SBS New Cap Sheet over Old SBS Cap Sheet


Yes, this is FORBIDDEN, but it also assumes new cap over new cap.

The old cap had white granules and has lost a lot of them - the roof is almost black now.

IF there were no granules, I am confident you could successfully blue down the new cap sheet. (I’m guessing the failure mode would be thermal expansion/contraction that would separate the granules from either their old cap or from he newly glued cap.)

So I am thinking of pressure washing the old cap to blow off as much granules as possible and NOT use new peel-n-stick cap, but rather old school bucket of adhesive and plain new cap.

I don’t want to nail down another glue sheet and then cap because 1) it puts nails through the existing with is in good shape and 2) there will be an air gap between the nail sheet and the old cap - and when there are gaps like that, there is always the possibility of water finding its way there which leads to other problems.

I know that Ames Research elastomeric coating would bond (and other products too), so I don’t see why it is impossible to bond another cap sheet.

So what am I missing? Opinions? Criticisms?
Thanks so much in advance,


Is this self adhered modified you are talking about?

How old is the existing roof?


The “old school bucket of adhesive” is the absolute worst way to install a new cap sheet in my opinion. If you really wanna go over an old roof I really think you are better off (I know you don’t want to) nailing a base sheet over the old then installing a self adhered cap sheet on top of that. While still farrrrrrr from a top of the line instillation, I still feel its superior than gluing new on top of old.

Also you would most likely need to install new drip edge around the edges.


Existing is cap sheet over nail sheet - I think the Life Expectancy is 10-15 years. The existing is about 50% through that life span.

REASON FOR ALL THIS: I’m reroofing the house and the front and back porches are SBS - I don’t want to have to splice new SBS in the next 10 years into the new dimensional roof.


BUCKET OF ADHESIVE: This was the way SBS was for years. The peel away is a new system. The reason I suggested bucket was existing granules make an uneven surface - peel away needs a smooth surface to work properly.

DRIP EDGE is perfect and OK to leave be.


This has disaster written all over it… good luck, I’m pulling for you!


Is there any reason why you aren’t using EPDM?

Can you post some pictures of what you are talking about.

EPDM will last the life of the shingle roof and is much less costly than peel & stick modified, IMO it’s better for most applications.


“BUCKET OF ADHESIVE: This was the way SBS was for years”…by people with who didn’t have the equipment or skills to install it in either of the superior and longer lasting ways (torch down or hot mop). Peel and stick is not as good as either of those systems but it is better than the cold process adhesive. Yes the peel and stick needs a smooth surface to work properly that’s why I am recommending you bite the bullet and nail down a base sheet.

The reason I told you that you should replace the drip edge is that the edges are the most important. They are where your roof will want to pull away from and you want them stuck down to fresh primed metal. You are asking for problems if you just stick (or glue) new edges on top of old.

Also, I fail to see how doing things in the way you suggested keeps you from " have to splice new SBS in the next 10 years into the new dimensional roof".


I’m seriously considering membrane because frankly, the SBS jobs I have done simply do not last as long as shingles.

Regarding membrane the question is TPO vs EPDM vs PVC. Basics I’ve heard is TPO has issues and PVC the longest life. I would also need a gray color to match the shingles.

As far as Cap over Cap - that is exactly what a transverse seam is. With this in mind, I really want to know why Cap over Cap is forbidden. And if I remember correctly, you use sealant on these laps of peeloff cap.


Done properly, the granules on end laps are embedded, and there isn’t a ‘cap over cap’ condition. But that’s was one of the most commonly missed installation flaws I used to observe back when I inspected modified roofs, especially in northern Florida for some reason…

If the granules have all worn off of the existing cap sheet then a fleece back thermoplastic roof would be an easy install provided you have the ability and skill to heat weld. Other then that look for a high quality coating, unless the roof itself is saturated with water?



Have decided to put 100% Silicone Roof Coating (probably Henri 887) on the SBS. 50 year or Lifetime Warranty is hard to beat.


look into GACO Roof.,


Yes! I discovered the Silicone Coatings when I was at ABC Supply looking at Stinger Cap Staplers (have decided to manually nail Grip Rite Button Caps for this 7 square job.)

I think they quoted something like $350 for 5 gal.

Then I found the Henry for $229,… and then GacoRoof for $224. But it appears BOTH companies have a PRO line for a lot more money.

What impressed me about the Henri is that the coverage is 1.5 gal per square and not the 1 gal per square of the GacoRoof.

I’m concerned about appearance because on of the flat roofs (1.5:12) is clearly visible from the street and the light gray, although better than white, may look ghetto against the dimensional medium grays I’m using.

