# Should I Use Extension Jambs



## twodogs (Feb 18, 2008)

*Attaching Extension Jambs*

Here is my dilemma:

I framed in a section of my basement for a bedroom and bathroom using 2x6 in order to hide the posts that support the overhead main beam (I encased the post into the framed wall for a nice clean look since space was not an issue). My prehung doors have a jamb width of 4 9/16 inches so I was going to purchase a 4 inch strip of pine and rip it down to be used on each side of the jamb as the extension (I have two 30" doors like this). 

I don't want to order doors with wider jambs since I got these solid pine doors at a tremendous price compared to what it will cost me to special order. I'm also smart enough to admit that I have no business trying to build my own jambs or even work with knock down pre hung doors for that matter.

Should I attach the extensions to the door jamb before hanging the door or should I wait and do it once I hang the door? I don't have a biscuit joiner and I am wondering if I should rent one for this little project? Any ideas how I could attach them without a biscuit joiner? I was thinking about glue and clamping but without fasteners I'm not sure the extensions will stay attached to the door jamb.

Thanks for the help.


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## borninpa (Jan 15, 2008)

I would probably hang it first and then attach the extensions. You can probably attach with screws in addition to glue. Pre-drill and counter sink the screw heads and you should be fine.


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## mikey48 (Dec 6, 2007)

Nail and glue. If you put these extensions on the door swing side you will need to use a 1/4 inch reveal or the door latch will hit you extensions.


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## AtlanticWBConst. (May 12, 2006)

twodogs said:


> ...Should I attach the extensions to the door jamb before hanging the door or should I wait and do it once I hang the door? I don't have a biscuit joiner and I am wondering if I should rent one for this little project? Any ideas how I could attach them without a biscuit joiner? I was thinking about glue and clamping but without fasteners I'm not sure the extensions will stay attached to the door jamb.
> 
> Thanks for the help.


Pre-hung doors are designed to be attached as 2 sections (each side of the door opening). The two sections are to be installed with the hinge side aligned in first, and the opposing side aligned to it. When all appears to dry fit properly (plumb, square, level, aligned) Then, the hinge side is attached, with the opposing side mated up to it.
(BTW: There is no need to use a biscuit joiner, let alone, it's not really possible on the narrow factory width pre-hung door jamb)

In the pictures shown, the unfinished jambs are part of the manufactured pre-hung door. The pre-stained trimwork is what we fabricated onsite.
In this case, we took a 1x5 and milled down a kerf to create a "male" bead along the edges of the "to-be-created" extension jambs. This would allow the new jamb extensions to recess into the pre-hung jamb-slots.
The hinged side of the frame was attached first, with the stained casing, as previously stated. 
The opposing side was then measured, section, by section, cut, and attached.
You may need to use shims, to properly align the new extension jambs.
We then attached the pre-stained colonial casing over the: new extension jamb.

Now, you can check your local Big Home Improvement Stores and see if they have any pre-shaped jambs that are wide enough for your extension needs. These already will have the kerf milled onto one side of it (to slide into the manufactured jamb slot). I do believe that you should be able to purchase it by the Linear Foot. Doing so, will save you the time of milling down the stock yourself.

Good Luck.


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## twodogs (Feb 18, 2008)

Thanks for the pictures, very nice finish work. I looked at my doors tonight, these jambs don't have a groove to accept the kerf. I was curious about that since the Anderson windows I put in were grooved and came with extension jambs pre-cut. 

Without a groove in the jamb I suppose I'm left to pre-drill the extension trim piece as well as the jamb and countersink a screw to attached the two along with some wood glue?

I don't have the machinery to cut a groove in such narrow stock as the jamb.


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## PKHI (Oct 23, 2007)

Atlantic, not everyone buys split jambs especially DIYers.


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## AtlanticWBConst. (May 12, 2006)

The concept is still the same. Fabricate extensions. Install shims as needed for the extension to match up to the installed jamb (with door). Glue extension to the existing jamb, and nail thru the shims.


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