How to Hang and Install a Window Box with Lag Bolts

Installing a window box with the use of lag bolts is the recommended method a builder, contractor, or handyman will use.  Lag bolts are basically thick screws that will not bend or break when a lot of weight is placed on them.  The advantage to lag bolts is that they can be used to anchor and hang a window box to the studs behind your siding.  If you have brick or rock, you can also lag bolt your window box into lag anchors that will secure the box to the home. 

It's recommended that you use 2 lag bolts for every 36" of window box length.  Space the lag bolts out evenly if possible. 

Wood and Siding Installation of Window Boxes

Step 1: Locate the studs from inside the home under the window using a stud finder.

Step 2: Transfer the mark up with a pencil to the window sill.

Step 3: From outside, hold the window box up in place and transfer the mark from the window sill to the window box.

Step 4: Line up with the mark and drill a 3/4" hole in the vertical center of the back of the window box.  This hole is larger than the lag bolts and this will help you level the box at the end.

Step 5: Hold the window box back up to the window and trace a mark through the drilled holes onto the home. 

Step 6: Place the box down and predrill the marks with a 1/4" drill bit.  This will make it easier to turn a 3/8" lag bolt to secure the box later

Step 7: Hold the window box back up one last time.  Tighten a lag bolt and washer through the back of the window box from the inside of the box.  The lag bolts should line up with your predrilled holes and will grab the framing studs as you tighten.  Viola!

Brick Installation of Window Boxes

Step 1: Evenly mark the desired number of holes on the back.  Drill a 3/4" hole in the vertical center of the back of the window box along each mark.  

Step 2: Hold the window box back up to the window and trace a mark through the drilled holes onto the home. 

Step 3: Place the box down and predrill the marks with a 5/8" masonary drill bit.  Insert a 5/8" lag shield into the hole.  Make sure the lag shield can receive a 3/8" lag bolt.

Step 4: Hold the window box back up one last time.  Tighten a lag bolt and washer through the back of the window box from the inside of the box.  The lag bolts should line up with your lag shields which will expand and grab as you tighten.