Roofing 3 to 12 pitch

I have a 3 - 12 roof in Chicago, IL. Can I have some opinions on if you can use arch shingles or not. I have had some say no, some say yes if you ice and water shield the entire roof, and some say yes (without the ice and water shield) as long as you put in enough venting.
P.S., I have been told that putting the ice and water shield on the entire roof is not good because it “seals the roof” and doesnt let it dry out property becouse of humidity.

you can shingle a 3:12, no problem. as for I/W, i dont know in your area, but around here, 15# felt would be just fine.

Underlayment on a 3/12 should be a minimum of double coverage 15# felt.
Ice & water shield would be much better.


I am glad you took my advice about seeking out additional information at this site and possibly the DIYchatroom Dot Com site for home owners to get help.

I will try to remain neutral in my comments, but one nice thing about the internet, is you can research the comments that a poster has made, by looking up their past history of comments, just by clicking their profile and viewing previous posts, so you can get a better handle on the type of person they are and what information they have a deep knowledge about.

Also, just Google the Users Name and all of the other forums they are on will show up too.

For facts, your roof was just a hair over 15*, which my pitch guage revealed to be a 3 1/4 rise over every 12 run, (3.25/12).

The original roof covering was a built-up roof, (BUR), with a gravel aggregate surfacing.

2 years ago, you had a friend help with installing the new shingles, (Tamko, architectural 30’s, color = Oxford Grey) directly on top of that BUR and installed Grace Ice and Water Shield only along the eave edges.

I was very surprised that I did not feel the bumps of the original gravel surfacing under foot while walking over the roof.

I neglected to ask you, but I presume that you swept the gravel surface as clean as possible before applying the new shingles?

The past 2 winters, leaks entered the home, not only through the soffit areas, through the soffit wood joint seams, the soffit vents themselves but also on the interior portions of the home.

You only have 6 of the 4" x 16" rectangular aluminum soffit vents on each side, with a total soffit width of 13".

There is NO roof top exhaust ventilation currently. No Gable ed louver vent, mushroom vent or ridge vents.

Your recommended options so far, have been to completely encapsulate the entire structure with Ice and Water Shield, after removing the one layer architectural shingle roof and the one layer hot tar and gravel roof and replacing 100% of the existing 1/2" plywood decking.

Or, after replacing the decking, use proper shingling techniques and install the Ice and Water Shield only along the bottom 3-6 feet along both eave edges.

Or, after decking replacement, install a modified bitumen roof.

For the sake of neutrality, I will only voice my own recommendations after this thread progresses a little more, so others can voice their unbiased opinions without being swayed by my opinions.

Regardless of the recommendations, one factor that needs to be reiterated, is that any “Salesman” can talk up a good storm, including myself. But, the final results are determined by the crew that actually does the installations. Referrals and testimonials have always been one of the keenest methods of separating the cream of the crop from the curdled muck that is so prevalent with the majority of companies that only subcontract out all of their work to the lowest priced subcontractor, usually staffed with non-english speaking youngsters with minimal training who often travel from Chicago to the Western Suburbs.

Staff trained long term dedicated and certified trained employees, in my opinion will always be the better choice for the actual crew who does the work.

Okay guys, give your diverse opinions.


probably going to be your most commonly suggested (and widely accepted among roofers) idea.

We once did shingle a 3:12. We did ice and water the entire thing. After a few phone calls we found out by the city that they would approve it and we have no had any problems with it. I+W on the whole thing seems to have made a big difference.

Find someone you are comfortable with and who is trustworthy. From reading all of Ed’s posts over the past years I have learned he may be one of the most knowledgable if not the very most knowledgable in this industry. Feel safe in what he tells you. I was actually going to refer you to him earlier today when I read this post but I did not have time to post. I am glad he responded.

Using two layers of 15 lb. felt is alright. But be and sure to stagger by 18 inches each layer of felt so that you do not have seam over seam of each layer. By staggering you shall kept them from ever leaking. And you can shingle over them with either the three tab shingle or an architectural shingle.

Does this mean you would not put the I&W on underneath? Thanks for your comments.

If your situation is as Ed describes, you will probably be best off with a Modified roof.

If I were to do your house in shingles I would use ice & water shield on at least 1/2 of it, 30# felt for the rest.

Double coverage with 15# felt is the manufacturers spec, ice and water shield is an upgrade from that.

If you have concerns about encapsulating the entire roof with IWS, then I would suggest going with the 2 layers of 15# felt. I also would suggest you use IWS in conjunction with the felt along valleys, rakes, eaves, and penetrations.

As for encapsulating the roof with IWS, I’ve seen it done on many a commercial building, but that is part of the design. One such project I was involved with that was not only watertight, but airtight as well, was the NJPAC. … rts-center

Another one I had the pleasure of dealing with that is sealed air and watertight, is the “Rockwell International” building, also known as the ultra-secret CIA building. … wanted=all

Now I’m dealing with schools that tie the waterproofing into the roofing to create relatively speaking, air and watertight systems. Once again, these buildings are designed so the HVAC system provides ventilation and keeps interior pressure, humidity, etc., stable. So, I would recommend the IWS on your house, but only if you have sufficient under-deck ventilation. If not, then I would go the 2x 15# route.

