If you have a garden shed and you live in an area where it often gets windy, one thing that you might want to consider doing is anchoring it down to a concrete slab. Doing so will help protect the shed from being blown over, and it will also help prevent the shed from suffering from water damage due to being in contact with the ground.
As for how to get the job done, that’s exactly what we are about to teach you right now.
How to Anchor a Shed to a Concrete Slab
Alright, so there are two scenarios that we want to cover here.
Newly-Built Shed
First off, let’s talk about how to anchor a shed to a concrete slab that you are building from scratch. This is best done with galvanized anchor bolts.
Step 1: Get Your Galvanized Anchor Bolts
If you are building a normal shed using 2x4s, then 1/2-inch anchor bolts will do just fine.
Remember that they need to be long enough to anchor into the concrete, go through the sill plate, and then through the wood, with enough room for the washer and nut. Therefore, we recommend 4-inch long anchor bolts. In terms of figuring out how many you need, remember that they need to be 12 inches or less from the corner, and should be no more than 6 feet apart. So, based on this, you might need about two for every side of the shed, although how many you use is up to you.
Step 2: Pour the Concrete and Set the Anchors
OK, so of course, the biggest thing here is that once the anchors are set in the concrete, they are permanent, so you better measure twice and make sure that you have found all of the right placements for each of the bolts. Now that you have figured that out, and once the frame for your concrete slab is in place, you can then pour the concrete.
Once the concrete has been poured, you can then place the anchors right into the wet concrete (making sure that enough of the anchors poke out for the sill, the wood frame, and the washer/nut). You now need to let the concrete cure totally.
Step 3: Place the Sill Plate
The sill plate is a thin and flat piece of metal that is placed between the concrete and the wooden frame. Get sills of the appropriate size for the wooden frame you are building or your shed. You now need to use a drill press or some other type of drill to drill holes into the metal sill plate that are just large enough to fit over the anchor bolts. Make sure to use the right kind of drill bit or tool for the type of metal sill you are using.
Once the holes have been drilled, you can then place the sills over the anchor bolts. If you want to make things extra secure, you can use some polyurethane glue for added security.
Step 4: Place the Wooden Frame
With the sill plates in place, all you need to do now is to drill holes through the 2x4s (or whatever wood you are using to build the frame of the base of the shed) that are just large enough to fit over the anchor bolts. Once this has been done, you can then place your wooden frame on the ground and onto the anchor bolts.
With this done, all that you need to do now is to add the washers, and then all of the nuts. Use a hex wrench to tighten all of the nuts, making sure that they are secure.
Pre-Existing Shed
Whereas the above method is designed to allow you to anchor a new shed that you are in the process of building to a concrete slab, now we want to talk about how to anchor a shed to a concrete slab that is already standing in place. What you need to know is that there are also several methods for doing this, but we want to cover the easiest one.
Generally speaking, you could do this with a foundation anchor plate, with a T-strap, or with Tapcon screws. Using Tapcon screws, which are really just reinforced concrete screws, is the easiest and fastest way to go, especially for your average DIYer, so this is what we will teach you here.
Step 1: Get Your Tapcon Screws
First off, you have to buy the right Tapcon screws. If you built just a normal shed using 2x4s for the frame, then 1/4-inch Tapcon screws with a length of 3 inches will do just fine (if you have used thicker wood for the frame of the shed, get Tapcon screws that are longer than 3 inches).
If you aren’t sure exactly how to choose a Tapcon screw for a specific purpose, we recommend first doing some more research on this front.
Step 2: Measure and Mark
As a rule of thumb, for your average shed, you will want to place a Tapcon screw through the floor frame and into the concrete about every 16 inches in between the studs, give or take. Now, this is somewhat subjective, because how many screws you use and what the spacing between them is like does depend on the shed itself. If it is a large shed built with super heavy materials, and you live in a very windy area, you might want to decrease that spacing to 12 inches.
For added strength and security, you can also consider placing Tapcon screws to both sides of each corner of the shed. Whatever you decide, make your marks with a marking utensil.
Step 3: Drill the Pilot Holes
What you need to do now is to drill the pilot holes. You do need to drill pilot holes here, maybe not for the wood, but definitely into the concrete. So, if you are using 1/4-inch diameter screws, you need a drill bit that is just under 1/4-inch (the pilot hole diameter should be ever so slightly smaller than the actual screw, to ensure a secure hold).
Also, make sure that you are using a hammer drill with a drill bit designed for concrete. A normal power drill will not work for concrete, nor will normal drill bits. You need the right tools. That said, you can swing using the hammer drill and concrete drill bit to make the pilot hole through the wood and right into the concrete. So, make your pilot holes, and if you have any laying around, use some compressed air to clean out the holes.
Step 4: Insert the Tapcon Screws
All you need to do now is to use a drill or socket wrench to drive the Tapcon screws into the pilot holes. Just be sure that you don’t over-tighten the screws because you don’t want to strip the concrete thread or snap them.
Mistakes to Avoid, Tips & Tricks
The one tip that we want to leave you with here is that both for pre-built and for existing sheds, there are multiple ways of anchoring them to concrete slabs, so if the above methods don’t suit you for whatever reason, we recommend looking into some of the other methods.
On the other hand, if you have no concrete slab to anchor your shed into, you might want to consider anchoring it into gravel instead.
Summary
Now that you know exactly how to anchor a shed to a concrete slab, you should be able to build a stable and secure shed from scratch, all without any outside help whatsoever.