Building with SIPs and ICFs


Did you ever notice how things tend to go in clusters? Lately we've had a cluster of inquiries about building with insulated concrete forms (ICFs) and with structural insulated panels (SIPs). In fact, we're in the middle of a project using both ICFs and SIPS, and I want to tell you a little bit about it.

Now, I'm not the construction manager and expert. That would be Wayne.  What you get from me is the simplified explanation. With pictures.  And cookies and chihuahuas.

The trouble with a story like this is that building a house is a little like making sausage -- the process is messy and you don't get to enjoy the tasty results til the end. If you're hoping for beautiful photos of the finished product, you'll be disappointed, because we haven't finished yet. But the process is pretty interesting, so keep reading.

Alternative building systems

There are all kinds of ways to build a house. One way is conventional wood framing using 2x4s or 2x6s -- builders call it stick framing. Structural insulated panels (SIPs) and insulated concrete forms (ICFs) are some alternative structural systems.

There are other systems, too -- adobe, steel, masonry block, for example. But we're only talking about SIPs and ICFs here.

About the project we're working on

In this project we're working on, the home owners have a concrete dome home. Talk about solid!  They wanted to add on to their home but wanted flexibility in the form and layout. Two major requirements were that the addition be able to withstand up to 200 mph winds, and that it be be super insulated and super energy-efficient.

After much discussion and research, Wayne and the home owners decided to build the walls using insulated concrete forms, and to build the roof structure using structural insulated panels.

Building with ICFs or SIPs is not for every project. But they make a lot of sense here.

Let's talk first about insulated concrete forms.

Insulated concrete form (ICF)


ICFs are usually made from expanded polystyrene (EPS), much like the material in a styrofoam beer cooler.

The form consists of two foam panels held together by plastic ties or something similar. It's roughly the size of an ordinary cinder block.

The forms are stacked together like Legos and reinforced with metal rebar.  And then the forms are filled with concrete, which cures to provide the structural wall system.

ICF wall before fill 350x233
ICF wall before fill 350x233

Here's a photo of the ICFs stacked together to form the walls of the new addition to the home.

Windows and doors are bucked in with wood framing.

Steel reinforcement supports the walls, because the next step is to fill the cores with concrete.

Filled ICF wall 350x233
Filled ICF wall 350x233

Here's a close-up of the core, filled now with concrete.

The exterior walls will be carefully wrapped with Tyvek to keep out moisture, and then they'll be covered with stone and metal.  It'll be really handsome.  The inside walls will be covered with drywall.

With foam + concrete, the walls are 11" thick. The thermal mass of concrete slows temperature swings and provides an effective air barrier against the summer heat. The foam provides insulation. Together,  they add up to a 50-80% savings on utility bills.  R-value is a measure of the efficiency of insulation in a home.   With this wall system, you get an effective R-value of 32.  Not too shabby.

Now let's talk about the SIPs used for the roof structure.

Structural insulated panels (SIPs)

Oreo cookie
Oreo cookie

Think of an Oreo cookie. (This is the cookie I promised you.  Get your own glass of milk.)

SIPs cut&labeled3 350x216
SIPs cut&labeled3 350x216

SIPs were used to build the roof structure.  The SIP we used here is two sturdy panels -- oriented strand board (OSB) -- glued under pressure to a super insulating layer of rigid foam (either polystyrene or polyisocyanurate).

The SIPs came from the factory cut and labeled, with detailed plans that tell the construction crew how to assemble them.

lifting SIP into place 350x217
lifting SIP into place 350x217

Here's the framing crew attaching the SIPs to the ridge beam.  It was really fun watching them.  They used a crane to lift the panels up to the second-story level.

These SIP roof panels are a little more than 8" thick.  They provide an excellent insulation and air infiltration barrier.

The panels will be covered with a metal roof.  A metal roof is important here for longevity and for harvesting rainwater.

Wayne has used another kind of structural insulated panel made from compressed wheat chaff. You can ask him about that.

Pros and Cons

The upfront cost of construction using SIPs or ICFs can be greater than traditional stick framing, but you have to balance that against the ongoing energy payback to the homeowner. Building with ICFs and SIPs can speed construction, but it takes a lot of careful upfront planning and engineering.

And then there are environmental factors to consider.  There's a high embedded energy cost of the concrete in ICFs, but that's balanced by the fact that it lasts longer.  The foam used in both ICFs and SIPs is a petroleum-based product with its own environmental cost, balanced by the overall energy savings in the home.

The point is, no one solution is perfect.  You just have to stop and think through the pros and cons and decide what makes sense for you and your goals.

Want more information?

If you want details and technical specs, please let me know.  I'll be happy to point you to information about the products we used, and Wayne can talk with you about construction details.

Oh, yeah, the chihuahua

chihuahua 350x262
chihuahua 350x262

Here's Pequeno, who came out with the framing crew that day to supervise the installation of the SIP roof panels.  Sweet little fellow.