ᐅ Insulating a basement ceiling: What formwork and type of polystyrene insulation should be used?

Hello

I am currently building a basement. Above it, there will be an open carport.
I am working on the formwork for the ceiling. I plan to place a 5cm (2 inch) thick layer of Styrofoam insulation on the formwork, then the reinforcement, followed by the concrete.
During the concrete pour, the Styrofoam will be under significant pressure. Later, after the formwork is removed, there will be no pressure on it anymore.
Can someone tell me which type of Styrofoam I should use?

Steven

You’ll probably have to calculate that yourself. EPS is available with different compressive strengths; if it gets more demanding, you’ll need XPS. Entire houses can be supported on that.
Why don’t you pour the slab first and then insulate from below with any type of boards?

Hello Alex

it will be about 400 kg per square meter.
I think the construction is coherent. If I pour the concrete first and then insulate with polystyrene, many cavities will form between the polystyrene and the concrete. If I place the polystyrene on the formwork and then pour, there will be no cavities.
That’s what I think.

Steven

The added insulation corresponds to common practice. The panels are glued. This is how new buildings are constructed and basement ceilings are insulated afterwards.

No idea if they will simply fall off when you remove the formwork.

Hello Alex

I’m also concerned about it falling off. That’s why, before pouring, I will insert drywall anchors into the styrofoam (5 per panel) and screw a stainless steel screw into each anchor. The screw will protrude about 3cm (1.2 inches). That should be enough to hold the panels permanently.

Steven

I think you are inventing a construction method that is simply unnecessary and also more expensive and time-consuming. Pour the slab and attach EPS insulation from below, and that's it.