Construction - Back to Dirt Work - Insulation/Watershed Umbrella (Cont'd)

The last post covered the first three layers of the insulation/watershed umbrella.  This post deals with the next six layers.  A subsequent post will talk about the last layer -- the topsoil.  
And the usual reminder:  click on any photo to enlarge it.

SAND
Now that the insulation and a thick layer of sand made for a rather squishy surface on which to work, wheel barrows were out of the

A thin layer of sand covers the foam board

question for subsequent layers of sand, so the real work began.  I brought loader buckets of sand to the periphery of the umbrella in three places then we broadcast the sand shovel-by-shovel and broomed the sand until the first layer of plastic was uniformly covered but only half as thick as the first layer of sand. The purpose of using another layer of sand is primarily to serve as a drainage plain in case any water penetrates the top layer of plastic. It also smooths out the transitions as the thicknesses of foam go from 4" to 3" to 2".  The drainage would have been even better by having a thin layer of sand between the first layer of plastic and the foam board as well as on top of the board but I was afraid that the sand would cause the foam board to scoot around when we walked on it and pitching sand was already getting to be a little tiresome.

Intermediate layer of plastic sheeting batten down for the night

PLASTIC SHEETING
We merely butted this second layer of sheeting against the foundation wall instead of mating it with the sheeting extending from under the cement board/stucco covering on the foundation and the retaining wall.  The purpose of this layer is to provide another barrier to water penetrating the umbrella should the top layer of plastic be breached.

SAND
Another thin layer shovel-broadcast and evenly spread.  The purpose of this layer of sand is to provide a drainage plain for any water penetrating the top layer of plastic sheeting. Without it, the weight of the topsoil layer would pinch the two sheets together so tightly that water would trapped between the sheets and not be able to escape down-slope.

PLASTIC SHEETING
This layer was butted against the foundation walls and the retaining wall then the second sheet hanging out from under the cement board/stucco foundation and the retaining wall was shingled over it.  As with the first two layers of plastic, one long piece went from the screened porch to the western end of the excavation, a distance of almost 60'.  A shorter piece was installed between the west wall of the house, the extent of the excavation and in front of the retaining wall, such that it overlapped the first piece in shingle fashion by a large margin.  The two together pretty much used up a 100' roll of plastic.

SAND
The top layer of plastic will be the primary barrier against moisture penetration into the envelope but it is imperative that any moisture it collects finds an unobstructed passage off of the umbrella.  So the last layer of sand provides the drainage plain through which water will easily exit the envelope.  I reasoned that this layer should be little thicker for drainage purposes and to withstand some redistribution as the carpet was tweaked into position.

SALVAGED CARPET
The primary function of the carpet is to protect the sheet plastic from physical damage caused by someone digging in the topsoil layer who doesn't know, or forgets, about the underlying umbrella.  It will discourage aggressive plant roots (although we plan to landscape with native ground-hugging plants with shallower roots).  And burying the carpet is also a green thing in that it keeps it out of the landfill.

I have been collecting used carpet for several years in anticipation of making it the last

The last layer of plastic has been covered with a substantial layer of
sand;  Pat and Roger are in the process of laying down the first layer
of carpet by simply laying it in place and unrolling it, thereby keeping the
appearance side up

layer of the envelope before backfilling with topsoil. Most of my stash of carpet came from friends and family who knew to keep the pieces as large as possible.  As it turned out, I was short by about 1,200 sq ft. Fortunately, +/- 800 sq ft appeared on Craigslist the first day I realized that I was short. For the remainder, I tried networking with carpet layers who are willing to keep the pieces large until I could come by and help carry them out. However, I found that carpet layers remove old carpet by cutting it into narrow strips that, when rolled up, are easy to carry out of the building, and that those I contacted did not want to bother with an alternative approach.  I ended up dumpster-diving behind a floor covering store (with permission) to find pieces big enough to finish the project.

We laid the carpet upside down in two layers, each in shingle fashion to shed water that

We ran out of carpet when the larger area in the distance
was covered with two layers but the area in the middle
distance had only one layer of carpet and the area in the
near distance had none; nevertheless, it was possible to
begin the backfilling while obtaining more carpet as
evidences by the track loader in the background

would be flowing on top of it and taking care to mismatch the junctions between pieces in the two layers so that all areas were sure to have at least two layers of protection between the topsoil and the sheet plastic.  We also unexpectedly found that it was best to lay the first layer right-side-up for a couple of reasons. First, and most important, rolled carpet always seems to come with the backing side out and, when unrolled, has the appearance side up.  If we were to have insisted that the first layer be upside down as originally planned, we would have had to unroll it and re-roll it to be able to position it correctly without disturbing the sand.  To say it another way, it would not have worked to have unrolled it then dragged it into position across the sand, as opposed to merely unrolling it across the area of sand that needed covering.  There was a second reason for laying the first layer right-side-up. After the first layer was in place and we were laying the second layer upside-down, it was easy to keep track of which areas had not been covered with the second layer. Having the "good side" of the first layer exposed meant that, at a glance, we could see which areas had not yet been covered with upside-down carpet.  The second layer was easier to lay in that it did not have to be unrolled precisely where it was to end up -- it could be unrolled close to its final destination and dragged to place across the first layer of carpet.

A Couple of Additional Nuggets
Hiat, the principal authority on the envelope, warned that the plastic sheeting would probably be punctured while laying it but not enough that its function would be compromised.  However, we saw no evidence of punctures.  6 mil plastic is pretty tough stuff and the layers of sand cushioned it from the underlying rough soil and gave it enough resiliency that we could walk on it with abandon.

The carpet must be of synthetic fibers, not wool, in order not to biodegrade in the soil.  Also, it is important to protect the carpet from UV rays while in storage which is as simple as covering it with tarps that are of sufficient quality to resist UV disintegration themselves. We had to discard a few yards of carpet that were not adequately protected by the tarps. Another benefit of keeping them covered is that they stay dry and are lighter when handling them for the umbrella.

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The topsoil backfill will be the subject of the next post, especially how we solved the dilemma of using the track loader on top of the envelope without crushing it.