If you are building your own home or if you are retrofitting your window openings for new windows it is important that you always follow the manufacture recommendations for door and window openings but in general all rough openings for windows and doors are made two inches wider and two inches taller than the size of the door or window that will fit the opening. Often this size is reduced to 1 inch on all sides which provides a much tighter opening requiring less spot insulation and problems with drafts.
This measurement is a standard across the industry however it requires that the carpenter that is framing the rough openings has information about the windows that are selected prior to building the stud wall.
If changes are made later in the design process studs can be removed and openings changed without too much problem but you will incur additional costs and delays which can be expensive and can also push the project timeline out of sync with other contractors that need to perform work.
Framing A Window Opening
The actual framing process is pretty simple. Walls are normally 16 inches on center meaning if you measure the distance between the vertical studs in the wall they are 16 inches apart. To create a larger opening for a window you have to remove the studs that are in the opening area and then support the floor or roof above the window with a header to bridge that gap.
Nearest the window you have a Jack Stud that holds up the Header above the window. On the outside of the Jack Stud you have a King Stud that travels from the bottom plate to the top plate of the wall. Below the window you have a Sill Plate that defines the lower opening of the window. Under the Sill Plate you have partial or Cripple Studs that support the Sill Plate.
All of the studs are nominal studs sizes and the Header is often made of two pieces of 2×12 inch joist lumber that is glued and nailed together. However some contractors will use stud and cripple studs in this area.
The total gap around the window should be a minimum of 3/8 inch on all sides to a maximum of 2 inches on all sides. As we said above normally a contractor that is comfortable with the general contractor and the quality of the windows will frame the opening either 1 inch or maybe less to reduce finish carpentry, insulation and draft problems.
Roughing Window Openings For Retrofit Replacement Windows
When you are retrofitting a home that has existing windows then you can purchase retrofit replacement windows that will fit the openings. Measurements are very important in this case and often the retailer will require not just suggest that they visit your home before they take your order.
One very important thing to remember when purchasing replacement windows is that you want to order windows that are standard sizes from the manufacturer. If your windows are not standard sizes they can be manufactured by the window company however if you purchase their most popular sizes the cost will be much less and your order will be processed much faster.
For this reason you really need to have a sales person that is working on your side. If you purchase your windows from a large retail home store you should ask to see their price sheet and then if your original openings are slightly larger than their lower cost window you can use additional framing and moldings to frame out the window opening for a smaller window and save substantial amounts of money. And when I say slightly smaller it might only be 2 inches which is not noticeable from the ground on your second story windows. So you have to consider all of your options and know the price scale before you make modifications.
Final Note
Framing for rough window openings is not very difficult if you know the size of the windows you expect to purchase. This is why the planning stage of any remodel or project has to be done before you start ripping out walls and hammering nails.
If for any reason you are unsure about an opening then just don’t frame it. Continue the stud wall 16 inches on center as you would a wall without a window and then come back later and build the header and insert the king studs where required.