Architectural model

Building the Eco Fortress

This is a earth covered home, having only one south facing wall with windows and is of concrete block and shotcrete construction. This design is low to zero maintenance, easy to heat and cool and tornado resistant.

I’d just like to state up front that I am NOT a professional builder or contractor of any kind. Remember that weird kid in your neighborhood when you were young, the one with the artistic, creative talent who built cool stuff from what seemed like nothing?…yeah, I’m one of those. I do have experience with all sorts of trades though, just not on a professional level. I’ve picked the brains of every tradesman I’ve ever met, and delivered building materials of every sort so I became familiar with most aspects of construction. This article is what has been in my head for sometime now, NO I haven’t built it YET..not in reality, but have built it and revised it and rebuilt it countless times till I think I have it sorted out to what anyone with SOME skill could build with a bit of effort. And YES, I will be building it as soon as possible, (Funding)..I’m close, even to the point of taking my hand drawn blueprints to the Building Inspectors / Permits office for a preliminary , He liked what he saw..and said…no problem, thought it was very well thought out and ahead of the curve. But in the mean time…here goes. Remember that this is based on what I want to build, but I hope SOME might find this useful.

Construction:

This is an alternative building method that anyone with a modest DIY skill set can accomplish. This is a workable alternative to using contractors , professional home builders or the myriad of available “kits” that are on the market. Utilizing locally available building materials and doing the bulk of the work yourself and perhaps a few friends, this home could be built incrementally over weekends, spare time or at whatever pace works for you.

Laying the ground work basics

Step 1. Assuming you have your land and your permits ,you begin by clearing and laying out your building site or “Pad”. This could be done with a hired backhoe/bulldozer operator or done yourself with rental equipment. I prefer some things done by Pro’s as opposed to renting the equipment. They can get it done quicker and sometimes cheaper than renting the equipment and doing it yourself.

Step 2. Once you have a pad cleared and leveled to the appropriate size you can start laying out your dimensional markers. This is done by measuring out and marking off the positions needed to put your footers with stake and string typically laid out off of “batter boards”. Footers can either be poured in trenches cut to the needed depth (at or below local frost line)or poured into forms laid out on a pad cut to the frost line depth. Attention should also be payed to the footers being LEVEL. Footers will have the required re bar in place along with re bar uprights sticking up at intervals for securing the walls to them and additional rebar uprights of 4 ft running parallel and outside of where the wall blocks will be and spaced 2 ft apart....(these will come into play later when shotcrete is applied to the whole structure as a shell)…. Be sure to leave an “Exit” under the footer that corresponds with where the sewer line will run to either a septic tank or city sewer connection. Some would also put in the electrical supply / water supply lines at this time, but in this plan we’ll have a utility space created between the floors.

Step 3. Once the footers are laid out and poured/cured we can start laying out a string grid to locate where the DWV (drain waste vent) plumbing will need to be located. This needs to be done before the concrete slab gets poured. These will be sewer line/drain lines for the kitchen and bathrooms. trenched to maintain a 1/4 inch drop per foot of linear travel to the “Exit” point under /thru the footer. leave about a foot or two of pipe sticking straight up, “Stubs” thru the concrete slab that will stand where needed to make appropriate connections. We will also need to lay our drain lines around the whole footer system and route it to carry ground water out and away from the building, we do NOT want rain/ ground water accumulating and putting pressure on our structure. If not level, you’ll need to start that first row of block in a bed of mortar to achieve level. otherwise you can roll or apply some adhesive to the block and glue directly to the footer, this row of block will serve as the form for the concrete slab floor. Pour the slab and finish as desired. The finish can be whatever you like, smooth plain concrete ready for tile or carpet, or stamped and colored to look like all sorts of finishes. These are just generalized steps in the ground work needed to really get things started, but looking up tutorials will make it easy for those who don’t fully understand what I just outlined.

