Materials for inflatable structure

Question

I want to make a sizeable inflatable structure about 15'x 15' with a height of around 15'. I want to extend my classroom's workspace during certain times on various days. I need some help with deciding on the material. It needs to be inexpensive but also durable. It would need to handle being outside for a few hours each day for about a month. I also need it not to have a bottom or floor. The shape of the structure could be similar to this:

I think it could be tied or snapped to anchors in the cement. I have read that people have used a 4-mill painter's tarp or Heavy Duty Poly Tarps. But maybe 6 mil Polyethylene Film, Plastic Sheeting, or Nylon Taslon TPU Coated Fabric would work. Do you guys have any suggestions?

Some more info: It will be outside in a patio area. My classroom has a garage door on one side that opens into a patio area flanked by pillars. The patio area in front of the garage doors is open to the sky. But on either side, the patio is covered by the second story of the building I am in. Imagine the space in front of my garage door as a large well. It is excellent for letting sunlight in, but we also get the rain and snow, which can be pretty hot in the summer. Sometimes this space is OK for my classes to utilize, but a lot of the time, it is a problematic space for us to work in. I thought a blow-up structure that could have some environmental controls would be fun and a bit magical. So this inflatable idea would hopefully solve the problem of my need to extend my classroom's workspace during certain times on various days without being completely at the mercy of the Texas weather. I have had inflatables be a project in my classes before, and we have made one about 20 feet square. Here are a few examples: Inflatables in Sculpture Class

Also here is a picture of the space where I am wanting to have an inflatable room - there is an inflatable sculpture that the students made that looks like a large white pillar.

Answer 1

If you just want to define some space, there are all kinds of options. You could inflate a large, light-weight weather baloon, or make the equivalent. You just need enough air pressure and volume on the inside to offset the weight of the material and any losses, and the material and seams need to be strong enough to not stretch or separate. From there, you start adding complications.

• Material and seam strength. Chances are, you won't have a blower that produces the precise amount of air needed to just perfectly inflate the room and keep it that way. Anything over that amount of air will stress the material and seams. Light-weight plastic film will be hard to seal without melting holes in it, and it will also stretch under pressure, eventually bursting. If you use plastic film, it generally needs to be thick and strong. Polyethylene sheeting will be hard to reliably join with adhesives; those seams are generally heat sealed. Vinyl sheeting can be heat sealed or joined with adhesives, but will have limited life in direct sunlight unless the material and any adhesives are designed for UV exposure.

  You could use Tyvek with adhesives or tape as long as you don't exceed the holding power of the adhesive (and the adhesive bond won't last forever). Tyvek also is not air-tight, so it only works with continuous inflation. Inflatable Tyvek structures are often used as the form for making sprayed foam or concrete domes.

  Fabric seams can be sewn, and there are various methods for making strong, long-lasting seams.

• Air losses. You can use almost any material if it has the right characteristics, but if the material or design has significant air leakage, the amount of air you need to pump in can get ridiculous. You could make the structure from an old parachute, especially if you treat it to seal the fabric better. You just need to pump in enough air to stay ahead of the leakage.

  No bottom/floor? Add a sealing skirt around the bottom edge, like used on a hover craft (not air-tight, but reduces the losses). Need for people to enter and exit? Add an air lock, like shown in your picture, or form the support structure from sealed inflatable tubes and then enclose it to add the room shell.

• Weather/environment. The outside environment adds many problems and considerations. Wind can add huge stresses. The structure shape can help (e.g., a dome will reduce the wind effect). Wind will deform the shape unless it is under substantial pressure (which means a lot of internal pressure, and strong material and seams). It will put tremendous strain on whatever is anchoring it in place. Sunlight will deteriorate many materials. It will soften plastic film. It will create a greenhouse inside, which can get very hot. You can counter this by using reflective film, like space blankets, to make or cover the roof. Precipitation adds a surprising amount of weight to the structure, which you would need to offset with increased air pressure.

• People inside. Using the structure as a room that people will occupy adds another whole dimension of considerations. It's possible to use what's basically a sealed shell that's inflated by internal pressure. But people add health and safety issues. You need proper replacement of the internal air for breathing, issues of volatile compounds in some plastics and adhesives that people will be breathing for an extended period, flamability risks, temperature and humidity need to be maintained at healthy levels, prolonged exposure to the blower noise can harm people's hearing, etc. There may be local codes or ordinances covering use of such rooms, and the inherent risks can create liability.

  This kind of structure becomes more practical for people if it doesn't need to be a sealed shell. You can use a supporting structure of inflated, sealed tubes. The structure can be a skeleton to which you add an appropriate shell to create the walls and ceiling (generally requires high air pressure for the supports, or very large supports that eat into the available space). Another way to do this is to make the walls and ceiling from such tubes. This is normally done with a double wall that is connected at intervals so the layers stay parallel and a uniform thickness. The wall is inflated, which gives it some rigidity.

• Conditioned space. Normal buildings are pretty well sealed and insulated. They are heated and cooled by recirculating the internal air, which is continuously and incrementally conditioned. Imagine trying to heat or cool a building with all the doors and windows open to the outside. Inflatable buildings that aren't sealed and insulated have huge losses like that. Even sealed structures that are a single wall of plastic film or coated fabric have very little insulation value.

  Structures with trapped, still air between double walls can provide insulation. But if the support structure is sealed tubes that are kept inflated by constantly-flowing air, the support structure will function as a heat exchanger, moving the internal room temperature toward that of whatever the air source is.

  Using portable air conditioning units as the inflation source for such a structure isn't likely to work; they probably won't put out enough air flow or air pressure to keep the room firmly inflated. The "practical" solution is a double-walled structure, with walls made of strong, well-sealed material with almost no air leakage. Inflating the walls provides the structure. Once inflated, you only need to periodically top off the pressure.

  You can use a portable heater or air conditioner to condition the air. In the winter, you may not need to add much heat if the room is insulated and occupied by people because people give off a lot of heat. But be careful of the type and placement of any heater you put inside because you don't want it to heat up the wall or ceiling material.

  You could theoretically make such a structure in this size from scratch, but it would be a huge amount of work and pains-taking testing. One way to make the job more manageable would be to make it from pre-made modules. The modules would be strong, air-tight, inflatable rectangles that you glue or tape together. Examples would be air mattresses or inflatable "raft" pool floats.

You mention using the structure a few hours per day. One thing to be aware of is that setup can take some time. Inflating a sealed sculpture can be done pretty fast. But the kind of structure that will be suitable for human occupancy and conditioned air could take considerable time to set up and inflate. It probably isn't something that would be practical to do each day for a few hours of use.

Answer 2

With a bit of additional kit, I think this inflatable tent listed as being for advertising purposes could complete your objective.

There are a number of inflatable designs with quite a wide range of dimensions, some with floors, which could be excised if other means of restricting the tubes are created.

Image from linked site.

The dimensions of this particular unit show as 16.4 feet in diameter, which would imply about half that height, which also would require some modification/additional kit to get the rather substantial height in your question.

I found a 20 person tent that is also an inflatable, but it has a floor that might not be easily removed and is certainly not an inexpensive purchase. Pricing is subjective, however and if not stated in the post, is open to interpretation.

You may be able to reach your 15 foot parameter by using a set of inflatable arches found at the bottom of the linked page, and creating your own covering using generic plastic sheeting or tarpaulins. No pricing is apparent, previous reference regarding inexpensive applies. Image from linked site.