Copyright 2014 by Joe Kordzi All rights reserved. This book and the accompanying SketchUp model or any portion thereof may not be reproduced or used in any manner whatsoever without the express written permission of the author except for the use of brief quotations in a book review. Cover Design by Colleen Kordzi First Edition www.woodcistern.com
Table of Contents 1.0 A Few Opening Remarks... 1 2.0 What s in the Box?... 2 3.0 Why Harvest Rainwater?... 2 4.0 Why Wood?... 3 5.0 Basic Wooden Water Cistern Construction Techniques... 6 5.1 Site Selection... 6 5.2 Overview of the Cistern Construction... 6 6.0 Getting Ready for Construction of the 3,000 Gallon Wooden Water Cistern... 10 6.1 Required Tools... 11 6.2. Selection and Storage of Lumber... 12 6.3 List of Materials... 15 6.4 A Good Foundation is Key... 16 6.5. General Notes on Cutting and Milling the Parts... 17 7.0. The Base... 18 7.1 Laying Out and Cutting the Base Notches... 21 7.1.1 Mark the Notches on the 6 x 6 Timbers... 22 7.1.2 Cutting the Notches in the Timbers and Assembly... 24 7.2 Making the Base Circular... 25 8.0 The Floor... 28 8.1 Machining the Floor Boards... 30 8.2 Drawing the Floor s Circular Perimeter... 30 8.3 Marking the Locations and Drilling the Floor Dowel Holes... 31 8.3.1 Marking the Dowel Locations... 32 8.3.2 Drilling the Dowel Holes... 32 9.0 The Staves... 35 9.1 Ripping the Bevels on the Staves... 36 9.2 Routing the Croze on the Staves... 37 9.3 Drilling the Dowel Holes in the Staves... 38 9.4 Trial Assembly of the Staves... 40 10.0 Making the Bands and Brackets... 43 10.1 Making the Brackets... 45 10.2 Cutting the Bands and Attaching the Brackets... 47 11.0 Construction of the Roof... 47 11.1 Construction of the Center Vent... 50 11.1.1 Positioning and Supporting the Center Vent... 52 11.2 The Rafters... 55 11.3 The Subfascia... 57 11.4 The Hatch Framework... 58 11.5 The Roof Joists... 63 11.6 The Roof Decking... 65 11.7 The Roof Center Vent Flashing and Cover... 67 11.7.1 Construction of the Center Vent Flashing... 68 ii
11.7.2 Construction of the Center Vent Cover... 69 11.7.3 Shaping the Center Vent to Match its Cover... 70 11.8 Milling the Fascia... 71 12.0 Use of a Plastic Liner... 72 13.0 Assembly... 73 13.1 Assembling the Base, Floor, and Staves... 74 13.2 Installing the Liner... 74 13.3 Erecting the Roof... 75 13.4 Installing the Decking and Roofing... 76 13.4.1 Installing the Vent Flashing and Cover... 77 13.5 Constructing the Hatch Cover... 77 13.6 Installing an Outlet Valve... 78 13.7 Installing the Soffit and Fascia... 80 13.7.1 Soffit Furring... 80 13.7.2 Soffit... 81 13.7.3 Fascia... 83 13.8 Installing the Inlet and Overflow Piping... 83 13.8.1 Construction and Function of the Inlet Piping... 84 13.8.2 Construction and Function of the Overflow Piping... 85 13.9 The Finish... 87 13.10 A Ladder... 87 14.0 What if I Need a Different Size Cistern?... 88 Acknowledgements... 94 References... 95 iii
5.0 Basic Wooden Water Cistern Construction Techniques There are a few different methods you may uncover for building a wooden water cistern, with varying degrees of quality in the end product. Some involve simply arranging boards vertically in a circle in order to support an interior liner, with nothing more than a gravel floor as a base. In contrast, the time honored and proven method incorporates a floor as an integral part of the structure, with steel hoops terminated in lugs that are tightened around the staves, with the classic conical roof. In this way, the floor contributes to the overall strength of the tank. This method incorporates design elements similar to the above mentioned wooden water pipes and may in fact be the inspiration for them. Both undoubtedly sprang from barrel making, or cooperage, and share some of the same terms (e.g., stave, croze, chime). This construction method results in a strong, long lasting, and leak proof design. It is the method used in the familiar railroad water stop 9 often seen in movies of the American Old West. It s also the same basic method used today by a number of companies to construct the wooden water storage tanks 10 that adorn the New York City skyline. This is the method I ve adopted, with a few (in my opinion) improvements. So let s get started! 5.1 Site Selection The first thing you must decide on is where to place your cistern. I placed mine right next to the side of my house, but other locations are possible. Assuming you intend to collect rainwater from a roof, the only real consideration is ensuring that the inlet of the cistern be below the rainwater collection point usually a gutter. This means you can move your cistern some distance away from the gutter and use piping to convey the water to the inlet, as long as that inlet remains below the gutter. It doesn t matter if the piping traverses the ground (or even goes underground), as water always seeks its own level. The cistern I describe herein has an overall outside diameter at the staves of 8 3 1/4. It has an overall height from the bottom of the base (or top of the foundation) to the tip of the center vent cover of 11 10 7/16. However, the maximum height from the bottom of the base to the bottom of the inlet pipe is 8 1/2. 