I've got a 15' x 23' stick garage on an uninsulated slab. The plan is to tear-down the stick and rebuild with ICF while adding a second story plus a roof with attic trusses for another half story. For by-law reasons, I have to keep the same foot print. Now come the questions to you ICF gurus: I've seen a lot of info on ICF applications for new builds and buildouts but I'm not sure about rebuilds especially since an allbeit inadequate foundation is in place? Can it be done? What about retrofitting the existing foundation for the new load? Then there is the question of insulating the slab to support radiant (air) heating. Please don't say that we'll have to take a jackhammer to it and start afresh. Can the existing slab be salvaged and heated? Please note that the garage is being converted for residential purposes. We plan to install a kitchen on the main and one bathroom each on the upper floors. Any responses provided would be greately appreciated. I am a fan of concrete because of familarity with block application in tropical climates but I'm a totally newby to insulated forms and cold climate construction here the Ontario, Canada.

1st - i would have an engineer look at it (and then armed with that data read the following ;))

That said. Here are some ideas. Engineer vary on whether you need more concrete in the slab or not for ICF. One side says the load is greater so you need quite a bit more steel and concrete in the slab. The other side (where i lean somewhat) is that the wall are in fact beams that are six inches wide and ten feet tall which results in a slab that is stronger due to the walls.

You may have heard of the floating slab -- common in Canada -- because it's fully insulated -- often they'll pour the slab after the walls are all the way up -- and use the walls as the form for the slab -- you want to look at drawings of this technique to show you how they protect the slab from elements and critters. Basically, you may be able to put your walls into the ground on new footers -- leave your slab in the middle - you're garage would grow a little and this may or not be okay?

Regarding the radiant heat there are types (i don't know about air) that can be retrofitted. I did this in our master bath but it's electric (not very efficient). Good luck.

Regarding the slab go search radiant tec they have pages and pages of every possible radiant retrofit. Easiest assume slab is not insulated and put down an inch of silverboard staple down tubing and pour your 2" slab. Your real issue will be supporting the walls as you know. You could attempt to excavate underneath the perimeter of the slab and pour a shallow frost wall. i am interested with your project I have the same type single bay garage attached to my house that I would love to raise. I hate to say it but if you pull the trusses and create a floor then then stick build the walls and replace the trusses, if this is possible you would save alot of money plus would be the greener thing to do.

Your other option take it all away and start fresh you could have the slab out of there in 2 days. Either way good luck

Thanks for the input. Ah well, all things considered I'd better get used to the idea of starting the foundation from scratch. It's just as well because the Legalett radiant system that I was researching for possible use does not support retrofit to an existing slab.

BTW, TexasICF, I don't think that floating slab would cut it with on this particular lot. Thanks though.