# flats and low slopes



## smalpierre (Jan 2, 2012)

What are you guys doing for flats / low slopes?

We are putting down either PVC or TPO unless it's visible, then we use mod bit peel and stick base/cap sheet (mule hide). I don't like those under 1:12 even though they are rated to 1/4:12. EPDM is out because of glued seams, and shrinkage, so I'm left with TPO or PVC.

I like PVC personally, TPO hasn't proven itself over time. The only advantage I've heard is that it's easier to deal with from a supply perspective when it comes to small pieces since we can go to the supply house and buy what we want rather than having to order and have shipped.

I've got some questions about that though. Are they compatible with asphalt shingles? I've heard that it's best to go three feet up the slope (where a flat porch meets a sloped roof), but why so far up if you're punching holes all in it anyway? Will the asphalt eat the membrane? I've heard of using coil stock under shingles, and over membrane ...

Biggest question, and this may be for the commercial guys - but what's the best attachment method - mechanically fastened, or fully adhered?

I saw something about mechanically fastened being better for wind uplift (my thought was REALLY???), and I've heard it's better if it's sloped so it doesn't slide down, but I use mod bit for that anyway. Personally I'd think fully adhered would be better, because wind could potentially balloon the roof up away from the surface otherwise, and make it flap to pieces - like waves on the ocean.

Other than speed of install, is there an advantage to mechanically fastened membranes?

We've been screwing down ISO board, and mechanically fastening the membrane, and going 3 feet under the shingles fyi ...


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## Miami Roofer (Jul 7, 2011)

We are using TPO,PVC,MB & BUR. We mop or torch our modified. In my area, epdm is not used at all. Miami has plenty of roofs that pond & the major manufacturers have created "ponding water specs" for South Florida. I've put them down a couple times but they get real expensive. Obviously, if possible, we taper our roofs.

As far as single-ply, I perfer PVC. We enjoy working with it and find it welds easier.(fewer cold welds) The suppliers carry both PVC & TPO but have more TPO in stock. We bring our PVC in direct & always keep extra on hand. It has worked well for us.

When tying in to a slope, I always check the manufacturers book & do it their recommended way. Usually, membrane through & up the break, a piece of sheet metal fastened over it with a slight kick that gets caulked & then the shingles or tile underlayment on top of the metal. It's best to keep your membrane out of contact with asphalt based products. PVC more so than TPO.

The attachment methods we use are based on the substrate & specification.
Wood and metal decks we mechanically fasten. Concrete, gyp & tectum we fully adhere. 

The highest uplifts I've seen are membrane fully adhered direct to the Concrete deck. When a deck is 1.5/12 or greater we have to back nail them because they will slip in our area. If the deck is combustible it's a whole different ball game as we need a class a UL. We usually add Dens Deck. 

Mechanically fastening PVC/TPO, when applicable, is more cost efficient for us both labor & material wise.

If you give me specifics on the type of deck,manufacturer and attachment method, I can get you the wind uplifts that have been submitted by the manufacturer for the High Velocity Hurricane Zone. 

Do you have to use wind uplift & design pressure calcs in your area?

http//:www.affordableroofingcontractors.com


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## smalpierre (Jan 2, 2012)

We're not in a high wind zone, I was wondering because some spec (forget which one, I think it was a global insurance data sheet) basically said that to get the higher wind rating, you had to mechanically fasten the membrane - which seems absurd. We screw down iso board and go over that.

We're using Duro-Last PVC, and I don't know which TPO we're using offhand. The Duro-Last has to be ordered for the job. I'd rather just get 10' goods and weld the seams personally.

We don't sell EPDM at all. From what I've seen, it's junk.


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## Miami Roofer (Jul 7, 2011)

I think you're talking about FM Global class 1-90. If you are, that applies to metal decks. At one time, there was a debate over how they reached their opinion and determined that fully adhered systems couldn't meet the classification even though fastener destiny was increased in the corner and perimeters. Guess that is why it's their spec. 

