2×6 or 2×8 Sill Plate (Which One is Better for Foundation)

Sill plates are known as the crucial connection between the foundation of your building and its framework.

But which one of the sill plates is better for the foundation, 2×6 or 2×8 sill plate?

2×6 is the better pick for a more cost-effective and available sill plate option. But keeping load-bearing capacity, anchor bolt placement, and deflection factors in mind, 2×8 is the better pick. However, 2×8 is more expensive and harder to find in hardware stores than 2×6 sill plates.

Do you need more information to decide between the plates? Look no further I have all the details right here:

2×6 or 2×8 Sill Plate: A Short Comparison

Before we move onto the detailed comparison of the two sill plate sizes let’s have a look at the difference at a glance:

Factor 2×6 Sill Plate 2×8 Sill Plate
Load bearing Capacity Can bear the weight of joists, beams, and girders All the same weights of 2×6 along with objects with higher weights.
Anchor Bolt Placement Placed ⅓ inches from the outside of the foundation Placed in the center of the 8-inch thick foundation.
Wall Height 2×6 size is sufficient for most wall heights Can be deemed unnecessary.
Deflection More deflection than 2×8 Less than 2×6.
Future Modifications Limited modification possible Better for modifications.
Cost Cheaper Expensive.
Availability Available in every hardware Harder to find.

Sill plate flush with foundation, which demands more details about these plates. With the table, you have an idea about the difference between these two sill plate options. But that’s not enough to decide.

So, let’s move on to a more detailed comparison:

Factor 1: Load-bearing Capacity

A 2×8 sill plate has a greater load-bearing capacity than a 2×6 sill plate. 2×6 and 2×8, both of these sill plates can effectively bear the load on a concrete foundation. 

But the 2×8 sill plate has some advantages over the other. It has better weight distribution and the ability to anchor to the interior side of the basement. This makes the 2×8 sill plate better at bearing higher loads.

On the contrary, 2×6 sill plates can do a good job of bearing the weight of beams, joists, and girders. 2×8 can bear these loads too but 2×6 gives you more adjustment options. Anytime you need to level out the floor you can easily adjust 2×6 sill plates.

You can’t do this while using 2×8 plates because of the 8-inch common footing. There is no free space for adjusting, which can sometimes compromise your building’s structural integrity.

Note: The specific load-bearing capacity of each sill plate depends on various factors like the type of wood used, the spacing of the framing members, and the size and spacing of the anchor bolts. So don’t pick 2×8 sill plates just because of the better load-bearing capacity.

Sill Plates Load bearing Capacity
Source: Gambrick

Factor 2: Anchor Bolt Placement

2×8 sill plates have anchor bolts in the center of the foundation. But 2×6 plates have them placed 1/3 in from the outside of the foundation.

Anchor bolts are used to prevent the structure from shifting or moving by securing the plates to the foundation. This placement affects the strength and stability of the structure.

The 2×8 sill plate places the anchor bolts right at the center of the 8-inch thick foundation. This provides much better strength and reduces the risk of structural failure.

However, the anchor bolts are placed 1/3 in from the outside of the foundation for 2×6 sill plates.

This means the bolts are at a distance of one-third of the width of the foundation from the outside edge of the foundation. This provides minimum stability but nothing that matches the stability of the 2×8 plate.  

Factor 3: Wall Height

2×8 sill plates are perfect for taller walls or structures that require greater support, while 2×6 sill plates are more cost-effective for shorter walls.

The International Residential Code (IRC) requires sill plate thickness to be an inch and a half, or 2x. Both 2×6 and 2×8 sill plates meet the minimum sill plate size code requirements.

So, for most wall heights, 2×6 sill plates are sufficient and 2×8 can seem unnecessary. But some wall heights may require 2×8 sill plates rather than 2×6. Sometimes, building codes and regulations can require one over the other.

Factor 4: Deflection

A 2×8 sill plate can reduce deflection over a more extended period of time compared to a 2×6 sill plate.

Deflection means the displacement of movement of a structural member from its original position when a load is applied.

This usually happens due to externally applied loads (point loads, shear loads, etc.) and the force of gravity. Sometimes the weight of the structure can cause this as well.

Due to better weight distribution, 2×8 sill plates can reduce deflection over a more extended period of time compared to a 2×6 sill plate. 2×8 plates have more strength due to the placement of anchor bolts in the center of the 8-inch thick foundation as well.

2×6 sill plate anchors on the other hand are placed on the outside. This makes them a little less capable than 2×8.

Factor 5: Future Modifications

2×8 sill plates provide better future modification capability than 2×6 sill plates.

You can easily fasten on the interior of the basement if 2×8 sill plates have been used. For taller structures, this is a big plus point. 2×6 sill plates can be fastened as well but it is limited compared to 2×8 plates.

Factor 6: Cost

2×8 are more expensive and hard to find than 2×6 sill plates.

2×6 sill plates are available in almost every hardware shop. They are mostly within the $100 range. This is because of the mass production of these plates.

Because of their size, 2×8 plates are quite expensive to produce, making them harder to find. Moreover, you need to decide what size lumber for the sill plate you need.

Moreover, 2×8 requires better bolt joints and reinforcements of structures. All of these exponentially increase the expense of construction.

2×6 or 2×8: Which is the Best Choice for A Sill Plate?

The use of sill plates ultimately depends on the budget and structural expectations of a specific project. Both 2×6 and 2×8 will provide good support for your foundation as they meet the IRC requirements.

For a more cost-effective option, 2×6 seems like the better choice. But keeping future modifications and better weight distribution in mind, 2×8 is the best choice.


Which Lumber Type is the Best Choice For A Sill Plate?

Pressure-treated (PT) lumber is the best choice for a sill plate. Their durability and resistance to decay and termites make them a popular choice. Redwood & cedar and Borate-treated lumber are popular alternatives for sill plates.

How Many Bolts Should Be Used for Per Sill Plates?

At least 2 bolts should be used for every sill plate. IRC or the International Residential Code(IRC) specifies the use of two or more per plate sections. One of these bolts needs to be located no more than 12 inches or less than 4 inches from each end of the plate.

Is a Sill Plate Considered a Structural Component?

Yes, a sill plate is considered a structural element. Usually made of pressure-treated lumber, it is a crucial component in house framing. It connects the frame to the foundation. It serves as the attachment point for vertical members while providing stability. 

End Words

That’s the end of our discussion on 2×6 or 2×8 sill plates. Ultimately the decision comes to the specific needs of the project and budget available.

For more insights on the structural requirements and building codes make sure to contact a licensed professional before buying any product.

Good luck!

Jim Boslice

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