LLOYD'S CONSTRUCTION TIPS
LOW PRESSURE AIR FORMS
The low pressure building method (as opposed to the Monolithic high pressure method) is known by insiders but has never been published. The average guy is defeated by Monolithic's steamroller like operation but might be very interested in something that is do-able.
Use a small (like, 14" diam, as in window swamp coolers) centrifugal fan to inflate airforms made of inexpensiveTyvek House Wrap. No airlock is necessary. Cinch up on a small lasso tied around the inflation tube to adjust the pressure. Do not try to control the pressure by venting the airform. It just doesn't work.
First, urethane foam layers and then shotcrete layers are applied to the inside of the inflated airform.
All of the work is done from inside the inflated airform. For the first layer of foam the operator just wets the inside surface, starting from one end and not stopping until the other end. The next pass is the same but adds a little thickness to the preceding layer. The third layer builds the thickness to about 2 inches. The point is to fix the outside curved surface so it doesn't deform by being attached to a thick layer of cooling foam that has a mind of its own.
It doesn't take any longer to quickly apply three thin layers to the entire interior surface than it does to apply one full thickness while standing in one spot.
Reinforced concrete, ferrocement or steel fiber reinforced shotcrete is applied in thin (1/2") layers to the inside foam surface. Allow each layer of shotcrete to set up overnight.
Depress the rough interior grade enough in each room to receive rebound shotcrete, then pour the slab to cover it.
Tyvek house wrap airforms are very strong, and because Tyvek doesn't inhibit the passage of moisture laden air, it is left in place and then coated on the outside with plaster and/or acrylic latex paint.
SUMMARY
Inexpensive Tyvek "housewrap" makes an ideal airform material.
Very important: None of these materials prevents the migration of moisture laden air.
Use a small (like, 14" diam, as in window swamp coolers) centrifugal fan to inflate airforms made of inexpensiveTyvek House Wrap. No airlock is necessary. Cinch up on a small lasso tied around the inflation tube to adjust the pressure. Do not try to control the pressure by venting the airform. It just doesn't work.
First, urethane foam layers and then shotcrete layers are applied to the inside of the inflated airform.
All of the work is done from inside the inflated airform. For the first layer of foam the operator just wets the inside surface, starting from one end and not stopping until the other end. The next pass is the same but adds a little thickness to the preceding layer. The third layer builds the thickness to about 2 inches. The point is to fix the outside curved surface so it doesn't deform by being attached to a thick layer of cooling foam that has a mind of its own.
It doesn't take any longer to quickly apply three thin layers to the entire interior surface than it does to apply one full thickness while standing in one spot.
Reinforced concrete, ferrocement or steel fiber reinforced shotcrete is applied in thin (1/2") layers to the inside foam surface. Allow each layer of shotcrete to set up overnight.
Depress the rough interior grade enough in each room to receive rebound shotcrete, then pour the slab to cover it.
Tyvek house wrap airforms are very strong, and because Tyvek doesn't inhibit the passage of moisture laden air, it is left in place and then coated on the outside with plaster and/or acrylic latex paint.
SUMMARY
Inexpensive Tyvek "housewrap" makes an ideal airform material.
- Spray urethane foam on the inside surface of a Tyvek airform.
- Reinforce and spray shotcrete on the inside surface of the foam.
- Finish the Tyvek outer surface with two coats of thick, latex paint.
Very important: None of these materials prevents the migration of moisture laden air.
CONSTRUCTING A SOAP-BUBBLE-CLUSTER HOME
LAYING IT OUT ON THE SITE:
Here is an easy way to transfer a regular floor plan to the field full size. Even with a plan as complex as a soap bubble
cluster , you can locate the room circles and any other key points in accurate relationship to one another using nothing
more than a measuring tape and a roll of string.
DIRECTIONS:
ON THE FLOOR PLAN: draw a bold, straight, colored line through the complex of circles and walls. Orient it exactly to North-South or East-West (your choice) and label it "BASE LINE". From any key point, such as the center of a soap bubble like circular room buried in a cluster of soap bubbles, draw a line perpendicular to and intersecting this base line. Mark down the distance (floor plan scale) of this point to the base line. At the start of the base line, not too far out from the edge of the building, make a dot. Label it "BASE". Measure from this dot along the base line to the first perpendicular and label the inter section "station point 1" (jot down its distance from the dot). Repeat this for "station point 2" and so on.
