Framing exterior walls of a home happens immediately after the floor is framed. Building codes require that exterior walls be sheated with plywood or oriented strand board, OSB. Walls in cooler climates are built with 2x6 framing and in warmer climates they are built with 2x4 framing. The most common layout for wall studs is 16 inches on center.
Framing exterior walls is different from interior walls. Exterior walls provide strength and rigidness to a home so they need to be anchored down with anchor bolts and sheeted with plywood or O.S.B. (Oriented Strand Board).
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The first step in building exterior walls is to mark the wall location on the floor with a chalk line. Make sure the plate will be at the edge of the concrete or framed floor so the sheeting on the wall will go over the edge. Measure back from the edge 3 1/2 inches for 2x4 walls and 5 1/2 inches for 2x6 walls. Put a mark at each end of the wall. Snap a chalk line between the two marks.
After the wall is located then the top and bottom plate are cut to length and put on the wall line mark. The plates are then laid out and marked with all the walls, doors, windows and other items in the wall. Try to cut top and bottom plate from single pieces of lumber but if the wall is longer than your top and bottom plates then place the joint on the center of a stud.
Crowning: The plates are now seperated and the wall studs are put between them. Make sure that the bow in all of the studs is curving up, this is called "crowning the studs".
Nailing: After all the framing members are installed and nailed off, 3 nails in each end of each stud for 2x6 walls and 2 nails in each end of each stud for 2x4 walls. Line the stud up with the mark on the plate, making sure it is on the correct side of the mark and nail the plate to the stud.
Nailing Order: Nail on the windows or doors headers first if there are any. It is easier to nail on trimmers and headers before the adjacent studs are installed because you need to nail on the side of the king stud into the header and trimmer and it is easier to do that if there is not a stud in the way.
Square The Wall: After the wall is nailed together it needs to be made square. Put the bottom plate of the wall on the exterior wall chalk line and toe nail the bottom plate to the floor, this keeps it straight while the wall is squared. With only the bottom plate nailed to the floor use your tape measure to measure diagonally from top corner to bottom corners across the wall. Move the top plate of the wall back and forth until the dimension is exactly the same going both ways, this tells you the wall is square.
Put a nail thru the top plate into the floor to hold it. Double check that the wall is square because once the sheeting is put on it will be impossible to change its squareness. Read the article How To Square A Wall for detailed information
Layout: Exterior walls are covered or "sheeted" with Oriented Strand Board, OSB, or Plywood to give them strength. Start by lay a piece of sheeting on the wall at the end you laid out the wall studs from. The edge of the sheeting should break exactly on the center of a wall stud. If you are framing on a wood floor with joists you will need to extend the sheeting so that it extends down to the sill plate on top of the foundation. If you are framing on a concrete slab make sure the sheeting does not extend past the sole plate because that would lift the wall off the floor when it is stood up. On wood framed walls built over floor joists this means that the OSB panel will not extend up the wall to the top plate. A block of wood will need to be installed at the joint between the upper and lower sheeting panel after the wall is stood up.
Nailing: Nailing of exterior wall sheeting is very important. It needs to be done according to building code standards or a structural engineers calculations. The requirements will tell you how many nails need to be put in. Make sure that the nail heads are flush with the surface and do not break the face of the osb. Check with your local building department to see what is required for your project.
Cutting the window or door openings is easiest to do as you go along and sheet so that you can see a part of the window or door opening and measure and mark it before it is totally covered up.
Once the OSB is nailed on the wall panel becomes very rigid and is ready to be stood up. The wall is stood up and nailed onto the floor in line with the chalk line. It must also be braced with long 2x4 members
Install the blocking board behind the joint on the wall where the upper and lower sheeting panels meet.
step 6 Straightening The Walls
To straighten a wall you will use a string line tied between two nails, one on each end of the wall at the tops of the wall. Put the nails in and leave the heads off the face of the wall about 1 inch. Tie the string line at 1/2" off the face of the sheeting and pull it tight enough so that it does not sag. Straighten the top of the wall so that it is 1/2" off the string line all the way along it. Use a 16' 2x4 nailed to the top of the wall and the floor to hold the wall in place once it is straight. These braces must be left in place until after the roof trusses are installed so the walls stay straight.
step 6 Double Top Plates
The double top plate strenthens the exterior walls to help them hold the load of the roof trusses and keep them straight. Joints in double top plates must overlap by 24 inches or more if you are using the IRC and overlap by 48" or more if you are using the IBC. There are two ways to install the double top plate, before or after the wall is raised.
Plating Before Raising: Some framers install the double top plate when the exterior wall is on the ground and then use a circular saw to cut out the plate after the interior walls are built. This makes the wall stronger when lifting it.
Plating After Raising: The walls can also be top plated after they are stood and the interior walls are built.
After the walls are straightened and braced and the top plates are nailed off you are ready to build the interior walls. Read the article How To Frame Interior Walls to learn about framing interior walls.
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