Foundation Description (as of July 1999)

- N. Christopher Phillips

The original plans did not include what to do about the concrete under the bathroom, or how to do the part of the foundation uphill from there. Nobody had figured out any easy way to deal with this section of concrete. The alternatives discussed were to build a section of foundation surrounding it (and sticking outside the house on the north and east sides) or to break it up and remove it. The large cracks in it now mostly developed (or at least were first noticed) after these discussions took place. The concrete is not very good, having been made with beach sand (which contains silt; this is known to lead to inferior concrete), and also containing mussel shells and other weak items.

In the following discussion, diagrams are not to scale (I have not measured anything), and the other side of the house (top of diagrams) is the side facing the bay (this iis not strictly speaking correct since the direction that side faces is somewhat west of north).

What is underneath: Almost all of the partially constructed new foundation is resting on what Grandad called "hardpan". (In some places, we actually dug into the hardpan. See below.) There are actually two kinds of this stuff: Gray stuff which can be dissolved in water to make very find silt (like the gray stuff on the Meek's beach), with occasional embedded rocks (I will call this "clay"); and a hard mixture of sand, gravel, and layer rocks, all brown (I will call this "conglomerate").

It is possible to dig in both clay and conglomerate, although it is easy in neither. If you attack the conglomerate with a pick, small pieces break off. If the conglomerate is exposed to air and allowed to dry out, it becomes very crumbly and weak, as poor a foundation as dirt. I don't know what happends to conglomerate with concrete sitting directly on top of it.

Roughly, there is clay under the part of the house east of the chimney, and conglomerate west of the chimney. Actually there is no boundary between the two kinds - in the general are of the chimney, the nature of the hardpan changes gradually from one type to the other.

Nobody has ever dug far enough down to reach solid rock anywhere under the house. There are some limits to how far down it can be, since there is solid rock at the top of the beach from the picnic area to the wharf, behind the picnic area, and behind the well and lawn. The well, however, is a shomwhat deep hole. The ditch at the back of the lawn has clay in its bottom in a number of places, and I think if you try to dig more than a foot or two down in the beach in front of the seawall, you encounter conglomerate.

The old concrete foundation, except under the east end of the house, consisted of isolated concrete posts. Those along the south side and along the middle are on hardpan, and those along the north side go down about four feet but do not reach hardpan (except possibly the northwest corner). In the new sections, the concrete along the middle is mostly sitting in a trench in the hardpan, a few inches deep. The area around the chimney is also dug into the hardpan, and everything else south of the middle concrete section is at least on hardpan. The concrete under the double door from the basement to the outside goes down 2-3 feet below the surface and is sitting on hardpan about 2/3 of the way to the corner of the house.

The foundation plan for all but the est end of the house had four phases.

Phase 1.

(See Diagram 1, at end.) Construct three concrete beams lengthwise (at the two sides and one roughly along the middle) and four beams across, one at the west end, one next to the bathroom concrete, and two in between). The back and center lengthwise beams are to rest on hardpan, while the first one is to be not very thick (only a foot or so) and is to tie together the existing concrete posts. The crosswise beams are to be heavy in the back and middle, but thinner a their north ends, and to support the beam along the north side in cantilever fashion. All lengthwise beams are to contain embedded jack posts, and also ends of bolts for the purpose of attaching walls. (See the xsiting center beam).

Note that the middle lengthwise beam is not really in the middle, but is underneath a supporting 6x6 that runs the length of the house and which the floor supports rest on.

There are 11 unusued jackposts in the inner basement (outside the bathroom).

Phase 2.

(This presumes something has also been done at the east end of the house.) Level the house by jacking up the jackposts. This may have to be done slowly, since the floor supports are bent (the front of the house has settled more than twice as much as the middle) and are old fir, so maybe hard to straighten without damage to the wood. Perhaps the leveling has to be done an inch or two per year. Then build rigid walls lengthwise, at the middle and front. (You can see the need for this by feeling the house vibrate when the refrigerator door is closed.) Design: Bolt sections of 2x6 to the top surfaces of the concrete using bolts provided for this purpose. Then use plywood, nailed to both these 2x6's and the 6x6 support beams above the concrete; also, there would be some vertical 2x6's to directly support the 6x6.