I figured your not in the HVHZ, but all our roofing systems must meet certain wind calcs. If you wanted, I would have let you know specifically what those numbers were and you'd know the failure point of certain roof designs.

I only worked with D/L a couple times so I know where your coming from. There's a bit of a learning curve with it. However, I've seen some really good & efficient crews install it. Guess it would be a bit of a headache if there was a mistake and you were short material. But, there is a + & - to everything.

Personally, I've seen some nice EPDM jobs that lasted-(though not locally). I don't believe it's junk at all. However, it's not really for the South Florida climate & won't last as long as most other systems do down here.

http://www.affordableroofingcontractors.com


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## tinner666 (Oct 28, 2008)

"EPDM is out because of glued seams, and shrinkage, so I'm left with TPO or PVC."

I've only seen shrinkage issues with the cheap.045. I only bid ans use .060 and thicker reinforced.


"I've got some questions about that though. Are they compatible with asphalt shingles? I've heard that it's best to go three feet up the slope (where a flat porch meets a sloped roof), but why so far up if you're punching holes all in it anyway? "

I go up 3' and leave 1'-2' exposed. I also add a sacrificial sheet to the break.


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## 1985gt (Dec 21, 2010)

We will install what ever the customer wants. Mostly it boils down to EPDM TPO and one form or another of BUR.


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## smalpierre (Jan 2, 2012)

I like the sacraficial sheet idea. Somebody I think in CT? said to run it up the slope, and put metal over it to prevent contact with asphalt.


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## tinner666 (Oct 28, 2008)

They say to use metal. It only seems to matter where Grace and some other I&W material is in contact. As a rule, I'm using slate and just run it to the slate and slate over it. No I&W or felt.


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## shazapple (Dec 3, 2010)

I spec modbit for 99% of the roofs I replace. Over a steel or wood deck the deck overlay (gypsum or fiberboard) is mechanically fastened according to FM 1-90 and then everything else is fully adhered (mech fastened gypsum, mopped vapour barrier, mopped insulation, mopped fiberboard, mopped base sheet, torched cap). Sometimes we use adhesives. Over a concrete deck we do the same minus the deck overlay. 

Low slope prefab buildings get a fleecebacked EPDM fully adhered. I've done a couple ballasted roofs with EPDM and they do stretch after 10 years, but that is the nature of the beast.

In terms of attachment method... it depends. Fully adhered is more expensive, but gets a better bond between surfaces (unless there is delamination). You dont have to worry about bubbling or fastener pullout. Mechanical fasteners can pull out and will conduct heat if they are put through insulation, but are cheaper/easier. You also don't have to worry about smell from adhesives or asphalt.


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## Pie in the Sky (Dec 21, 2011)

Great Thread guys!!!! 

I am a flat roof guy and hate to hear you say that EPDM is out. What a great, long lasting product that has proven itself over the years. Definitely not Junk, in fact I have seen sheets from improper formulations that have lasted longer than “Good TPO’s. Most residential flat roofs are relatively small. I have used Non reinforced EPDM (60 mil) many times for this application. Shrinkage isn’t really the problem it used to be 10-15 years ago but we will solve that anyway by fully adhering it. Normally I would say Reinforced EPDM is the way to go for any application, but if you don’t have skilled laborers to install tape, you can order non-reinforced EPDM in wider rolls and avoid seams all together. In theory this roof will never leak. I would be confident in any climate the EPDM will hold up 30+ years and 50 wouldn’t surprise me. So I would actually recommend this system over a Dens Deck Prime cover board. 

Personally I avoid TPO’s but there are some good ones out there I would choose before Durolast. Durolast seems to be extremely susceptible to hail so consider that in your area and ALWAYS use a HARD cover board below it, not just insulation. 

When I designed roofs, I personally always use a metal separator between products in this detail. When designing for snow regions, I would specify 12” butyl tape below the metal as a self-sealing flange to nail through. Its expensive but avoids the inevitable headaches of winter leaks in these areas. 