11 Other inlet arrangements are possible, including running it through the roof. A consideration of the inlet height also involves the finished height of the foundation. In any case, you must ensure that your site selection allows the inlet to your cistern to be below your gutter. Lastly, you must decide whether the site you have in mind allows for the construction of a proper foundation, which I will touch on a bit later. 5.2 Overview of the Cistern Construction I m first going to provide a brief summary of some of how the cistern is constructed, and then we ll get into selecting and storing the wood, followed by milling the pieces. Lastly, I ll 9 http://en.wikipedia.org/wiki/water_stop 10 Throughout this guide, I ve chosen to use the term tank as the generic water storage vessel, reserving the term cistern to refer specifically to a water tank that is used to harvest rainwater. 11 This assumes that the inlet pipe goes through the fascia and subfascia and through a stave at the highest point where a full circular hole can still be drilled through the stave. 6
cover how to assemble the pieces. Figure 4 below is a section cut of the cistern, illustrating most of the parts. This, and the subsequent illustrations I will present, were done using the SketchUp model I made of my cistern, which you now have access to with the purchase of this guide. Figure 4: Section cut of the cistern 7
Note that although SketchUp draws objects in 3D very well, the objects created are actually hollow. Therefore, when they are sectioned as above, they are effectively cut open like a box, exposing their hollow nature. As you can see, each stave fits tightly against its neighbor. This due to the fact that in cross section, the sides of the staves are not parallel, as Figure 5 indicates below: Figure 5: Detail of the staves and their dowels Notice that each stave has three rows of dowels (six per stave). This is one of those areas I mentioned above in which I ve attempted to improve on the traditional design. In the traditional design, dowels are used in the floor planks, but often only one row of dowels is used per stave, or no dowels are used in the staves at all. The traditional design largely depends on tightly drawn hoops (with a few blows from a sledge hammer) to align the staves and determine how circular the perimeter of the top of the tank ends up being. In contrast, the stave dowels in my design accomplish three things: (1) they align the staves, keeping the top of the cistern perfectly circular, (2) they add strength to the structure, and (3) they allow the structure to be self-supporting as the staves are assembled. As in the traditional design, each stave has a slot (dado) cut near its end, as shown in the next illustration. In tank construction parlance this is called a croze. It allows the staves, when drawn tightly together by the bands, to be pulled onto the floor, thus adding to the rigidity of the overall structure. Capturing the floor in the croze allows the weight of the tank (especially when full of water) to be borne by the base. It also lifts the staves off the ground, thus preventing them from rotting. This is an important design feature that is missing in some newer designs, in which, as mentioned above, the staves merely surround a liner that rests directly on the ground. By the way, the part of the staves that overhangs the floor is called the chime. These features are displayed in Figure 6, below: 8
Figure 6: Detail of the base, floor, chime, and croze Lastly, I d like to provide an overview of how the roof system is constructed. In Figure 7 below, two of the triangular plywood decking pieces have been removed in order to display the inside of the cistern. The center vent cover and its flashing have also been lifted up to expose the eight-sided center vent itself. The center vent has two purposes it not only functions as the center support for the rafters, but as its name states, it vents the interior of the cistern in an effort to reduce the humidity inside the cistern. Notice that the roof rafters are beveled so the plywood decking pieces lie flat to them when screwed down. 9
