Making concrete footings for any structure can be intimidating to the average DIYer. After all, mixing and pouring concrete is a big, messy job and if you mess it up, it’s pretty hard to just clean up and redo. One of the big questions folks have before they pour is how to put rebar in concrete footings.
Using rebar in concrete footings will make it stronger and less resistant to shifting due to temperature and humidity. Concrete is the construction material of choice for footings because of its compression strength. However, it is not strong when subjected to forces that pull – such as shifting earth. Rebar-reinforced concrete helps negate the effects of those forces.
There are some projects you’ll use concrete for that simply don’t require rebar, such as setting a fence post or filling a form for a basketball net. Footings are an instance where you want rebar since footings will be supporting a structure that you want to make sure remains as stable as possible for the lifetime of that structure.
In this article, we’ll go over everything you need to know about reinforcing concrete with rebar. We Will touch on the types of rebar you can put in your concrete, as well as methods, best practices, and other accessories you might find useful when it comes time to pour your concrete footings.
- What is Rebar?
- Types of Rebar
- Do You Need Rebar in Concrete Footings?
- Rebar in Footings Code Requirements
- Is Rebar Needed in Deck Piers?
- Rebar Placement in Concrete Footings
- What Size Rebar for Footings?
- Rebar Spacing
- Rebar Calculator: How Much Rebar Do I Need?
- How to Tie Rebar
- How to Install Rebar in Footings
- How Much Does Rebar Cost?
- Do I Need Rebar in Sonotubes
- How To Set Vertical Rebar in Footings
What is Rebar?
Rebar is short for “reinforcing bar”. Rebar is most commonly found as either a steel bar or steel mesh inserted into concrete to increase its tensile strength. This steel gets the name “reinforcing” when used in conjunction with concrete to reduce cracking and movement.
Types of Rebar
There are many different types of rebar, and you can find many different shapes and forms to accommodate various types of concrete forms. Rebar shaped like hooks or stirrups is often used in different types of footings. Steel mesh is a different version of rebar that resembles a fence and reinforces concrete flooring.
Beyond the shape of the rebar, there are many different versions you can buy with different coatings. First, you can either purchase smooth or “deformed” rebar. Smooth is not ideal for concrete reinforcement as it does not bond as well to the material and can “slip”. Most rebar you’ll see has dimples or ribs, which is ideal for concrete.
You’ll also find rebar available in different coatings. Epoxy coated rebar is green and is highly resistant to corrosion. However, the epoxy coating itself is not strong and scratches easily, reducing its effectiveness.
There is also galvanized rebar and stainless steel rebar. Galvanized is extremely durable, and stainless even more durable, although both cost significantly more than standard rebar, with stainless being the most expensive.
Finally, there are various sizes of rebar. Size is determined by the diameter of the rod, and rebar size is numbered in increments of ⅛”. Therefore, #2 rebar is ⅛” + ⅛” = ¼” in diameter. #3 rebar is ⅜” in diameter, #4 is ½” in diameter, and so on.
You’ll find that #3, #4, and #5 size rebar is most commonly found in home reno stores and used in footings for homes and other domestic structures.
Do You Need Rebar in Concrete Footings?
Including rebar in a concrete footing means that you can reduce the risk of the concrete being pushed and pulled apart – cracking – from ground force pressures. Knowing this, it is generally a good idea to use rebar in footings for any structure. However, it is not required in many cases.
Reinforcing concrete will not eradicate cracking. It will, however, reduce cracking and movement of the overall footing. Placed properly, it can resist lateral forces that would otherwise reduce a non-reinforced footing to cracks and moisture penetration.
Use rebar in concrete when you are pouring a footing for a home or garage and in concrete slabs that will support a home, shed, garage, or another outbuilding, you’d like to remain structurally sound. Rebar reinforcement in concrete piles holding up decks and other similar structures is also a good idea.
Rebar in Footings Code Requirements
Only footings in certain seismic areas are required to have rebar in foundations, according to the IRC. If you live in those areas, then expect to put vertical rebar – usually #4 – a minimum of 48” on center throughout the footing. Horizontal rebar will run at the top and bottom of the footing and masonry or concrete wall, also #4 with a few exceptions.
What is a seismic area? Simply put, it’s an area that is more likely to experience ground movement from seismic activity. In the U.S., much of the western half of the country is in a seismic zone, along with some places in the Midwest and a few on the east coast.
Slabs on grade with turned-down footings require a horizontal #4 bar running no less than 3” from the bottom and top of the footing, or just one horizontal #5 bar in the middle of the turned-down footings. #3 rebar with hooked ends is used for vertical placement, at a minimum of 48” on center.
