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.

Ceiling Insulation

Ceiling Insulation

Our ceiling insulation material is from Nudura, the same manufacturer as our Insulated Concrete Blocks in the exterior walls.  The Nudura Ceiling Technology is a 2.5″ or 3.5″ sheets of EPS with built-in wood strappings for simple installation of drywall.  These were delivered onsite as 4’x8′ sheets with ship lap edges, which provides a tight fit at the seams.

Our installation consisted of, from top to bottom, the roof truss, a 1/2″ sheet of drywall, a 3.5″ sheet of the Ceiling Technology, followed by another 3.5″ sheet running in perpendicular direction, and finally a finish sheet of 1/2″ sheet of drywall.  The ceiling insulation “sandwich” assembly hangs on the underside of the roof truss system, which completely eliminates any thermal bridging of wood.

In total, we have 7″ of EPS, which would in theory only net an R27 based on the EPS alone, and below what the Ontario Building Code requires.  However, because of the reduced thermal bridging and the greatly reduced air leakage, Nudura has tested the product in the field and have shown for the product to perform at an equal or greater than an R60 fiberglass batt or loose fill type insulation.

For our project, there was a cost increase of approximately $7,500 compared to a 12″ loose fill sprayed in cellulose, but with far better performance in heat loss as well as air infiltration.

CaGBC LEED for Homes – Points can be acheived in Energy and Atmosphere, in Insulation (EA 2), or exceptional energy performance (EA 1.2) via the ERS/HERS method.

Spray Foam and Air Sealing

One of the biggest challenges to creating an energy efficient house is to reduce the air leakage as much as possible.  While we have chosen to use ICF and SIP framing to greatly reduce the air leakage in the walls, and Nudura Ceiling for ceiling insulation, the gaps and interfaces need to be sealed as well in order to be air tight as possible, and the choice of the casement fiberglass windows.

We chose to spray foam insulate the weak points of the house; the ledger board area where the SIP interfaces to the ICF, the penetrations around the house to the outside, the pot light wire penetrations into the attic, and where the walls on the 2nd floor meet the ceiling.

Slab Insulation and Radiant Heating

Before the basement concrete slab was poured, a 2″ thick EPS (R7) was put in place to reduce the heat transfer to the soil beneath.  In addition, PEX tubing was run in 90% of the basement floor space to allow for in-floor radiant heating.  In-floor radiant heating allows for a more comfortable basement floor as it is no longer cold to walk on, and is efficient as heat rises throughout the house in the winter, as well as a reduction in the heating area that the fan coil has to service.  The garage was insulated and roughed-in with the same system for the ability in the future of a heated garage.

The tubes are connected to the Daikin Altherma system, which provides radiant heating to the basement floor as well as the fan coil to heat the ground and second floors, as well as heating the hot water for the house.