Anybody with flat roof experience?

[bzinsky]

So I have a roof with an old coating of silvercoat. It probably covers 50% of the roof currently due to it flaking away. Some of it is still well adhered, some of it is not.

If I want to repair a section by adding some torch down, I'm assuming it won't work out to well on top of silvercoat. Do I need to remove the section if it still has the coating on it? Are there any tricks to removing the coating instead of removing the old torch down?

Also, at some point, someone threw down some aspalt sheets, not sure what they are called but I frequently see them on flat roofs. Can I lay torch down on top of asphalt?

Thanks in advance

 

[big.jim]

rip the lot off and rubbaroof it

 

[Falcon67]

Last flat roof we had done (back patio roof) was a complete tear off to bare deck, then hot mop, tar paper and torch down roll. It's been through two more hail storms in the last 15 years and is still fine for the new owners of that house.

 

[CNGsaves]

Let's SEE what you're talking about.

 

[aka Larry]

Who was the genius that came up with the idea of a flat roof in the first place?

 

[BlackTalon]

pics desperately needed...

 

[CNGsaves]

Who was the genius that came up with the idea of a flat roof in the first place?

There was unique concrete house in ex-wife's hometown that had totally flat roof on purpose. It was built to be flooded with water during hot months to keep house cool. Think of the weight of that water as it was several inches deep !!

 

[Falcon67]

My wife's dads house in Albuquerque had a flat roof, as did many other older NM homes. Common in some places. At our old place, it was a PO's idea of a mess. But we left it.

 

[BlackTalon]

There was unique concrete house in ex-wife's hometown that had totally flat roof on purpose. It was built to be flooded with water during hot months to keep house cool. Think of the weight of that water as it was several inches deep !!

A water-cooled roofs would have had the supporting structure designed to carry the load. Same for water-retention roofs.

These worked well when coal tar was the roofing bitumen in the built-up membranes. Asphalt-based membranes proved to not hold up nearly as well.

 

[rodm1]

rip the lot off and rubbaroof it

This!!

 

[bgarrett]

Who was the genius that came up with the idea of a flat roof in the first place?

I did property management for 150 buildings and always wondered the same thing. If I ever have a flat roof in my possession, I will gable roof over it. Flat roofs are a constant source of leaks and aggravation and none of the 'professionals ' could do better than short term fixes

 

[7echo]

Hot mop is going away, at least around here. A couple roof guys I deal with said they rarely use the kettles anymore, one outfit said they have not used hot applied in 5 years. TPO is real popular, we will see how the longevity is on that stuff. I have a torch down roll roof, no granules, has held up very well for 11 years. 2 in 12 pitch so nearly flat. When I replace mine in a few years I will likely go with TPO.

 

[BlackTalon]

TPO is only popular because the first makers jumped on the rode the EnergyStar/ LEEDs train. Sure, it's easier to install than a BUR, but the long-term performance potential really isn't there. Now that some newer info is out in the wild that indicates reflective roofs aren't the best thing to use in areas where you heat a bit more than you cool the market share will likely drop off a bit.

Down in GA it's likely a TPO will save you some $ in AC costs. Although the BUR industry finally has cap sheets, etc. that will also meet EnergyStar/ LEEDs so now you can stick with a 30+ year flat roof and still realize the energy savings.

 

[MBfreak]

Yes, unfortunately.
We bought our present house 1994 , it was then 20 years old.
The house, L-shaped, has a nice and very well designed and constructed gabled roof covered with cement tiles, never a problem.
The garage ( 7x8m) however has been designed by a total *****, although it was built at the same time and tries to match the house ( brick)
Not only does it have a flat roof. The drainage is done so that the lowest point is in the middle of the roof, with the drain connected to an INTERNAL drainpipe which then goes over to a wall, down in a built in part, and then under the slab to the day-water drain.

The roof has no internal supports and the beams are in massive wood .

And then, just to add insult to injury, the drain that goes down thru the roof connecting to the drainpipe was made in galvanized sheetmetal.

When we had lived here the 2 years, the entire ceiling came down. Great fun.
The galvanized drain had developed a leak ( corrosion straight thru) and the vapor barrier collected a little lake up there , soaked all insulation ( 60 cm) and then the sheetrock got wet enough to collapse.

The ONE and only good luck was that since it was an internal, non-inspectable leak, insurance covered all of it. No questions, just send us the bills.

