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Interior Design General

Star Decide on the look you want to achieve and develop a consistent design syntax.



It is good to try to get some consistency with the interior design.  Try to establish a limited set of ways of doing things.

You need to have somewhere to route the wiring and you need to have room to mount the power connectors and Cat-6 connectors, as well as route water pipes etc.  My solution to this is to implement a 1'9" high wainscot.  That gives a close to 4" wide channel for routing.

The wall above the wainscot is done by removing the inside ICF EPS and using stucco directly on the ICF concrete.

At the top of the of the wall a large cornice made from hot-wire cut polystyrene is used to provide a place for the up-lighting.


Master diagram

Interior master diagram 

An important thing to have is a CAD drawing that sets your dimension standards.  It sets things such as the height that your wainscoting will be from the floor.  You don't want this to vary or it will look weird.


Removing ICF EPS on inside

I decided that to maximize room size and to closely couple the thermal mass of the concrete walls with the interior conditioned space that I would strip off the ICF EPS on the inside.  This leaves a rough concrete finish.

The ICF EPS is stripped off using the claw end of a hammer and then the grooves cleaned up with an old screwdriver.



The wainscot uses 3/8" MgO drywall and a 5-3/4" wide 1-1/2" thick  wooden shelf above.  That gives 3-7/8" of space behind the drywall.

Back corner with ledge

The drywall is held in place by the electrical faceplates.  This approach means that during house construction and potentially during the first year or two of house occupation it is possible to remove the drywall to run additional wires and pipes.  The downside is that it is necessary to have lots of electrical outlets (which some may consider a benefit rather than a negative).  The positioning of the electrical boxes is arranged to meet the needs of holding particular 8 foot lengths of drywall.  That typically equates to about 3 electrical boxes per 8' length of drywall.  Putting the drywall joins halfway through electrical boxes results in the least number of electrical boxes (one every 4 feet), but sometimes the situation and placement of doors etc will result in more.  Using an occasional Cat6 connector mounted in the lower position is a useful substitute to help reduce the number of electrical outlets.

Double width electrical boxes are used throughout (both for power sockets and Cat6 etc), even if it means one position has a blank insert.

Wooden 1'9" high spacer posts are glued to the wall either side of where the electrical boxes are positioned.  They have three holes in strategic places to allow wires to be routed.  Typically low voltage wiring is routed through the top hole and power wiring through the lower hole.

Also marked on the spacer posts are the standardized positions for the electrical boxes.  The usual electrical box is centered 11-5/8" from the underside of the wooden shelf (ie the top of the spacer post).  There is room for eg an electrical box for a cat-6 socket above the electrical box (centered 5-5/8" below the underside of the shelf, ie 6" above the usual electrical box).

Drywall electrical support 

The spacer posts are 3-7/8" wide and are glued (using PL-Premium) to the raw but cleaned-up ICF concrete (not on the stucco). 

Drywall electrical spacers glued to wall

You can make use of the old bracing 2-by-4s that are cutoff to the 1'9 height, but using them is not essential because gluing on spacer posts is easy to do.  Even if they are used, there still needs to be a spacer post 4" away.  You can use a 4" wide spacer while the spacer posts are being glued.

Electrical boxes clamped with spacer 

The shelf is glued to the top of the spacer posts (using PL-Premium)).

Electrical boxes and sockets fitted

Once the electrical boxes have been fitted and the shelf glued on, you can measure everything to produce a hand drawing of the piece (or pieces) of drywall needed to cover everything.  If you are uncertain of the measurements then make the electrical box holes small initially and then enlarge then later.

Drywall ready to be fitted

The holes in the drywall are cut big enough at the top and the bottom such that the drywall just fits over the installed electrical sockets.  Don't make the hole any bigger than necessary because the hole needs to be covered by the electrical faceplate.

