Window Fitters Guide to Window Installation 87 ©2022 AWDI, LLC Do not reproduce without permission The measurement from the nailing fin to the exterior edge of the new window frame is typically 1-1/2”. If the measurement of the pocket depth (the interior trim to the edge of the substrate) is 3/4”, then the interior edge of the slot in the blocking will be cut at 3/4”. 4. Measure the width and height of the replacement window. Because you will be cutting 45 degree cuts on each end, add at least 5” to the width and height measurements. Cut a length of the 1-1/2” x 1-1/2” blocking to a length(s) that will allow you to cut the individual blocking for the new window. 5. Cut the slot in the blocking on a table saw. Use a thin kerf blade so that the block fits snugly on the nailing fin of the new window. Set the saw blade for the required measurement away from the rip fence. Then set the saw blade height slightly taller then the depth of the nailing fin (typically 1-1/16” will suffice). 6. Once the slots are cut, cut the blocking to length using a 45 degree miter cut, as shown. Excluding the nailing fin, measure the new window frame to establish the lengths needed for the head, jambs and sill block- ing. For each of the blocking pieces, measure from the shorter end of the initial miter to what will be the shorter end of the opposite miter cut. Be careful. Better to be 1/16” longer than necessary, than 1/16” shorter. Also take care that the header and sill pieces, and the two jamb pieces are identical in length. 7. Apply a thin bead of caulk the nailing fin on the exterior side. Place the blocking over the nailing fins of the head, sill and jambs — making sure the interior side of the blocking is facing the interior side of the window on all four sides. 8. Butt the edges of the blocking against the window frame, and bring the mitered ends together. Seal the entire gap between the mitered ends with caulking. Nail the ends of the blocking together (as shown). The window is ready to install. 9. Run a continuous bead of caulking around the perimeter of the rough opening where the blocking will seat against it. 10. The new installation should have a drip cap. If the old drip cap is in place, remove it and replace it with a newly prepared cap that will extend out, over the header blocking. The drip cap can be fashioned using cap stock and a metal brake. 11. Place the window in the opening. Press tightly against the caulk bead to assure a good seal. If measurements were accurate, the interior edge of the new window will butt up against the interior trim (drywall return or jamb extensions). You can use new “J” Channel as long as you are able to fit it under the trimmed siding in proper fashion for proper drainage and in accordance with good flashing techniques. 12. Square and plumb the window, and check the sash reveal. 13. Fasten the window to the rough opening through the blocking using #16 stainless steel or corrosion resistant finishing nails. Nails should be placed within 4” from each corner and spaced no greater than 14” apart. Drill pilot holes through blocking, if necessary. 14. Run a continuous bead of caulk around the perimeter of the window, between the blocking and the existing siding, as shown. Also caulk along the joint of the mitered corners. 15. Run a continuous bead of caulk around the window where the frame meets the blocking. 16. Caulk the interior where the new window meets the interior extension jamb or drywall return, and tool the bead smooth. Finish the blocking on the outside to match the existing siding. SAMPLE MANUAL
View this content as a flipbook by clicking here.