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TPO Over Mod-bit On Flat Residence

 
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Old 04-16-2019, 11:19 AM   #1
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TPO Over Mod-bit On Flat Residence


I have a scenario that I would value any input on.
Old Florida "modern" ranch house - built 1953 with flat roof. Flat, in this case, means 1/4" in 12, and with the usual settlement and dips they should not have used mod-bit on this when the house was flipped 5 years ago. Pooling happens behind most every overlap for this reason and roof life has been shortened greatly. I have worked on it myself with leveling, coating, etc - but figure it would be smarter to just do it right (TPO or similar).

One roofer tells me that the tapered insulation is not needed because the ponding is so slight and the roof does drain....they suggest just a roof cover board on top of the single mod-bit and then TPO - all mechanically fastened (deck is solid, probably 1.5 T&G, but we can't see it). Their claim is that trying to tear off most glued down and torched down mod-bit is almost impossible - that they've even ended up tearing up wood since the glue-on or torch on sticks TOO well.

Since the deck and bit-mod is very solid, this makes some sense - a cover board and then the TPO, but I would always like to make sure! One concern I have is that the pooling on the rood (small amounts) occurs behind where the sheets overlap - those are the "high points" - so if they install the cover sheet and some of the seams fall right behind those humps, the slope of the roof wouldn't be properly evened out.

This may sound like a nutty idea, but my though is that if we could somehow "grind" down those mid-bit lap humps with a stripper of sort (floor type belt sander or other tool), I'd be more comfortable with the overlay.

Tapered insulation could be done - at double the cost and also with some harm to the look of the modern house (the front of the house would be the high side, so there would have to be large drip edge or larger fascia).

Other basics.....
1. There is no ventilation on this roof nor will there ever be....since it is exposed beams type and flat. There have been no problem with this over the 65 year life of the house. There is also little or no insulation - just the deck and perhaps a small board inside which hides the underside of the decking (my guess is an old 1/2" FG board of some sort which is painted and visible from inside).

2. In our area - the chances are this house will be eventually be purchased and torn down and replaced with a bigger block house....so decisions can be based on a 20 year life...not "as long as possible" or forever as it might be with some houses.

3. Even without insulation, the A/C and total electric costs are very low....<100 per month for all (1200 sq. ft in Florida). Although insulation would be nice, it's not required nor will it pay for itself.

And so my "ask" is just comments on the various options....does it sound OK to just go over the solid mod-bit and deck with cover board and then TOP and mechanically fasten all?

Is the idea of somehow cutting/grinding down those overlaps of the old mod-bit crazy? doable? It might even be able to be done manually with one of those tools they use to square logs! (draw knife)....

Thanks for any input. I want to do it right, but at the same time don't want to do overkill.
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Old 04-16-2019, 07:23 PM   #2
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Re: TPO Over Mod-bit On Flat Residence


I dont believe you are a contractor whatsoever...I'd listen to your florida licensed roofer

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Old 04-16-2019, 07:26 PM   #3
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Re: TPO Over Mod-bit On Flat Residence


Tapered insulation isn't that noticable, i mean they make the stuff with as little as 1/8" slope.it is very expensive though.

However do your homework and look at what the tpo benefits are
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Old 04-16-2019, 07:28 PM   #4
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Re: TPO Over Mod-bit On Flat Residence


....

Last edited by A&E Exteriors; 04-16-2019 at 08:47 PM.
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Old 04-20-2019, 07:15 PM   #5
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Re: TPO Over Mod-bit On Flat Residence


Quote:
Originally Posted by A&E Exteriors View Post
I dont believe you are a contractor whatsoever...I'd listen to your florida licensed roofer
Ha! Andy I was thinking the same thing when I was reading it.. bit mod. !! When they went into the numbered options I got this image in my head of some valley girl rambling on and on... I thought "is this dude a chick?".

Hey if it ain't leaking don't fix it! Damn.. ponding is normal. But if you were a roofer you'd know that.

And yeah definitely sand down the humps. But you'll have to hand sand it with a fine grit paper.. should turn out great.

And ps GTFO
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Old 04-20-2019, 11:37 PM   #6
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Re: TPO Over Mod-bit On Flat Residence


We call them bird baths. They happen.


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Old 04-21-2019, 12:17 AM   #7
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Re: TPO Over Mod-bit On Flat Residence


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Ha! Andy I was thinking the same thing when I was reading it.. bit mod. !! When they went into the numbered options I got this image in my head of some valley girl rambling on and on... I thought "is this dude a chick?".

Hey if it ain't leaking don't fix it! Damn.. ponding is normal. But if you were a roofer you'd know that.

And yeah definitely sand down the humps. But you'll have to hand sand it with a fine grit paper.. should turn out great.

And ps GTFO
Way to many questions about their own house by an "hvac" contractor with no other posts...lol
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Old 04-21-2019, 02:55 AM   #8
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Re: TPO Over Mod-bit On Flat Residence


I vote for draw knife, sandpaper clogs to easy.
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Old 05-04-2019, 12:18 PM   #9
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Re: TPO Over Mod-bit On Flat Residence


Quote:
Originally Posted by A&E Exteriors View Post
I dont believe you are a contractor whatsoever...I'd listen to your florida licensed roofer
Your beliefs are not important here. I started framing house when I was 19 and owned my own remodeling company - and then a much larger HVAC retail, wholesale, distribution and installation company for 20 years.

In other words, I have done 10's of millions in residential contracting and have built houses, additions and much more from the ground up. I also have patented inventions in the HVAC field which I manufactured.

If your point is that I am retired....well, you are largely correct. But I do take care of 4 houses....

