Raft slab / Discussions

Can I connect a new slab addition to an existing (engineered) slab on grade?

...slab and new part of the garage to 40 ft Not sure if this can be done as it would technically be 2 seperate slabs (connected or touching) with 1 building on both slabs? There should be no reason that you couldn't attach a new slab on grade foundation to an existing slab provided the existing slab is not showing signs o...

Posted by Corey Porteous April 9, 2025 Slab on Grade 1 response

What are the best below grade drainage layers for a slab on grade foundation?

...raft slab can be built on any soil that an edge-loaded footing foundation can be built on, but not the other way around. A Raft slab spreads the weight evenly over the whole surface which greatly reduces the risk of heave, uneven settling, and slabs cracking. You need to be sure (and your engineer needs to confirm) tha...

Posted by stephan prystanski April 7, 2025 Slab on Grade 1 response

What's the ideal concrete thickness for concrete slab floors?

...Slab Foundation: This concrete floor is not intended as a structural slab foundation. Should I directly design it as a traditional slab foundation? In this case, the thickness would be around 4-to-6 inches. Floor Sandwich Structure: I'd like to understand how the layers of the floor system should be structured for this...

Posted by Abdulkadir Al-Jazari March 28, 2025 Basements

What is the proper way to build a Slab on Grade Foundation?

...Slab on Grade foundation. Reinforced concrete perimeter footings approximately 12" x 40" deep, and a 4" thick concrete slab on top of 2" rigid insulation. This will be a monolithic pour. The top of slab will be approx 12" above the soil. I plan to isulate the outside face of the perimeter footings with 2" rigid foam bo...

Posted by John Schureman March 25, 2025 Slab on Grade 3 responses

Can I use thermal evacuated tubing with a Legalett radiant air system in a raft slab?

...raft slab as well. Legalett is an independent company, we just feature it here as we do other systems that we like, and so far we have not found any other company that does infloor heating with air tubes such as this. But there are a lot of advantages, you can see here on our page comparing the advantages of air heated...

Posted by kathryn saunders Jan. 20, 2023 Renewable energy 1 response

What is the best way to build a slab foundation on a slope?

...slab to the one below. Thanks, Keri   There are many ways to build a slab on grade foundation on sloped building lots, but doing three separate slabs isn’t necessarily the cheapest option. Did you specifically want a 3 level house or is that something you have chosen simply to adapt to the terrain? I ask this because i...

Posted by keri gelenian Nov. 23, 2020 Foundation choices 2 responses

How much does it cost to build a slab on grade for a 1200 square foot house?

...slab on grade prefab kit? If so, see this page on Legalett Geoslab foundation kits and air heated floors and you can contact them through there. If that's not what you mean let us know but I can't think of any other system you'd be referring to.

Posted by Walter Hale Oct. 1, 2020 Slab on Grade 1 response

Could we use a raft slab with ICF walls on a sloped site?

...raft slab / slab on grade shallow foundation and and ICF block wall. But I think building the slab on grade would be more simple than you think, you can read more here if you haven’t already found this page- Raft slabs – how to build a slab on grade or basement on problem soils A raft slab is engineered to spread the ...

Posted by Paul Fischer Sept. 15, 2020 Slab on Grade 1 response

What are the pros and cons of building a house on a slab on grade foundation?

...slab still be in tact? What happens if the slab cracks and part of the house tilts? Here you have lots of old houses on basements that are still standing. With a basements you can redo basement walls, easily get to plumbing etc. With a slab what happens when a pipe breaks in the slab? How can you even find leaks? What ...

Posted by Debra Kroening Jan. 5, 2022 New foundations and slab-on-grade 6 responses

What is the best way to build a slab on grade foundation?

...slab this slab it really needs an experienced engineer, so I would check with your engineer that this is within their wheelhouse, if not I would look into a company that specializes in providing engineered slab on grade prefab kits where point loads are all considered and engineered for you, as well as skirting.  

Posted by Earl Williams Nov. 30, 2021 Slab on Grade 3 responses

What is the best way to install slab on grade insulation?

...slab EPS foam insulation is nothing compared to the labor required to switch to an entirely different method of insulating. I would first point you to this page -  Slab on grade technical guide We have other pages on slab construction as well that are worth looking at, you can find them if you enter slab on grade in th...

Posted by paul fowler Aug. 26, 2021 Slab on Grade 3 responses

Can you leave a Legalett slab in winter in Canada without the heat on?

...slab on grade install video here. Really all you have to do is tell the company what you want and they take care of the rest. This is different than engaging an individual designer or engineer to build a one-off slab, slabs are their specialty and they’ve been at it for decades. I’d have no concern whatsoever with fros...

Posted by Gamog Cladhaire April 29, 2021 Slab on Grade 3 responses

What is the best method of building a slab on grade?

...slab will heave, crack, etc.  Also, do you have a list of foundation contractors who have experience with building these slabs? Having built several LEED certified High performance homes on slabs with different methods, our preferred method on how to build a slab on grade would be with an engineered prefab raft slab ki...

Posted by Jay Law April 19, 2021 Slab on Grade 1 response

Can I use a Legalett slab in Florida if I don't want floor heat?

...slab, or do you have something like this without the heated floors that would work better? A Legalett raft slab has an optional air heated radiant floor, but it is not necessary. They are installed in all climates from the far north to the south, and even in cold climates they don’t always include floor heating. Many P...

Posted by Harry Dickinson March 25, 2021 Slab on Grade 1 response

How much perimeter skirt insulation should go around a concrete slab?

...slab w/ 2" hard foam insulation under slab (+ crushed stone & eps vapor barrier), and 2" hard foam insulation vertically around sides/edges of slab and subfloor above.  On top of the slab will be a wood subfloor web-truss system where the electric & plumbing & hydronic floor heating panels w/ PEX tubing wil...

Posted by Insinuendo Insinuendo Aug. 5, 2022 Slab on Grade 3 responses

What are the best practices for a pier foundation on sloped bedrock?

...slab on grade instead, which is more efficient, more valuable, and likely competitively priced compared to a home built on piers if you consider the added insulation you’ll need due to letting air flow underneath. Here is a slab on grade with no footing that is great for building on problem soils, it may be a solution ...

Posted by s w July 12, 2022 New foundations and slab-on-grade 1 response

What is the minimum insulation value for insulation between the edge of the slab and foundation wall?

...slab foundations and homes, I would first check our BC Step Code made easy page for information on that. Building codes vary too much between states, provinces and even cities for us to keep up with unfortunately.

Posted by Arsh Deep July 12, 2022 Slab on Grade 1 response

Can we backfill a basement and then do slab on grade?

...slab on grade foundation, so to speak. We live in a high ranch, with the front door cut into the existing foundation, so the idea would be to bring the foundation to "level" (tying in door, window spaces)  and then having a slab at that height, which would put us well above water. Of course this would need to be engine...

Posted by susannahandjared mcisaac March 3, 2022 Slab on Grade 1 response