IN THE FIELD: use a long cord stretched between two stakes for the base line and orient it to the same N-S or E-W as the base line on the floor plan. The first stake will be the "BASE". Al l you need is a non stretch cord to find the perpendiculars to this line: mark each station point along the base line with a f lag tied around the cord. From the flag make two marks out on the base line, one toward the BASE and the other away from the BASE. You don' t have to measure anything but these marks must be the same distance from the flag. Using each mark as a center, strike two short arcs in the dirt using a radius much greater than their distance from the f lag (the length of the short arcs are not important nor is the length of the radii as long as the length of the radii used to make them is the same. Strike a line between where these two arcs cross and the original station point f lag and you have made a perpendicular to the
base line at that station point. Measure out along this perpendicular and drive a stake in the ground at the circle' s center . Leave this stake in place. Use this stake to strike a circle on the surface representing this room. Repeat the process for the rest of the intersecting circle and straight walls.
STARTING THE CONSTRUCTION:
Dig trenches for the foundation (or footing, footer , or whatever it is cal led in your area) centered under each straight or curved wall. At this time put in place anything that goes underground such as electrical conduits, plumbing, and water pipes. See your engineer or code book about the size, reinf , slab thickness, drain rock, W/P membranes, and other details. After these foundations have been poured but before they have set up, locate the exact outside face of the curved walls (using the center stake you left in place) and jamb in short lengths of 3/8" rebar vertically at about 3' center s. These should extend above the foundation about 4". Also jamb in longer lengths of 1/2" rebar about 5" inboard from the curved outer perimeter of each room and along al l of the interior straight walls. These should be spaced about 2' or 3' apart and extend up vertically about 18" or 20". After the foundation has set, wire a 4" or 6" wide (depending on your slab thickness) bender board to the outside of the short rebar stubs. This bender board is the curved outside formwork for the floor slab and is to remain in place after the pour {Later , the bottom of the air forms will be stapled to it). While the slab is still fresh, with the claw end of a hammer , gouge "keyways" between these vertical rebars. The keyway will help anchor the concrete shell .
THE LOW PRESSURE, LIGHTWEIGHT AIRFORMS:
The 18" rebar gets bent over toward the center of each room to get it out of the way before installing the air forms and stays like that until after the foaming operation. Staple the base of the air forms to the outside face of these bender board forms (using a simple T-50 spring loaded hand stapler ) and to the tops of the temporary interior stud walls controlling the valleys between bubbles in the roof , then pressurize the whole house with a small centrifugal fan. At this point the airhouse will probably drop down and then rise up again whenever anyone enters. Not to worry. Make any corrections in the inflated shape using a mat knife, a pliers stapler and package wrapping tape. Coat the inflated air forms from the inside with about 3" of urethane foam (sprayed in thin layers so as to not cause the shape to deform due to the internal stresses in a single thick layer of cooling foam). When finished, turn off the fan, turn on the lights (you are now in a night atmosphere inside of a rigid structure made of foam on the outside walls and open 1"X4" stud walls on the interior walls. From the outside it now looks like the finished curvilinear house without backfill and without openings.
THE HARD STRUCTURE:
After applying the foam layer to the inside surface of the entire inflated house, bend the 18" rebar back up vertically. They should end up an inch or so out from, and parallel to, the inside face of the foam layer . These rebars are intended to hold the concrete shells into the keyways and receive any steel used to reinforce the shells. Next, replace the temporary interior stud walls, 4' at a time, with 4' wide 3D panels. Use diamond coated blades to cut the top of each panel to match the curve of the (roof ) valley above it (3D panels are made with very tough high carbon steel wire). Wherever you want skylights and windows in the outer walls and roof fasten 2" thick foam blanks (or however thick you are going to make the concrete walls and roof ) on the inside surface. Do this by shoving long nails at an angle through the blanks into the foam shell . Again, working from the inside, gunite or hand plaster al l walls and ceilings to the edge of these window blanks. Use tied rebar or fiber reinforced gunite or fc for the curved shells and unreinforced gunite on the 3D panels. After this operation, remove the 2" foam window blanks and cut through the original foam shell from the inside using a kitchen bread knife. You can now turn the lights off . The windows, skylights, and door details, and backfill and exterior skin details will be described later .
Here is an easy way to transfer a regular floor plan to the field full size. Even with a plan as complex as a soap bubble
cluster , you can locate the room circles and any other key points in accurate relationship to one another using nothing
more than a measuring tape and a roll of string.
DIRECTIONS:
ON THE FLOOR PLAN: draw a bold, straight, colored line through the complex of circles and walls. Orient it exactly to North-South or East-West (your choice) and label it "BASE LINE". From any key point, such as the center of a soap bubble like circular room buried in a cluster of soap bubbles, draw a line perpendicular to and intersecting this base line. Mark down the distance (floor plan scale) of this point to the base line. At the start of the base line, not too far out from the edge of the building, make a dot. Label it "BASE". Measure from this dot along the base line to the first perpendicular and label the inter section "station point 1" (jot down its distance from the dot). Repeat this for "station point 2" and so on.