Figure 7: Detail of the roof structure and center vent The roof is another area in which I tried to make improvements. Traditionally, the roof is constructed in place, piece by piece, after the staves are erected. This type of roof only serves as a covering and adds little to the overall strength of the structure. In contrast, the roof in my design is premade in the shop and is very rigid. When the roof is lifted into place and attached to the staves, it greatly adds to the rigidity of the overall structure. In order to do this, of course, you have to be able to depend on the staves being perfectly circular when the cistern is erected. 12 Because all the staves have the same side bevels, and due to the aligning feature of the dowels, the top of the cistern will be perfectly circular when assembled. In some roof designs the joists are omitted, which means the integrity of the tank depends entirely on the hoops or bands that draw the staves tightly together. However, joists are a key part of my roof design, ensuring not only that the rafters do not splay outward, but allowing the rafters to become structural members. Other roof details, like the soffit and fascia and the hatch opening are also shown in Figure 7. 6.0 Getting Ready for Construction of the 3,000 Gallon Wooden Water Cistern Now that you have a good understanding of the interrelationship of the basic parts and construction techniques, I m going to take you through the entire process, literally from the ground up. We ll start with a listing of the tools needed. Following that, I ll provide a few 12 I ll show you an easy way to accomplish that a bit later. 10
plane the best side, which ensures it faces the inside of the cistern. 26 Note that if you need to joint your boards to prior to planning them, then they are likely going to be too thin to use. Joint one edge of all the boards you are going to use for the floor, staves, and roof rafters, so you will have a straight edge for ripping the edges later. 27 Restack with stickers when you are through. 7.0. The Base The wooden water cistern itself sits on a base constructed of 6 X 6 and 4 X 6 pressure treated timbers. This is the only use of pressure treated lumber in the project and does not present a hazard since it is separated from the water by both the floor and the liner described below. Traditionally, the base was composed of chine joists that were not connected, and merely arranged perpendicular to the floor planks. This is another area in which I attempted to improve upon the original design. My goal here was to not only create a solid base that provides even support, but to prevent the entrance of any rodents and insects. My base is constructed in a circular grid using four 6 X 6 beams that have been notched through half their thickness to receive four 4 X 6 beams which have correspondingly been notched. Additional sections of 4 X 6 lumber have been screwed into the edges of these beams to complete the perimeter of the base, which provides support for the floor all the way to its edge. The base is slightly smaller in diameter that the floor which rests upon it, to allow for the overhang of the staves. Below in Figure 8 is a picture of my base resting on its foundation: 26 Most planers, especially the smaller models, have a tendency to scallop or snipe the end of the board as it exits the planer. I have found the single best way to eliminate snipe is to provide a long outfeed table that is dead even with the base of the planer and to press down firmly on the board as it exits the planer. 27 Now is a good time to decide which boards you are going to keep and which you are going to set aside to return later after you are sure you aren t going to need them. 18
Figure 8: Cistern base and foundation Below in Figure 9 is a partially exploded illustration of the base showing how all the pieces are assembled: 19
Figure 9: Partially exploded view of base You can see how the 6 X 6 and 4 X 6 timbers that have been notched to fit tightly together into a strong grid. Below in Figure 10 is an illustration of the assembled base showing its dimensions: 20
Setup proper outfeed supports and run the board with its jointed edge against the fence and make the bevel cut. I was able to flip the board around and rip the bevel on the opposing edge without any adjustments. If you need to reset the fence in order to do that, first rip the bevel on all the boards on one edge first, then adjust your fence and repeat on the opposing edge. 9.2 Routing the Croze on the Staves Yes, you could decide to cut the croze (essentially a large dado) using a hand held crosscut saw and a sharp chisel and once you became proficient it might only take you ten minutes or so per stave. But I decided to do this with my router, using a simple jig and a 3/4 straight cutting router bit. Figure 22, below is a picture of that jig: Figure 22: Router jig for cutting the croze The jig essentially consists of two short sections of 2 X 6 stave material approximately a foot in length that butt up to another piece of scrap wood. These pieces are screwed onto the bench and have some 1 X 2 firing strips screwed onto them to form a box. The router rides in this box and is thus constrained to create the croze. The short sections of stave material 37