Without knowing the exact makeup of the system you are installing, I will open myself up for comment by saying a properly installed fully adhered roof is a better system for wind uplift. I say properly installed because I have seen many partial blow-offs of fully adhered systems and none of them were installed correctly. I have been involved previously with full scale wind uplift testing (12’ x 24’) and have come to the conclusion that fully adhered is slightly better for wind, mostly for the reason you suspected, Mechanical fasteners can allow the membrane to inflate, flutter, tear… But for the most part, in most regions within the united states, a properly installed Mechanically fastened roof system, is more than adequate to resist uplift pressures. Believe it or not the most common means of failure on a fully adhered roof is the fastener plate pulling through the insulation. Pretty neat, one more argument for using a dens deck cover board to help resist that. 

I was involved mostly in commercial design so I am unaware of your residential code requirements but I designed to the specifications called out in ASCE-07 (American Society of Civil Engineers – Components and Cladding) as required by IBC. These requirements are slightly less stringent than FM’s requirements. (FM is Factory Mutual, nothing more than an insurance company who over-engineers to prevent loss) ASCE -07 also include enhancements at the corners and perimeters but keep in mind, recent studies of real world wind events are indicating these past requirements are not adequate. Keep your eyes open for more testing on the way.

All this stated, I worry more about Nails. Most of the wind damage I see as far as full and partial blow-offs go, are a result of blocking or metal fascia installed with nails which pull out or improperly nailed structural members. Threaded fasteners do wonders in wood blocking. 

Also, Mod Bit is my Top Choice but rarely recommend it unless I know the people installing it are confident, and consider cold adhesive. It is the Future of built up roofing.

Let me know if I need to clarify anything...



*Dustin T.** Smoot, RRC, RRO, LEED AP**| Forensic Specialist | Pie Forensic Consultants* | Corporate Headquarters: 6275 Joyce Drive, Suite 200 | Arvada, CO 80403-7541 | Nationwide: 1.866.552.5246 | Local: 303.552.0177 | www.pieforensic.com | http://blog.pieforensic.com/


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## Pie in the Sky (Dec 21, 2011)

*Tinner*, It looks like your sacrificial sheet is just nailed in there maybe 6" OC???? Maybe I’m not really sure what I am looking at. I could imagine adhering a sacrificial sheet in this area if you get alot of Ice build-up and movement but I personally would never put a nail through a flat roof membrane. Can you explain the picture a little for us? 
Thanks, 

D

*Dustin T.** Smoot, RRC, RRO, LEED AP**| Forensic Specialist | Pie Forensic Consultants* | Corporate Headquarters: 6275 Joyce Drive, Suite 200 | Arvada, CO 80403-7541 | Nationwide: 1.866.552.5246 | Local: 303.552.0177 | www.pieforensic.com | http://blog.pieforensic.com/


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## tinner666 (Oct 28, 2008)

Pie in the Sky said:


> *Tinner*, It looks like your sacrificial sheet is just nailed in there maybe 6" OC???? Maybe I’m not really sure what I am looking at. I could imagine adhering a sacrificial sheet in this area if you get alot of Ice build-up and movement but I personally would never put a nail through a flat roof membrane. Can you explain the picture a little for us?
> Thanks,
> 
> D
> ...


Pretty simple really. That chalk line represents where the bottom edge of the slate I reinstall will go. I added another 100 nails to it. Plenty of ice slides here.


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## tinner666 (Oct 28, 2008)

I can't find my 'finished' pic. Here's what it looked like before I redid it.

I ran my first row somewhat higher.


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## tinner666 (Oct 28, 2008)

PS, this is what small was referring to. This little thing was all stretched out and balloned 1/2 across the roof. I did it in .060 reinforced. Replaced all the siding, and reflashed that wall, and installed a new pipe collar.


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## Pie in the Sky (Dec 21, 2011)

Awesome, Looks great... I've read enough of your posts that I didnt really think that was your finished product. Thanks for the clarification! 

