Monday, January 24, 2011

7. Insul-Deck

For the structure of the main floor, we decided to go with Insul-Deck lightweight concrete forms. Like the ICF blocks we used for the basement walls, these are pre-cast styrofoam forms for pouring concrete and also provide ceiling insulation for the life of the building. In our case, the architect and engineer carefully measured each piece which would be required so that the lengths could be pre-cut (to rough measurements) at the factory. They did a pretty good job at these estimates -  even with all the angles there was very little waste.

There are several brands of these overhead lightweight concrete forms. Insul-Deck was one of the first, and was readily available through my local material supplier, so we went with that brand. Since that time, other types have come on the market which might have a slight advatage for some building situations. Embedded within the styrofoam are metal "ribs" which keep the form stiff during construction.These also act as ceiling joists later on, providing a firm anchor for attaching drywall, ceiling lights, etc. My engineer went with a different brand on later projects, primarily because they had heftier "ribs", and did not need as much shoring to support the wet concrete. Other than that, the Insul-Deck forms have worked out extremely well for me.

Construction is fairly straghtforward: Install a plywood "dam" around the perimeter, build temporary 2x4 walls to support the forms from underneath, and start laying the forms across them. The bottom edges of the forms touch each other, and form a nearly-waterproof seal (it's surprising how little leakage comes through when you pour the cement on top). The forms are plenty sturdy enough to walk on while placing the steel and pouring cement. They have two large hollow tubes and four small ones running throughout their length. These spaces can be used to run water tubing, sewage pipes, and electrical lines. You can also chisel out as much of the styrofoam as necessary from the bottom side to insert flush-mount ceiling cans for light fixtures. The amount of steel used was engineered for the clear span over the room below, but I still had the cement contractor put a 1" crown in the center of the garage floor.  I'm glad I did, because two years later the floor is virtually level.

We started by pouring the garage floor.  It was the easiest section, because there were no heating tubes or expansion joints. We used a regular hose-pump for the floors, not the crane. It took about an hour to fill the section with concrete, then the rest of the day to finish it off. No power floats were used, all the leveling and smoothing was done by hand.

If I had this part to do again, I might have put expansion joints in the garage floor. Now (over two years later), a lot of hairline cracks have appeared in the floor. They won't show, because this part will be covered by an epoxy coating. 

It took several weeks to pour all the sections of the main floor. Most of this level has heated floors, so there were a lot of heating tubes to install.  Care must be taken to keep them away from future walls, because it's easy to drill into the tubes when putting in wall anchors.  When all the tubes are in place, the system is pressurized to 100 PSI. After all the walls are in place, you know you haven't punctured anything if it's still holding pressure.
With the final section of floor poured, we just had to keep it wet for a few days so that it would cure slowly.


  1. How thick is the concrete? With this method do you still need load bearing walls? What is the maximum free span with this sytem? Looks like an awfull lot of steel went into this, I think I have seen bridges built with less.

    Your ceiling is then attached directly to the styrofoam? As in glueing ceiling tiles or drywall to the foam?

  2. There is about 5" of concrete on top of the Insul-Deck, and the grooves between the forms are about 10" deep. They can easily span 30 feet, so only the perimeter walls really need to be load-bearing.

    The ceiling (drywall, ceiling tiles, wood strips, etc.) is screwed to the metal "ribs" in the Insul-Deck with sheet-metal screws.

  3. Do you know of the brand your engineer switch instead of lite deck for future project?

  4. Sorry, I mean from Insul Deck.
    Currently we are building a house in NJ and using Lite Deck.

  5. I believe he switched to AmDeck, because it doesn't require nearly as much shoring as Insul-Deck (now known as Quad-Deck) or Lite-Deck. The massive amount of shoring in my project was a major expense.

  6. Great choice of Insul-Deck! It can be an insulator and concrete at the same time. Good to know it worked well for you. How’s your house now? It’s been three years and I hope you’re enjoying your place.

  7. Hi, Tony - Nope, still haven't moved in. Since the recession, I've been working on the place all alone, so it's going pretty slowly. Maybe one more year.