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Need advice on building door jambs

Bpawb's picture

   Hi, I'm getting toward the end of (Building our own house by myself ) Project.

    Next on the list is building from scratch all of the interior door jambs and trim.   there are 12 in all that I have to build.

   1st. question... do I build the frame/jamb and then install the door slabs?........( this seems like the easy'er way to me, being i'm working solo)


 .........should I build the door frame/jamb and slab as a unit...and the install into the rough opening?




(post #107555, reply #1 of 16)

When I build jambs, I cut the legs and head to width and length, then mortice the hinges into one jamb leg, then transfer the placement to the door, and mortice them in, then assemble the jamb.

If you decide to hang the jamb and door as a unit, you'll need to temporarily tack the door into the jamb. Being as I'm getting lazy in my old age, I take the door off the jamb,  set the jamb frame in place, level the head, and plumb, shim, and nail the hinge side. I then re-hang the door, and shim and nail the strike jamb so it has an even margin to the door.

(post #107555, reply #2 of 16)

Don't count on every door to be the same size.  When we build custom jambs, we build each jamb to fit a particular door, and build them to much tighter tolerances than your typical prehung door.

Make sure your doors are tapered on the edges or do it yourself.

We also taper the edges of the jambs.

We never install a door with the door attached to the jambs while you are installing it.  We use plumb blocking on the hinge side stud, attach the hinge jamb, then hang the door on the hinge and fit the top and lock side.  You know it's going to fit perfectly because you just made the whole setup!

Don't forget to cross string the rough opening before you start anything to make sure it's on a plane.  Nothing worse than making a perfect jamb and door and then not being able to fit it properly because the r.o. is wracked out of shape.

(post #107555, reply #7 of 16)

"We also taper the edges of the jambs"

New one on me, always bevelled the latch edge of the door, sometimes the hinge side, but the jamb as well?, how do you do that? and why?


(post #107555, reply #8 of 16)

I'm also curious about the 'tapering' of the jambs that Bojangles refers to. I can't wrap my mind around that one.

(post #107555, reply #9 of 16)

Since he talks about "tapering" the doors, too, I'm sure he means what we might call bevelling.

On a jamb, that would be the edge that will be cased that gets "tapered," just as almost all commercially-made jambs are bevelled, to ensure a tight joint even if the jamb is proud of the wall.


(post #107555, reply #11 of 16)

Sorry!!   I did mean bevel.   Slip of the tongue!

(post #107555, reply #12 of 16)

I was following you all the way! Good description of your process.

And cross-stringing is a good idea. I picked up an old trick in FHB -- I think it was from Larry Haun -- about cross-sighting, instead:

Stand off to the side a few feet, so that your line of sight through the RO is very narrow. From this vantage point, any out-of parallel in the trimmers will be detectable.

Sight the jambs as well after you have set them in place.

With french doors, I try to hang them before the walls have been boarded on both sides, because there's no cheating the stops: the doors have to meet perfectly at the astragal.

And if one or both doors has a bit of a twist, stringing or sighting is immaterial. All that matters is, do the doors meet, or not? If they don't, it's time to get out the BFH and start shifting the bottom plates around!

It's a 3D world out there fer sure, ain't it?


(post #107555, reply #13 of 16)

I always cross-string when installing jambs/pre-hungs. The strings absolutely do not lie. And when there really is no moving of the framing, I can still use the strings to gauge a happy medium for the jambs and casing.

(post #107555, reply #14 of 16)

Yep. But I bet your eye doesn't lie all that much, either. How many times have you eyeballed a mark halfway between two marks 3/8" to 1/2" apart, say, and you're less than 1/64" off?

Do a comparison some time with the stringing and sighting. I've never done it, but I have a feeling I'd get comparable results. And sighting takes less than five seconds, which is hard to beat.

"happy medium." That's what we have to figure out all day long, eh? That's when our work changes from a science to an art! If they only knew how much we cheat things this way and that, all to make things look perfect!


(post #107555, reply #15 of 16)

I sight across the jambs, too. Plus I like to check and see how the door hits the strike side stops before I nail that side off, and make any adjustmants.

(post #107555, reply #16 of 16)

My step daughter bought a bunch of doors with out jams. the local building supplier has a door shop and they used their fixtures to build the jams for $ 2.oo more than buying the stock inside their retail store.

(post #107555, reply #10 of 16)

Bevel the two edges about 5 degrees, starting about 3/16" from the finished face of the jamb. 

It makes it much easier to fit the casing to walls where the drywall or plaster is not lined up perfectly with the width of the door jamb.

(post #107555, reply #3 of 16)

I've done quite a few doors this way (From Scratch), usually because I can get better results than the prehung units that you can buy.  I prefer to build and hang the jambs, mortice them, then install the slabs. 

There are several articles under the how to tab at the top of the page that have helped me in the past. 

Gary Katz's book on hanging and installing doors will tell you everything you would need to know.  I also have used Craig Savage's book to get me started years ago before I ever heard of Mr. Katz. 

Both are excellent books.

Finally, there is a thread in here started by Basswood, that has a lot of neat and useful details with pictures. 

If you choose the assembly line approach, do at least one opening from start to finish, that will help you catch any mistakes before you do a whole houseful.  Another good idea is to test your hinge mortising setup on scraps before using it on the doors.



(post #107555, reply #4 of 16)

Good advice from you guys...I appreciate the time each of you took to reply!



(post #107555, reply #5 of 16)

I would start off like shep says but leave the unit assembled and hang like a prehung only with trim completed on one side. You don't have to tack the door to the jamb, use wedges or shims as required so the door acts as the perfect template. The more doors you have to do the easier it becomes and 12 is plenty to perfect an efficient system. You might tack a temporary brace across the bottom side of the untrimmed face just even with the jambs to hold it during the tilt up. To back up I like to put shims at the hinge side first plumb and straight with a 6.5' level. I would check all the openings and make up an assortment of plywood pieces jamb width by 3" or so by expected thickness needed. It's nice to have a little hoard of 1/8" plywood handy to supplement the more common plywood scrap sizes but you can improvise. 

Retired until my next job.


(post #107555, reply #6 of 16)

I do a lot of what Shep does. I first take a reading of the floor, if it's out of level & how much, then I add that on to the appropriate leg of the jamb.
If it's level then I just cut sides & head to length, mortise the hinge side leg to the door, usually three hinges. I mortise the hinges all on the door first, unpin the top hinge then using the same backset I mortise the top hinge leaf to the leg, (adding 1/8" down from the head, pin the leaves back together, and then open the leaves of the other two hinges flat onto the jamb and mark top & bottom with a knife. Remove the jamb from the door by unpinning the top hinge and then mortise your other two hinges using the same backset. your frame routing in a 1/4" for the head at the top of the legs. Set the jamb-frame in place ( you can do the trim-first route...that works fine, but I never do), tack things in place plumb & level. Hang your door onto the hinges. Drive 3" screws through the jamb into the RO where shimmed. Install your hardware first to where the tongue glides easily into the strike plate hole. Lastly set your stops. Add casings.

I can do this in my sleep and each door only takes maybe a half hour to 45 minutes to do if I'm making my own jambs. Obviously, I do this much better than I explain it.