Why are all sill plates defaulting to 5 1/2"?

[Browneye]

Just to make sure I am not confusing normal terms with what the software calls a sill plate, I define a sill plate (a.k.a bottom plate) as the wood bottom piece of a wall.  In the case of a monolithic slab on grade, the sill plate it treated and is bolted to the slab.  There is also usually a sill seal between the bottom plate and the concrete.  Typically the bottom plate is the same dimension as the wall being built so 3 1/2" for a 2x4 wall and 5 1/2 for a 2X6 wall.  

 

I just checked my 2x4 walls and all show a 5 1/2 sill plate.  Shouldn't this be 3 1/2".   If I'm correct on all this, maybe I'm expecting too much from the software meaning it should know what size sill plate to put based on the wall thickness?   I'm really hoping I'm confused on this because its a pain to go change every single wall that is 2X4.

[Rookie65]

See what your foundation default has. It may be using the default 5-1/2" sill plate from there.Maybe change that to 3-1/2", or change it to no sill plate and see if it goes away.

Sill plate is usually the term for the sill on top of a foundation between the concrete and the floor joists/rim joist. The bottom of a wall is often refereed to as a "shoe", at least here.. 

[Browneye]

Thanks.  I have no floor joist or rim joist because I have monolithic slab.  At least it seems I have the same definition as you and the software.   Its silly that they define this in the foundation vs. letting the software default it to the wall thickness with the option to change it only when you want a sill plate that is different than the wall thickness.  The only scenario I can imagine where someone would want option would be if you had an extremely thick interior wall material and wanted to bring the sill plate out past the wall for base board backing.

[Rookie65]

I know you have a monolithic slab. I'm just wondering if it's a default item for any foundation if it's not removed? Without seeing your plan, it's just guesswork. 

[Browneye]

It does appear to be a default item for any foundation.  I guess if I'd changed it to 3 1/2" I wouldn't have had to change so many walls.  I only have a few 2X6 walls for drainage pipes.  Didn't want to completely remove it as I do need sill plates and wasn't sure how much work it would be to add them all back.

[Rookie65]

Ok. Might need to add foundation breaks for the areas that need the 2x6, and set the default to 2x4, whichever is easier for you at this point.

[Oldhouseguy]

On 8/8/2026 at 5:00 PM, Browneye said:

 Its silly that they define this in the foundation vs. letting the software default it to the wall thickness with the option to change it only when you want a sill plate that is different than the wall thickness.  The only scenario I can imagine where someone would want option would be if you had an extremely thick interior wall material and wanted to bring the sill plate out past the wall for base board backing.

speaking as a builder the sill plate would be on the top of the foundation wall and would be at least a 2x6. i have never seen a 2x4 plate on top of a foundation wall. Most houses have foundations with floor joists so it is logical that the software defaults to 2x6

[Browneye]

You said on top of the foundation wall which does not exist in a monolithic slab.  The way you worded it confused me.  Yes, top of foundation wall but it’s at the bottom of a studded wall. 
 

The sill plate (also called the sole plate or bottom plate) is at the bottom of the wall.

 

• Sill plate/sole plate — bottom of the wall, anchored to the foundation; wall studs sit on top of it

• Top plate — at the top of the wall, where the ceiling joists or roof trusses rest

 

One nuance: “sill plate” technically refers to the plate that sits directly on the foundation (often pressure-treated and bolted down with anchor bolts), while “sole plate” can refer to any bottom plate of a wall assembly, including interior walls not touching the foundation. In everyday framing talk, though, people often use the terms interchangeably for “the bottom horizontal 2x board of a wall.”

[y-g-m-n]

I have seen this as we do slab homes here in Southern MS.

 

If you look at actual walls it frames it will make bottom plate the same width as wall studs.

 

As above person said the software uses SILL plate for the top of a foundation wall like they do up north and then put floor joists on top.

 

So I have ignored it after always changing them as it means nothing for those who use Monolithic slab foundations.

 

Even in the garage area where it will make short stem walls to be the same elevation as the house slab it is only as wide as stud.

 

 

[Browneye]

Ok, now I understand.  Thanks.  My build is in South Louisiana near Miss. 

[TheMadCadder]

I've always referred to the foundation plate as the sill plate and the bottom plate of a wall as the sole plate.

 

This is the technical code definition although many people in the trades use them interchangeably.

 

FYI...there is no code that specifically requires a 2x6 wide sill plate although other factors such as anchor bolt spacing, doubling rim joists offsetting joist bearings on sills that would naturally require a sill plate wider than a 2x4.

[Rookie65]

Plus a wider sill plate helps with allowable spans of the joists. Sometimes even a 2x8 sill on a 10" poured foundation wall can help with framing joist spans determination 

[y-g-m-n]

This is nomenclature thingy.

 

Framers around here throw around the words

Base Plate,

Bottom plate

Sill plate

Anchor plate

All made from Pressure treated wood with a thin foam like gasket to seal bottom to concrete to help prevent air flow.

 

All mean the same thing - plate at bottom of wall that is bolted to slab.

 

Tomato TomAHto

 

Would be nice if software help kind had better explanation maybe a definition page?

as we all use different terms if based on where you live