*Dustin T. Smoot, RRC, RRO, LEED AP| Forensic Specialist | Pie Forensic Consultants* | Corporate Headquarters: 6275 Joyce Drive, Suite 200 | Arvada, CO 80403-7541 | Nationwide: 1.866.552.5246 | Local: 303.552.0177 | www.pieforensic.com | http://blog.pieforensic.com/


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## tinner666 (Oct 28, 2008)

Found them. I pig-eared that intersection at the wall. Then covered it with another piece of EPDM and then ran my first flashing past it too.
Thanks for the compliment.


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## Pie in the Sky (Dec 21, 2011)

Nice job... Now you have a detail that will last almost as long as the slates... ALMOST... 

*Dustin T. Smoot, RRC, RRO, LEED AP| Forensic Specialist | Pie Forensic Consultants* | Corporate Headquarters: 6275 Joyce Drive, Suite 200 | Arvada, CO 80403-7541 | Nationwide: 1.866.552.5246 | Local: 303.552.0177 | www.pieforensic.com | http://blog.pieforensic.com/


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## tinner666 (Oct 28, 2008)

That's the way I roll. I hate going back. I was roofer #4 for this HO.


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## Pie in the Sky (Dec 21, 2011)

tinner666 said:


> That's the way I roll. I hate going back. I was roofer #4 for this HO.


Sounds like that homeowner learned his lesson on choosing a quality contractor. :thumbup:

*Dustin T. Smoot, RRC, RRO, LEED AP| Forensic Specialist | Pie Forensic Consultants* | Corporate Headquarters: 6275 Joyce Drive, Suite 200 | Arvada, CO 80403-7541 | Nationwide: 1.866.552.5246 | Local: 303.552.0177 | www.pieforensic.com | http://blog.pieforensic.com/


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## tinner666 (Oct 28, 2008)

They had hired one of the largest to do the last roof according to the Mrs. They were real gunshy to say the least. When a tropical storm dumped a load on us shortly after I did it, that sat there that night watching it. They weren't going to sheetrock the inside again just to tear it back out! They called the next day to say they were tickled pink.

BTW, I always thought step flashing was idiot proof. The ones on the wall were too short, nor were they nailed, sliding out and causing leaks there too. The same house has two other walls done the same way. I'll be redoing them this spring.


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## smalpierre (Jan 2, 2012)

Ok, as I posted in another thread - I don't have a lot of single ply experience, or any other low slope system for that matter.

I stand corrected with the EPDM thing, I was on a roof today that had a good EPDM install with quality materials. Nothing like the junk I've seen before. It was leaking, but it was in a tough spot to roof no matter how you go about it.

I still don't like the idea of adhered seams when you can weld them - but a cold welded seam can be as bad as an improperly adhered one. This stuff wasn't ballooned or tented ANYWHERE, and there was more than an opportunity for this to go down. It was a reinforced 60 mil if I had to guess - I didn't measure the thickness.

It wasn't leaking at a seam either - it was at a dead valley / wall interface. I should have taken pics ...


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## smalpierre (Jan 2, 2012)

When it comes to low slopes, I get a lot of conflicting information, so please pardon my noobishness 

I'm still trying to figure out what the best solutions are from both performance and safety perspectives. I will NEVER torch down a roof, even though I know performance wise, it's a good option. The "dragon wagon" isn't something I want any part of!

Same goes for hot mop BUR - it's a great system that's time proven, but hard to diagnose and find leaks, and it's hazardous and labor intensive to install. Molten lava and the fumes make it a no go for me. I'd rather put down a quality EPDM.

To the guy that has done ballasted roofs - my stepdad is a mechanical engineer that's been working for FEMA for years. It's not an install I will ever do. The ballast becomes ballistic in high winds ... also, I've heard a bit about how adhered sections were still pliable and weldable, but ballasted sections were brittle and basically done. Two strikes. Three if you count the ballast hitting things across the street!


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## smalpierre (Jan 2, 2012)

tinner666 said:


> They had hired one of the largest to do the last roof according to the Mrs. Tehy were real gunshy to say the least. When a tropical storm dumped a load on us shortly after I did it, that sat there that night watching it. They weren't going to sheetrock the inside again just to tear it back out! They called the next day to say they were tickled pink.
> 
> BTW, I always thought step flashing was idiot proof. The ones on the wall were too short, nor were they nailed, sliding out and causing leaks there too. The same house has two other walls done the same way. I'll be redoing them this spring.


