Flat roof: epdm vs tpo?


Ok, that was helpful.
It shows that the decking/ceilings is 2 1/2 inches thick and That is just fantastic.
So not to worry about over penetration.

I would install modified bitumen roof
Or standing seam metal roof.

Your roofer will need to know that his trim metal will be custom made for an extra large face
Such as the existing.
I suggest steel, painted on both sides.
Make sure your roofing will be compatible with this custom metal trim.


Super! I was leaning towards ModBit! Would you have any concerns about fire hazards with installation? What depth insulation would you suggest? Would I have to replace the existing sheet metal fascia? (sorry to pile on questions!)


No, dont have to replace metal fascia.
One inch iso board with 2 inch inch screws would be fine.


The roofer should probably do a core on the existing roof to see if it has multiple layers. The building code allows only two roofs installed. If you have two then at least one (usually both) must be removed to put on a new roof. When they remove the old roof, if they have to, the insulation will go with it. That means your bid must not only have the roofing system but the insulation figured in the bid. Also, while you are replacing insulation, bring it up to code thickness as a minimum. It will keep your energy bills down and make the home much more comfortable. The old Eichler style has lots and lots of windows which look nice but make the house pretty darn cold/hot due to weather.
You might consider having a roof consultant take a look at the existing roof before getting a lot of wild bids. You’ll find them on the RCI website (Roof Consulting Institute).


Oh good. One bid included replacing the fascia. That bid was very high.


Last time I looked into roof replacement a core sample established there were two roofs already and all would have to be stripped. This time, one of the roofers who came by did another core sample. Though he said I could share it with other roofers, he hasn’t offered and I haven’t asked. I kind of hate to ask since his estimate is the sky-high bid that would replace all the fascia and I wasn’t thinking of going with that.

It’s actually not too cold in here right now, despite near-zero temperatures. It’s usually not too bad in winter, I guess cause heat rises. The downstairs in front of the windows gets really cold.

I didn’t know there was a Roof Consulting Institute! I’ll look into it, thank you!


We are those guys who take a core sample and give you a high bid up front. We like to know exactly What We are getting into and bid for the complete right job up front.

It would be well worth your money bringing in a consultant. Determine exactly what you have and what you need, then get bids to a spec.

Most residential roofing contractors have no clue what they are bidding when they bid a low slope roof system. After change orders from the low bidder on an inferior roofing system The job can end up costing you more Than the high bid from an experienced company using better products.

Personally I would recommend a 3 ply modified.


3 ply mod bit. Thanks, I’ll relay that to the roofers. Here is correspondence with the one I was most considering:

—is your estimate for TPO, ModBit or what other roofing surface?
ModBit – Certainteed Flintlastic was the option I quoted. Here is a link.

—what does page 2 of your estimate refer to?
This references the R-Value of ISO. I included that as a help to figure out how much we would need once we were able to identify how much current R-value you have in your house. This way we could meet code.

—I would like a Mod Bit estimate if possible.
I believe ModBit is the best under for your house based off all the trees over head. It is the most durable to impact.

—would sheet metal fascia have to be replaced?
No, we would use a new drip edge over the roofing and that would lap onto the existing fascia metal. Only in you need more than 4” of ISO would fascia metal possibly come into play.

—what would be maximum depth of insulation allowable by existing fascia?
4” is the largest that would work with standard drip edge. If we needed to go larger, we could custom bend metal to work. You still shouldn’t need to switch existing metal.

—please note mechanical fastening should not show through wood interior ceiling and exterior sheet metal fascia
With the Flintlastic application, only metal cap nails would be used for the base installation. Those only typically go through the decking ¼” As long as your ceiling is not also the roof deck (which you said it is not), then we are fine.

—do you have a written gaurantee of homeowner lien protection?
We provide a written warranty upon completion, a lien waiver from KMI and a lien waiver from the supplier.

—proof of insurance for home and all workers?
Providing general liability and work comp is easy to do and will be provided upon request. If you picked us, I would go ahead and have our agent provide certificates with you listed as additional insured.


I feel a bit surreptitious slipping this correspondence to you, but wanted to make sure I’m on the right track. It does seem to be a good outfit. All A+ with the BBB and all 5 star online reviews, but there are only 5 reviews for them.


If you are going with modified make sure it is torch applied.


