Flat roof to flat roof tie-in detail

Hello, bit of an interesting post for my first post.....

I need some assistance regarding tie-in details. We are reroofing a flat roof. Multi-unit dwelling, one continuous flat roof, no breaks, expansion joints, walls, nothing. The unit owner wants a 3 layer Polyglass peel and stick system. Existing is a 3 or 4 ply hot mop BUR. I'm struggling with tie-in details on the permit. Has anyone done such a roof? There will be only one tie in, she is the end unit, but I want to get the detail drawing right so I don't have to submit the permit more than once...

This is S. Florida, PBC, non HVHZ zone.

Hello, bit of an interesting post for my first post.....

I need some assistance regarding tie-in details. We are reroofing a flat roof. Multi-unit dwelling, one continuous flat roof, no breaks, expansion joints, walls, nothing. The unit owner wants a 3 layer Polyglass peel and stick system. Existing is a 3 or 4 ply hot mop BUR. I'm struggling with tie-in details on the permit. Has anyone done such a roof? There will be only one tie in, she is the end unit, but I want to get the detail drawing right so I don't have to submit the permit more than once...

This is S. Florida, PBC, non HVHZ zone.

-roofer83

Egg that last post, as usual, is excellent.

Vaa, I assumed OP was in the US. Shouldn't assume anything, but it was a hurried post. The key, as egg described, is a flush roof. Substitute a layer of 1/2" or 3 layers of 2x4, etc. As needed to maintain a flush roof level.

The expansion joint issue only presents itself here because none of us have a really clear picture of the site. We do give it our best anyway, though, don't we.

You can still get down to the deck as Mr. Hicks describes (and I kind of suspect he's assuming the two by six is taking the place of a small strip of inch and a half foam which said condition would not create an expansion joint per se as the top would remain level...but again, we don't really know the site) and I highly second his opinion. Very highly.

It's funny; when I'm doing them myself, for myself, even just a skylight retrofit, I always get down to the deck and isolate my work at deck level from existing. Then I sit at the computer and even after all these years, my mind skips right over that little detail. Oh yeah, when you're there, your body knowledge takes over. You never fail to get it because as Woody says, it's going to be presumed that you own any leak showing up anywhere near that zone and yes you absolutely do know that. On site you can feel it. Your deck level connection is your line in the sand.

That magic moment when you listen to the speculation about how the leak is occurring and then you go, "Yes, I see what you're saying and that is a very likely explanation except for the fact that we're sealed to the deck."

I was asked to do a Hail Mary repair around a wood shove jack one winter. Turns out there were three tar and gravel roofs on this thing, an original and two overlays. There was water between every layer. Stair-stepped repair with a lot of careful prep: Sealed to the deck, sealed to roof one, sealed to roof two, and sealed to roof three. It worked just fine and we tore it all off the following summer at which time we gave her a straight-up roof, the first one she'd had in decades. The problem is when you win at this stuff, you get asked to do it again. Don't know about anyone else here, but I don't really enjoy that kind of repair work.

It's fun to wear the white hat but then you go and get mastic all over it.

You need a very basic tie-in - Just make sure your detail is accepted by the manufacture.

FWIW, I like to get down to the deck and eliminate all possibility of water travelling between the two systems. Her leaks will remain hers, and your's stay your's.

Cut splice to the deck about 6" wide. Lay first layer down into the cut, set in a full bed of the appropriate sealant, foaming deck flutes if it's cross direction on metal deck. Lay a 2x6 over the membrane and fasten to the deck. Fold membrane back over the 2x6 and seal to itself on your side. Second layer gets extra attention to the bond above the 2x6 to assure no interply water travel between roofs, and sealed well to the adjacent roof. Third layer extends over them all, past the second, and is sealed well to the old, and topped with a good dose of 3 or 5 course cement and mesh.

Appropriate preparation of the old roof is assumed.

It's an expensive, but effective permanent tie.

call your manuf rep.......

Mike, why don't you re-post that link from long ago showing you doing your stellar de-granule prep work. I would still use some modified asphalt sealant under the last grab of the splice, with some bleed-out and spreading of new granules when still fresh. Most self-adhered sheets remain a little sketchy at the very outer edge imho. When the mastic flashes off it pretty much locks anything from peeling or curling.

Thank you, good information, I appreciate it.

egg Said: Ok. Couple more comments then.

I like to get my splice sheets both under and over the material Im splicing to. Just the same, in my opinion, as perimeter metal detailing. I mean the concept is the same. I wouldnt disturb the existing IF doing so causes it to stretch, meaning that if it wont break loose from the substrate easily I fasten it down at the leading edge before I do any splicing. Dont want the splice to be moving with exp/contraction cycles.

I advise against Z-metal because it introduces a dissimilar material into the splice zone and its going to create an unstable ridge there as it passes over the cap sheet laps and irregular mop build-up.

