Odd shaped roofing waterproofing challenge - Please help


Hello everyone!

I have a little “shed” on my property that I would like to use as a gym. It’s got a metal half cylinder roof and concrete blocks for a facade and also under where the “half cylinder” rests. My goal is to waterproof it entirely so that the equipment doesnt get damaged and obviously so i dont get puddles of water pooling on the floor.

As you can see from the picture its a little challenging. I thought that I could use peel and seal to cover the entire roof starting from the bottom on either side and working my way up so the overlap is above the p&s below it (check side_profile pic)

I do not know what to do about the side seam where the concrete block meets the metal roof. I researched foam and they say closed cell foam is waterproof so maybe it could work? ie: spray the side seams with closed cell foam then put the peal and seal over that then maybe caulk where the p&s hits the wall. I have no idea. This is why im coming to you guys for advice.

What do you think, how can I best waterproof this thing without spending too much (under $1000 budget)?

Thanks in advance.




How big is it? What’s the framing like? Depending on the size, If you wouldn’t loose too much headroom I would reframe a more traditional roof on it. That metal looks plenty rotten, I wouldn’t trust it with just peel and stick. Even with primer


2 different coatings and the fabric.

Impossible to do correctly without someone very, very experienced with it.
They will charge you at least three times your budget
And you havent even paid for the material yet.


A way to do it in my mind would be a flashing, depending on the concrete wall.

You would have to take Ice and Water shield and run it up the wall and onto the metal. The whole seam. Then you would have to do the flashing and counter flashing. This would be the tricky part. You would need someone that is good with shapes. You could get artistic with it also. Sand blast the top of that thing, prime and paint it, then do the flashing. You could paint the metal or leave it shiny. I’d love to tackle it for $1000 but not possible right now.

Or, you could just buy some ice and water shield from a roofing supply company in your local area. Clean off some of the rust and slap it up there. Should really consider painting it though. You should be able to rent a sandblaster, buy what you need, even spray paint or whatever you want to use. One roll of ice and water shield goes 66’ when it is three foot wide. You could cut that in half longways and have more than enough to do that whole thing. One roll costs $50-$75.

Where are you located?



You could probably coat it with silicon. You will need to talk directly to product rep for preparation for specific product.


I was going to say the same thing. I would use a phosphorous acid converter. I use GEM rust killer. You can pump up sprayer it on. Then use Gaco liquid tape to coat the wall to the metal. Use it to coat any areas of concern, like seams. Coat the whole thing with Gaco Roof. I would advise 2 coats. One Coat is iffy.


Would really clean it up too.


I can only post one pic at a time, but ill post more to better show what I described.


The inside is nearly ready but i havent moved anything in there yet as its still leaking… in the pic you can see there was a latch door that corresponds to the patch you see from the outside of the “shed” in the other pics… I removed them (one on other side too) as they were leaking and were not flush with the rest of the metal roof. the idea was to create a flat “smooth” surface on which to apply the peel and seal (original plan)


I’m in Homestead, FL so lots of rain, lots of sun , and hurricane winds every 4-5 years.

From the pictures you can kind of extrapolate the size


When the welder came to do the patch work he was able to clean off to bare metal with a grinder pretty easily so while it looks like its in bad shape because of all the rust, it is superficial surface rust were the paint chipped.

It appears as if the previous owner used some kind of tar like substance where the wall meets the metal. Its black, and for the most part it seems to have held up well. from the inside at the apex of the cylinder on the back side it drips down the wall.

i calculated about $800 worth of peel and seal but no one here has mentioned it, so its probably not a good idea (remember im a complete noobie).

Thank you for all of the ideas.


here is a before photo, i had already removed 1/2 the stuff left behind…


A bit of history on this. From what i was told the guy that lived on this land before me worked at Turkey Point nuclear power plant and this was housing for some type of generator. He took it home and made something with it after they decommissioned it.

Im not sure if thats true or not but its a cool background if true.


I watched a YT video on the ice and water shield and it appears as if they nail it down. How could you use that product on a metal surface?


Not too big … no more than 250sq ft on the inside and its almost a perfect square


From the feedback everyone seems to recommend rust removal and or sandblasting.

I got a quote on sandblasting and it was way too expensive, around 3 large way more than i am willing to invest on this.

i was hoping to just go over the rust with something, and pray it lasts me at least 5-10 years.


Do you have a product name for this silicon i can use on the side?


Gaco roof is the most popular, several other brands out there, mule hide, Palmer, Henry.

With the slope that steep and it being metal, and Florida heat, it is going to be hard to use ice shield or a rolled flat roof product without pinning it in place. Over time any rolled asphault based product is going to want to say down as it hears up over time.

You could look into doing it with one sheet of tpo or epdm up and over, but with the round shape there is going to be a lot of flashing work at the walls and then alot of counter flashing.

I am normally not the first guy to say throw silicone on something, but in your situation I think it would be your best bet. I would go to your local roofing supply distributor, see what they sell and ask them to get you in contact with the local rep. Silicone is fairly new in the roofing world, in my area there are plenty of reps around looking to promote their products and are more than willing to talk and come out in person and look at jobs before hand.


It seems like polyurea would be perfect for this application.