How To Install Exterior Window Trim

By Robert Robillard on How To

Building and Installing Pre-Assembled Exterior Window Trim

This article will explicate how to install exterior window trim by using a pre-assembly method. Pre-assembling trim is faster, more efficient, neater, and produces almost-perfect joints every time. This approach is different from installing trim on the window one piece at a time, it requires a completely different way of working.

Pre-Associates Surround vs Slice Meal Trim

Slice-by-slice trim installation requires y'all to travel back and forth between your miter saw and wall, or upwards and downwardly a ladder or scaffold. Additionally, the joints are virtually always off or not affluent, due to the nailing flange or unevenness in the wall, which translates into uneven/open up trim joints.

It's far easier to build the trim surround every bit i piece on a flat surface. When installed every bit ane piece information technology sits better with tight joints.

PVC Trim Is Rot Resistant

PVC trim boards are widely popular for being weather-resistant, termite-proof, and rot-proof, making them one of the most reliable materials for exterior edifice. One of the biggest advantages is that it doesn't demand to be painted.

Measuring and Fitting

Measuring pre-assembled trim should e'er be done off the window itself. You can attain this on the ground, prior to installation, or later the window is installed. When feasible, I prefer the one-time method. With multiple, aforementioned size, windows, this method can get an efficient, fast, best exercise way to finish a project's exterior window trim.

Pro Tip:

When measuring horizontally, measure out the furthest protruding part of the window. Have your measurement point to point to outermost point – and Add together ane/8" plus the thickness of your trim X2 to that measurement. This gives y'all the total length of the top trim and windowsill. This 1/viii" measurement gives some adjustment room for fitting and sealant.
When measuring vertically measure out the furthest protruding part of the window. Take your measurement Indicate to bespeak to the outermost point – and Add together 1/8" to that measurement, this will give you some aligning room for fitting and sealant. This measurement is the length of your window trim.

Bevel Bottom at Windosill and Cutting "Rabbit" Channel for Nailing Flange

Y'all will demand to determine the bevel cut of your windowsill and cut the lesser of each leg trim to fit the sill. [bevel]

Pro Tip:

Prior to cutting your rabbit channel marking the back of the leg parts to avoid errors. It's piece of cake to flip a lath effectually and cut a bevel or a rabbit channel on the incorrect finish or edge. I marking the dorsum the trim bevel end and rabbit edge to avoid these errors. Cutting a rabbit aqueduct on the dorsum of the trim by making two cuts on a table saw. The rabbit width cut is usually ¼" wider than the nailing flange and 1/16-1/8" deeper than the thickest office. This rabbit creates a space for the nailing flange so the trim tin sit tight to the wall sheathing, without rocking or interference.

Window Sill Material

Exterior PVC sill tin be bought or made on-site; we chose to use a pre-made sill for this projection. Windowsills typically have a 10–xv-degree bevel to drain water out and away from the window. The sill should project out away from the window, leg trim, and siding for h2o management, off and abroad, from the business firm.

The bottom edge of the sill should take a drip groove installed to interruption the surface tension of the h2o and foreclose the h2o from running dorsum to the house siding. A rear groove under the backside of the sill allows for business firm siding to constrict upwards and under the sill for overlapping weather coverage.

Window Trim Environs Assembly

Preassembly requires 8 [eight] screws total. Each vertical window leg gets ii exterior pocket screws [4 total] and PVC cement to secure the legs to the caput. The windowsill to leg attachment will receive 4 longer, exterior-class screws and glue.

Note – You lot should always use PVC cement adhesive to secure the joints and prevent separation or visible gaps between the boards.

The all-time practice to keep your joints tight, and boards secure is to use a combination of glue and mechanical fasteners.

Drill ii pocket holes into the tops of each window leg casing. Apply PVC cement to both parts being fastened and allow the glue to become tacky. The glue melts the PVC creating a permanent, new bond to each other.
Align the vertical leg to the meridian casing and clamp so the joint is flush. In one case your pieces are aligned, install the pocket hole screws. Repeat the procedure on the other end. The screws concur the articulation tight, without the need for clamps. Note – Use pocket hole screws are rated for exterior, they're like shooting fish in a barrel to spot as they are blue in color.

Pro Tip:

If you have a pocket screw blow out because you drove it too far, get out it in identify until the PVC glue has dried. In one case dry out, dorsum out or remove that spiral and fix information technology on the sanding stage. After associates, sand off the mucilage, or whatever unevenness at the vertical leg and head trim joint.

Fastening the Windowsill

With the window trim assembly back side facing up, line up the back of the windowsill with the pre-cutting nailing flange channels on the vertical legs. Clampdown the leg casing and drill 2 pilot holes through the sill into the leg casing. Utilize exterior screws, long enough to penetrate the leg casing by an inch, preferably more than.

Installing The Trim Surround

Slide the trim associates over the window frame, evenly splitting your reveal gap. Install 2-three/4" Cortex subconscious fasteners every 16-20 inches apart.

The Cortex fastener fleck installs the screw and creates a perfect hole to insert a PVC plug. When fastening, take intendance to drive the fasteners straight/perpendicular to the trim surface, so the plugs sit apartment. Once the fastener is installed place a tapered PVC plug into the hole and tap it affluent.