Insulated Concrete Forms (ICF)

ICF as installed

For our house, we have chosen to use insulated concrete forms (ICF) as the primary wall system for the exterior walls of the house, with sections that are structural insulated panels (SIP).

ICFs are made of 2 sheets of expanded polystyrene (EPS, aka Styrofoam) with concrete poured in between.  The materials comes in blocks, and is assembled on-site in a similar fashion to Lego blocks.  The blocks act as the form work for the concrete as it is poured into the cavities between the two sheets of EPS, and is a stay-in-place form work, as the blocks of EPS are not removed after the curing of the concrete.  The EPS acts as the insulation for the wall, and the concrete provides the strength, and a total air and thermal break between the inside and outside of the walls.

On the inside, drywall is directly fastened to the ICF, as the ICF have built-in plastic strappings that act both as a structural component for strength and for holding the EPS together, as well as for screwing the drywall into the straps.  For electrical, the EPS is thick enough to accomodate the mounting of the electrical boxes, with the wires being embedded into the EPS.  No penetrations through the concrete is required, except for venting purposes.

This method of building provides a much stronger structure, which may be an advantage if you are in an natural disaster prone area.  Other benefits include a much tighter building envelope, as the concrete wall system is a monolithic system and no possible penetrations for air leakage.  This translates into a significant reduction of heat loss, as up to 1/2 of the heat loss of a house can be attributed to air leakage.  If you live near a noisy environment, another benefit is the significant noise reduction from the outside.

In using the ICF, we decided to go from basement to the roof, except in areas on the second floor where there was nothing underneath to bear the weight of the concrete.  For the basement walls, this is fairly cost competitive with traditional poured concrete walls or cement blocks.  Once we went above ground, however, it becomes a significant cost upgrade to use ICF.  For this reason, there are some builders that will choose to use ICF for the basement, and either traditional timber frame (cheapest) or SIPs (more expensive than traditional, less expensive than ICF) for above grade exterior walls.  Expect an upcharge of $8-10/sq.ft. wall space material and labour from traditional timber frame, and an upcharge of $5-7/sq.ft. wall space from SIP, depending on complexity of project.

In our house, we have chosen to use blocks manufacturered by Nudura, supplied through our contractor for the exterior “framing” (Stevens Construction).  The blocks consists of 2 5/8″ sheets of EPS on the outsides, with a 6″ cavity for the concrete.  Other cavity thicknesses are available, starting at 4″ and increasing in 2″ increments.

CaGBC LEED for Homes – Points can be acheived in Energy and Atmosphere, either via the air leakage tests (EA 3.3) or exceptional energy performance (EA 1.2) via the ERS/HERS method.  In our case, it would qualify for Material and Resources (MR 2.2) for local content, as the concrete and the ICF are both manufactured within 800km.

Structural Insulated Panels (SIP)

SIPs as Installed

Part of our exterior wall system were constructed with structured insulated panels (SIP).  We used these panels in two areas:  in areas where we could not use ICF because of a lack of a supporting wall underneath to bear the weight of the concrete in the ICF, and in wall areas that faced into an unconditioned area, such as the wall separating the garage and the living space, and a section of walls that faced into the lower attic.

Our SIPs are made of two sheets of oriented strand boards (OSB), with expanded polystyrene (EPS, aka Styrofoam) sandwiched in between.  Various sizes and thickness are available, and for the majority of the SIPs we used had either 4’x9′ or 4’x10′ sheets that were 8 1/4″ thick in total (7 1/4″ EPS).  Channels at the edge are carved out for installation of splines using 2×8 lumber as well as for the plates.  Every 4′ a spline was installed, and glued and nailed together to the OSB.  In our case, we had ordered the panels with built-in channels for electrical wiring.  What surprised us was how rigid the wall system as we were installing even without the nails in place; the tight fit of the spline to the OSB and the rigidness of the SIP allowed it to stand on the base plate with no flex whatsoever.

Benefits include an air tight structure, and reduced thermal bridging compared to traditional timber frame, as “studs” are every 48″ instead of every 16″.  The fit between the OSB and the spline/plates are also very tight and glued together to minimize potential air leakages.

In costs, we estimated this to be about a $3/sq.ft. wall space upcharge for material and labour from traditional timber framing, and about $6/sq.ft. less than the ICF.

Our SIPs are from Insulspan, sourced through Kent Trusses (who also supplied our floor and roof trusses).  The SIPs were ordered in 6 1/2″ and 8 1/4″ thicknesses, in 4’x9′ and 4’x10′ sheets, with wiring channels put in at 14″ and 44″ from floor.

CaGBC LEED for Homes – Points can be achieved in Energy and Atmosphere, either via the air leakage tests (EA 3.3) or exceptional energy performance (EA 1.2) via the ERS/HERS method.  Points is also available in Material and Resources (MR 1.4) for SIP and MR 2.2 for local content.

Stucco

Dryvit Terraneo Stucco

The original architectural design called for a combination of stone and stucco for the exterior of the house.  But considering the majority of the house was wrapped in ICF and EPS, the most logical choice of material was stucco, as it required an EPS substrate.  After we had priced the stone installation, made more difficult with the ICF and EPS as the surface material was not structural, we decided to change the design to an all stucco exterior cladding.

Our choice was to use the Dryvit TAFS (textured acrylic finish system) on the ICF, primarily because of their TerraNeo finish, which gave it a granite look without the cost of stone.  Dryvit is one of the leading stucco systems manufacturer in the world, and their TerraNeo finish has chipped granite flakes in the mix to give it a more interesting and pleasing aesthetics for accent areas, a combination that gave it a very unique look, and a glimmer and sheen that can be seen at varying sun angles or on an overcast day.

 

Dryvit Terraneo Stucco