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ABSTRACT: The following instructions are intended to instruct a qualified window and door expert on how to assemble window and doors in various mullion conditions including standard mulls, 3/8" mull reinforcement, space mulls, and LVL mulls. These instructions assume a high level of user competency and that they are confident using power and hand tools, modifying the frame of the window or door, and performing all the tasks within. Read these instructions thoroughly before beginning.
These instructions are used for the following products:
Don’t try this in California!
Don’t try this anywhere else!
A ribbon or stacked (standard) mull is one in which the frames are joined tightly together with no reinforcement or space between.
Mull Reinforcement or MRF are vertical or horizontal mulls that have aluminum reinforcement members attached to the them and are clipped and fastened together making the mull 3/8" wide.
Space Mulls are vertical or horizontal mulls with wood blocking between them to a specified width. They are sealed at each end and covered at the exterior with a metal space mull cap. Space mulls come in 3/8", 1, 2, 3, 4 and 6" size widths.
LVL Mulls are used for structural applications and come from Marvin in 1" and 2" widths (other widths may be available from other sources). Similar to space mulls and MRFs they are sealed at the ends and covered to the exterior with a metal mull cap.
Stud Pocket Mulls are similar to space mulls except the wood blocking is removed just prior to the window being installed.
All mull configurations are diagrammed with the same rules as viewed from the exterior. The alphabetical label denotes the horizontal row starting with the top. The numerical label denotes the vertical column starting from the left. For example, A1 is always the top left unit as viewed from the exterior.
When laying out your assembly, refer to the quote diagram and the corresponding label on the unit.
If you have ordered your assembly factory prepped for mulling, verify that the correct corners have been notched. If not refer to the steps below starting with step 3.
1. Any corner that intersects a mull must have a notch cut out of the accessory kerf cladding such as that shown in Figure 8. Notching allows room to apply the mull cap and frame trim later.
2. The following shows the correct location for notched corners in various configurations regardless of mull type.
3. To make a notch, remove the exterior wall of the accessory kerf with a sharp chisel. Only remove material from the accessory kerf that is perpendicular to a mull. (multiple high multiple wide configurations will have both walls of the corner(s) notched out). See Figure 12 and Figure 13.
This section focuses on preparing an assembly for mull reinforcement if it has NOT been factory applied. Refer to your mull diagram to identify the location of your mull reinforcement(s).
1. MRF KERF: If the units in your assembly have not been prepped for MRF and have no accessory kerf in the wood sides of the jamb, you will need to cut a 1/8" wide by 1/4" deep kerf. Use a circular saw and guide to cut the kerf 2 1/4" (32) from the edge of the frame. See Figure 14
NOTE: Some full frame units will not have a factory fabricated kerf. All narrow frame product does have a kerf. Images throughout this section show a full frame unit but narrow frame applies as well.
2. Apply MRF Components to the frames. Apply a 3/8" bead of Dow Corning ® 791 (or equivalent) to the jambs in a wiggle pattern. See Figure 15.
3. The MRF components come in two parts. The beige piece always has the hooked end to the interior. The black piece always has the “hooked” end to the exterior. Insert the alignment leg on the MRF component into the MRF kerf in the frame. Flush the MRF component with the end of the mull and fasten to the frame with #8x5/8 screws in every hole of the MRF. See Figure 16.
1. If at all possible, remove operating sash from frames and set aside.
2. Refer to your mull assembly diagram and place the individual units on a flat sturdy surface in the correct orientation exterior side up. If already applied, remove drip cap(s) and jamb nailing fin where units will be mulled.
3. Notch your corners at the appropriate locations (if not already done). Refer to the section, Corner Notches on notching for details if you need to do this.
4. Apply mull sealant tape to one unit ensuring that it is located flush with the exterior edge of the cladding as shown in Figure 18. The tape should extend past the mull and wrap around the corner by at least 1/8". Remove the paper backing.
5. Join the units close to each other so the notched corners are together and slide the aluminum mull clip over the mull as shown Figure 19. Pound the clip in with a plastic headed hammer or wood block and framing hammer until the clip contacts the other side.
Be careful not to kink or bend the mull clip when installing.
6. Fasten the ends of the mulls with three 1 1/4" 16 gauge staples spaced evenly to the interior side of the kerf in the wood members.See Figure 20.
7. Carefully turn the assembly over, interior side up. Lightly clamp the units together on the wood frame members ensuring they are flush on the interior and even at the ends of the mull.
8. Fasten the units together with 5/8" x 1/2" staples as shown. Three staples spaced at 2" intervals must be placed on both ends, starting approximately 2" from the edge of the frame. Space the remaining staples at 5-8" intervals. See Figure 21.
