I am walling myself off my house.

It's a rather strange house, of the sort that passed for Colonial during the postwar (WWII) building boom. My neighbor, out of whose side yard our lot was cut, says a man and his two sons built it from plans sketched on the back of an envelope. You could do things like that in those days because Arlington had no building code.

The brickwork had reached the second-floor level, my neighor says, when the two boys, working from opposite ends of the scaffold, started arguing. The old man was appealed to and fetched out the envelope. He turned it this way and that, looking from it to the half-house, and then all three of them knocked off for the day.

Next morning they tore it all down and started over.

What they did was to rebuild the walls in a slightly different place, without altering the foundation. It must be strong, for the house has stood these 30 years, but it was definitely nonstandard as electricians, plumbers, carpenters and masons have told me since, in pretty much the same words:

"This is some goddam house you got here, fella."

Like the evelope, the house turned out long and narrow. The put in a downstairs bedroom opening off the dining room. They put a large pantry and a tiny kitchen. Upstairs, they started to put in a huge closet, and then had a change of heart and made it a minature bedroom. You had to walk through another one to get it.

Ten years later a new owner decided the driveway was in the wrong place and moved it around the corner, leaving a front lawn underlain by two feet of rubble. Then they built a new garage to go with the new driveway and put a porch on top of that. Its roof touched, but was not connected to, the rest of the house, as I discovered when carpenter ants determined the supports and the house and the addition parted company. The downstairs bedroom became a passageway to the porch, leaving a two-bedroom house with three walk-in closets or a 2 1/2-bedroom house with two closets.

That was all right, because we were going to have just the two kids anyway. The girls got one bedroom, with attached playcloset, and we took the other.

As the girls grew in stature and in decibels we grew so desperate for peace and quiet I enclosed the porch and made them play there. It was an awful job, complicated by my ignorance and such discoveries as the fact that the courses of brick I was trying to match up didn't match up to each other. I broke down and hired a bricklayer, who managed to do a job just as sloppy s the original.

There was one benefit I hadn't anticipated. When the porch became their playroom it ceased, psychologically anyway, to br part of my problem; I ceased to feel a sense of stewartship, and the part of the house for which I felt responsible diminished significantly.

Then the boy came along, bless him, and anyway the girls had reached that stage where they can't live with each other. We put him in the closet and I went to the basement to see what I could do about turning the putative recreation room into a bedroom for the bigger girl.

I took some measurements and then took them again, because nothing was coming out right. The room was a three dimensional trapezoid, without a vertical wall or right-angle corner. Karen would be waiting yet for her room-of-her-own if Grandaddy hadn't come to the rescue.

"We'll just build another room inside it," he said. And we did, over the space of a couple of years.

Finally the big day came when Karen could lock Laura out. She also locked me out of what was now her personal space, and another big section of the house was lifted from my shoulders.

Laura soon after began to complain, with justice, that she couldn't lock Karen out because that would lock Mark $2in ).

The obvious thing to do was build a wall across one end of the room, giving Laura privacy and Mark a passway to his closet.

The starting point in partition-building is the baseline. The new wall wants to be parallel or at right angles to the others. The new wall was disappointed in this case because the room was another Trapezoid; I struck an average.

At one stroke the creation of two rooms from one end and a half removed half the upstairs from my jurdiction. Now, if I could just arrange another little accident (I have names for him or her picked out already), I could wall off the living room and get the house down to manageable proportions.

But the lady involved says I'll have to talk to my second wife about that. CAPTION: Illustration, no caption, By Zarko Karabatic