IN THE FIELD: use a long cord stretched between two stakes for the base line and orient it to the same N-S or E-W as the base line on the floor plan. The first stake will be the "BASE". Al l you need is a non stretch cord to find the perpendiculars to this line: mark each station point along the base line with a f lag tied around the cord. From the flag make two marks out on the base line, one toward the BASE and the other away from the BASE. You don' t have to measure anything but these marks must be the same distance from the flag. Using each mark as a center, strike two short arcs in the dirt using a radius much greater than their distance from the f lag (the length of the short arcs are not important nor is the length of the radii as long as the length of the radii used to make them is the same. Strike a line between where these two arcs cross and the original station point f lag and you have made a perpendicular to the
base line at that station point. Measure out along this perpendicular and drive a stake in the ground at the circle' s center . Leave this stake in place. Use this stake to strike a circle on the surface representing this room. Repeat the process for the rest of the intersecting circle and straight walls.
STARTING THE CONSTRUCTION:
Dig trenches for the foundation (or footing, footer , or whatever it is cal led in your area) centered under each straight or curved wall. At this time put in place anything that goes underground such as electrical conduits, plumbing, and water pipes. See your engineer or code book about the size, reinf , slab thickness, drain rock, W/P membranes, and other details. After these foundations have been poured but before they have set up, locate the exact outside face of the curved walls (using the center stake you left in place) and jamb in short lengths of 3/8" rebar vertically at about 3' center s. These should extend above the foundation about 4". Also jamb in longer lengths of 1/2" rebar about 5" inboard from the curved outer perimeter of each room and along al l of the interior straight walls. These should be spaced about 2' or 3' apart and extend up vertically about 18" or 20". After the foundation has set, wire a 4" or 6" wide (depending on your slab thickness) bender board to the outside of the short rebar stubs. This bender board is the curved outside formwork for the floor slab and is to remain in place after the pour {Later , the bottom of the air forms will be stapled to it). While the slab is still fresh, with the claw end of a hammer , gouge "keyways" between these vertical rebars. The keyway will help anchor the concrete shell .
THE LOW PRESSURE, LIGHTWEIGHT AIRFORMS:
The 18" rebar gets bent over toward the center of each room to get it out of the way before installing the air forms and stays like that until after the foaming operation. Staple the base of the air forms to the outside face of these bender board forms (using a simple T-50 spring loaded hand stapler ) and to the tops of the temporary interior stud walls controlling the valleys between bubbles in the roof , then pressurize the whole house with a small centrifugal fan. At this point the airhouse will probably drop down and then rise up again whenever anyone enters. Not to worry. Make any corrections in the inflated shape using a mat knife, a pliers stapler and package wrapping tape. Coat the inflated air forms from the inside with about 3" of urethane foam (sprayed in thin layers so as to not cause the shape to deform due to the internal stresses in a single thick layer of cooling foam). When finished, turn off the fan, turn on the lights (you are now in a night atmosphere inside of a rigid structure made of foam on the outside walls and open 1"X4" stud walls on the interior walls. From the outside it now looks like the finished curvilinear house without backfill and without openings.
THE HARD STRUCTURE:
After applying the foam layer to the inside surface of the entire inflated house, bend the 18" rebar back up vertically. They should end up an inch or so out from, and parallel to, the inside face of the foam layer . These rebars are intended to hold the concrete shells into the keyways and receive any steel used to reinforce the shells. Next, replace the temporary interior stud walls, 4' at a time, with 4' wide 3D panels. Use diamond coated blades to cut the top of each panel to match the curve of the (roof ) valley above it (3D panels are made with very tough high carbon steel wire). Wherever you want skylights and windows in the outer walls and roof fasten 2" thick foam blanks (or however thick you are going to make the concrete walls and roof ) on the inside surface. Do this by shoving long nails at an angle through the blanks into the foam shell . Again, working from the inside, gunite or hand plaster al l walls and ceilings to the edge of these window blanks. Use tied rebar or fiber reinforced gunite or fc for the curved shells and unreinforced gunite on the 3D panels. After this operation, remove the 2" foam window blanks and cut through the original foam shell from the inside using a kitchen bread knife. You can now turn the lights off . The windows, skylights, and door details, and backfill and exterior skin details will be described later .
DESIGNING AIRFORMS OF DIFFERENT SHAPES
Here is an easy way to design and make airforms for any shaped dome: hemisphere, catenary, onion, mushroom, anything.