1. Set the units on a flat surface interior side up. Hook the MRF pieces together. Align the frames so they are flush and the ends are even. You may need to seat the assembly together with a rubber mallet. Secure the MRF with #8 x 5/8" undercut head screws through the pre-drilled interior face of the beige component. See Figure 23.
Remove the interior covers/stops where mulls will take place.
1. Set the units on a flat surface interior side up. Apply adhesive in a wiggle pattern on the window frame. See Figure 24.
2. Clamp the LVL member to one of the units flush with the interior. Fasten the LVL to the unit with #8x 1 1/4" screws from the interior 4"(102) and 12-15" (305-381) on center (same plane as the jamb screw holes). See Figure 25.
3. Apply adhesive in a wiggle pattern on the LVL or space mull. See Figure 26.
4. Clamp the two units together and repeat screwing through the jambs as before.See Figure 27
5. Proceed to section, Applying Mull
Caps on Space Mulls, 3/8" MRF, and LVL.
Remove the interior covers/stops where mulls will take place. You will be screwing through the jambs/sills/head jambs to fasten to lvl or blocking.
1. Set the units on a flat surface interior side up. Apply adhesive in a wiggle pattern on the sill of the window frame of the top unit.See Figure 28
2. (CUDHNG and CUGL, skip to next step) Clamp the space mull block or lvl to the bottom of the upper unit flush with the interior. Fasten through the sill into the block with #8 2/3 thread screws 4" (102) from each end and every 12-15" (305-381) after (follow fastener length from table below). See Figure 29.
3. On CUDHNG and CUGL Horizontal Mulls, clamp the space mull block flush with the interior of the top unit and fasten through the block into the sill with #8 2/3 thread screws 4" (102) from each end and every 12-15" (305-381) after. See Figure 30. (See table below for proper length)
4. Apply adhesive in a wiggle pattern on the LVL or space mull. See Figure 31.
5. Clamp the two units together and screw through the head jamb and into the blocking above 4" from each end and 12-15" OC after.See Figure 32.
6. On double hung units, remove the head jamb parting stop (on double hung operator units) from the bottom unit or stops from other Then drive #8 2/3 thread screws through the head jamb and into the space mull block. See Figure 33. (See fastener table above for proper length).
NOTE: Make sure to place fasteners going through the head jamb offset about 1" from those fastening the block to the sill of the upper unit.
7. Replace the stops you removed earlier.
1. With the assembly facing exterior up, make sure the corner notches are made in the right places. Refer to the previous sectionCorner Notches for details.
2. Apply frame kerf weatherstrip in the accessory kerf along the mullion and all open kerfs that run perpendicular to the mull. Roll the weatherstrip into the kerf with a screen spline roller or similar tool. See Figure 34.
3. If not done already cut two pieces of A148 frame trim. Measure the outside frame measurement and subtract 5/32” (4) for the finished length. Set these aside until sealant application is complete. See Figure 35.
4. If not done already cut the mull caps to length. Measure to the inside of the accessory kerf. Set these aside until sealant application is complete.See Figure 36.
1. Apply 3/4" foam backer rod to the full length of the mullion. See Figure 37.
2. Apply a 1/8" bead of clear sealant 2-3" long on each end of the mull and at any intersections along both edges of the mull.See Figure 38.
1. Apply a u-shaped bead of sealant over the ends of the space mull block. Press the foam block into place (notched side down) and apply additional beads of sealant on top. See Figure 39.
2. Apply a 1/8" bead of clear sealant 2-3" long in the accessory kerf on each end of the mull and at any intersections along both edges of the mull. See Figure 40.
1. Use a plastic headed hammer to make minor dents in the cladding accessory kerf where the A148 frame trim will be applied. The frame trim will always run perpendicular to any non-direct mull. See Figure 41.
Avoid "over-denting" the edges of the frame and use the side of the plastic headed hammer.
2. Apply the A148 frame trim to the assembly at each end of a non-standard (direct) mull. Pound the trim on with a plastic headed hammer or block of wood and framing hammer. See Figure 42.
3. Apply the mull cap by inserting one end into the frame kerf and tapping the cap into place with a plastic hammer or rubber mallet the first 6-10" from the end. Then insert the opposite end into the frame kerf and tap into place along the length of the mull. See Figure 43.
1. Mull clips are sent cut to length for one high or one wide assemblies. On multi high multi wide assemblies all clips are sent long and you will need to cut them to fit.
2. Mull all direct assemblies first.
3. Mull space mulls, MRFs and LVLs last.