Drywall fits over electrical outlets



Standard floor and wainscot height

The 1'9" wainscot height is measured from the structural concrete slab/floor.  The standard height for the finished floor above the structural concrete slab is 3-3/4".  In practice there are lots of ways that the flooring will be done in different rooms.  Sometimes it will be tiles, sometimes a self leveling concrete topping layer, sometimes 3/4" hardwood flooring, sometimes my own cut softwood.  Sticking to a standard height avoids floor level transitions (which are a tripping hazard). 

Floor leveling

It is assumed that the structural concrete slab will be level to within +/-1/2".  This variation will be taken out with 2-by planking that has an air gap underneath of between 0" and 1".  Wooden spacers are used to level the planks using a self leveling laser.  When additional height is needed (as it typically is) then the air gap will be increased.  The air gap can be used to route wires, but this is not the norm because wires typically go in the wainscoting.

Water radiant heating

PEX pipe is routed in groves in the 2x4 planking.  The 2-by-4 planks with the PEX pipe grooves are 10-1/2" on center.  This fits with the 3-1/2" plank width and the smallest radius that you can bend 1/2" PEX pipe.  It is necessary in AutoCAD to do a drawing for the entire room area to get all the different groove pieces in the right places (also need input and output grooves to get to the manifold).

The 2-by-4 planks that just have the long PEX groove down one side are installed first (laid flat).  Spacers of length 3", width 1-1/2", and of variable heights to take out the variation and provide any additional air gap (Up to about 2-1/4") are used with a spacing of about 18" to level these using a self leveling laser.  A 7" wide spacer is used to get the planks the right distance apart (no need for gaps between the planks because they typically shrink over time inside the house rather than expand, especially if they are my own cut lumber).  The long groove planks and their variable height spacers are glued to the concrete using PL-Premium.  Once all the long groove planks have been installed and verified to be completely level then 7-1/2" variable height spacer strips (again on about an 18" spacing and tucked slighting under the long groove planks) can be laid on the floor between the long groove planks and glued to the concrete.  The additional 2-by-4 planks (with their grooves for the PEX radius) can then be glued in place.  Glue is also used between the edges of the 2-by-4s to get everything locked together to form a solid base.  The net result is the entire floor area covered in 2-by-4s with a continuous groove for the PEX piping.

PEX pipe in roof grooves - checking it fits


Wet rooms

In the case of a bathroom that is designed to be a full wet room it is best to deviate from the floor standard height and make it one inch lower.  This means the water will go down the floor drain rather than spill out of the room.  You will need a height transition of about a tile width (12") as you come through the door.


The following gives how the standard height will be achieved for the different flooring types...

Tiled floor (PEX radiant heating)

1/2"        Air gap of between 0"-1" to take out slab height variations.
1"           Additional air gap (leave this out if you want the room to be a full wet room)
1-1/2"     2-by-4 lumber with PEX radiant heating pipe in a groove.
1/8"        Thinset to hold Ditra.
1/8"        Ditra
1/8"        Thinset to hold tiles.
3/8"        Porcelain tiles.

Hardwood floor (PEX radiant heating)

1/2"        Air gap of between 0"-1" to take out slab height variations.
1"           Additional air gap.
1-1/2"     2-by-4 lumber with PEX radiant heating pipe in a groove.
3/4"        Hardwood flooring.

Self leveling concrete floor (PEX radiant heating)

1/2"        Air gap of between 0"-1" to take out slab height variations.
1-1/4"     Additional air gap.
1-1/2"     2-by-4 lumber with PEX radiant heating pipe in a groove.
1/2"        Self-leveling concrete.

Softwood floor (PEX radiant heating)

1/2"        Air gap of between 0"-1" to take out slab height variations.
3/4"        Additional air gap.
1-1/2"     2-by-4 lumber with PEX radiant heating pipe in a groove.
1"           Softwood planks.

Softwood floor (electric radiant heating)

1/2"        Air gap of between 0"-1" to take out slab height variations.
3/8"        Additional air gap.
1-1/2"     2-by-4 lumber.
1/8"        Thinset to hold heating mat.
1/8"        Electric heating mat.
1/8"        Thinset protect heating mat.
1"           Softwood planks.



