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Discussion Starter · #1 ·
I am installing a TPO roof on a relatively small project (7 squares) and could use some help. I have decided to use Mule-Hide/Carslislie TPO .60 on my flat roof using a fully adhered system. We are planning on a total tear-off of two layers of asphalt rolled roofing down to what I assume is plywood decking.

My question is regarding the decking. I'm guessing some of the decking is damaged, and we plan on replacing those sheets so that we have a clean even surface to adhere to. Or should I go over it with another type of decking material, OSB, densdeck, etc.? Or is it better to put in 2" ISO board? Would I then need to put a decking board over the ISO? I would prefer to keep this simple and to fix or recover the existing decking without adding cost/labor of more insulation. I'm a bit frustrated looking at this as I've gotten a few conflicting answers and could use a bit of helpful direction.

Note: There is already sufficient insulation in the ceiling.

Question number 2. In order that the job get done right I had planned on hiring a full time roofer to do the hand welding. I think we'd do fine but I want a guy that can get it right. Can a roofer that knows his hand welding (I have a Sievert hand held) get his welding close to that of a robotic seam? Hopefully this isn't triggering some age old debate. Thanks!
 

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Assuming the substrate is plywood, I would go back with CDX plywood, not less than a 4 ply or equal thickness. I dislike OSB.

What would be the purpose of placing a 2" ISO of rotten decking? Who ever told you that was ok, slap in the face and spit on them.

Put a cover board 1/2" HD ISO, Dens Deck or put a 1" regular ISO, and you'll be fine with a good substrate. What is the use of the roof, that would somewhat determine the type of cover board to be used.

Are you adhering or fastening your cover board? Also the use of the roof would determine how the board is to be secured.

No age old debate, on any roof less than 20 squares we hand weld the entire thing. It's just not worth luggin a robot up on the roof. Plus you can't use the robot for everything, like walls for example, so a good roofer with welding experience will do as well, actually possibly better, by hand. There is also more room for error but I have yet to have a cold weld in the last 5 or 6 years <knocks on wood>. Hand welding takes much longer, but the roof is only 7 squares so actually there is no room for a robot IMO. I wouldn't even get it out of the garage for a job this small.
 

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Discussion Starter · #3 ·
Grumpy-

I really appreciate your taking the time to help me out. Thanks for the clarification on hand welding...I can stop asking strangers at the grocery if they have a welding robot.

CDX, no less than 4 ply got it...check. What I didn't quite understand from your post was the minimum I can do while still doing a professional job. Are you saying to put the CDX over the existing ply and then put 1/2 HD ISO, Densdeck or 1" ISO on top of the CDX? I take it your suggesting a cover board means I can't adhere to the CDX (sorry if this is a dumb question). I would most likely mechanically fasten the cover board.

As for use of the roof...really none, other than the occasional maintenance check. The roof will eventually have solar panels put on it which will go on an aluminum frame and that frame will need to be attached. Thanks.
 

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Step 1) Replace damaged decking with equal thickness. Cut out the old rotten, install the new fresh.

Step 2) Over entire substrate Install cover board of not less than 1/2" thickness. 1" ISO would be fine if it's not a trafficed roof.

Some would argue that you can use CDX as a cover board but I would not. Infact some would argue to save a step and overlay all the existing with CDX and then this would kill two boards with one stone of fixing your substrate and functioning as your cover board, but again I would not. And if if I were to do this, I would still cut out and repair anything rotten. I just can't bring myself to cover up rotten wood.
 

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Discussion Starter · #5 ·
Grumpy - Thanks! Got it....all rotten decking and anything else to be replaced. Then come back with cover board. Probably use your suggestion of 1" ISO since there won't be much traffic....why the ISO and does it need to be HD (I assume this is high density?). Is this for the insulating factor and uniformity for adhering the TPO? I guess I'm saying why not use a cover board that would stand up to more traffic...is there another choice? Really appreciate your help.
 

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1" ISO because I don't think they sell 1/2" ISO, you said you didn't want R value.

High Density (HD) if you were going to walk on it regularly or place flower pots, deck etc... Dens Deck or Secure rock would be the ultimate high density. However if you were going to have a traffic rated roof, I would adhere the cover board with a low rise foam like Dash Dual Cartridge or Spot Shot, in lieu of fasteners. http://www.reliableamerican.us/articles/chicago_roof_decks-what_you_need_to_know.html
 

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Everyone has their own Ideas But Grumpy is right on...

Although Personally I would Use Dens deck. if there is any chance of Hail, it will make the membrane MUCH more resistant. Iso HD doesnt protect against hail. I could also Argue that with Dens Deck Adds fire resistance to the roof where Iso Does not. Might want to check your local code.

What is it about OSB that we hate? I hate it too Grump... I think for me it is cause once it gets wet you cant trust it.. it swells and never goes back. Its not as strong... CDX is the way to go. if you end up gluing to the wood make sure the "C side" is facing up. but the right thing to do is a cover board.
 

