Sunday, April 26, 2015

Construction - French Drains - Rationale, Fabrication and Installation (cont'd)

This is the second of three posts on the French drains.  The first post delt with the rationale for and the prefabrication of the drains from culverts.   This post bridges from the prefabrication phase to the installation phase in the third post.

Overall Design
The individual homemade drains were detailed in an earlier post and can be seen in the distant background in second photo.  The
12" double wall conduit for the manifold
perforated portion of each 8' drain is 60' long to which enough additional un-perforated pipe was added to reach daylight downhill near the future rain garden or to empty into a common 12" manifold that went to daylight near the garden. The perforated sections and one 20' section of unperforated pipe were assembled ahead of time. The remainder of the system had to be assembled on site as the trenches became available.

Entire system ready for installation

Professional Help
The need for an elaborate system of French drains and its cost was not anticipated when budgeting originally. Consequently, I tried to imagine ways of trenching and backfilling without professional help (original plan). However, it became clear that the additional cost of help could somewhat, but not entirely, be justified by savings of time, materials and equipment rental. 

In terms of time, it took only two days to lay the French drains in mid-April which allowed us to get a leg up on what is usually our wet season in May and early June. This was perhaps the primary benefit of seeking help.

In terms of materials, rock dropped from a height of 5' is sufficiently self-compacting to support foundation footings and slabs. Therefore, rock is preferable to soil for backfilling because soil has to have the correct moisture content then must be compacted in shallow layers (lifts) with compacting equipment. In terms of material costs, the pay-off from using professionals is that they have the right combination of equipment to minimize the amount of dirt that has to be removed.and replaced with expensive rock.

In terms of equipment rental, no mini-excavator or compactor was necessary -- no small savings.

Brian Hayes Construction
Consequently, we did the right thing in hiring Brian Hayes, a local contractor, at a time when he was not overbooked and able to do the work himself.   As luck would have it, his Dad (with a lot of help from a youthful Brian) had DIYed their home-place in which, as a science teacher, Mr Hayes had incorporated sustainability concepts that were way ahead of the curve.  

Brian was not only willing to work with a DIYer but seemed to take genuine ownership of our energy-neutral project (perhaps partly in his Dad's memory?).  He provided the rock and did the trenching and backfilling for the French drains. He facilitated the rapid installation of the AGS system, he graded the house footprint to final depth in preparation for the rock sub-base for the concrete slab and he dug the shallow trenches for the foundation footings -- all of this in essentially five working days despite having to deal with an amateur track-loader operator (me) and a volunteer crew.  Conservatively, he saved us as much as two months time over DIYing the French drains and the AGS system.

Brian's invoice equaled +/- 20% of our total home-building budget.  The ratio for the French drains to the AGS system was 8:2, i.e., 80 % of the 20% went for the drains, a cost that is somewhat easier to reconcile by knowing that any conscientious construction let into our wet hillside would have required them irrespective of our need to use them to protect the AGS system.  The 20% for installing the AGS system was more in line with what was budgeted.  

Our hope is that unanticipated synergies during the remainder of construction will help to offset the French drains costs.

Prime Examples of Unanticipated Synergies Immediately
Our project already has enough life to attract unanticipated synergies, most of which so far have taken the form of volunteer labor and opportunities for salvage.  Brian brought another dimension.  His 35-year experience in the field, and I, with my research-based design, were able to collaborate amiably on the fly as the French drains and AGS conduits were laid, producing much better outcomes than I would have had sticking to the original design. Since part of Brian's business is razing old buildings (60 or more per year), he now plans to watch in our behalf for salvaged lumber opportunities - another unanticipated synergy.  Still another:  I thought our narrow dead-end street precluded semi-truck deliveries, which meant unloading onto a main street and using the track loader to schlep individual skids several blocks (as I did with the pallet of geo-textile material). Through Brian's connections, a vacant contractor's property at the end of the street will be available as a turn-around for semi's.

First the Driveway
But back to the actual construction of the French drains, the first thing Brian prescribed was to site and rock a driveway to give access for the delivery of rock for the French drains and a place to dump it.   It also would be mandatory for the
Rough-in for drive and turn-around area near future garage
Ready-Mix trucks and others delivering materials later. Accordingly, I used garden hose, then marking paint, to outline
 the driveway to the street and the turn-around area near the future garage.   With the track loader, I removed about a foot of soil. 

As a naive DIYer laying out his first driveway with garden-hose-and-paint precision, I envisioned a nice driveway from the time the first gravel arrived until we moved in. Wrong!   By the time gravel truck after travel truck arrived, it was deeply rutted and had to be repaired over and over.  And, when dumping space closer to the house footprint was usurped by installation of French drains, the driveway to the street became the default site for several more truckloads of gravel which spilled over the sides of the original driveway footprint to the extent that it became impossible to tell exactly where the driveway was supposed to be.  Oh, well!

To continue the story on French drains go on to the third post.