Step flashing IS idiot proof. If you do it wrong, it proves you're an idiot!


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## tinner666 (Oct 28, 2008)

smalpierre said:


> Step flashing IS idiot proof. If you do it wrong, it proves you're an idiot!


 Yes indeed! There were idiots on this one! I was speechless, to say the least.


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## Pie in the Sky (Dec 21, 2011)

smalpierre said:


> To the guy that has done ballasted roofs - my stepdad is a mechanical engineer that's been working for FEMA for years. It's not an install I will ever do. The ballast becomes ballistic in high winds ... also, I've heard a bit about how adhered sections were still pliable and weldable, but ballasted sections were brittle and basically done. Two strikes. Three if you count the ballast hitting things across the street!


I dont mind bassasted rooofs. They are inexpensive and can be very effective. I personally have done a bunch of hurricane work and have NEVER seen winds actually pick up a peice of ballast and throw it. This would take an incredible force! I just need to see it before I believe it. I know you cant even use river rock on a roof in Miami Dade County. I think its crazy, Ive been on old Ballasted EPDMs that have been through the worst hurricanes and all I ever see is some wind scour in the corners. 

As far as Brittleness, ballast carries organics which can expidite the migration of plasticizers in a PVC membrane. I am pretty sure that PVC manufacturers do not allow its use now. Now TPOs are sometimes balasted but lack the plasticisers in PVC so there is nothing to leach out. Now if you were one of the many schools out west that recieved a Black TPO from JPS that was ballasted, that ballast made the field of your roof last because it protected it from the sun. The flashings all failed at 10 years but could be repaired. 

It seems like your looking for a single, black and white answer about whats the best flat roof, I could never give an answer like that. There is a use for every system. Taped Seams are "new" technology, and anyone who had worked with glued seams in the past knows they are pretty impressive. As you learn more about low sloped roofing you will understand there is a place for almost any system. And everyone can argue a different system and everyone can make a good point... It would be best to post your proposed system and application and get feedback from the people on this site.



*Dustin T. Smoot, RRC, RRO, LEED AP| Forensic Specialist | Pie Forensic Consultants* | Corporate Headquarters: 6275 Joyce Drive, Suite 200 | Arvada, CO 80403-7541 | Nationwide: 1.866.552.5246 | Local: 303.552.0177 | www.pieforensic.com | http://blog.pieforensic.com/


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## 1985gt (Dec 21, 2010)

Pie in the Sky said:


> I dont mind bassasted rooofs. They are inexpensive and can be very effective. I personally have done a bunch of hurricane work and have NEVER seen winds actually pick up a peice of ballast and throw it. This would take an incredible force! I just need to see it before I believe it. I know you cant even use river rock on a roof in Miami Dade County. I think its crazy, Ive been on old Ballasted EPDMs that have been through the worst hurricanes and all I ever see is some wind scour in the corners.
> 
> As far as Brittleness, ballast carries organics which can expidite the migration of plasticizers in a PVC membrane. I am pretty sure that PVC manufacturers do not allow its use now. Now TPOs are sometimes balasted but lack the plasticisers in PVC so there is nothing to leach out. Now if you were one of the many schools out west that recieved a Black TPO from JPS that was ballasted, that ballast made the field of your roof last because it protected it from the sun. The flashings all failed at 10 years but could be repaired.
> 
> It seems like your looking for a single, black and white answer about whats the best flat roof, I could never give an answer like that. There is a use for every system. Taped Seams are "new" technology, and anyone who had worked with glued seams in the past knows they are pretty impressive. As you learn more about low sloped roofing you will understand there is a place for almost any system. And everyone can argue a different system and everyone can make a good point... It would be best to post your proposed system and application and get feedback from the people on this site.