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I be the thorn in the side.

1.) Fix the decking.
2.) Add 1/2 plywood or OSB. Glue directly to that, Make sure to caulk all joints and screw heads, Yes screw the OSB/plywood down.

I hate OSB I really do BUT it's cheap.

Gluing to the wood substrate will give you the hail resistance and a good surface to walk on.

Caulking the edges of the plywood helps avoid splinters, caulking the screw heads helps ensure they won't back out.

What are the dimensions of the roof? It's likely you can do it in one sheet with out having to weld a seem. What are you doing for edge details, ect?



It's Friday I feel like being a bit ornery. Plus there is a new puppy in the house and I didn't get much sleep.
 

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I hate OSB because it swells like Pie said. GT, OSB isn't all that much cheaper than CDX, last time I even dared price OSB it was a couple bucks per sheet less than CDX and I remember saying to msyelf, why would anyone use this cheap crap for only a couple bucks per board difference?

Why go to all that extra work caulking when you could do an iso cover board?

Oh, A grade plywood is a requirement for some PVC deck membranes as a cover board. They require you to gouge the joints, fill with mastic and cover screw heads with mastic.

HD fiberboard is also an option, but not one I would suggest under 60 mil. If it were 45 mil I would be suggesting the fiberboard.
 

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you know, Reinforced EPDM may be a good choice.. No Seams! I think I can buy a 20 foot sheet locally to whatever length I want...

THere are a million Ideas!!! All of these are good from good roofers. Whats good But cheapest? Funny thing is, people may have a different Idea about that. Im going to agree with Grump this time. Hes already in a Bad mood, I saw him tear apart some storm chaser in the introduction catagory a few minutes ago! :laughing:
 

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Discussion Starter · #12 · (Edited)
I went to the roofing supply house yesterday and picked up the bulk of the materials for the TPO 7 square job (32' x 22' w/ 2' parapets at the perimeter). I plan on doing the tear off when I get a sufficient weather window. Following Grumpy's advice, I ordered coated 1/2" Densdeck which I will lay after fixing any damaged, rotted decking with CDX. I am skipping putting down additional insulation as the cost has come in higher than anticipated and the house has always felt well insulated.

When I repair any decking sheets I will replace them with CDX, should I nail or screw this down? Any caulking around joints or over screw heads, etc? Same with the Densdeck...I know to stagger the joints relative to the CDX. How should it be fastened, caulked at seams, screw heads, etc. (I did get both barbed plates and 3" washers from the roofing supply co.).

Then we'll come back and begin our adhered TPO. At the parapet walls, as long as the plywood is in good shape should I be able to adhere directly to this plywood without putting on an additional cover board. I'm not sure I could get a cover board of any thickness to fit under the sheet metal caps at the top of the parapet. We'll terminate the run of TPO by going over the top of the parapet wall and affixing the TPO at some point with term bar with a mastic behind the TPO.

While it's raining, we'll be spending our afternoons practicing seam welding. If I feel like we can't get it right...I'll hire an experienced guy to come in and do it. I have to say..you guys deserve all the money you earn, more skills and work than first meets the eye.

With the money I save, I plan on renting the house and taking my girlfriend to the South Pacific/Indonesia to feral surf locales. I have the kind of girlfriend that actually wants to do this. It won't be high living, mostly in a tent...but it'll provide some adventure. Roofing and tent living...don't know how I chose this life. I've ridden by bicycle to the tip of South America (from CO) and spent a year living out of a camper surfing Mexico mainland thus far. Thanks again, for the help.
 

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If you're placing densdeck over the plywood substrate, you can go ahead and nail it down. No need for the caulking on the plywood seams and screw heads previously mentioned. That was IF you were adhering directly to the plywood.

Barbed plates are for seams, not for the densdeck. The 3" plates is what you will use to put down the dens deck. I would install not less than 5 screws in a 4x8, but normally we will install at least 6 sometimes 8 screws per 4x8.

If you are going over the top of the parapet wall, a termination bar is acceptable on the outside wall, however why not just install a coping? I am assuming you will remove the existing coping before wrapping the wall. Is there an existing coping? Normally we remove the coping, wrap the wall and then reinstall or install new coping. Therefore a term bar isn't needed.



I personally wouldn't ride a bike through Central and South America without a fully automatic rifle and reliable sidearm.
 

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Discussion Starter · #15 ·
I'll have to work on my target practice from my bicycle seat, paying particular attention to getting off a good shot with my rifle, hands-free. I can't speak for Chicago but cycling thru South America was nearly problem free. You don't really become much of a target until you have something of value...when you've got your King Ranch F350 w/ camper....keep your sidearm handy. Bicycle, not so much.

There is coping, which I assume are metal flashing/caps. I will wrap the walls as you suggest.. My thought would be to adhere the TPO up the wall, over the top, and down a short amount on the outside wall before replacing the coping. Sounds like we will omit the term bar and that this is enough. No need for mastic, etc?

