Roofing materials before a solar install?

I want to get solar panels and I really do need a new roof. I’m going to go down to the wood because I have some spongy spots and want to take care of that now rather than after.

I’ve been told to use EPDM, TPO, and double layer a torch-down granulated rubber.

As a general product, I’ve been told granulated rubber doesn’t last as long as TPO or EPDM, but that 2 layers should last longer than either and will provide better protection against punctures (like if someone steps on a nail or zombies are crawling onto my roof during my last stand).

I’m in Philadelphia,PA if that helps…



granulated rubber = app modified bitumen (1 layer smooth, 1 layer w/granules). How are you going to install the solar? Ballasted or on mounts? Easier and better with single ply EPDM or TPO. Put a cross on the solar so the zombies stay away.

1 Like

IMO 2 ( 3 ply) layers of APP modified is superiour and it lasts even longer if the cap sheet is smooth with aluminum coating.

1 Like

2nd vote for 3 ply modified bitumen (Ventilated, mechanically fastened base, smooth, granular) that is our go to product for residential flat roofing. We have install over 30yrs old with no issues. If you are installing hard mounts for the solar I would laminate them bewtween the 2nd and 3rd layor.

1 Like

Thanks for the responses.

I was thinking that the Panels will be mounted to racks that will have a custom 3" square base with a predrilled hole in the center. The stanchion posts of the rack fit in them. I don’t know the precise details, but an engineering friend of mine did this on his system because he wasn’t happy with small footprint of the cylindrical base that came with the racks he used.

He used EPDM and his roofer simply doubled up under the bases where the rack was attached to the roof…

On the other hand, I think this looks simple and should be inexpensive:

When you say “Laminate” do you just mean adding an extra layer since there will be a penetration point? I like the idea of laminating between layers rather than on top since that would create a slight “slope” away from the base of the racks.

I didn’t even think about smooth with aluminum coating. I’ll have to discuss with my roofer. Anyone else wanna chime in on that?

(I admit I only know as much a s a dude with an internet connection).

When I say laminated, install the first two layors, then install pipes or rods welded to a 12x12 square primed steel plate, install the plate on the 2nd layor, set in flashing cement, then install the 3rd layor. That is how we install railings and other permanent fittings in multi ply systems. You end up with 0 fasteners penetrating the finished roof surface.

1 Like

The granules on the granulated Modified is to protect it from the sun, granulated is used to match shingles or otherwise blend in aesthetically.

The aluminum coating does the same thing but does it better and can be reapplied.

When using granulated the seams should be coated with additional granules were the bleed out from seaming occurs, I rarely see this done by anyone but myself.

1 Like

Got a shelf in the shop with 10 different color granuals.

1 Like

APP modified bitumen with granulated cap is a good way to go. A mechanically attached base sheet, smooth APP mid ply and granulated APP cap sheet and base flashing is a very strong system.

With regard to flashing your solar panel stands through the roof to a structural base, the best flashing kits I have found are the Chem Curbs and the Chem Link pourable sealant system. The curbs can be configured to odd shapes if need be and when correctly installed (it’s actually very easy) it is a bulletproof system. I have never had a Chem Curb fail in close to 20 years.

1 Like

Hi everyone,
I’m pretty sure I have chosen my roofer and these are the 2 options they’ve given me. For a couple hundred bucks difference, I’d rather get the better option, so that doesn’t make any difference; I’m happy to save money, but at the end of 20 years, I going to be happier with a better roof. :slight_smile:
Any recommendations?

1). “Instal 1/2” dense recovery board on the flat roof before installing the new rubber roof. Recovery Board provides a new roof substrate along with added insulation and sound proofing. The recovery board will really give you a great roof. The warranty with the recovery board will increase to 20 years.
The additional price for the recovery board is roughly $2,000 to $2,100."

2). “If you wanted two layers of roof membrane the additional price would be $2,400.00 additional.”

Thanks again; I appreciate people taking their time to answer a homeowner’s questions.

By “rubber roof” do you mean EPDM?

Sometimes people refer to Modified bitumen as a “rubber roof”, it is not.

I am not aware of any instance where 2 layers of EPDM would be used.

Yeah, that was my impression too. But on the original estimate it says “torch down rubber roof”

APP (atactic polyproplyne) is the most common mod bit torch down product. The modifier is plasticized.

SBS (styrene butidene stryene) is the other mod bit product. It is primaly hot-mop applied, but has three other application methods being cold process, self-adhered and torch applied. The modifier is, in fact, rubberized.

So, technically a mod bit could be a torch applied SBS rubber roof.

But, most roof coverings that are considered “rubber” are EPDM.

From my understanding, the 1/2" recovery board is a worthwhile investment to protect the roof, yes?
Better than 2 layers of bitumen, yes?

If they are using dens deck in lieu of base sheet that is a good but for a great maintenance free roof go with two plies of modified on top, one smooth one granular the roof will last significantly longer. If you just go with one ply the roof will not last as long and you will need to recoat every 5 years. So if you plan on staying in the house if is well worth the investment.


We’re going to go with 2 layers of torch down modified bitumen
Is it cool to apply this over the old roof? Here’s a pic:

If you are investing in a quality roof tear the old one of and install it right. If a roofer is telling you it doesn’t make a difference if you tear it off or not, find a new roofer.