch plank height exactly right.  Use wood shims under the stiffening 2x4 to adjust the height of the groove plank.

Need the grove plank on the internal concrete walls too.  Note that there is an offset relative to the plank on the outer footing.

Mark jig positions

Number and mark the places where the jigs go so you can easily remove and refit them to allow you to fit rebar.

Walkway system

This walkway system will stay in place even while doing 90% of the concrete pour for the foundations.  It consists of 8" wide planks between the 8" wood cubes.  It is designed to not get in the way of the rebar that will be over the slab.  The planks will be screwed to the wood cubes (2 screws each end) and thus ensure that the cubes do not move and thus the groove planks do not move.  The lengths of the planks are as per your AutoCAD drawing.  Put tape over the screw heads so the heads do not get clogged with concrete.  The planks can be removed as needed during the concrete screeding.

The 8" high blocks will stay in place during the concrete pour and concrete setting.  The screeding is done off the 8" high wooden cubes.  The holes in the slab left will be filled with bagged concrete later.


Key notch fitted 

Key notch level 

Support for key notch lumber 

Wire to adjust key notch rectangle 




Squaring up groove planks

First ensure the sides of the rectangle are exactly straight.  You can do this by shining a laser along the edge of the 2x4 key notch lumber.

Before screwing down the inner ends of the support lumber it is necessary to get the key notch lumber rectangle exactly square, ie have exactly right angle corners.  This is done by measuring the diagonals of the rectangle to ensure they are exactly the same length.  The distance should also be the same as your AutoCAD drawing shows.

Measure diagonal key notch rectangle

Initially one diagonal will be longer than the other.  Attach some garden wire between the corners of the longest diagonal and with a spare bit of 2x4 gradually twist it to pull the long corners in.  Keep measuring and stop twisting when both diagonals measure the same.

Wire tensioning diagonal adjust 

Bracing creativity for key notch lumber 

After the key notch rectangle is exactly square and straight. and a self leveling laser has been used to get it exactly the right height, then the inner ends of the support lumber can be screwed to the walkway (preferably above he support cubes).  You will typically need to put a few shims under the inner end to set the height to get the support lumber level.  Having the support lumber exactly level should mean that the top of the key notch lumber is at the same height as the top of the outer Form-a-drain.

Check the levelness

The final step is to make sure the key notch boards (and the top of the outer Form-a-drain) are accurately level.  They should be unless there has been some uneven settling.  It's worth checking just to be certain.  Use a self leveling laser to check the levelness.

Self leveling laser  

Put the laser in its regular reference place and use a length of 2" white PVC with a marker pen mark.