Making the Best of Nature’s Worst: A Firm Foundation for a Hillside Hideaway

Making the Best of Nature’s Worst – Introduction

People who build vacation cabins seem deliberately to choose bad building sites: they seek land that's covered with deep snow in winter because they like to ski; they choose sites with the steep hills that invite erosion and washouts in order to enjoy rugged terrain or a stunning view; they select open land along the sea, where wind- storms—which can tear the roof off a building—gather force as they blow over expanses of water.

On these less-than-ideal sites, safety can sometimes be built right into the structure. A cabin that's in the path of down-rushing water may be built high and dry with a pole foundation; one vulnerable to wind may be tied together with metal strapping at all its joints to resist dangerous gusts. In snow country, a cabin may have a roof with an especially steep pitch to shed snow before it accumulates to a dangerous weight.

Some of these hazards may be better dealt with by working on the land than by employing special building techniques. On a breezy site, one to three rows of black spruce or black pine—Japanese black pine in coastal areas—will make an efficient and attractive wind screen. Leave a space between the trees so the rows break the force of the wind; rows that are planted too closely together will deflect the wind up and over the treetops, creating fierce eddies on the leeward side. A louvered fence, its slats oriented at an angle to the wind, can funnel wind around a cabin, and a deck or patio built on the lee side will be washed by a cool, filtered breeze all summer. Outbuildings, too, can serve double duty as windscreens if they are built on the windward side—generally the west or northwest side— of a cabin. Windward screens and outbuildings will also help to control snow; the winter wind will force the flakes against the wind block and keep them from drifting deep against the main building.

Simple improvements of a building site also can keep rushing streams of storm water from washing out hillsides or foundation pilings. With a few hours of shovel work, for example, you can sculpt hillside rand with a series of shallow drainage channels, called swales, to turn aside the flow. Pile the dirt from the channels on the downhill side to make a lip, or berm, that will further help trap the water. To slow the velocity of the water without redirecting it, install baffles across a hill; the easiest ones are simply railroad ties, half- buried in a shallow trench and spiked down with long steel pins. Some leafy ground-cover plants also will help to slow flowing water, and the tough roots of some species will even hold soil against erosion. Pachysaridra and English ivy are good choices throughout the East; dune grass is particularly hardy in seaside regions; dichondra thrives in desert and mountain areas.

78 Special materials for special hazards. The oddly shaped masonry block at top, technically called a speed block, is designed to accommodate the vertical and horizontal reinforcing bars that stiffen the foundation of a cabin built in earthquake country. In an area of high wind, steel strapping and plates are fastened to the structure with ordinary galvanized nails, strengthening the vulnerable joints between joists, studs and rafters.

A Firm Foundation for a Hillside Hideaway

Many a vacation cabin perches on the slope of a hill or the side of a mountain. The view is often breathtaking—and the lot is generally cheaper than a level one. Though any of the foundations described in Section 1 of this guide can be built on such a site, a pole platform is the easiest to erect. Using methods adapted from those on , and working from scaffolds adjusted to the slope, you can set rows of poles rising to different heights above the ground in order to support a level platform on which to build a cabin.

The first adaptation you must make is in the size of the holes in which you sink the poles: sloping sites call for especially deep and wide holes, specified in the chart below. If the soil is deep enough for you to reach about 1½’ below the correct depth but large rocks made digging difficult, you can simplify the job with a pole necklace—a concrete collar 12” thick, set around the pole. Using the necklace, you need to dig a hole of the required width only a foot below the frost line, then go down to the increased depth with a narrower hole. The pole will have as much strength as one with a soil-and-cement jacket of the required width, but the hole is much easier to dig.

Sometimes, however, the soil cover on a slope may be so shallow that you can not reach the required depth. In that situation, consult a structural engineer. He may advise you that drilling into bed rock—a job best done by professionals— is the only way to anchor the poles.

Where drilling is not required, you can use the easier and less expensive anchoring techniques shown on. In this method the row of poles across the top of the slope is replaced by a masonry foundation wall called a key wall, and the downhill poles are secured in the shallow soil by concrete pads.

The key wall is the crucial element in the design; while the poles merely sup port the platform from below, the wall anchors both poles and platform against the pull of gravity downslope. Design your key wall with the help of a professional who is familiar with local soil conditions. One of his main concerns will be to show you how to channel the flow of water downhill so that it does not under mine the wall. Part of the solution to this problem is built right into the wall and its footing, in the form of passages, called weep holes, that let water pass through the masonry structure (d 83, Steps 2 and 4). You also will probably have to preserve or replant vegetation to prevent erosion, and dig a gully uphill from the building site to channel runoff water around the key wall.

After building the wall and setting the poles, make a final adaptation of the basic pole-platform technique. Diagonal braces (Steps 8 and 9) must run within each row of poles across the slope and from row to row up the slope to keep the poles from slipping or racking above their shallow holes.