At any convenient scale, say 1 " = 1' draw a vertical building section through the apex. For example a hemispherical dome would be a semi-circle springing up from a horizontal base line.
On one side of the semi-circle (from the base to the apex), starting at the base and continuing up to the apex at the very top, make a dot on the curved line at every foot.
Strike lines parallel to the base through each of these dots and extend them horizontally through the entire building, or, alternately, to a vertical centerline passing through the apex (double this for the full width).
Each of these horizontal lines represents the edge view of a horizontal plane cut through the building at every foot along the edge line. It is a circle in plan view.
Find the circumference of each of these circles (3.14 16 X its diameter In inches).
To find the width of the gore at each foot along the gore pattern centerline divide the circumference of each circle (previous step) by the number of panels needed to make the airform. The number of panels is found by dividing the maximum width of your fabric in inches (your choice) into the circumference (inches) at the base. Generally, the more panels, the smoother the shape. For small domes (15' -20 ' ) use a panel width of between 3 or 4 feet at the base.
With the above information, draw a full size single gore on a long piece of butcher paper. Place this on top of a stack of Tyvek or polyethylene sheets (all of the gores you will need for the airform). Tack these down with small brads (right on the line if you intend to sew the gores together, 1 " out from the line if you intend to tape the gores together). Cut all the gores out all out at once with a sharp utility knife. Cut 1/4" out from the line if you are going to sew the gores together, on the line if you intend to tape the gores together. The nails should be randomly spaced (1/2" to 1-1/2" apart) if you elect to sew the gores together. The random spaced nail holes become a code to aid in registering adjacent gores in the sewing machine.
A 2 ' or 3 ' circular "eye" at the top will help the problem of so many gores converging at that point. Leave a little extra at the base for anchoring.
At any convenient scale, say 1 " = 1' draw a vertical building section through the apex. For example a hemispherical dome would be a semi-circle springing up from a horizontal base line.
On one side of the semi-circle (from the base to the apex), starting at the base and continuing up to the apex at the very top, make a dot on the curved line at every foot.
Strike lines parallel to the base through each of these dots and extend them horizontally through the entire building, or, alternately, to a vertical centerline passing through the apex (double this for the full width).
Each of these horizontal lines represents the edge view of a horizontal plane cut through the building at every foot along the edge line. It is a circle in plan view.
Find the circumference of each of these circles (3.14 16 X its diameter In inches).
To find the width of the gore at each foot along the gore pattern centerline divide the circumference of each circle (previous step) by the number of panels needed to make the airform. The number of panels is found by dividing the maximum width of your fabric in inches (your choice) into the circumference (inches) at the base. Generally, the more panels, the smoother the shape. For small domes (15' -20 ' ) use a panel width of between 3 or 4 feet at the base.
With the above information, draw a full size single gore on a long piece of butcher paper. Place this on top of a stack of Tyvek or polyethylene sheets (all of the gores you will need for the airform). Tack these down with small brads (right on the line if you intend to sew the gores together, 1 " out from the line if you intend to tape the gores together). Cut all the gores out all out at once with a sharp utility knife. Cut 1/4" out from the line if you are going to sew the gores together, on the line if you intend to tape the gores together. The nails should be randomly spaced (1/2" to 1-1/2" apart) if you elect to sew the gores together. The random spaced nail holes become a code to aid in registering adjacent gores in the sewing machine.
A 2 ' or 3 ' circular "eye" at the top will help the problem of so many gores converging at that point. Leave a little extra at the base for anchoring.
THE TAPING JIG
Here's an easy way of making airforms by using tape to join the gores together.
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At any convenient scale (say 1"=1') draw a vertical section through a drawing of a dome (that would be a straight floor line and a curved semicircle for a simple hemispherical dome). Draw one straight line from the apex of the dome at the top to the junction of the dome and floor on one side. Make a full size rigid frame of this "segment" with the curve being its top and the straight line being its base. This frame is surprisingly small (for a 20' diameter hemisphere it is less than 14 feet long and it will rise less than 3 feet). A 1" X 4" works for the straight base at the bottom and a long 4" wide wood trim piece works for the curve. Hold the curve in place using some vertical 1" X 4" studs of various lengths and spaced at random. Before the bender board is bent, while it is still flat on the ground, with a broad nib marker, use a tight cord to draw a straight centerline from one end to the other (the board may wander but you want this centerline straight). Construct the curved frame. Coat the top surface with Photomount or Spraymount spray adhesive. Let it dry. You are finished with the frame.
