It probably started as a 34 inch door. since the door jamb is cobbled together and not correct anyway, why not install a 34 inch door. I like the white one but changing it's size is a bit much for Vala. try to get your new door with the doorjamb. the doorjamb you have isn't right , it should have a rebate they installed 1/4 round instead.
figure 4-18 gives you an idea how a door frame should be constructed. note how the sill ties in , it should be about a 4 degree angle. it shows the wedges I mentioned. a lot of times you can buy a used door along with the frame and that might be best if you don't feel comfortable creating that.
http://www.free-ed.net/free-ed/Resource ... ?iNum=1102or, if you like the white door you can buy or make a frame to fit.
usually there is a rebate for the door to stop against.
You can have a double rebate so the door closes against one side and then a screen door can fit the other side. sometimes people dont; want to cut the rebate so they just use a strip of wood instead but in old houses it is usually cut in, not an added strip.
http://www.trademasterjoinery.com.au/do ... jamb-165mmI would just make the frame from scratch and I would use fir. You can buy the whole thing as a kit, and that might be easier, but if it were me I wouldn't be happy with Home depot made in china finger-jointed crapwood.. you could likely get a pre made 34" frame with the sill that is made of fir but you might have to look outside the box stores.
there are a lot of newer techniques and materials, and things like metal jambs. metal thresholds. but since you do value the heritage I would do it the traditional way. use wood. you can add a little weatherstrip later if you need it.
If you go to a 32 rather than 34 you can.. I think I'd have a look at the other doors in the house and if that is your only 34" door think about how that will limit furniture movement. If you have other wide ones then it might be less of an issue and if you like the white door then you can change the opening to fit.
I'd source the door you want there and decide that first because you might find another used door you love and it might be off size too.
it looks like there is a transom window , so if that is the case that might limit how much you change the door opening.
sometimes screw holes pull out and people fix it in different ways. I would get it set up the way you like using short screws and once you have it adjusted pretty close you an back them out and put long screws right through into the studs.. this is because it is really easy to pry doors open by sticking a screwdriver or pry bar in the hinge side and prying the hinge side open. the door frame then splits.. If the screws are long this is harder to do.
the wood sill in the line drawing makes a statement that it is done traditional way. That could be fit properly at the same time. it's kind of one of the first things you see when you enter. to me things like metal thresholds are just like adding metal windows and metal screen doors. they work fine but if keeping the heritage is what you want, the old techniques have been tried and proven over centuries. same for window construction.
I think if you can uy a pre made frame , you might be able to tackle shortening it a little if the door is loose in the opening.. I dont think you want to make the whole thing.
I'd suggest finding the parts you need and doing it in good weather. it can be a trying job if your time is limited and you are standing in the cold draft trying to fit it all in properly.
I noticed a good tip in there, dont; drive all your nails in completely until you get it fitted in case you want to pull the nails and readjust.
once you get it all fitted , before you put your casings back you can pack the gaps with insulation. you can use spray foam but watch it doesn't shift the frame and make the door too tight. sometimes the expanding foam can do that.