Window Jamb Extensions

Submitted by Ana White on Tue, 07/30/2013 - 12:28

Remember when we built these guys?

And then we stacked foam blocks around them?


And then poured concrete in the foam blocks around the boxes?

And then hung windows on the outsides of the boxes?

Well, today's the day that we are going to start finishing out the inside of the windows!

Step 1 Diagram
Step 1

The walls of the Momplex are almost a foot thick, so we'll need something to extend the window jambs flush to the drywall.

We've gone back and forth on what material to use.

We considered different composite materials, but because of the potential for water damage due to exteme cold weather condensation (not likely because of the super insulated walls, but were not taking chances), we passed ...

We opted not to just drywall the insides of the windows (what fun would that be?) and because drywall isn't good friends with moisture either ....

We opted not to slurge on a moisture resitant hardwood (super pricey for these widths) just because we are on a DIY budget, and whatever we do choose is just getting several coats of white paint ....

So we choose ......

Step 2 Diagram
Step 2 Instructions

Yep, plywood.

We build furniture and kitchen cabinets out of it ... so why not extend our window jambs with it?

And once all the window trim is painted, you'll never know!

Well, you'll know 'cause you're awesome and you read this blog, but you won't tell on us, will you?

We ripped the plywood into strips the width we'll need the jamb extensions to be.

Step 3 Diagram
Step 3 Instructions

We've done lots of window jamb extensions in the past. Normally, we cut each piece, nail it to the inside of the window rough opening, and then add another.

But this time, we decided to try something new and build the entire window jamb extension first, and then as a complete unit, slide it into the window rough opening.

So we cut all the window jamb extension pieces first, leaving about 1/4" to allow for shimming and getting the box in there, and drilled pocket holes with our Kreg Jig on the outsides

Step 4 Diagram
Step 4 Instructions

And then just clamped and screwed

Step 5 Diagram
Step 5 Instructions

We kept all the pocket holes to the outside, so they'll be hidden ...

Step 6 Diagram
Step 6 Instructions

Then hauled all the window jamb extensions upstairs.

By we, I actually mean the Ram.

Step 7 Diagram
Step 7 Instructions

There are some benefits of being preggers.

Step 8 Diagram
Step 8 Instructions

Once the windows are all hauled upstairs

Step 9 Diagram
Step 9 Instructions

We give the window openings a good cleaning.

Step 10 Diagram
Step 10 Instructions

And then here's the magic moment .... will it fit???

Step 11 Diagram
Step 11

Our meticulous efforts to build everything super square paid off - the window slid right in perfectly!

Step 12 Diagram
Step 12

Some of the bigger windows were a little more stubborn

Step 13 Diagram
Step 13

But we got them in!

Step 14 Diagram
Step 14

The window jamb extensions fit in perfectly, but we'll wait until after we attach the outer trim before nailing them to the framing.

Step 15 Diagram
Step 15

It's these little tasks, one by one, that are starting to make the Momplex look more like Mom's home.

We are so excited .... just gotta put doors in and we'll be on to trim!

XO Ana



Mon, 12/29/2014 - 11:55

what thickness plywood did you use? Also, is the depth measured from the window to the edge of the drywall? does this need to go in before or after drywall or does it matter?