Regardless of the system to be used, ventilation will be key, in my opinion.

Especially with the extreme low slope of this roof, the ventilation will be even more critical.

I did one a little over one year ago, that has now weather our 2 most extreme winters in the past 10 years, with no adverse affects at all and the ventilation system I designed even required a mid-roof application of the /smart Vent Product, due to the modular set-up of that particular home,

So, even with an intake vent located in the middle of the roof, all the way across the entire structure, i felt confident that the ventilation leaks that previous customer had would completely go away.

One thought I was considering was a fully adhered e.p.d.m. roof, versus the modified bitumen, but once again, the final aesthetics of the finished appeal of the home are an essential consideration. but I prefer Function over Form anytime.


just a little fyi. if you i&w the entire roof it makes tearing it off almost impossible without replacing decking.i would get a price on three or four different “systems” before deciding whats best.

I would suggest tearing off down to plywood and installing a metal roof.Snap lock design. Deck armor underlayment.

if your 3/12 is really a 2/12 and your just wishing it was a 3/12 you better not put arcs on a 2/12.
youll be askin for trouble.
3tab shingles are on those low slopes for a reason
other than the previous owner bein cheap.
they shed water better on low slopes.

make shure it a 3/12 and yes it will be fine.



It was measured with a pitch guage at exactly 15*, which is a 3.25/12 pitch.


First, a question - how in the world did they get the gravel to stay on that 3.25:12 roof. Most of it should have washed off (or at least, washed downslope).

I, too, have done 3:12’s with shingles (both 3-tabs, and laminates, but not at the same time :slight_smile: ).

In one case, we just used felt, as it was a small patio, well protected from the wind. Many hard blowing rains since, and no leaks.

The others, we used Tamko TW on the whole thing. No problems whatsoever. I’m in Texas, and I&W doesn’t get much use around here, but I was sold on the TW as soon as I handled it and put a nail in it.

We did stick it down directly to the decking, and, yes, it will be extra trouble when it comes time to replace again, but I’m planning to be the one doing any replacements so it will be my headache and nobody to talk trash about my roof.

I also use it where the stupid architects run multiple valleys together onto a small low-slope, making a tiny spout for the water to run off. I have no idea why they think this is OK, but it is not uncommon here in N. Texas. After I replace the rotten decking, I use the I&W to make the area into a bathtub, since re-framing generally isn’t an option.

On my own house, I reframed the roof to add several dormers when we replaced the roof in 2003 (hail). Three of these dormers are large sheds with 2:12 pitch (I needed the headroom). I wanted to put standing seam on the dormers (GAF Slate lam’s on the rest), but didn’t win that discussion, so I went with the I&W and put the 30’s on over that. Never a drop gets through.

Last comment: I’ve never done it this way, but if you want to use the I&W to seal around the nails but still be able to peel it off later, you could do the double-staggered-#15-felt, THEN put the I&W over the felt. There’s no reason in the world why it shouldn’t work; it just requires a lot of effort.

I have read many roofers here say that they don’t use three tab shingles. They only use architects.
It told me right away that they are not roofers.
Salesman, owners- maybe but not good roofers.

I love architects. I try to put them on most homes.
But Architects are designed for steeper pitches only.

Three-tab shingles are designed for low slope.
Not just because they are less expensive.

If someone wants a three-tab shingle because they are looking at price but they have a steeper roof–i will argue to install architects.

If someone wants architects because they want it to look good but they have a low slope roof-- i will argue to install three-tabs.
I will install a product thats designed to look like architects but have three-tab “qualitys”
Or if they want true quality and are willing to pay i will install a standing seam metal roof.

Traditional Architects on a low slope roof regardless of underlayments is out of the question for me.

What is low slope to me here in florida?
I will install architects on a 5/12 or above if i am using a crew where every man is not a perfectionist.
If i am laying the shingle and every man with me is a perfectionist than i will install them on a 4/12.

If i was living north of me in an area that snowed a lot, then i would only install architects on a 5/12 minimum. And if i was using a crew that i didn’t train personally, than that minimum would be a 6/12.

So to answer your question, NO WAY would i put Architects on a 3/12. I’ll give you something that looks like architects though…
If you want real quality, longevity, and looks for your 3/12-- choose a standing seam metal roof.

I bring a pitch gauge with me to every roof.
And thats even with me out-guessing the pitch of the roof better than anyone i’ve ever met.
The pitch determines the material design(not the homeowner) and i take it dead seriously.

Look maw, it’s a roofer. It’s amazing.

rooflover wrote;Three-tab shingles are designed for low slope.
Not just because they are less expensive.

No they were’nt,they have low slope shingles,but only two tabs.

While i wouldn’t recommend it [laminates on a 3-12] it can be done . when i reroofed my own house [2 1/2-12] in 2002 i was on a tight budget so used pabco 30 yr laminates with 30lb felt as an underlay.and i’ve never had a problem i also maintain my roof twice a year something the average homeowner may not do. my next roof will be a 24 gauge snap lock metal with matching steel gutters