Well said. Nothing in flat/slope slope is a one size fits all. I happen to love when people say EPDM sucks. It's because they are misinformed. I've seen Ballasted 60 mill EPDM's last close to 30 years. We have installed a number of 90 Mil warranty jobs. The companies wont warranty something that will not last. 60 mill EPDM is our go to roof. We generally do not like to do ballast roofs but some times you have to do what you have to do. PVC is almost never installed here except for a few places that spec it. TPO is a lot better then it once was, but comparing it to another roof system is like apples and oranges. 

BUR on the other hand is tops for me. Nothing is better to install then a BUR and gravel roof. Thats just me though.


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## Pie in the Sky (Dec 21, 2011)

1985gt said:


> BUR on the other hand is tops for me. Nothing is better to install then a BUR and gravel roof. Thats just me though.


Totally agree, problem is few contractors want to install them and this drives the price up. The ones that do are installing them wrong (see my other post on Mod Bits). I still think it would work out as the best choice if you looked at the life cycle costing.

In mod Bits, I prefer cold process. After 6 months to a year, thats then tightest smoothest roof youve ever seen. I think as my prefered long term systems, cold process Mod bit is near the top of the list.


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## 1985gt (Dec 21, 2010)

Coal tar pitch and gravel with the edges and drains built up to pond water. 50+ year roof easy.


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## Pie in the Sky (Dec 21, 2011)

We did mostly public work and could not specify Coal tar Pitch because it was only made by one manufacturer (Koppers?). As far as best possible roofs, you are dead on with Coal tar. When I started consulting I was called to a power plant with a 70 year old coal tar pitch roof. They said they need it to last 20 more years and dont have any money for maintenance. I said" well it shouldnt have lasted this long, so I guess it could last 20 more". The trick with the old coal tar roofs is the fiberglass insulation. You dont get those splits you get with a more ridgid insulation.


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## 1985gt (Dec 21, 2010)

That's a long lasting roof. I think your right on the fiberglass insulation though. Man does it suck to tear off!

I thought I would never see us put on a coal tar roof again, interestingly enough we did two last year. Both underground buildings, too bad we didn't get to do the excavation work also. I doubt the roof will ever have to be replaced, being they are under 3-4' of dirt and irrigated grass at that.


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## Pie in the Sky (Dec 21, 2011)

1985gt said:


> That's a long lasting roof. I think your right on the fiberglass insulation though. Man does it suck to tear off!
> 
> I thought I would never see us put on a coal tar roof again, interestingly enough we did two last year. Both underground buildings, too bad we didn't get to do the excavation work also. I doubt the roof will ever have to be replaced, being they are under 3-4' of dirt and irrigated grass at that.


NEAT! Ive seen some Coal Tar Pitch (CTP) below grade waterproofing. A great use for that product if you have no cracks or do not anticipate them. 

When I roofed I Worked mostly state jobs with CTP roofs. Ive been burned bad. Seems the older the roof you are tearing off, the worse the burn. Honeslty after that, I didnt mind the fiberglass.. A super cold shower really helps get it out of your poors...


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## 1985gt (Dec 21, 2010)

Pie in the Sky said:


> NEAT! Ive seen some Coal Tar Pitch (CTP) below grade waterproofing. A great use for that product if you have no cracks or do not anticipate them.
> 
> When I roofed I Worked mostly state jobs with CTP roofs. Ive been burned bad. Seems the older the roof you are tearing off, the worse the burn. Honeslty after that, I didnt mind the fiberglass.. A super cold shower really helps get it out of your poors...


They were both fairly small if I remember right around 30 or so sq. Both poured concrete decks. 

Pitch dies out over time and doesn't burn as bad. Fiberglass is cake compared to a pitch burn. Only time a cold dark basement and a 12 pack of beer helps and that just temporary. 

Best thing for fiberglass on your skin while taking a cold shower, a luffa(SP?) the fully thing the wife uses to was her self. It will pull the fiberglass right out of your pores. I would probably buy her a new one though after you use it.


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## Pie in the Sky (Dec 21, 2011)

Hahahahaha


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