This illustration shows some details on how to help keep this home DRY from ground water / moisture infiltration

ground water mitigation

And now the building method:

This is where the alternative approach comes in. We will be using the “dry stack” method of cement block construction, but with the added step of using construction adhesive to bond the blocks together. You won’t need a skilled mason to do this method and the blocks go up quick and easy. I’ve looked at a number of adhesives that will do the job, from Liquid Nails applied from caulking tubes to the roll on type like Blue Max. The Blue Max is similar to the “surface bonded” method of laying cement block. The adhesive will NOT be what holds the walls together in the long term, its just a way to keep them stable while stacking them up.

Step 1. We will be using 8x8x16 standard block, 8x8x8 half blocks and 8x8x16 and 8x8x8 bond beam blocks. We’ll also need a few pallets worth of narrower blocks 4x6x16 and 8x6x16 for ledge creation (these come into play later) actual block dimensions are 7- 5/8 X 7- 5/8 x 15–5/8 etc etc…but we’ll just use the standard here for simplicity and measurements are approximates. Mark where your doors will be and start on either side of that opening. I do a dry run first just to see how they line out, start with a full block and lay end to end going around the whole outline of your building, leaving a gap where any secondary doors will be. You may have to adjust the blocks along that wall with the door as to how it lines up with the corners and also make allowance for the door frame. Second row will need to start with a half block and then full blocks to achieve the overlaping joints . After completing two rows (above the slab), we need to think about electrical outlet placement in the walls, these will be in conduit and need to be pre-placed in positions to proved electrical outlets to the living spaces. Its not to hard to cut cement block with a circular saw and a masonry cutoff blade. You will have to notch to account for the conduit. and outlets. Now we add upright conduit to supply power for the wall outlet circuits and vertical rebar into the hollows of the block walls. Leave the rebar and conduit uprights extending up to at least 5ft (60in)level ..this third row of block is a Bond beam row but Bond Beam rows will be on every fourth row here after, (see Fig : 1) they leave a horizontal cavity running the whole course. that cavity will get two #4 (1/2 in ) rebar . Now we fill the wall with concrete, a concrete pump makes this easy. We can lay another row on top of this. OK, so we should be about 38in in wall height all the way around now, so lets think about our window locations. Doing window sill heights now gets you compliant with the minimum sill height regs which typically call for no more than 44 inch sill heights (its all a part of the emergency exit regs) On this design, we have only one wall that gets windows so this is the time to make allowances for those openings. You can make wood templates of your window dimensions and stand them up at the appropriate locations, make sure to account for your sills. One method would be to outline your window templates with U-channel block standing on end glued together, work both sides up and do the curved arch top section last. Even if your not going with arched windows…this feature makes the opening structurally VERY strong, but for regular windows you’ll still have to put in a header of some type. Back to laying block rows until you reach your desired wall height, and some blocks will need to be cut when you reach the arches above the window openings. Remember to do a bond beam row as every fourth row of block for structural integrity and to continue upward with your electrical conduit and vertical rebar. filling each new “lift” (4 rows of block) with concrete. Remember to do your wall switch box for your ceiling fan/light and the conduit up to the top of the wall.

