The best way to put a AC condenser on a flat roof?


#21

[quote=“garya505”]What would be the best sealant to use under this type of curb?
-Neoprene type such as Black Jack 1010
-Ruberized asphalt type such as Henry 906
-Polyurethane type such as Loctite PL

With the attached cant strip, these are going to have a sealing area all around the perimeter of approximately 3" to 6" wide. Are there any curing issues with any of these flashing cement types, considering a sealing area this wide?[/quote]

There shouldn’t be any ‘sealing area’. The roof will come up tot he top, and the lid covers that. BTW, the lid can be 2" wider all the way around to make running the roof up and self sealing much easier.


#22

[quote=“tinner666”]

[quote=“garya505”]What would be the best sealant to use under this type of curb?
-Neoprene type such as Black Jack 1010
-Ruberized asphalt type such as Henry 906
-Polyurethane type such as Loctite PL

With the attached cant strip, these are going to have a sealing area all around the perimeter of approximately 3" to 6" wide. Are there any curing issues with any of these flashing cement types, considering a sealing area this wide?[/quote]

There shouldn’t be any ‘sealing area’. The roof will come up tot he top, and the lid covers that. BTW, the lid can be 2" wider all the way around to make running the roof up and self sealing much easier.[/quote]

What I meant was, what should I use to stick it to the roof so it doesn’t move around.

I’m getting the cap made from 18ga sheet metal. With a 2" wider cap will the edges be subject to bending from careless workers, etc.? I don’t have any experience with 18ga so I don’t know how rigid it is (or isn’t).


#23

I forget what your roof deck is. Steel or wood, screw it down. 18 ga. is pretty strong. There shouldn’t be any problem. You can put ‘Not a Step’ signs on too.


#24

It’s just wood with what appears to be rolled roofing, maybe modified bitumen from what I’ve learned here.


#25

Just run some 3" or whatever is appropiate sized screws through there. No need for sealant, but you can use it if you want. BJ Neoprene is good. If water gets through the roof material to the sealant, you’ll know it.


#26

There is no penetration through the roof, other than the bolts/screws used to hold it down. So, does the roofing under the curb need to be removed? What difference does it make, other than the thickness of the roofing material?


#27

“What difference does it make, other than the thickness of the roofing material?”

I don’t know the exact composition of your roof or underlay. I prefer to attach straight to the deck. It’s the preferred method.
It’s not always feasible, and not always the best option in every situation.
Your AC will compress the roof material some. How much depends on many factors; weight, underlay material, etc. The question cannot be answered from here. It could range from 1/32" to ???


#28

[quote=“tinner666”]“What difference does it make, other than the thickness of the roofing material?”

I don’t know the exact composition of your roof or underlay. I prefer to attach straight to the deck. It’s the preferred method.
It’s not always feasible, and not always the best option in every situation.
Your AC will compress the roof material some. How much depends on many factors; weight, underlay material, etc. The question cannot be answered from here. It could range from 1/32" to ???[/quote]

From the cross-section that I’ve seen, it’s about 1/8" roofing over what looks like 7/16 plywood sheathing. I think it’s what you call a modified bitumen roof.


#29

Then I suspect it only has the potential to sag 1/16" then. I wouldn’t worry about it one way or the other then.


#30

Was it torched directly to the plywood? 1/8" sounds like EPDM to me. I thought Mod-Bit APP was 1/4".


#31

I think it’s definitely not EPDM. Looks like some kind of black asphalt stuff, with granular stone on top. I saw some rolls of APP modified bitumen at HD that looked somewhat like it. The black stuff seems to be stuck to the plywood pretty good. You can see the thickness in the pic.

[attachment=0]P1090316a.JPG[/attachment]


#32

OK. Compression won’t be an issue. Just set it where you want it, screw it down and roof it.


#33

Hey, thanks for the help. I might have some minor repairs to do on the roof, so I can get a roofer to do the flashing and repairs at the same time. It’s about 9 years old so I figure if I maintain it I can squeeze a few more years out of it before reroofing.

Does that pic look like modified bitumen to you?


#34

"Does that pic look like modified bitumen to you?"
I honestly can’t tell. Lack of flat roof practice. I left commercial 20+ years ago for slate and metal so I’m shaky on some ID’s and some details.


#35

OK, the base is installed. I’m looking for a simple way to tie down the AC unit, without penetrating the metal cap on the base. I thought of running a couple of eye bolts through the sides of the base, just below the edge of the lip on the cover. Then I could use some steel cable that would run through the eyebolts and the base of the AC unit. Got any better ideas?


#36

I was also thinking of foaming the dead space inside of the condenser base to reduce any vibration noise. Any thoughts?


#37

On second thought I think I’ll just fill it with some left-over insulation I have. In case there is any noise that should dampen it.


#38

How’s this look? Note that I don’t have the supporting blocks for the copper lines in place (2nd photo). And, notice the Alumi-flash portal I installed. BTW, I bent and routed the copper lines myself too. :slight_smile: [attachment=1]P1090535a.JPG[/attachment] [attachment=0]P1090537a.JPG[/attachment]

ETA: Oh, and it’s bolted to the roof with six 1/4" x 5" lag bolts. The length of the bolt was selected to penetrate 1.5" into the roof trusses. In other words, it ain’t movin’. I made the cant strips by cutting a 2x2 at a diagonal, the long way. Temporary protection was done with Henry 209 elastomeric mastic with embedded mesh. The next time I have the roof repaired or redone, I’ll have them flash it in properly with roofing material.

I used Black Neoprene flashing cement on the alumi-flash portal in the second photo. It probably doesn’t need to be flashed with roofing material. That BJ Neoprene cures fast and seems really tough. It is pricey though!


#41

Nice. It was a few years ago that I did mine. I ended up building a roof jack and flashed it into the roofing. Your Platform Pro would have been much easier.