If your footing has a concrete or masonry wall on top of it, then you’ll need a horizontal #4 bar within 12” of the top of the wall and a #4 bar no closer than 3” from the bottom of the footing. This bar will be hooked, with the hooked end protruding into the footing at the bottom. #4 bars should be placed vertically at 48” on center or less and should be at least 18” up into the wall.
Is Rebar Needed in Deck Piers?
Rebar is mandated in deck piers only in some jurisdictions. The common minimum diameter for deck piers is 12”, but only some localities require #3 – or 10mm in Canada – rebar in the center of the pier, no closer than 1 ½” from the surface on either end.
Typically, the further north you go, the more likely it is that local code will mandate that you’ll need rebar in your deck pier. For instance, many Canadian municipalities require rebar in deck piers, but only slightly south. In New York, they do not require rebar in deck piers.
Rebar Placement in Concrete Footings
Rebar cannot be placed on the edge – close to the surface of the concrete. Otherwise, the steel is at risk of corrosion, which will cause the concrete to fail as it disintegrates and causes premature cracking.
Footings that are poured below grade, with masonry walls on top, will typically have two courses of horizontal #4 rebar, one 3” from the top and the other 3” from the bottom. Any closer to the edge is not allowed. Use of plastic or concrete spacers is allowed to keep rebar off the ground when pouring.
If there is a poured concrete or masonry wall on top of the footing, you’ll need #3 or greater vertical rebar at a minimum of 48” on center. These bars have hooks at the bottom extending laterally towards the edge of the footing. They must protrude at least 18” from the footing, although it is good practice to run it higher.
Poured concrete or masonry walls also need horizontal rebar, #4, at least, no less than 12” from the top of the wall. As rebar intersects with one another, it is tied off with 16 gauge steel wire that is annealed, meaning that it has been heated so that it is easier to manipulate.
A footing rebar diagram is useful when pouring a footing, and the IRC code has many useful images in section 403.1.3 that refer to footing rebar in more detail. Keep in mind that the minimum use for rebar is just that – minimal – and you’ll find diagrams that use much more rebar than outlined in the IRC, which is common as many home footings are overbuilt.
What Size Rebar for Footings?
For most house and garage footings, #4 rebar – or ½” diameter – is used. Larger is acceptable, too, although adjustments may be needed to ensure proper coverage is still achieved. If you live in Canada, then this is about #13 rebar – 13mm.
Deck footings that require rebar will call for #3, or 10mm, rebar. Typically this is run vertically through the center of the footing. Since these footings will be directly exposed to earth at all times, it is important to ensure the vertical rebar is at least 3” from the top and 3” from the bottom of the footing.
For residential footing use, spacing depends on the type of footing you have. For footings that are poured before the slab, two #4 horizontal pieces of rebar are required – one 3” from the top and the other 3” from the bottom. You’ll also need vertical rebar hooks protruding at least 6” into the footing and out at least 18” every 48”, or less.
If footings are poured at the same time as the slab, you’ll need to ensure, first, that the perimeter of the “slab” is actually a footing – at least 12” deep. For this type of footing, called monolithic, you’ll only need horizontal runs such as those mentioned above.
Depending on your wall type, you may need vertical rebar unless you place wood on top, such as a slab on grade for a shed.
Footings below grade that will have masonry (block) walls on top require #4 rebar with hooks placed vertically at a maximum of 48” on center. They must go at least 6” into the footing – the hooked end – and protrude at least 14” above into the masonry walls.
Finally, footings with narrower walls on top, such as poured concrete that is 5” thick or less, then the spacing mentioned above would decrease for the vertical rebar to 24” on center, maximum. The thinner the wall, the more reinforcement you’ll need to add to your footing, which will connect to the walls.
Rebar Calculator: How Much Rebar Do I Need?
If you aren’t sure about how much rebar you’ll need, a rebar calculator can come in handy. The version linked here is useful as it has a diagram that gives dimensions for your rebar spacing, although it does not provide a price input, so you’ll have to know your prices at your local supplier and do that math yourself.
Let’s say you want a 10×10 shed that will be storage for some potentially very heavy items. You’ll be pouring a 6” thick slab so that your rebar is 3” away from either edge. If you want rebar in a grid pattern with roughly 12” spacing, you’ll first need to account for the fact that each piece of rebar must be 3” from all edges.
If that is the case, each piece must be 9’ 6” long – subtract 3” from either end. If you start at one end, 3” from the end, you’ll realize that you need 11 pieces running in one direction and 11 pieces running the other – all the same length. Rebar comes in 20’ pieces, so you can purchase 11 pieces and cut each to size with a circular saw.
How to Tie Rebar
Rebar in a grid pattern and horizontal rebar that intersects with a vertical piece must be tied together with 16 gauge steel wire. Any store that sells rebar will sell rebar ties. For the average DIYer, one spool of rebar tie should be enough, and it is very cheap.