Step 2. Once the desired wall height is reached, we stop with a final bond beam course and we will add several extra vertical rebar for connecting to the ceiling rebar, these extra’s will be bent over before the next row. This is where a row of 4x6x16 come in, We set this row on top of the bond beam flush with the out side (over the extra rebar for the ceiling connection)and concrete fill this last “lift”, this is how we achieve a ledge, this ledge is integral to the Bowstring arch we will be creating. Some aspects of finished wall height will be governed by your particular home design, as in if its a one or two story home, and where the walls need to fill the arched area. Either way its at this point we look at roof curvature creation. I’ve come up with a simple method of making bow string arch trusses. They are 1x6 planks of a length dependent on the span your looking to cross, and how much of an arch. For example if your wanting to span 14 ft and have an arch with about a 3 ft (+/-) rise at the middle (crown) of the arch, you’d need at least a 15 ft plank, you can trim the ends to fit after the arch is achieved. Other center rises could be created by longer board lengths or shorter spans. The arch is maintained under tension by the use of a connecting rod of 3/8th rebar attached to the ends of the board by 2 ft lengths of chain and 8 inch long carriage bolts thru both ends of the board. The bowing is achieved by use of a ratchet strap and tension being applied till the desired bowing is reached and the span length is achieved…then the chain and rod is attached to hold it. several of these will need to be made in order to hold up the sheathing ( 3/8th OSB plywood) which will be attached by screws thru the arch planks from below so later removal will be possible once the concrete overlay has cured. These simple bowstring arch trusses, with the osb sheathing are very strong, and will hold the 2 to 3 inches of concrete applied. A good choice for the planks are called 5/4 X 6 X 16 standard Decking ( actual 1 x 5.5 x 16) they seem to bend well without having to steam them or bending them slowly.

Components for making a Bowstring Arch

Step 3. Now we have our walls up and are casting our vaulted curved ceilings. These ceilings will be of the first floor bedrooms, but this same principle applies if it was for the main roof substructure. This is where some magic can happen if your so inclined to get creative. Some of these steps could be omitted or other methods could be used such as bought trusses to achieve second floor support, but here I’ll be showing how to create barrel vault ceilings that will also help in a second floor support system. Along the top edge of the longest opposite walls you will be attaching 2x4’s that run the length of each wall, these will be set down from the top edge about 2 inches and attached with lag bolts or concrete screws about every 4 ft (won’t have to be super strong connections as we can do upright supports up from the floor to bolster them). These will serve as a rest for the bowstring arches we made, so you will need enough of these arches to place one every 2 ft apart. Start with an arch at each end wall and space the rest between those trying not to have more than 2 ft between any two arches. Attach your OSB sheets from the outside but screw them on from below(inside ceiling side). Orientate the plywood sheets in whatever works best for your dimensions. Now we’ll cover that with plastic sheeting that is taped down all around the outer edge, trimmed to fit and tape sheets at any joints/overlaps making it as smooth as possible. Now if you would like to add any features like inlaid designs, those can be done with styrofoam panels attached to the plastic. So if you’d like to create a coffered effect,( think Pantheon) you could attached square panels spaced appropriately. This is also the time to get your ceiling box and conduit in position for the ceiling Fan/light. Now comes the reinforcement, as in wire mesh, 6x6 would be a good choice and #4 rebar, start with a layer of wire mesh that covers the entire plastic area, then run #4 rebar from edge to edge mirroring the way the arches ran and then run some rebar perpendicular to the first ones making 12" x 12 “ squares ,tying them all together where they cross each other with rebar tie wire or use the plastic clips. add some tie wire ties to slightly raise the mesh from the plastic. Now we can pour/pump the concrete onto this to about 2 to 3 inches in thickness , apply the concrete evenly, distributing the weight from side to side, the whole perimeter and finishing at the crest and screed/trowel it long enough to maintain the arched shape and a uniform thickness , then cover with plastic to cure it slowly.

Here is a rough sketch up, its not to scale but should help in visualizing the procedure. note how the ceiling concrete ties in with the walls. some rebar stubs (not shown) should also be bent over ( from the bond beam/below the 4x6x16 )to tie in with the ceiling rebar.

curved barrel vault ceiling

Step 4. After at least a 7 day cure time, (the longer the better) 28 days is best, we can start laying second floor support across. We’ll need to bring the side walls up a few rows and leave a ledge by switching to a row of narrower block like 8x4x16 or you could opt for using truss hangers. Either use 2x6 or 2x8 on edge or TJI members to span across from wall to wall with the top of the curved ceiling being a central rest for the crossing floor supports. This method will give an extremely strong floor with little to NO deflection (give) in the center as the arch ceiling below will now act like a support. Before any floor sheathing is put in place, attention must go back to continuing on with the electrical conduits and any upstairs bathroom water and drain concerns which will need to travel between the floor /ceiling space created to where they will connect to the power supply, drain /water lines etc. This part may seem complicated but if attention and some forethought is given its very workable. Remember to schedule inspections prior to covering these with flooring. Repeat steps 2, 3 and 4 for other rooms getting this type of ceiling.

