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Decking and Porticos


The porticos are just built like any other ICF walls.  The decking is just a very large balcony.  The decking is built from concrete and, as per a balcony, is thermally isolated from the main concrete of the house.  The technique for building balconies is described here .

To provide the thermal isolation involves implementing a concrete lip around the outside of the house wall, one foot below where the concrete decking will attach.  The concrete lip is formed using a box arrangement made from ripped 2x10 lumber.

Decking support box 

The concrete balconies and porticos are only used on the main house (not the evaluation building) but to try out the principle I did implement a concrete lip on the evaluation building wall.

It is good to implement the concrete lip all the way round the outside of the building even in areas where a deck or balcony is not required.  The reason is that it allows a temporary wooden platform to be built so you can stand on it to build the floor above.


Decking support lip

When wanting to have external thermally isolated balconies or decking it is necessary to form a lip of concrete that juts out from the wall.  The concrete actually extends 6-5/8" beyond the normal concrete cavity of the ICF wall.

To constrain the wet concrete to form the required protrusion, it is necessary to construct wooden forming.  Basically it is a box that has an outside height of 1 foot.  This is made from 2x10 cut down to be 9" wide with more 2-by on the top and bottom to make 12" high.  The top and bottom pieces are 2x10 cut down to 8-1/8" wide.  The internal cavity of the box is 9" high by 6-5/8" deep.  The box is made whatever width is necessary to fit between the windows and walls.

The box is made exactly 1 foot high so it is the same height as an ICF block.  It sits on an ICF block under it, but you will need to cut off the polystyrene turrets.  The ICF block above rests on the top of the box (no cutting needed).

Note that the ICF bracing (and the bracing legs on the window bucking assemblies) need to be accurately cut to the required height of the bottom of the box.  For an 8 foot deck underside that means the box will start at 7 feet, so the bracing needs to be 7 feet long.  Under the bracing verticals will potentially be shims to make the bracing vertical start at the exact bottom of the first course of ICF blocks (to compensate for any unevenness in the concrete slab).

To locate the box on the ICF block underneath and to locate the ICF block above, it is necessary to add pieces of 2x4 on the top and the bottom.  These are screwed on to their edges.  They need to be cut such that they fit between the vertical ICF bracing.

To hold the open side of the box the right distance apart (9" internal) it is necessary to use some 1/2" studding, nuts, and washers.  The studding also goes through the 2x4s (edge on) as this avoids the studding getting in the way of the ICF blocks.

Three foot long lengths of 1/2" studding are used horizontally through the box to the box or ICF EPS on the other side of the wall.  These should be spaced about every 2 feet but more often if it is a short width of box.  The studding holds the boxes in place during the concrete pour and also provides a useful mounting mechanism for whatever is attached to the concrete lip.  They typically go through at positions corresponding to the vertical bracing, ie at ICF web positions.

It is important to use a laser to get the lumber assembly for the concrete lip exactly horizontal.  It may be necessary to use some shims to level it up.  You want the downward force to properly transfer to the vertical bracing (rather than have it distort the polystyrene walls).

Concrete lip lumber forming 

Site with internal bracing 


Install Rebar for joining decking

Rebar 90 degree bends used to tie the concrete decking to the wall.

For the moment the rebar will be left sticking through the ICF.  Need to poke the bent rebar through from the outside.

Brace up the hole through the outer ICF (using 2-by lumber) so the concrete does not leak out.  It's at the top of the wall pour so the pressure will not be much.


Install rebar for column bases

Implementing the portico floors is part of this phase (the basement phase).  Need to provide some stainless rebar sticking up from the floor where the columns will be.


Install rain water inlet pipes

Rain water from gutters will run down pipes in the outer columns of both the north and south porticos.  This will be routed to a switching point in the basement.

Use 4" ABS pipe.

Try to make the pipe sections long enough so they can rest on the floor slab to support them and stick above the portico floor by about a foot.