it depends on the spacing used between the glass. there are vinyl sweeps that slide onto the edge of the glass similar to the one that should have been used along the bottom and actually top. problem with these are that they take away from the 'frameless' look even thought they are clear plastic. how long has it been since you had this installed? Here is a link that might be useful: vinyl sweep

I'm not an expert in transoms or steam shower design, but I'm surprised nobody has yet said why they were invented, get installed, and are used. 1/ Steam machines make steam. More and more of it. Without new steam, the experience of a steam shower can be less and less enjoyable. New steam is needed. It actually puts pressure on the walls, and in 24hour commercial steam showers this is a big thing. But, even at home, where does all the water vapor go? It doesn't all become liquid (condensation) and go into the drain. 2/ :: Plan where it will go, otherwise it will go places you don't want it to go. A transom is a safety valve putting your excess steam into the bathroom, from where the fan exhausts it. 3/ :: Otherwise steam seeps into everything. Wall-ceiling junctions. Light fixtures. Into the attic insulation. Water vapor can penetrate anything, because it has time on its side, and the world's best solvent: H2O molecules. The opposite approach is "If you only use the steam shower for a short time and not often, who cares?" Anyone want to defend that point of view? I think there is no point building something that you "really ought not to let run". Some future user might want long steam showers, or frequent steam showers. Without a transom, you are guaranteeing that your escape route for water vapor will be confused, since it's unplanned, uncoordinated and unwanted, and your result will eventually lead to problems. As far as I know. Anyone reading this thread so far would be well advised to look more into it instead of concluding that transoms are just for fun. Many homeowners don't care much about codes or practices and will allow anyone to build anything for them. After that, it may or may not work as expected, and ultimately the homeowner may or may not be satisfied. This applied to all fields of construction. My writing this out is not to say that anyone here has been intending to do the wrong thing deliberately. Hth

You can use a u-channel and there are several really wonderful examples of showers that have been installed with them. TreasureTheDay's stands out as a recent example. But you can also use clips and it will be just fine. We installed a steam shower about two months ago with a set up very similar to yours (fan outside) and used clips with silicone sealing the space between the glass and solid surface. Though it's been hot, we've used the steam shower at least once a week -- it's great for aching muscles after a day of gardening! Your glass installer is quite right that no residential steam shower enclosure is perfectly steam-tight. But even with our transom, we have minimal leakage. It is not a problem. It's tough to get far enough back to get a picture + glare from lights, but here's ours. From Bathroom

I have glass tiles but I guess mine are different. But I will say this if you get 10 glass door companies out there you will get 10 opinions on what needs to happen. The people that don't bring levels and such get rid of them first. They wanted to put support rods across the top of mine and drill into my floor. Here is how mine is constructed maybe you can tweak it to fit your needs. I have a 28" wide x 80" tall 3/8" thick door that has 45 deg hinges that swings off of a 1/2" thick piece of glass that goes from floor to ceiling. There are 2 clips on the wall and one at the top where this glass goes to the ceiling. This holds the panel steady. It is just siliconed at the wall and bottom, no drilling into floor. The other fixed panel is 28" wide x 80" tall 3/8" thick and has only one small attachment at the top corner the rest is siliconed in. It works beautifully and you see the true beauty of the glass not a bunch of hardware and head rails. My Glass tiles are bullet proof as it is glass laminated onto porcelain and it is really tough to drill through but I don't think they should have a problem using the correct drill bit and possibly keeping it wet while drilling with acetone or water to keep it cool. This company might have had problems before and they are now nervous with the situation. I suggest that you keep getting quotes. It's a pain and slows the process but in the end positive results.