In the area between the top of the wainscoting and the cornice, I decided to use stucco as the wall finish.

I searched long and hard for the most healthy stucco to use.  Even clay earth stucco contains silica.  Some clay is just as bad as concrete from a silica % perspective.

There's a good website here .

In the end, this is what I settled on using...

For the bulk fill areas such as the 45 degree edges of windows, just use regular Sakrete concrete mix.  Like all concrete it unfortunately has lots of silica, but at $3 per bag it is a cheap fill.  For small fill, eg to fill in the groves on the ICF wall then use Sakrete stucco mortar ($5 per 80lb bag).

For the top coat, use the lowest silica content while plaster you can find.  That will be less than 5% by weight in the legal MSDS document and in the description is called "trace amounts of silica" or "percentage weight not measured".  The one I chose was Beadex Topping Pre-Mixed Joint Compound.

Topping Pre-Mixed Joint Compound   Details are here .



1)  Fill in the big voids with Sakrete concrete mix.  It is used to make the 45 degree edges on either side of the windows.   Applying it with your hands (wearing neoprene gloves) works well.

Concrete Bagged Sakrete   Details are here .

2)  Apply the scratch coat of stucco mortar that is used for filling in all the groves in the rough ICF concrete and getting a basically flat surface.   Applying it with your hands (wearing neoprene gloves) works well.

Mortar Stucco Sakrete 

3)  Apply the second coat (called the brown coat) to make a nice flat surface for the wall.  Typically a nice long magnesium mortar float is used to get it flat and smooth.

Stucco on ICF concrete 

Stucco scratch coat 

Stucco scratch coat 

4)  Apply Beadex Topping Pre-Mixed Joint Compound.  Use a long trowel to get it smooth.

5)  Finally the wall is painted with latex paint to seal it.


Electrical boxes

These want to all be at a standard height.  Personally I like them to be low down, just above the level of your highest floor.  The lower electrical box position (the position that is typically used) is 11-5/8" below the bottom of the wooden shelf (top of the spacer post).

It is important to mount the electrical boxes accurately, both in height and in the amount they are set forward relative to what will be the back of the drywall.  Assuming 3/8" thick drywall (MgO drywall) then the electrical box should be 3/8" set forward.  A spacer is used to set this distance consistently while screwing on the boxes.

Electrical box protrusion spacer 

Use a clamp too get the box positioned on the height line and with the right protrusion.  Use a long extension on the screwdriver so the angle is not enough to cause the box to get pulled back by the screw tightening.  The screw makes its own hole in the plastic and then into the wood.  Two screws are used on each side so the box is rigidly supported.

Screwing clamped electrical boxes

Joining wires 

Power sockets wired 

Power sockets electrical box 

The electrical sockets are wired and screwed into the boxes before the drywall is fitted.

Electrical outlets fitted to box

Electrical wall plates

In order to hide the larger than normal holes in the drywall necessary to clear the pre-installed electrical sockets it is necessary to use the biggest height wall plates you can get.  The ones I use are from Lutron and they also look nice because they have no exposed screws.  They have a base part that screws on to the spare holes in the electrical sockets and then the top part snaps on to hide the screws.

Electrical decora plates Lutron   Purchasing details are here .

Lutron cover plate

The electrical plates are used to hold on the drywall.  Rather than using the screws that come with the Lutron wall plates, you need to use long screws, eg 1.5".

Electrical Faceplate Long Screws    Details are here .

Long screws hold on plate base 

Plate base fitted electrical

Internet Cat6

Cat-6 sockets are mounted using adapter plates that make them into Decora size inserts so that the same Lutron wall plates can be used.  They are mounted such that the tabs on the Cat-6 cables are at the bottom.

(Replace the following picture with one the right way up)

Cat6 plate and blank in box

Where necessary, put the Cat-6 in the top position, ie the secondary position.  It is also ok to put it in the lower position when power outlets are not required at that location.