I woke up this morning wondering about the Densdeck. I'm sure you'll tell me Densdeck is fine but the idea of a gypsum product up on the roof doesn't sound right. The roofing supply guys were emphatic that the Densdeck not receive any moisture when I transport it to the site. Putting a product that can't handle any moisture whatsover doesn't sound like what I'm looking for in a roofing product. I think I'd feel better about 1/2" ISO. Just have to find someone in the Denver area that carries 1/2 HD ISO, my roofing supply store said they didn't. Any brand recommendations? Regardless of whether I put down the Densdeck or the ISO, do the plates and screws need any treatment to keep them from backing out under the TPO?

I also have a second question regarding crickets. I plan to put in some tapered ISO or EPS to make positive drainage to the scuppers. There will be 3 triangular crickets, one in each corner leading to the corresponding scupper and a third cricket triangle in between the scuppers. How do I go about laying the TPO over the crickets so that it lays flat. I'm know we'll have to seam it, just not sure where. Again, thanks to everyone who has pitched in to help me get this project done. Here is a fairly lame diagram of my roof, the drains are marked but not labeled:
 

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Not reason to adhere the outerwall, just leave 2" at least loose and hanging over the outer wall, the coping should cover that right up. No need for water block/cutoff in this detail.

HD ISOis special order at all my suppliers. I agree with your concerns, that's one of the same things you will note we said about OSB. We did a job with secure rock, and we taped the seams and applied elastomeric. Well short story, the elastomeric had failed and in a couple spots after a couple years, the secure rock was no longer existent. We chose secure rock over dens deck because they claimed it could take water indefenite. Even showed us a little sample soaking in water, probably put it in the water that day. I can attest secure rock won't take water indefinite.

IF the roof doesn't leak you will be fine. But EVERY roof will leak eventually. The only difference between a good and bad roofer is how long it takes before the leaking happens.

On such a small area the tpo may lay flat enough on it's own that it won't wrinkle at the tapered, but relief cuts may also be necessary. You may need to cut triangles the shape of your taper and seam it at the ridge and valley.
 

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DensDeck is the way to go. It will take on very little water, will not change dimensionally, and will maintain most of its compressive strength. You will need to use DensDeck "Prime" if you are adhering or it soaks up a ton of Glue.
In Denver, where I am, you want a real cover board. Dens Deck is the only way to go. We get hail every year. In fact I would recommend EPDM rather than TPO. But TPO isn’t too bad for hail resistance. Plus you may want to make a claim one day.
Grump, When a secure rock distributor came into our office and showed us that sample in water we didn’t believe it so we did our own with dens deck and secure rock. After 2 weeks the secure rock was soft and had turned black with mold. The dens deck was a little heavier but still intact. Secure Rock is preferred by most roofers because it’s easier to handle and Cut. But really I want the best product.
HD Iso I have also seen destroyed by hail, although it would probably be fine directly over Plywood....
 

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Just laying the TPO out flat should be fine, that is unless your crickets are more then the standard 1/2" per foot even if it is more the TPO will normally lay flat unless it's an extreme slope.

If your using EPS crickets make sure you put the densdeck or what ever coverboard your using on top. Glue and EPS don't mix.
 

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Discussion Starter · #20 ·
Thanks again for your insightful comments and help. I haven't posted to this thread as I've been experiencing the great joy that comes with doing a tear-off (insert sarcasm here). I think I put in 60 hours of work in the last 6 days. We pulled off 2 layers of rolled roofing and found the decking was in OK shape..but not so great in some areas...after fooling with it I figured I'd be a lot happier if I just replaced all the decking w 1/2" inch CDX spaced with sheathing clips. So I did that. We put the 2 roof tear-off in one of the green canvas "Bagsters" (green plastic bags sized 4' x 8' x 30") and they were able to crane the entire thing (over 3000 lbs) into their truck for $65....plus $30 for the bag. I was psyched to see the roof go and figured it was a fricking miracle they could lift that weight in a plastic bag. The roofing supply co. ordered in 5/8" Densdeck primed on accident but agreed to charge me for the 1/2" I originally ordered...so that's the next step. I found the screw pattern/qty. from Densdeck and per Grumpy I'll use 8 fasteners per board. The parapet walls also had crappy fiberboard that I could almost put my finger thru...so we'll be replacing all that with CDX 1/2" as well. I'm sure we could get away with OSB...but again...just wanna do it right. Must be getting older. Pie in the Sky...thanks for your comments on Densdeck...we did some soaking experiments of our own and it looks like the gypsum eventually soaked up water but retained more breaking strength than I thought it would. Obviously my kitchen water glass tests are far from scientific. The roofing supply company also beat up the corners on some of the Densdeck...any suggestions on what to fill the voids with so the TPO will lay flat and adhere? I'll post some photos before long.
 
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