Topic 2 – Layout Exterior Wall Plates
Rough Openings
Rough openings are often supplied by the manufacturer, however there are circumstances where the rough opening may need to be calculated by carpenters. Two measurements are given for rough openings, with the width always being written first. For example, an opening 1.2 m x 1.8 m is 1.2 meters wide and 1.8 meters high. When finding an R.O., always find the width first as it effects the lintel required, its bearing, and subsequently the lengths of the trimmers and cripples. It is also the measurement required when doing the wall layout.
Generally, the rough opening will always allow ½” of room on all sides around a fixture. This includes exterior doors and windows. This means 1” is added to the width, with 1” added to the height of windows and ½” added to the height of doors. The exception to this rule is vinyl windows which are recommended to have 3/8” of room on all sides (3/4” added to each dimension).
Rough Openings for Exterior Doors
Doors, both exterior and interior, are sized according to the door slab. A typical exterior door measures 32” x 80”. These measurements do not include the jambs on sides and top, the threshold at the bottom, or the ½” clearance for installation. To calculate the rough opening for exterior doors, these must be added.
To calculate the width of an R.O. for an exterior door, we will need to know (see figure 11 below):
In the example above, we have 1 ¼” jambs with ½” rabbets. The jambs that remain beside the door are equal to ¾” (1 ¼” – ½”). Here, the rough opening would be equal to the door width plus 2 x ¾” plus 1” for clearance:
Example: Calculate the R.O. width for a 2’-4” door with 1 ¼” jambs with ½” rabbets.
*** Try to calculate the R.O. width of a 760 mm x 2082 mm exterior door with 19 mm jambs
Three pieces of information are required to calculate the rough opening height for exterior doors:
The formula for calculating R.O. height would be as follows:
Example: Calculate the R.O. height for a 2’-4” x 6’-8” exterior door with ¾” jambs and 1 ½” sill:
- R.O. height = 1 ½” + 80” + ¾” + ½” = 82 ¾”
***Try calculating the R.O. (width x height) for the following (both doors have ¾” (19 mm) jambs and 1 ¾” (45 mm) sills):
- Door size = 2’-8” x 6’-8”
- Door size = 910 x 2130
Windows are much more straightforward. As with doors, the rough opening required is often given by the supplier. If it is not, simply add clearance according to window construction:
***Try calculating the R.O for the following windows:
- 32” x 46” wooden window
- 986 mm x 1200 mm PVC window
- 4’-8” x 2’-6” wooden window
Laying Out Exterior Wall Plates
Laying out exterior wall plates should be done in the following steps:
- Cut plates to length
- Deduct sheathing thickness at each end
- Butt joints on plate should be on a stud center
- The tape is cut a wall thickness on intersecting walls
- Mark partition centers
- Indicated to centerlines, mark edges of partition
- Some partition centers may not be i