The drain is now in tig-welded 1,2 mm stainless steel, and I have added a one piece rubber sheath warranted for twenty years over the entire bitumen covering. The internal drain can now be inspected by a simple removal of a detachable part of the ceiling.
Sorry no pics, this happened when I had no digi-camera.

Ola

 

[dogdog]

modified bitumen roof cold press might be better than torched one, they are the same except ModBit are applied with a tar like chemical to glue them together instead of torching them. Less dangerous and easier to work with provide that you don't smoke during the application or barn fire on the roof.... if you are doing just sections make sure you also seal ALL the seams with fabric and medium flashing cement(applied with hand and double dish washing glove nasty stuff.) on all joints and allow plenty overlaps... if you did a bad job water might seep through those seams. Hopefully the sections you are replacing is on the high spots not the low.....

 

[BlackTalon]

7 or 8 layers? By code you can only have a maximum of two layers (for a reason). If you keep adding more layers of mod bit over the years you are increasing the dead load by quite a bit.

 

[dogdog]

7 or 8 layers? By code you can only have a maximum of two layers (for a reason). If you keep adding more layers of mod bit over the years you are increasing the dead load by quite a bit.

yes 7 or 8 layer is fine for flat roof.... this is not the shingles pitched roof. wind will not blow these sheets away.Don't think code is the same for pitched roof and flat roof. Deadload wise, haven't had any issues yet past 5 years since last ModBit layer.

 

[Architorture]

why was the silver coat added in the first place and why are you repairing it?

probably a good chance that really solving the problem will require tearing off the roof as any moisture that has managed to penetrate down into the system is going to cause problems from below even after the repair is made.

 

[Architorture]

yes 7 or 8 layer is fine for flat roof.... this is not the shingles pitched roof. wind will not blow these sheets away.Don't think code is the same for pitched roof and flat roof. Deadload wise, haven't had any issues yet past 5 years since last ModBit layer.

are you talking about the layers within the system or the number of roof systems?

 

[BlackTalon]

yes 7 or 8 layer is fine for flat roof.... this is not the shingles pitched roof. wind will not blow these sheets away.Don't think code is the same for pitched roof and flat roof. Deadload wise, haven't had any issues yet past 5 years since last ModBit layer.

You would be incorrect. If there are two roofing membranes in place the Code prohibits installing a third.

We are talking full membranes here, which could be a 4-5 ply BUR, or a 2-ply mod bit. But you cannot keep adding full single-ply mod bit membranes on top of what is there and not both violate the Code and increase the dead load on the structure. 7 layers of modified bitumen membrane is likely a bit heavier than you imagine, and the roof structure may have been designed to carry only a 5-10 psf roofing system dead load in addition to the required live load/ snow load/ wind load capacity. Unless you have the strucutral information it would be difficult for you to assess how much dead load you can have.

 

[dogdog]

You would be incorrect. If there are two roofing membranes in place the Code prohibits installing a third.

We are talking full membranes here, which could be a 4-5 ply BUR, or a 2-ply mod bit. But you cannot keep adding full single-ply mod bit membranes on top of what is there and not both violate the Code and increase the dead load on the structure. 7 layers of modified bitumen membrane is likely a bit heavier than you imagine, and the roof structure may have been designed to carry only a 5-10 psf roofing system dead load in addition to the required live load/ snow load/ wind load capacity. Unless you have the strucutral information it would be difficult for you to assess how much dead load you can have.

I think you are correct code wise. Guess will have to remove all the next re-roofing. .... those fine prints .

http://www.nyc.gov/html/dob/downloads/pdf/cc_chapter15.pdf


1510.3 Recovering versus replacement.
New roof coverings
shall not be installed without first removing all existing layers
of roof coverings where any of the following conditions occur:
1. Where the existing roof or roof covering is water soaked
or has deteriorated to the point that the existing roof or
roof covering is not adequate as a base for additional
roofing.
2. Where the existing roof covering is wood shake, slate,
clay, cement or asbestos-cement tile.
3. Where the existing roof has two or more applications of
any type of roof covering

 

[CTyankee]

We do lots of torch downs on flat "roofs". Most of these are done during new construction and have a sleeper panel deck system that sets on top of them.

Even if it was allowed by code...I would never do any work on an existing flat roof system without taking it down to it's sheathing. Whatever roofing material system you decide to use, strip it down to it's base so you can be sure there are no hidden problems. You can't assume that any previous work was done correctly.