Window Jamb Extensions

Tom5151 · 09-22-2009, 05:01 PM

Hello,

We have a little cabin up north. We are slowly renovating the entire thing. We are replacing evey window with new windows. Our contractor is doing a wonderful job but the labor cost is something that I want to minimize by doing the rest of the project myself. I have never done anything to a window except to open and close one and occasionally wash one. I am comfortable with DIY projects and have no trouble attemtping things.

I need to know the real basics for how to make and install a jamb extension on a new window. It's a vinyl window already installed and in place. The interior sashes are pine. The cabin is old and very little is square and plumb. The finish material on the walls wil be 3/4 #2 tongue and groove pine so the extensions will need to come out far enough to meet that for casing work. I have never done this before ever. Should I build the extension in place or build the box first and set it in place and shim? I really need a very simple, plain explanation how to do this.

Could someone give me a good explaination how to do this or at least maybe point me in a direction where I can find the information? I have searched all over the internet and haven't really come up with anything that helps much

Thank you in advance

oldfrt · 09-22-2009, 08:04 PM

Tom,
I think your on the right track by thinking about building the' box'first.

Are there any jambs on the windows?
Are you just trying to extend them?

Anyways, build the box ,set it in the opening,and nail in place using shims to square it up and take up slack between box and framing.

Scuba_Dave · 09-22-2009, 08:15 PM

I cut pine to the depth needed all the way around
Then nail each piece in
My house has 3/4" sheathing outside & 3/4" combo rock/plaster like stuff inside
So standard windows/jamb extensions do not fit
Plsu they are freekin' expensive
I tend to put big window sills in to put plants on
This set (3 windows) I added some custom cut supports underneath
I then cut pine as surrounding pine - 45 angle cut to match the rest of the house

Best thing to do is buy a GOOD mitre saw

Tom5151 · 09-22-2009, 10:23 PM

Thanks guys........I appreciate it......

There are no jambs currently. Just the vinyl frame. I would be butting the outside edge of the box right up against the vinyl window frame. Given that, I cannot nail into the vinyl so should i nail through the extension into the rough 2X4 framing? Do I just nail right through the shims? Do I shim the bottom of the extension or does that just get nailed directly to the sill plate?

ARI001 · 09-23-2009, 07:57 AM

Quote:

Originally Posted by Tom5151

Thanks guys........I appreciate it......

There are no jambs currently. Just the vinyl frame. I would be butting the outside edge of the box right up against the vinyl window frame. Given that, I cannot nail into the vinyl so should i nail through the extension into the rough 2X4 framing? Do I just nail right through the shims? Do I shim the bottom of the extension or does that just get nailed directly to the sill plate?

Yes, nail through the shims. If you pre-build the jamb extension there should be no reason to nail the head jamb or sill (assumes you are going with picture frame style) unless you have to shim the jamb extension up to keep the reveals equal.

Tom5151 · 09-23-2009, 10:31 AM

This is incredibly helpful....

I am going with picture frame style. What is an appropariate reveal for the vinyl frame? I will have to use pretty thick shims to get a small reveal. I was thinking about making the jamb extension box the exact same size as the outside dimensions of the vinyl frame and then maybe using something like a shoe molding or quarter round on the inside of the entire box to cover up as much of the vinyl as possible. Is that acceptable? I could just miter the corners of the molding to make nice corners. I had read someplace where someone did that but not sure if i should go that route or just use thicker shims to get a smaller reveal.

ARI001 · 09-23-2009, 11:46 AM

I like to set reveals at 3/16". The purpose of the reveal is to allow the wood to expand and contract naturally without making the fluctuations obvious to the eye. If you where to mount shoe moulding flush to the edge the natural movement of the wood may cause the moulding to expand over the sash which would be somewhat unsightly.

You can pre-nail wood blocks into the opening and then adjust with standard shims as necessary.

Tom5151 · 09-23-2009, 11:52 AM

ah okay.....that makes sense.....

so nail the wood blocking in first and then shim off of those....great idea....this is probabaly a dumb question but is there a general rule for how many shims i should use?...how far apart they should be?........the height of the window is about 60 inches and the width is about that is not a little wider....sorry i dont have exact dimensions here but just wondered how i should position and space out the shims......

ARI001 · 09-23-2009, 12:22 PM

For the application you are doing you should be OK with shimming at the top, center, and bottom. Do not shim the head jamb, you can leave that floating.