I would spud the granules as well as possible. If its old, the asphalt in the sheet that the granules are pressed into is degraded and is fixing to lift. Dont want to be tying onto something that will separate down the road. Prime and prep. Prep is everything.

If you dont want to disturb the existing on the end unit, then do your splice entirely on your new side. Snap a line at the unit wall and splice on your side of that with at least an 18 splice zone.

It helps me to think backwards on these things. Instead of laying up the new bulk and then dealing with the tie-in, I get the tie in done first so I know I can trust the adhesion of it to the existing. I leave a three-foot splice in a clean, smooth, finished state with base showing below the mid-ply and no cap sheet having been installed yet. Then its a simple and sane approach to come from the new side, laying onto my own splice with Cap sheet following onto an already secured joint.

Wherever Im jumping up onto a full-thickness membrane I feather the cut edge first. I dont want any ridging to occur there.

Ok. Couple more comments then.

I like to get my splice sheets both under and over the material I'm splicing to. Just the same, in my opinion, as perimeter metal detailing. I mean the concept is the same. I wouldn't disturb the existing IF doing so causes it to stretch, meaning that if it won't break loose from the substrate easily I fasten it down at the leading edge before I do any splicing. Don't want the splice to be moving with exp/contraction cycles.

I advise against Z-metal because it introduces a dissimilar material into the splice zone and it's going to create an unstable ridge there as it passes over the cap sheet laps and irregular mop build-up.

I would spud the granules as well as possible. If it's old, the asphalt in the sheet that the granules are pressed into is degraded and is fixing to lift. Don't want to be tying onto something that will separate down the road. Prime and prep. Prep is everything.

If you don't want to disturb the existing on the end unit, then do your splice entirely on your new side. Snap a line at the unit wall and splice on your side of that with at least an 18" splice zone.

It helps me to think backwards on these things. Instead of laying up the new bulk and then dealing with the tie-in, I get the tie in done first so I know I can trust the adhesion of it to the existing. I leave a three-foot splice in a clean, smooth, finished state with base showing below the mid-ply and no cap sheet having been installed yet. Then it's a simple and sane approach to come from the new side, laying onto my own splice with Cap sheet following onto an already secured joint.

Wherever I'm jumping up onto a full-thickness membrane I feather the cut edge first. I don't want any ridging to occur there.

It is a tear-off, new lapping onto old, no gravel. I hadn't considered an expansion joint, I have others strongly advising me NOT to disturb or otherwise pry up the neighboring roof.

egg Said: Just my two cents:

That sounds right but the project description is a bit vague. Is the BUR a gravel surface? If it is, your success will depend on religiously prepping the edge of the BUR to receive the splice. Spudding and priming, no dirt, no bumps, no moisture and a healthy overlap. I would also seriously fasten the edge of the BUR before I spliced onto it. I like to get a base sheet under the existing and seal to the bottom side of the BUR before I fasten the edge. Sometimes the existing BUR wont come loose to do that. Usually it will. Put the best guy on it, not the one who gets easily frustrated. The splice is the money.

Is it a tear-off with the new system lapping onto the old? If so, I would very carefully feather the edge of the old with graduated SA strips before the new portion gets rolled onto it. The new roof field is sweat, strain, pressure, and amps; the splice is care, patience and 100 per cent finesse.

If its not a tear off, it should be.

Can you install an expansion joint instead of trying to mate the two?

Hard to say much definitively without seeing it in the flesh.

Hope it goes well.

Thanks for the input. No gravel. Just a granulated cap sheet. A splice would be relatively simple if it was a hot mop, but the peel and stick against the hot mop makes this interesting.

Roofing cement definitively in the mix. I was thinking of placing a zbar between the two roofs. Lower bar on the base sheet embedded in roofing cement and screwed in, and upper bar on the neighbors roof embedded in cement. I could lap the cap sheet over the bar...

Just my two cents:

That sounds right but the project description is a bit vague. Is the BUR a gravel surface? If it is, your success will depend on religiously prepping the edge of the BUR to receive the splice. Spudding and priming, no dirt, no bumps, no moisture and a healthy overlap. I would also seriously fasten the edge of the BUR before I spliced onto it. I like to get a base sheet under the existing and seal to the bottom side of the BUR before I fasten the edge. Sometimes the existing BUR won't come loose to do that. Usually it will. Put the best guy on it, not the one who gets easily frustrated. The splice is the money.

Is it a tear-off with the new system lapping onto the old? If so, I would very carefully feather the edge of the old with graduated SA strips before the new portion gets rolled onto it. The new roof field is sweat, strain, pressure, and amps; the splice is care, patience and 100 per cent finesse.

If it's not a tear off, it should be.

Can you install an expansion joint instead of trying to mate the two?

Hard to say much definitively without seeing it in the flesh.

Hope it goes well.

Embed in roof cement and 3 course or heat weld to the existing BUR and 3 course .