Some comments: The southwest corner was two inches higher than anywhere else. It was intended to remove the concrete support there and drop that corner two inches. Some of the 6x6 along the south side is missing; it had dry rot which had penetrated some distance along it, and it is possible that not all the dry rot has been removed. There is another place farther west where there is untreated dry rot. (The dry rot started at places where this 6x6 was resting on blocks of wood that in turn were directly on the ground. This was the original foundation, before there was any concete at all, and two of those blocks, thoroughly rotten, were still in place when the new foundatin project was started.)

Phase 3.

Build another concrete wall lengthwise, with base below the level of the floor in the main part of the basement. The part of this behind the chimney has been done.

Phase 4.

Put in concrete floors between the middle Phase 1 beam and the north edge of the house, and between the middle Phase 1 beam and the Phase 3 wall. The floor meeting the Phase 3 wall is to be at the same level as the other floor, so requires substantial digging in hardpan. The part of this floor around the base of the chimney already exists. Also, there are reinforcing rods sticking out of both sides of the existing middle lengthwise beam, for the purpose of attaching this floor. Note that the base of the wall of Phase 3 needs tobe low enough to meet this floor.

Defects and oddities

(1) The section of concrete under the main basement door is not very well connected to the other part. There is reinforcing rod in it, but the cross section of the connection is only about 1 foot x 1 foot, and you can see that the concrete in there has gaps in it. (The bottom of the lengthwise beam at its west end is only four to six inches below the intended floor level, perhaps even less at the very end where it surrounds the older concrete.)

(2) There is difficulty making the crosswise beam next to the bathroom properly thick in the middle without blocking the inner basement door. The other two (not the one at the west end) are supposed to stick out a foot or more into the main part of the basement - see the arrangement of reinforcing rods, especially at the partially completed one.

(3) The hardpan slopes downward as you go east (as well as the much greater downward slope as you go north). The middle lengthwise beam (the one that already exists) sticks at its eastern end about two feet down into a hole int he clay, dug for the purpose.

(4) Drainage is essential. There are drain pipes crossing the existing lengthwise beam at several places, but I don't know exactly where (they could be found by digging). It was also intended to have a drain pipe along the back of this beam, and it exists under the place where there is concrete already poured behind it. There should also be a drain pipe at the uphill side of the south lengthwise beam. That has never been put in, and this is the reason the hole behind it was never filled in.

(5) There could be drainage at the intended floor level behind the middle lengthwise beam, out to the front somewhere. (One should be able to wash the floor and have the water run out.) No such drain exists in any of the concrete poured, and the only reamining place it could go is into the underground drains (bad), or out to the west end of the house.

(6) The lowest wood in the reconstructed front (north) wall is to be a few inches *above* the floor level, not at it, so that one can wash the basement floor without worrying about rotting the wood.

(7) The completion of Phase 1, especially if one omitted for the time being the two crosswise beams not already started, would probably not require much more excavation, and much of what needs to be dug out could be left temporarily in the hole behind the middle lengthwise beam at its western end. This reduced Phase 1 could probably provide enough support to start jacking up the house, exacept at the east end. Any further work would require lots of excavation, and one would need a place to put the dirt. Some more could be put in front of the house, and there are always places up the hill.

It is important not to do anything that precludes substantial further excavation since the space is possibly needed (for example, for firewood).

Deck support:

The basement floor level at the north side of the house is on fill. The area outside the north side is also fill, even deeper. The area with laurel bushes has actually been filled twice: once when the house was built, and once more when I was doing the excavation for the new foundation. Most of the dirt I dug out went there, although some went up the hill. (Several sections of the trail are on fill taken from the basement or the gravel pit areas).

Post hole diggers are unlikely to be of much use, since both the fil and the two kinds of hardpan contain large embedded rocks. Manual digging might allow one to reah hardpan at several places along the front of the house, but I don not see any way to reach solid rock anywhere, or even hardpan in the place one would put deck supports, without machinery.

While rare, two feet of heavy wet snow is possible, and the deck needs to be able to support that. Morever, under such conditions snow might slide from the roof onto the deck.

Expanding on the uphill side.

(1) In principle one could get up to four more feet this way but that ignores the need for steps up to the doors. I think two feet is more realistic.

(2) One should check whether an increase in the size of this scale would trigger the rquirment to have a new septic system (apparently at a cost of about $50,000). Apparently we can't increase the number of bedrooms. I don't kow about a loft; internal remodelling might not need a permit.

Diagram --

(to follow)