Step 5. Now lets look about the main roof structure. Its basically the same as doing the vaulted curved ceiling as earlier but with an added level of concrete ,wire mesh and rebar which overlays and spans from one side of the whole structure to the other, this layer would be at least a 4 inch thick layer, and when added to the previous ceiling vault layer, gives us a final thickness of 6 to 7 inches. In this application, the upper rooms are all arched vaulted ceilings,and are all completed. And even the main great room expanse is done in the same fashion only on a larger scale. All 2nd floor arch trusses will remain in place for this procedure and the full 28 days will have elapsed. The rebar and mesh for the whole structure is in place and the shotcrete is applied from the bottom and working all the way around and UP until the entire structure is covered in a monolithic shell. As shown in the illustration below, there will be voids that serve as plumbing,conduit and hvac channels between the first and second floor, but on the roof stage those will be filled with styrofoam shaped to give the desired structural benefit plus eliminates unnecessary weight, and helps create our desired shape for all the strength. So basically we create a shell over a series of smaller shells. The wire mesh and rebar configuration will be more robust and ties in with the rebar and mesh which will be applied to the outside of the structure walls prior to the final shotcrete shell.

the grid squares are 2 ft x 2 ft
front view
ground cover removed
roof removed
shows underground hallway tube to shop/garage
3/4 view

As you can see from the pictures I plan on additional out structures like 2 car garage and workshop, along with two castle like towers that also serve as utility, storage and integral support for a large porch roof/ balcony. These would be built using the same dry stack method as the main structure.

The reasoning behind this method as opposed to using concrete forms and poured walls is..Forms are expensive, have to be erected and then removed, and if you rent them your tied to a time frame on getting this done as quick as possible due to the rental cost keeps climbing…using block and filling with concrete gets you the same strength as poured walls… no forms to take down, they don’t care how quickly you work, and provide a nice interior surface for plastering or other finishes.

Completing the build: In finishing the whole completed structure before any earth covering is done, We must concern ourselves with ground water mitigation and creating a thermal break. The draining away of ground water is critical as is preventing any water penetration. to do this we’ll be using a few methods in a redundant manner. first we address any surface cracks that usually appear in any cured concrete, their more cosmetic than a structural concern but we’ll go over the whole thing and patch as needed with mortar mix. Next we apply a coating of a water proofing material like Blue Max or sprayed on Bitumin/Tar type products. Then I’d overlay the whole thing with 10 mil plastic sheeting. The plastic sheeting would get sealed at the leading edges where it comes in contact with the front vertical wall with additional Tar/Blue Max .

Thermal Break: Contrary to what most might think, we do NOT want to have our home tied to the ground temperature. We want our home isolated from the earth temperature as we will be concerned with controlling the inside temps. What we’re looking to avoid is a nasty thing called “condensation” which occurs when two temperatures collide. So what we’ll do is cover the entire structure in closed cell spray foam at a thickness of about an inch at the bottom of the structure (deepest) and getting thicker as we approach the top (shallowest), making the final thickness over the entire roof area at about 3 inches. Over this closed cell foam we’ll apply another 10 mill covering of plastic and seal the edges down.

Back Filling: care must be taken here as to not damage our waterproofing/ thermal break, so take it slow and easy on getting this done. Start with clean washed drainage rock / gravel at the bottom, covering all the drainage lines by about 2 ft. In placing your back fill, you want to do it in such a way that the structure gets a layer of gravel closest to it while also getting the more typical backfill soil in place as general covering. This is to help insure that rainfall can quickly and easily make its way away from the structure and down to the drainage system thus avoiding any hydrostatic pressure building up.