Was wondering if granules on top would make a difference, or maybe a darker gray.

Also concerned about the wet slippery characteristic of the silicone coating.

The Henri Pro has a Silicone Coating w/Fibers and a bunch of related specialized product. For instance, SBS seams should be coated with a “butter” grade silicone.l Their information is contradictory: 1 ply Lifetime Warranty, but on the Pro-Grade sheet, you get 20 year with a primer coat and top silicone coat.

Maybe the GacoRoof is simpler to use?


Just did a 55 sq silicone coating job over one of our sta roofs last week. I dont know if I would ever do it on someone else work, not knowing exactly what was there. There were 3 roof top units and over 100’ of roof top duct work so it was the best option to extend life of the roof with out major mechanical work.

We did alot of research and went with mule Hyde which is owned by ABC. You need to do alot of reading on the product vs system warranty. For the full “system” warranty that We cover labor for first 2 years and they cover cover the next 8 on top of material warranty, they did a pre and post inspection. Like any shingle warranty it’s full of loopholes. We buttered and embedded tape in all of the ductwork and penetration seams, they said because it was torched with 6" laps did not need to do roll seams, primed, Then coated at 1.5 gallons per square.

All in all turned out looking great and took care of the leaks they had, mainly duct work related. It is very slippery and they highly recommend as little traffic as possible.


Was it slippery when dry?

I have to chuckle, the Henry tech said not to topcoat silicone with granules and yet, on one of their application guides (don’t remember which one) they stated 20-30#/square granules for walk areas. Further, lots or granule topping discussed on the internet.

I confess, this is going over SBS at about 1/2 its life expectancy and it is my home. I figure 20 more years is the most I can expect from Life… (ugh, advancing decrepitude sucks…)


It’s extremity slippery when still wet… Pretty much waking on oil. With a little morning dew it is like walking on ice. Dry it is still slippery. Honestly once you buy the cleaner, the seam sealer and tape, the primer, and the coating material cost is going to be over 2$ a sq ft. With the Mule Hyde applied over granular or aged smooth they say 1 gallon of primer and 1.5 gallons of coating per square.

If it is your house and you are doing the work yourself, do yourself a favor and tear it off and put on a new GTA or SA roof to match the shingles.


Extremely slippery worries me: Pitch is 1.5 in 12 and just how dangerous will it be to get off a ladder during a rainstorm or wet roof when inspecting or looking or damage?

This SBS is in good condition so primer should not be a problem.

Henry 887 says one coat - they even mention granules @ 20-30# per square. However all discussion of granules includes another coat. What I don’t know is if the other coat is for traffic or to embed the granules properly. My use for granules is not traffic but mitigating the slipperiness.


My 2 cents: just because the label says 50 year warranty, that doesn’t mean you are getting that. Maybe if you follow all the procedures and recoat every 10 years it could be possible. If all the products performed the same wouldn’t everyone just choose the cheapest one everytime?

Seeing as this is your house you may be better suited for an acrylic coating. You have a large variety of color choices. The dirt sticks to the silicone extremely well. It wipes clean easily with a wet rage, but generally doesn’t get cleaned from the rain.

I’m working next to a large silicone coating roof we did 3 months ago and I’ll try to take a picture. The urban environment this is located I’m has made it look much older due to the dirt accumulation.

Specs from the tech department can be a little puzzling at times. Anytime you need clarification on something from the manufacturer it’s best to get the response emailed to you for future reference. If a problem arises in the future you will need more proof that you did as was specified. Saying you called and talked to some guy might not cut it.


I’m thinking a bit against the silicone. It sounds like a durable product, but expensive and I don’t like slippery roofs!

I actually put Ames Research Super Elasto-Barrier on my tongue and groove porch floor! I had full basement under it and used it for storage but wind driven rain would seep through and make a damp, moldy mess. 100% humidity was common. The SEB totally sealed and did not crack at the t&g seams. I finishing troweled it on, not particularly carefully but now it’s at least 10 years old and while still functioning is starting to aligator - it is not UV proof and needs a top-coat I never applied.

I’m tempted to use this stuff although there may be better product out there - maybe something with one step and he color I want.


Sir, let me assure you he wasn’t exagerating when he said the coatings in question are slippery.
He explained in perfect detail.
Like dont you even dare put your feet up on that roof until all morning dew is completely dried off!
It would happen even if the roof is dead flat!!
No pitch at all is required for both feet to come out from under you at the same time.
Im not saying dont use the product.
Just do NOT touch your feet to that product while it has Any moisture on it at all.