There are several preliminary steps that must be taken before a hardwood floor can be installed, such as making accurate base lines to guide the first rows of wood. Also, if the door jambs are not removed, the jambs may need to be cut off.

At the beginning of this project we had ripped up the carpet and old painted softwood flooring . Then we fastened a layer of 7/16″ OSB (Oriented Strand Board) on top of the old sub-floor, to provide a secure and gap-free surface.

The original sub-floor is made of wide 1-by planks, most of which are 11 to 15 inches wide, but some are as wide as 19 inches. That’s like a 1×20. You don’t find that kind of lumber any more.
One problem with the old sub-floor is the wide gaps between planks. Some of these gaps are big enough to lose a dog through them! But seriously, the gaps, as big as 3/8″ in places, allow movement of air, water, bugs, rodents, and, in the worst case, easier spread of fire.

Drawbacks of OSB:
Since installing the OSB I have read about some drawbacks to particle board sheathing materials. If OSB gets wet repeatedly it will swell much more than plywood, and after a few wettings it becomes more absorbent, which is a troubling feature. Also, OSB impedes the flow of water vapor, sometimes resulting in fungus formation on the underside of the sheet. With a full basement below, fungal growth should not be a problem, but OSB installed on a floor over a crawl space could let fungus build up as water vapor rises up from damp soil and cannot escape.
If we had to do it over again, we would have used 1/2″ plywood, which costs about twice as much as 7/16″ OSB.

Unlike other rooms we remodeled, we left the door and jambs in place on this room.

But when it came time to prepare for the hardwood floor , we realized that we needed to install some strips of flooring directly under the door jambs. Otherwise, when we remodel the adjoining room (the dining room) we would have to remove the door, causing a newly finished room to have no protection from the dust and dirt of the work in the next project area.
So we peeled back the carpeting (that brown surface is the original floor) and lopped off a chunk.
We pried up the small pieces of carpet tack strip.Then we used a circular saw to cut through the old flooring in the doorway.
The old softwood flooring was removed with a flat pry bar.
The original sub-floor was exposed. See what I mean about wide gaps?
We installed a strip of 7/16″ OSB to extend the extra sub-floor we installed at the beginning of this project.
Some Mistakes Needed Correcting:
When we installed the OSB supplemental sub-floor, we foolishly failed to follow the instructions (printed on every sheet of OSB) and did not leave the required 1/8″ gap all around the panel. As the summer weather progressed, we noticed that the OSB was curling up around the edges, wherever the panels were butted close together.
To correct this problem, I simply cut along the edge of the OSB panels with a circular saw, with the depth set to cut only the thickness of the OSB.
It took about two minutes, and the proper gaps were created.

I spent another minute smoothing out the curled edges with a belt sander.

Cutting The Door Jambs:
This handy tool is a Japanese pull saw. The blade is very thin, very flexible, and quite sharp. It cuts on the pull stroke. We laid the pull saw on top of a scrap of flooring and carefully cut the jambs.
We placed a piece of flooring under the jambs to test the fit. The thin blade left a tiny gap that will surely not be noticed.
Before the evidence got concealed, we took a few minutes to mark the joist locations and stud locations on the lower part of the wall. These marks will be covered by the 7 inch tall baseboard.
We caulked the gap at the bottom of the wall. This should prevent some cold air infiltration, and possibly reduce the number of bugs that crawl in.
This is an opportunity that is passed up by virtually every contractor whose work I have seen. It just doesn’t add any visible value, but costs (a little) money. If people become aware of this, maybe they will demand it.
Smoothing the caulk is quick and simple and gives the best result.
For 26 feet of exterior wall it took half a tube of caulk and a whopping ten minutes of work.
We rolled out the red carpet.
Actually this is red rosin paper, which is used as an underlayment for wood flooring .
This innocent-looking tool is called a hammer-tacker, but I call it a finger-wrecker. It’s a staple gun that drives a staple on impact. You swing it like a hammer…only it doesn’t really work that way. A hammer head hits the board and leaves room for your hand. In order to keep from bashing your knuckles, you’ll instinctively hold the hammer-tacker like this, but at this angle it doesn’t drive staples worth a darn.
When it works well, which is rarely, it still leaves the staples sticking up a bit. This staple could interfere with theflooring . So all the staples had to be tapped down with a hammer.
Plus it tends to puncture the material being stapled.
Laying Out The Reference Lines:
We decided that the door jambs represented the best base line for the layout of the flooring . The wall nearest the first row, which is the most logical choice for a base line, had a bad warp to it, so it was ruled out. We set a straightedge across the jamb (with blocks to space it away from the plaster) and made a mark. Then we used the biggest square we could find and set it against the straightedge. We made a line.
These are the first two layout lines, which have been digitally enhanced to make them more visible.
From this geometry we made a longer reference line with an ordinary chalk line.

The end result looked something like this.

At this point we were ready to proceed with the hardwood floor installation .