To tie rebar that is intersecting in a grid pattern:
- Use a saddle tie.
- Hold either end of the wire and place it above your first piece of rebar – hold it, so both ends are of equal length.
- Loop both ends beneath the perpendicular piece of rebar below on either side.
Last, loop both ends up over the original piece on the other side of the perpendicular rebar and twist with pliers.
How to Install Rebar in Footings
Once you’ve determined the amount of rebar needed and where it will be placed, the installation is fairly straightforward. You’ll need some specific tools and an extra hand, as tying all the intersections of a rebar grid can be pretty tedious.
- Spacers: plastic or pre-cast concrete
- Circular saw with carbide tip metal blade or bolt cutters
Decide Which Type of Footing to Install
The most important step is determining your type of footing. Slabs on grade for sheds will likely suffice with a traditional 3 ½” thick slab and no extra depth for footings. If you plan on parking a classic car or storing bags of concrete, then you might opt for a slab with turned-down footings or simply a thicker slab.
Either way, this is the most critical part of your job and if it is for a house, an engineer and city worker will amend your plans accordingly if you’ve made a mistake with your footing plans.
Plan Your Materials
Calculate your footing materials using the rebar calculator linked above and a concrete calculator. You can take your time with setting the rebar because once you pour concrete, there is no fixing your rebar grid. Check each tie and spacing from the ground to ensure 3” between your concrete edge and the nearest rebar rod.
Dig and Create Your Forms
Create your concrete footing forms. A 12” minimum depth should be used for most structures with isolated or turned down footings, such as a garage or house. This is when you’ll also place your rebar spacers to ensure rebar is up and off the ground.
Many footings require horizontal rebar at 3” from the bottom. You’ll need plastic spacers to prop up this continuous run of rebar around your footing.
Place Your Rebar
Install your rebar. During the next step, we’ll get everything tied together, but placing your rebar simply requires you to ensure you have proper clearances from all angles. Check your local code to ensure you have all the necessary rods dictated, vertical and horizontal, and that you are using hooks and saddles when called for.
For sonotubes, you’ll only be placing one stick of rebar unless you want to over-engineer. In that case, you’ll need a spacer beneath to keep the bottom 3” from the ground and a spacer sitting on top to keep the rod centered. A piece of wood fastened to something outside the tube will suffice.
Tie Rebar Together
Make sure each intersection is tied properly with either a saddle or figure-8 style tie. Use your hands to check each area of rebar to make sure there is little to no movement. Once they are tied, there should be virtually no movement of the rebar. Concrete pours can dislodge loose materials, so you want every tie extremely tight.
Once it is time to pour, your rebar job is effectively done. The main consideration when pouring concrete over rebar is to ensure you pour all at once. Pouring in increments can result in breaks in the concrete where air pockets can occur, causing premature cracking and rendering the rebar useless.
How Much Does Rebar Cost?
A 20’ piece of #4 rebar – which is ½” diameter – costs around or just above $15 at the time of writing. Big box retailers will sell smaller pieces in 10’ and even 2’ lengths for smaller projects, but a 20’ length is the most economical. A #5 piece costs around $20 for a 20’ length.
Do I Need Rebar in Sonotubes
Yes, you need rebar in sonotubes. It’s easy to install with spacers and very cheap. The added strength and stability it will add to your deck or another outbuilding is worth the extra time and effort to install.
Not all municipalities will call for rebar in sonotubes. The further north you go, such as in Canada, the more likely it is they’ll call for rebar in the tubes. On the other hand, in New York state, only slightly further south, they do not call for rebar in sonotubes.
Either way, your sonotubes should be a minimum of 12” in diameter and have a piece of #3 rebar running down the center, at a minimum. You can choose to add rebar as you see fit. However, you’ll want to be careful as you must keep the rebar away from the edges as corrosion can happen easily as sonotubes are extremely exposed to the elements.
How To Set Vertical Rebar in Footings
When setting vertical rebar in a sonotube, use a plastic spacer in the center of the sonotube on the bottom. Place the sonotube over the plastic spacer, then insert the rebar on top of the spacer. Once done, you can use rebar wire and punch small holes through the sonotube on top to hold the rebar centered.
Have everything secure before pouring. You can’t hold the rebar in place, and putting it in after pouring will result in an improper placement. Wire it into place, secure the rebar, and feel confident with a solid sonotube pour.
Remember that the placement of rebar depends heavily on the type of footing you are using. Be sure to reference the building code in your area, which will give you minimums and maximums to use as a guideline.
Also, remember that over – and under – engineering a footing is not a good idea. Too much rebar can inhibit the concrete from settling and compacting properly. Too little rebar can lead to structural failure. Go by the code for the best results.