A Hole for Every Soil and Site

• Pole height (in inches)
• Slope
• Good soil
• Average soil
• Below-average soil

Choosing hole dimensions. The figures in this chart indicate the depth (in feet) and width (inches) of the holes required for platform poles that are 7 to 9” thick and set 8’ apart on a sloping site. These figures vary with the height of the pole aboveground, the steepness of the slope and the quality of the soil. Though the hole dimensions provide good guides for a variety of situations, check the dimensions for your site with a structural engineer.

Relatively short poles, generally near the top of the site, are covered in the first three vertical columns of the chart; higher poles in the last three. Slopes are given in civil engineer’s notation, as ratios; a slope of 1:10, for example, has a 1-foot rise in every 10 horizontal’. Soils are classified by their composition: good soil consists of compact sand, gravel or hard clay; average soil, of loose gravel or compacted clay: below- average soil, of soft clay, clay with large amounts of silt, or loosely compacted sand.

To use the chart, match the height of a pole to the slope of the site to locate the correct vertical column, then read down the column to the horizontal row that matches the quality of your soil: the intersection of the column and row gives the dimensions of the required hole. For example, a pole 7’ high, on a site with a slope of 1:3 and average soil, needs a hole 7’ deep and 24” wide. Note that two spaces in the chart contain dashes rather than dimensions. These situations, characterized by steep slopes and below-average soils, require holes so large that digging them becomes impractical.

How to Level a Scaffold

81 Fitting the uprights to the site. To make flat supports for the uprights of a scaffold, wedge 3- foot lengths of 2-by-4 into the ground at the uphill and downhill points you have chosen for the uprights; if necessary, clear out some soil to make the tops of the 2-by-4s level. Stack addition al 2-by-4s upon the two bases to reach a height that's level with the ground 7” uphill, then set level lengths of 2-by-8s between the stacked 2-by-4s and the ground. In poor soil, drive stakes at the downhill edges of these lumber levelers. Remove the wheels from the scaffold uprights, set the uprights on the wooden bases you have made and fit the platform sup ports to the position holes of the uprights that will make the platform level.

A Necklace for Stony Soil

Making a pole necklace. Dig a hole of the diameter called for in the chart, down to a foot below the frost line, then reduce the width of the hole to 14” and extend it down 1½’ below the depth called for in the chart (near right). Set eight evenly spaced ½” lag bolts in a ring around the pole at a point that will be 6” below the frost line, with the bolt heads protruding 6” from the surface of the pole. When you have braced the pole in place, fill the narrow part of the hole with earth and fill the wider part, up to the frost line, with concrete. After the concrete has hardened, fill the hole above the concrete necklace with a final layer of earth.

A Wall and Pads for Shallow Soil

1. Digging the key-wall footing. Locate the building lines (Steps 1, 2), then dig a trench 3’ deep and 16” wide Just outside the line you have established across the top of the slope. Undercut the downhill edge of the trench slightly, so that the bottom of the trench is wider than the top.

2. Making weep holes for the trench. At 4-foot intervals, dig pockets 3” wide and 4” deep into opposite sides of the trench, halfway up from the bottom. Insert a length of 1½” rigid plastic pipe, capped at one end with galvanized mesh, into each pair of pockets, with the capped end in the uphill pocket. Run two lengths of reinforcing bar along the trench, securing them to the plastic pipes with tie wire.

3. Starting the key wall. Restring the building lines, pour concrete up to the downhill edge of the trench and push a masonry block 2” into the concrete, using the building lines as guides. Lay two more blocks of this course.

4. Making weep holes in the wall. At the fourth block position, lay a hollow-core partition block on its side and a half-height block atop it. Complete the first course, laying hollow-core partition and half-height blocks at every fourth block position, and install joint reinforcement over the top of the course (Step 2).

5. Finishing the wall. Sink a reinforcing bar through one core of each block, with the bottom of the reinforcing bar about 2’ into the footing and the top protruding 14” above the top of the block, then let the concrete harden. Beginning with a half block, lay a second course of regular blocks; then lay a third course of regular blocks alone. Fill the hollow cores of all the blocks down to the footing with concrete, and install a sill plate and a header joist as you would on a continuous foundation wall Steps 1 and 2).

6. Setting the poles. After digging holes at the pole locations, pour a concrete pad 4” deep in the bottom of each hole and sink the pole 2” into the wet concrete; to set a pole longer than 8’, use the method shown on , Step 1. Align, plumb and brace the pole immediately (, Step 2), let the pad dry for a day, then fill the hole with soil.

7. Putting in the joists. Install double floor beams parallel to the key wall and set the floor joists in place. Fasten these joists to the beams by the techniques shown on , Step 7; and to the sill and header Joist by the techniques on , Step 3.

8. Bracing the poles laterally. To secure a row of three poles across the bottom of the slope, fasten 2-by-4 braces running from the bottoms of the outside poles to points on the inner surface of a floor beam near the middle pole, using two lag bolts at each connection. On the opposite side of the same row, fasten a brace running from the bottom of the middle pole to a point on the in side surface of the other floor beam, close to either of the outside poles.

9. Bracing the poles uphill. Fasten braces between the bottoms of the longer poles and the tops of the shorter poles, just below the floor beams. Brace the bottom of each shorter pole to a joist at a point near the key wall.