Tom5151 · 09-23-2009, 12:27 PM

Quote:

Originally Posted by ARI001

For the application you are doing you should be OK with shimming at the top, center, and bottom. Do not shim the head jamb, you can leave that floating.

perfect...thank you sir......i can't tell you how helpful this is......

ARI001 · 09-23-2009, 12:28 PM

You're welcome.

Tom5151 · 09-23-2009, 12:30 PM

Quote:

Originally Posted by ARI001

You're welcome.

oops one last question.......do you butt the joint the extension box or use rabbets?.....just nail and glue or glue and screw?

ARI001 · 09-23-2009, 12:40 PM

Either way will work, however there is no real added benefit to cutting rabbits in this scenario. If you do use rabbits don't shim them to tight and/or make sure to slightly over cut the rabbits to allow for movement or you could end up with windows that have seasonal sticking.

Tom5151 · 09-23-2009, 12:46 PM

got it....i think I'll just butt joint and glue and screw.....

can I ask you a similar question about interior doors?

ARI001 · 09-23-2009, 01:50 PM

Quote:

Originally Posted by Tom5151

got it....i think I'll just butt joint and glue and screw.....

can I ask you a similar question about interior doors?

Yes, go ahead.

09-22-2009, 05:01 PM	#1
Tom5151 Member Join Date: Apr 2009 Posts: 65	Window Jamb Extensions Hello, We have a little cabin up north. We are slowly renovating the entire thing. We are replacing evey window with new windows. Our contractor is doing a wonderful job but the labor cost is something that I want to minimize by doing the rest of the project myself. I have never done anything to a window except to open and close one and occasionally wash one. I am comfortable with DIY projects and have no trouble attemtping things. I need to know the real basics for how to make and install a jamb extension on a new window. It's a vinyl window already installed and in place. The interior sashes are pine. The cabin is old and very little is square and plumb. The finish material on the walls wil be 3/4 #2 tongue and groove pine so the extensions will need to come out far enough to meet that for casing work. I have never done this before ever. Should I build the extension in place or build the box first and set it in place and shim? I really need a very simple, plain explanation how to do this. Could someone give me a good explaination how to do this or at least maybe point me in a direction where I can find the information? I have searched all over the internet and haven't really come up with anything that helps much Thank you in advance

09-22-2009, 08:15 PM	#3
Scuba_Dave Xtreme DIY'r Join Date: Jan 2009 Location: South of Boston, MA Posts: 17,248	Window Jamb Extensions I cut pine to the depth needed all the way around Then nail each piece in My house has 3/4" sheathing outside & 3/4" combo rock/plaster like stuff inside So standard windows/jamb extensions do not fit Plsu they are freekin' expensive I tend to put big window sills in to put plants on This set (3 windows) I added some custom cut supports underneath I then cut pine as surrounding pine - 45 angle cut to match the rest of the house Best thing to do is buy a GOOD mitre saw

09-22-2009, 10:23 PM	#4
Tom5151 Member Join Date: Apr 2009 Posts: 65	Window Jamb Extensions Thanks guys........I appreciate it...... There are no jambs currently. Just the vinyl frame. I would be butting the outside edge of the box right up against the vinyl window frame. Given that, I cannot nail into the vinyl so should i nail through the extension into the rough 2X4 framing? Do I just nail right through the shims? Do I shim the bottom of the extension or does that just get nailed directly to the sill plate?

09-23-2009, 10:31 AM	#6
Tom5151 Member Join Date: Apr 2009 Posts: 65	Window Jamb Extensions This is incredibly helpful.... I am going with picture frame style. What is an appropariate reveal for the vinyl frame? I will have to use pretty thick shims to get a small reveal. I was thinking about making the jamb extension box the exact same size as the outside dimensions of the vinyl frame and then maybe using something like a shoe molding or quarter round on the inside of the entire box to cover up as much of the vinyl as possible. Is that acceptable? I could just miter the corners of the molding to make nice corners. I had read someplace where someone did that but not sure if i should go that route or just use thicker shims to get a smaller reveal.

09-23-2009, 11:46 AM	#7
ARI001 General Contractor Join Date: Jun 2009 Location: Stafford, VA Posts: 534	Window Jamb Extensions I like to set reveals at 3/16". The purpose of the reveal is to allow the wood to expand and contract naturally without making the fluctuations obvious to the eye. If you where to mount shoe moulding flush to the edge the natural movement of the wood may cause the moulding to expand over the sash which would be somewhat unsightly. You can pre-nail wood blocks into the opening and then adjust with standard shims as necessary.

Window Jamb Extensions