THE GORES:
Make a neat stack of all of the rectangular panels of Tyvek or other thin, strong fabric. Lay the gore pattern on the top. Using shingle nails, nail through the pattern and the entire stack every 2' or so and an inch or so outside of the pattern line. Cut through the pattern and all the panels right on the pattern line using a utility knife. .
I've done many airforms on the same piece of carpet for years without leaving any scars. You need a soft top surface like carpet to improve the cutting action of a thin sharp blade and you need wood underneath to nail into. Don't worry about ruining the carpet. Just don't use a too heavy touch.
Make "Tick marks" (little notches or marks) located at random every couple of feet along the cut gore edges to help align adjacent gore edges on the taping jig. Do this while they are still stacked after being cut from the rectangular stack of Tyvek panels. The tick marks will be used as a "code" and should be unique to each side.
Leave a little extra at the base (say 6") for anchoring the airform. Mark the "BASE" line on every gore.
TAPING:
Starting at one end of a gore, stick its edge down one side of this bender board line. Press an adjacent gore edge down on the other side(with this curved setup the gore edges will stay on the line and not wander away). Reverse every second gore so that the coded tick marks will be matched. Press a single long strip of package wrapping tape or duct tape over the seam. Peel off the now taped together gore panels and move to the next. Easy.
A 2 or 3 foot flat circular "eye" of Tyvek solves the problem of so many gores coming together at the apex. Tape this eye in place while the otherwise completed airhouse is draped over a small circular table.
Usually the more gores the smoother the inflated shape.
Refresh the adhesive from time to time.
----
At any convenient scale (say 1"=1') draw a vertical section through a drawing of a dome (that would be a straight floor line and a curved semicircle for a simple hemispherical dome). Draw one straight line from the apex of the dome at the top to the junction of the dome and floor on one side. Make a full size rigid frame of this "segment" with the curve being its top and the straight line being its base. This frame is surprisingly small (for a 20' diameter hemisphere it is less than 14 feet long and it will rise less than 3 feet). A 1" X 4" works for the straight base at the bottom and a long 4" wide wood trim piece works for the curve. Hold the curve in place using some vertical 1" X 4" studs of various lengths and spaced at random. Before the bender board is bent, while it is still flat on the ground, with a broad nib marker, use a tight cord to draw a straight centerline from one end to the other (the board may wander but you want this centerline straight). Construct the curved frame. Coat the top surface with Photomount or Spraymount spray adhesive. Let it dry. You are finished with the frame.
THE GORES:
Make a neat stack of all of the rectangular panels of Tyvek or other thin, strong fabric. Lay the gore pattern on the top. Using shingle nails, nail through the pattern and the entire stack every 2' or so and an inch or so outside of the pattern line. Cut through the pattern and all the panels right on the pattern line using a utility knife. .
I've done many airforms on the same piece of carpet for years without leaving any scars. You need a soft top surface like carpet to improve the cutting action of a thin sharp blade and you need wood underneath to nail into. Don't worry about ruining the carpet. Just don't use a too heavy touch.
Make "Tick marks" (little notches or marks) located at random every couple of feet along the cut gore edges to help align adjacent gore edges on the taping jig. Do this while they are still stacked after being cut from the rectangular stack of Tyvek panels. The tick marks will be used as a "code" and should be unique to each side.
Leave a little extra at the base (say 6") for anchoring the airform. Mark the "BASE" line on every gore.
TAPING:
Starting at one end of a gore, stick its edge down one side of this bender board line. Press an adjacent gore edge down on the other side(with this curved setup the gore edges will stay on the line and not wander away). Reverse every second gore so that the coded tick marks will be matched. Press a single long strip of package wrapping tape or duct tape over the seam. Peel off the now taped together gore panels and move to the next. Easy.
A 2 or 3 foot flat circular "eye" of Tyvek solves the problem of so many gores coming together at the apex. Tape this eye in place while the otherwise completed airhouse is draped over a small circular table.
Usually the more gores the smoother the inflated shape.
Refresh the adhesive from time to time.
STEVE'S COMMENTS
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Lloyd sent us a beautiful air form for a conference in Oregon at Nolan's place. My idea was to be mean to the airform and try to get a shell shape out of it-- by tieing ropes over it. Lloyd was a little horrified with the idea but This worked well. The inside surface was wrinkled but it was sea shell-like--much more interesting than a simple dome for my taste. I'd do this again. Especially with huge domes which are kinda boring inside.
We then tried to plaster the outside surface of the airform-- without much success. Spraying the inside, overhead has always seemed strange to me (dangerous/expensive/high tec). I'll be more excited about airforms as soon as you can spray the outside and build up the roof from the outside. Placing concrete overhead is complicated. More details can be found here about Thin Shell Construction. |
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