Not sure if the requirement here is "you are currently working for unrelated people for money", but if it is I am guilty as charged.
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Old 05-04-2019, 12:30 PM   #10
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Re: TPO Over Mod-bit On Flat Residence


Quote:
Originally Posted by madrina View Post
Ha! Andy I was thinking the same thing when I was reading it.. bit mod. !! When they went into the numbered options I got this image in my head of some valley girl rambling on and on... I thought "is this dude a chick?".

Hey if it ain't leaking don't fix it! Damn.. ponding is normal. But if you were a roofer you'd know that.

And yeah definitely sand down the humps. But you'll have to hand sand it with a fine grit paper.. should turn out great.

And ps GTFO
I've dealt with many flat roofs in my time...successfully. But, as most contractors know, there is no job exactly like another.

In this case we have amazing amounts of leaves, pollen, acorns and other life forms falling on this roof surface for at least 5 months of the year. It's not unheard of to have a complete covering of the decks and driveways (and the roof, of course) after just one day...at the right time of year.

And so, ponding can create these places where all the pollen and other jazz builds up and eventually starts to support various forms of life. Then, when the pond dry up there are large areas with these various brews affixed to them.

My desire to want at least SOME slope, even if only the true 1/4", is based more on the idea of a surface that a rainstorm and/or even a hose or light PW would clean a little easier...

"Listen to the roofer" would be great if the professional, licensed and manufacturer-approved roofers sung the same tune! But they don't. This is why it's always nice to get opinions from those who take a little more time. The pro that looked last month (I've had two pros come) said tapered insulation would be a problem (even tho it would not be!) and priced it very low without building up the slope.

The first roofer actually priced it with insulation AND with taking off the mod-bit, which seems not to be needed....

So, yeah, I believe the 2nd folks who stated that you might actually hurt the roof by trying to pull up the existing.

I am satisfied that the name brand TPO will do the job as a roofing material - so really my queries had more to do with the all-important prep and underlay.

Thanks to all....
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Old 05-04-2019, 12:57 PM   #11
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Re: TPO Over Mod-bit On Flat Residence


Quote:
Originally Posted by craigifl View Post
I've dealt with many flat roofs in my time...successfully. But, as most contractors know, there is no job exactly like another.



In this case we have amazing amounts of leaves, pollen, acorns and other life forms falling on this roof surface for at least 5 months of the year. It's not unheard of to have a complete covering of the decks and driveways (and the roof, of course) after just one day...at the right time of year.



And so, ponding can create these places where all the pollen and other jazz builds up and eventually starts to support various forms of life. Then, when the pond dry up there are large areas with these various brews affixed to them.



My desire to want at least SOME slope, even if only the true 1/4", is based more on the idea of a surface that a rainstorm and/or even a hose or light PW would clean a little easier...



"Listen to the roofer" would be great if the professional, licensed and manufacturer-approved roofers sung the same tune! But they don't. This is why it's always nice to get opinions from those who take a little more time. The pro that looked last month (I've had two pros come) said tapered insulation would be a problem (even tho it would not be!) and priced it very low without building up the slope.



The first roofer actually priced it with insulation AND with taking off the mod-bit, which seems not to be needed....



So, yeah, I believe the 2nd folks who stated that you might actually hurt the roof by trying to pull up the existing.



I am satisfied that the name brand TPO will do the job as a roofing material - so really my queries had more to do with the all-important prep and underlay.



Thanks to all....
Well, flat roofs require regular maintenance so.....
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Old 05-04-2019, 09:29 PM   #12
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Re: TPO Over Mod-bit On Flat Residence


How do they know itís single layer mod bit roof if they donít know if itís torch down or SA?
Sounds like you have some lazy roofers that want to maximize their profits with minimal work and not whatís best for the customer and roof life.
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Old 05-20-2019, 07:46 AM   #13
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Re: TPO Over Mod-bit On Flat Residence


Regardless of the material - Mod-bit, Torch-down, or single ply rolled roofing.. it is adhered to the surface below. I am guessing the sub-surface is 1/4"/ft sloped ISO board over the roof deck. Trying to remove will destroy the ISO below and cause much additional cost. Roofing over is the best option.

There are really only 3 options: another layer of self adhered mod bit, TPO, or EPDM.

Personally, I am not a big fan of mod-bit for anything other than a porch roof. The only advantage I can come up with is that it carries a granular look, and the aesthetic benefit of blending with a shingle roof. That is not a benefit here. TPO comes in three primary colors, white, grey, or tan (without special order). These look OK on a commercial structure, but not on a residence normally. I would go with EPDM.

Lay over the existing mod-bit with 1/2" fiberboard - plate and screwed 12"OC - fully adhered EPDM with cover tape for seams and edges - sandwich in 2x3 galvanized drip for the perimeter.
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Old 05-20-2019, 08:54 AM   #14
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Re: TPO Over Mod-bit On Flat Residence


Quote:
Originally Posted by GoodStuff View Post
Regardless of the material - Mod-bit, Torch-down, or single ply rolled roofing.. it is adhered to the surface below. I am guessing the sub-surface is 1/4"/ft sloped ISO board over the roof deck. Trying to remove will destroy the ISO below and cause much additional cost. Roofing over is the best option.



There are really only 3 options: another layer of self adhered mod bit, TPO, or EPDM.



Personally, I am not a big fan of mod-bit for anything other than a porch roof. The only advantage I can come up with is that it carries a granular look, and the aesthetic benefit of blending with a shingle roof. That is not a benefit here. TPO comes in three primary colors, white, grey, or tan (without special order). These look OK on a commercial structure, but not on a residence normally. I would go with EPDM.



Lay over the existing mod-bit with 1/2" fiberboard - plate and screwed 12"OC - fully adhered EPDM with cover tape for seams and edges - sandwich in 2x3 galvanized drip for the perimeter.
Florida has pretty much abandoned EPDM years ago. now you get TPO or modified

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