How thick should foam be under slab?

Because concrete is solid, heat or air won't escape as easily as other floors. Therefore, when adding insulation, keep it at least two inches thick, depending on the type of insulation you use.
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How much foam do you put under a concrete slab?

A 2-inch layer of rigid foam insulation is forty times more efficient at trapping heat than concrete alone. Although rigid foam can be expensive at the outset, the savings over the next few decades will far outweigh it.
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What kind of foam goes under concrete slab?

The most common insulation materials for use under a concrete slab are extruded polystyrene (XPS) and expanded polystyrene (EPS). Of these two materials, green builders prefer EPS, because EPS is manufactured with a more environmentally benign blowing agent than XPS.
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Should you put foam under concrete?

For under-slab applications, the rigid foam insulation typically should be installed over a gravel base, with a poly vapor diffusion retarder between the gravel and insulation. Additional insulation is applied along the edges of the slab, because that is a primary surface for heat loss.
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Should I put foam under garage slab?

“Generally speaking, however, the only place underslab insulation is required is when the slab itself is heated.
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The RIGHT WAY to Insulate Your Concrete Floor



Can you put foam board under concrete?

Finally, some contractors in cold climates began installing a continuous horizontal layer of rigid foam insulation under their concrete slabs. The foam layer isolates the room-temperature slab from the cold soil under the slab.
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Should I insulate under slab?

If in-slab heating (or cooling) is to be used, then the slab should be fully insulated, both underneath and along the edge, to reduce the energy losses from (or gains to) the slab. o Regular slabs can be fully insulated as well, and there's a range of foam products designed specifically for under-slab use.
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Why do they put foam in slabs?

Foam insulation under concrete slab avoids thermal discrepancies caused by uncontrollable temperature variations, heat transfers and losses and variable environmental conditions. This will help to reduce energy costs.
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How much weight can a 2 inch slab of concrete hold?

A 2-inch concrete slab can hold 750 psi of weight. The stronger the slab will be, the more concrete is normally put at a thickness of 2 inches or more. A slab's thickness is most commonly four inches.
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Can you cement over foam?

After installing Styrofoam, you must use some cement or mortar to cover it up and harden the surface. If you want a highly reinforced structure, especially if you use a cheaper and "softer" polystyrene insulation, use some fiberglass mesh on the surface and apply a coat of mortar on the mesh.
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What do you put under a concrete slab?

Because concrete is a very porous material, it will absorb any moisture that it contacts. This can cause pooling. Without crushed stone, pooling water will settle under it and erode your slab. Adding a layer of crushed stone will add proper drainage, as well as create a barrier between your slab and the ground.
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Is 4 inches of concrete enough?

For a concrete patio, the ideal slab thickness is at least four inches. There are times where thicker slabs will make more sense, but, most of the time, 4 inches is the perfect thickness for a concrete slab. It is, however, wise to make the perimeter of the slab an inch or two thicker.
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How thick does concrete need to be to not crack?

To prevent load-stress cracking, make sure a slab is built over a uniformly compacted, well-drained subgrade, and is thick enough to withstand the kind of use it will get. In residential concrete, 4 inches is the minimum thickness for walkways and patios.
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What PSI should I use for concrete?

The ideal concrete psi for a given project depends on various factors, but the bare minimum for any project usually starts around 2,500 to 3,000 psi. Each concrete structure has a normally acceptable psi range. Concrete footings and slabs on grade typically require a concrete of 3,500 to 4,000 psi.
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Do you need rebar for 3 inch slab?

Rebar is not necessary for every concrete project. The general rule of thumb is that if you are pouring concrete that is more than 5 inches in depth, you are probably going to want to add in some rebar to help reinforce the entire structure.
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How do I keep my slab foundation from cracking?

The best protection against structural cracking in residential structures is good compaction of the soil and gravel underneath the slab. In addition, rebar should be placed in the footings around the perimeter of the slab and at post bases within the slab.
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How thick should a concrete pad be?

Standard concrete floor slab thickness in residential construction is 4 inches. Five to six inches is recommended if the concrete will receive occasional heavy loads, such as motor homes or garbage trucks.
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Does a 4 inch slab need rebar?

No, rebar is not required for a 4-inch slab of concrete on grade. A 4-inch-thick slab cast on the ground and in constant touch with it will float, with no need for rebar. For concrete that is 5–6 inches thick, rebar is suggested.
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How thick should slab foundation be?

A slab foundation is made of concrete that is typically 4" to 6" thick in the center. The concrete slab is often placed on a layer of sand for drainage or to act as a cushion. Houses built on a slab lack crawlspaces, and there is no space under the floor.
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How thick should a garage slab be?

The concrete slab should be four inches thick at least; it needs to be thicker if heavy equipment will rest on it. Building codes offer requirements for the concrete mix, which vary by region. The standards are expressed in terms of "compressive strength," which boils down to the amount of water used in the mix.
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What is the best material under concrete slab?

What is the Best Base for a Concrete Slab? Most people build a driveway or a patio so in that case, a good choice would be a mix of coarse and fine aggregate which will create a compactable base. Overall, a mix of crushed stone and stone dust is the best base material for any concrete flatwork.
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Is vapor barrier required under slab?

Although a vapor retarder or barrier isn't required under slabs used for unheated garages and outbuildings, it is recommended. Moisture moving through a concrete slab into the building structure can cause dampness issues, and even cause metal sitting on the pad to corrode and stain the concrete.
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Can foam be used for foundation?

The foam is placed under the entire slab on grade and wraps around and underneath the footings at the building perimeter. The 4 inch foam thickness is reduced to 1 inch at bearing wall locations, resulting in a thickened slab with reinforcement, to serve as footings for those walls at the building interior.
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