(Replace the following picture with one the right way up)

Cat6 above electrical 


Flat screen wall mounting

The flat panel VESA mount can be attached directly to the concrete wall using a thin piece of wood glued to the concrete with a couple of bolts fitted.  The VESA mount plate hooks over the bolt nuts.

Mount for flat screen 

Also provided is a power outlet that will be hidden behind the drywall.

Drywall with a hole just big enough to allow room for the VESA mount is attached.


Window sills

Window sill glued on

Window sills are made from 2x12 lumber.  The width is cut such that the sills protrude 1.5" past the drywall.  The edge is rounded off using two 45 degree cuts.  The cuts are 3/8" and are done on the table saw with the blade set at 45 degrees.  Moving the table gate in by half an inch with the blade moved to 45 degrees will produce a 3/8" cut (because you lose 1/8" when the blade is moved to 45 degrees).  They are cut to size and glued on using PL-Premium adhesive.



In order to readily meet Washington State Energy code without having to have lots of discussions about the house not needing much heating given all the insulation and thermal mass etc, I decided to use a bunch of electric radiators.  To hide their ugliness, I mount them behind the drywall and provide wooden grills top and bottom.

Radiator boxed-in 

Radiator wooden grills 

Wooden grate   Purchasing details are here .


Grab Bars


Info on the type I use is here .


Extractor Fan Countdown Timer

Extractor fan countdown timer Defiant Info on the type I use is here .


Floor tiling

Tiles in wet areas need to be glued on using modified thin-set.  Modified thin-set is concrete mortar with a latex glue additive.  Because it is concrete it is not possible to buy it as a pre-mix.  Anything that is a pre-mix is a mastic rather than a proper thin-set and cannot be used in wet areas.



Attic lighting

Light fitting using small box 

Attic lighting wooden strip 

Attic lights turned on 


Window sills

Inner sills below the window

These are make from 2x12 or 2x10 lumber and are glue to the window bucking.  No screws are used because you don't want any screw heads visible.

The edges have a 3/8" 45 degree bevel on them.  This is done using a table saw with the blade set at 45 degrees and the width set to half an inch less than the wood width (you lose 1/8" when setting the blade at 45 degrees).

Once the glue has fully dried the can be sanded and blended in with the sliding bucking wood.

Window upper sills

In addition to the 2x12 lumber glued on to make the inner window sills below the window, there are also sills of the same size and bevel glued on above the window.  Temporary 2x4s cut to the appropriate length hold them in place while the glue dries.

Upper Window Sill Meets Light Screen 



It is nice to show wooden beams.  It lends detail to the overhead plane.  The downside is that there is nowhere to hide ducting and wiring.


Large-format porcelain tile

Large-format porcelain tiles give the look and feel of natural stone at a much lower cost.


TV Location

When considering living room design you want to think about the various "focus of interest".  Typically they are three "focus of interest", ie the TV, the fireplace, and the view through the window.  You want to have these separated by not more than 90 degrees (the maximum comfortable turning angle of your head).

You cannot make every seat in the living room the optimum seating position but you need to have at least two seats that are optimum.  Other people in the room will have to put up with less than ideal seating.

Ideally the center of the TV should be at eye height when seated.  That equates to 42" off the floor.

The ideal viewing distance is between 1.5 times and 2.5 times the diagonal screen width.  For a 60" TV that means 7'6" - 12'6".

There is some logic for putting a TV above a fireplace because that combines two "focus of interests" in one place, but that means that the center of the TV will be way too high for optimal viewing.

Choosing a screen

If your living room is large then you want the biggest screen you can afford.  This will allow more chairs in the room to have optimal viewing because they can be set further back so the arc distance is longer.

Personally I like a screen that has a very thin border bezel.  As well as looking stylish, this means less of the window view behind is blocked.

Secondary screen

You may decide to have a primary viewing screen and a secondary screen.  The main video entertainment will be on the main screen and the secondary screen will be used for displaying photos or news feeds or house control functions.

To allow for someone in the kitchen to not miss a vital part of the movie, it is sometimes useful to have a second screen that is also playing the main entertainment feed.