What is a Bottom Plate?
When framing a building, the bottom plate, as well as the studs, top plate, sills, and ceiling or roof joists, are the essentials to the structural integrity of the building. Also known as a sole plate, bottom plates can be thought of as an extension of the foundation upon which the roof, ceilings, and walls rest. In a wood-frame building, the bottom plates would most likely be wood, though various other materials may be used, such as steel, concrete, or composite materials.
On a straightforward wood-frame building construction project, the sole, or bottom plate is affixed to the subfloor, or rough floor. On an interior-wall project, the vertical studs are fitted, and then nailed or screwed in place through the subfloor and bottom plate, or if that would result in damage to the floor, simply toe-nailed into the bottom plate. The studs are then nailed or screwed into the top plate, which is at ceiling level. Thus, the bottom plate is the foot of the wall, the studs are the ribs, and the top plate is the head of the wall.
As a rule, interior framing in a completed structure must be done vertically; bottom plate nailed to the subfloor, studs nailed or screwed to the bottom plate, then to the top plate. Exterior wall construction is ordinarily accomplished horizontally. Bottom plate, top plate and studs are nailed or screwed together horizontally on the subfloor, and the entire construction then lifted, all as one complete assembly, into the proper position on the subfloor. Roofs and ceilings are generally not yet built, therefore allowing the uninhibited erection of the wall.
In a wood-frame construction, bottom plates, studs, and top plates are commonly Douglass fir, pine, or hemlock. Wood is readily available, comparatively inexpensive, and sturdy enough to ensure reasonable durability of construction. Wood beams, generally larger than the two-by four or two-by-six boards ordinarily used in the construction of wood buildings, may be used as either top or bottom plates for extra load-bearing strength.
Often enough, novices in construction will confuse bottom and top plates with footers and headers. A header is used in the installation or construction of window or door opening, and footer is a term for the bottom of a building’s foundation. Though similar in concept, the terms are differentiated in the interests of clarification. One would not want to construct a window or door frame, or pour a foundation, when a wall frame is what is actually wanted.
@kentuckycat - Very good questions. I'll try to help. The woods that were mentioned are usually called framing wood, since they are often used for the frame, or shell, of a building. All of those woods are softwoods, which means they come from evergreens. In generally, the wood is pretty bland and doesn't have much character. Like you said, it all kind of looks the same. There are subtle differences if you know what you are looking for, but any type will be okay.
The reason softwoods are used instead of hardwoods (like oak and maple) is that softwoods are much, much cheaper. Oak and maple have very desirable grains and are usually used for cabinets and floors. Since no one sees the inside of a wall, no one cares what the wood looks like.
I don't really know much about construction or home improvement, but I guess I'm just curious. Since the article mentions pine, Douglas fir, and hemlock, which one is best for buildings? If I were building my own house, how would I even tell the difference between the wood types? 2x4s all seem to look the same to me.
Along the same lines, could you use something like oak or maple or one of the other popular woods?
@titans62 - I might be able to give you a little help. When I was growing up, my dad used to build outdoor sheds that he would sell to people. I certainly don't have the kind of skill that he had, so I try to stay away from the power tools, now. I still remember a few things from helping him, though.
Whenever he made the side walls, he would always screw the studs into the bottom plate from below. Since the buildings were meant for the outdoors, he always used galvanized screws. I would imagine that for indoor use, any screws would work. Unfortunately, I don't know enough to tell you what size they were. Maybe someone else can answer that part if you need to know.
Since the article mentions screws and nails, I would assume that both would work as long as you were sure you had fasteners that were approved for your specific use.
Does it matter whether you use nails or screws to attach studs to the bottom plate? Should one be used in a certain situation and not in another? What determines their uses?
Can anyone here offer suggestions on how to go about replacing a bottom plate?
I just bought a mobile home that I plan to rent out. In one of the back rooms, there has been some previous water damage that is more severe than I originally thought. I have replaced subfloors before, but don't have any experience with the bottom plate.
Will I have to remove each of the studs individually and replace them at the end, or should I be able to get the fasteners out of the studs and only replace the bottom plate?
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