I believe your father installed the 1 1/2 inch insulation board.
I think he went over and above what he needed.
So dont even think about going thicker.
This is a spec you would use if the decking was 1x6.
2 1/2 T@G ceiling/decking is its own heat barrier. It is so awesome, it is something to behold.
Remember, the thicker the insulation, the larger the face of the trim metal needs to be
And at a certain point the metal looses its strength to stay together on the corners
You dont want the face of your trim metal to be any larger.
You will not need the “gravel stop” so that will shorten the length of the face.


Ok, so the guy you are most interested in,
He doesnt know yet that the decking is 2 1/2.
And may or may not know that there is 1 1/2 insulation.
So he already needs custom metal bent even eliminating the “gravel stop” height.

His proposal should already include the exact thickness of his insulation board.
Or none at all.
It just sounds like its up in the air.
And that he thinks he is going to use easily available stock metal trim.
Which is under 3 inches.
He didnt notice that the trim was extra large.
I think he thought All the extra inches height was for the “gravel stop” ( to keep the rocks from falling)

Keeping with the 1 1/2 inch insulation along with 2 1/2 decking/ceiling… that puts you at 4 inches
You want your metal hanging past that.
Lets give it 3/4 of an inch.
So your face needs to be about 4 3/4 inches tall.
Stock trim is under 3 inches.
He needs to know this before he starts your job if you let him.
Dont be upset that he doesnt already know.
He’s probably never seen this 2 1/2 inch thick ceiling/decking before.


Thanks, roof lover! Yes, the roofer in question did not see the sheet metal specs prior to estimate, as I only found them in my dad’s old flat files a couple of days ago. And the roofer doesn’t have a core sample. Should I ask him to do a core sample?

(Both times following core samples there have been new leaks. Or maybe it’s just cause roofers walking around up there stresses and splits old worn out seams.)


He should confirm your discoveries so that he can prepare the metal fabricator to have the metal ready before the job starts.
I tell my metal guy at least a week before i need it and that is pushing it.

So he also knows the correct size underlayment fastener to use.
But he should be able to discover and overcome that issue on the spot on the day of tear-off also.
Sounds like he needs some 2 1/2 inch simplex
If the 1 1/2 inch insulation is still there. :slight_smile:


Just curious if you have had problems with cold applied Modified, (peel and stick).


Peel and stick SA (self adheared), and cold applied modified bitumen are two different products.

SA has its place in the market. If you have a simple roof with good slope such as a shed dormer or porch addition that drains into a gutter It can be a good choice. It is not a good choice when you have very little slope, complicated scupper details, lots of penetration, skylight and mechanical curbs, or parapet walls. There are details in the spec for all of them but torch applied details are faster and better imo. It needs to be stored and installed at the proper temperatures for the install to hold up. If it is sunny and over 90 out it’s better to just go home for the day. One downside is whatever you stick it to, plywood, curbs, walls will need to be torn off with the roof in the future because she. It sticks good it does not come off.

Cold applied modified is modified bitumen set in MBA or other adhesives. In my option it is only used for one reason, either the installer can not afford or get insurance. I have never had a reason to used cold applied, but know experienced flat guys who work for companys who use it. They all say it is junk, messy, horrible to work with, and inferior to torch applied. We have replaced several of these roofs, they always seem to fail at seams, penetration, and curbs. It is great to tear off though, peels apart like lasagna.


MPA, tilemans question if i could say it better…
He is asking Have you had a problem with self-adhered cap sheet while in cold weather?


Thank you roof lover, that is my fault for the wording. We have
Installed three ply self adhered, (base, smooth, cap) on smaller jobs and it seems like a good system if there is at least a 1-12” slope. We like it’s puncture resistance more than pvc around trees and it’s
aesthetics on visible roofs. Seems like the cost may be the main deterrent but I’m not a flat roof specialist.


Touchdown is a no-no in our area unless you want to pay a lot of extra for liability.


You don’t want to know what our insurance costs. Ideally sa should be above 50 degrees, but pain over 80 so limits it’s use a bit. When I do use it I go over it with a 100# steel roller so that helps when it’s colder.


I appreciate all the professional knowledge and technical experience represented in this thread!

But I’m thinking even if there was such a thing as “Flat Roofing for Dummies,” it would probably be over my head : (