What's the difference between a slab on grade and a monolithic foundation?
I've been looking for a manufacturer of frost protected shallow foundation foam forms to get a quote for an addition in Michigan and keep reading about slab on grade and monolithic foundation styrofoam forms - is there a difference or are they the same thing?
A slab on grade literally means a slab of concrete on grade (ground level), as opposed to ‘below grade’ like a basement. And a slab on grade can be built in a variety of ways (monolithic or not), you can learn the basics on this page –
Slab on Grade or Foundation and Basement - Which is Best?
But to answer your question a bit more specifically, first you need to realize that the word ‘monolithic’ simply means is that it can done in one pour. The more traditional method for building a slab on grade is to first pour a footing, wait a few days, then pay those very expensive concrete trucks to come back a second time to pour the slab of your house. and it’s even worse with a basement because it takes 3 trips – once to pour the footing, once for the walls, then later for the slab floor.
You say you are considering a slab on grade foundation form kit, what sort of product are you looking at? Some are for monolithic slabs and some are not. If it is a full kit with exterior edge insulation and sub-slab flat stock then it may be monolithic, if it’s just an insulated footing form then you may end up doing it in two pours.
Yo Mike, thanks for the quick response. The product we're looking at that was at a local homeshow we went to is a Geoslab by Legalet - so definitely a one pour solution I think. As we're planning for a pretty large addition on the north facing wall with a cathedral ceiling, and our furnace is already up to it's limit - the thinking is that we may also opt for the electric powered air heating as we don't want baseboard heaters (smell, aesthetic, noise, rate of energy use, comfort.) The room we're creating will be our main living area, windows on East and West for morning and evening sun, and it will have a wood burner as a focal point. The current kitchen will be extended into the current living space to make a big family area on one side, and have a big island into the new room on the addition side. We then intend to continue a remodel to the rest of the house by insulating from the outside while getting rid of the tired vinyl siding and replacing windows. The current house has a pretty dank crawlspace area with frost walls, so we will also be making the home split level with the lower on grade foundation on the new part which appeals and turns the island on that side to a full height for weekday dining. Hope you can picture it? So, in what I describe, a slab on grade and monolithic foundation are going to pretty much mean the same thing?
Wrong answer Mike,slab on grade foundation form kit is only one pours !!and is structural slab that the perimeter transfert load from edge to 12' inside (military technic and commercial technic from to many years.)
Hi Benoit, thanks for sharing your thoughts. I'm afraid I don’t fully understand, but if you’re saying what I think you’re saying, I believe we are actually in agreement so let me give it a shot–
Yes, a slab on grade form kit can be done in one pour. If my comment that 'IF' it was an ‘insulated footing form’ then it may take two pours confused you, sorry about that. Ronaldo didn’t indicate which product they were considering, and I have seen form kits that are intended only for footings, in which case an interior slab would need to be poured afterwards, at an additional cost. Without knowing which product this person is considering, I wouldn’t want to mislead them to think all form kits are monolithic. Hope that clears it up for you Benoit, I'm pretty sure we're both fans of monolithic slabs!