22, just to the left of the router jig are the two scraps of wood that serve to locate the stave. Also note that the end of the stave butts up against the router jig. Thus, both the routing of the croze and the drilling of the dowel holes are done simultaneously in one location. In Figure 24, below, the jig is being used to mark the holes: Figure 24: Using a jig to mark the location of the dowel holes To make this jig, screw a stop block to the end of the plywood strip as shown in the first picture. Then three holes have to be drilled in the center of the 1 5/8 wide plywood strip from the point from where the bottom of the stave begins to 2 8, 5 1, and 7 6. The ice pick serves to both mark the location of the dowel holes and start the hole for the 3/4 spade bit, shown above in the figure 18. Before we leave this section on constructing the staves, be advised that there are three special staves that are different from all the others. First, the final stave is not fitted with dowels, as it would be very difficult to install it. Therefore not only is it not drilled for dowel 39
Figure 39: Subfascia dimensions As shown in Figure 39, the subfascia has a top bevel cut and has miter cuts on the ends. The top bevel cut, shown to be 59.5 degrees is ripped on the table saw. You may notice that it is only slightly different from the front and rear miter cuts of 61.5 degrees made on the rafters. This is due to the necessity to project the angle outward by the value of the subfascia s miter cut of 22.5 degrees. Although I show the design length of the subfascia to be 3 6 1/16, I strongly suggest you first verify this measurement. The subfascia is attached using No. 10 X 3 1/2 exterior screws. Attach them by placing every other piece of subfascia between the rafters and screwing directly through the rafters into the subfascia using two screws on each end. The remaining four pieces of subfascia must then be toenail-screwed into the rafters. 11.4 The Hatch Framework Of course, we must provide a way to enter the cistern, and the hatch framing serves that function. My design results in an opening that is 1 5 1/4 X 1 3 3/4, which easily accommodates my 5 11, 200 pound frame, but you are free to modify it to suit your needs. The hatch is made from unplanned material and so its thickness in this section is treated as somewhat arbitrary, although in my SketchUp model I made it 1 5/8. Figure 40 illustrates its construction: 58
Figure 40: Hatch framework The hatch framework ends are arranged so that they are perpendicular to the rafters. This requires compound miter cuts on the front and back pieces where they meet the rafters. The side pieces and the blocking that provides support for the decking are all made with 90 degree straight cuts. Although I provide a dimension of 11 15/16 for locating the front piece from its midpoint to the end of the rafter, you should view it as a close approximation. However, if you decide to build the hatch according to the dimensions I supply below, you can simply slide it up toward the center vent until it fits. In Figure 41, the front piece of the hatch is removed from the rafters in order to illustrate its dimensions: 59
Figure 58: Hatch cover The hatch cover frame is made from two pieces of western redcedar measuring 1 1/4 X 2 X 1 10 and two pieces measuring 1 1/4 X 2 X 1 9. This provides 1/4 of clearance between the hatch framework and the hatch cover frame. The hatch frame is screwed together at each end using two No. 8 X 2 1/2 exterior screws. The cover boards are all ripped to a width of 3 3/4, except for the right most board, which is ripped to a width of 3 3/8. This ensures that when the 3/8 X 3/8 shiplap joint is cut on the table saw, all the exposed boards have a seam-to-seam width of 3 3/8. Use two 1 1/2 exterior screws to attach each board end to the frame. Like the rest of the cistern, all the exposed surfaces are rough textured. I bent a simple gate hasp to attach both the bottom (as shown by Figure 57), and the top of the hatch to the roof. 13.6 Installing an Outlet Valve I used a plain 3/4-in male brass hose bibb as my outlet valve so I can attach a garden hose to my cistern. If you d like a higher rate of flow, you can install a ball valve instead. This valve is attached to a PVC plastic reducer bushing, which is in turn screwed into a ABS plastic bulkhead fitting. 51 Figure 59 shows this arrangement: 51 I obtained my bushing and bulkhead fitting from www.flexpvc.com. The reducer is part number 439-210 and is a 1 1/2 MPT X 3/4 FPT. The bulkhead fitting is part number 9115-TT and is a 1 1/2 FPT X FPT. 78