How would you install on a 3:12 pitch roof?

We are building a 16 x 24 sunroom addition to our little cape style house. We have not yet selected a shingle ( would like some input ) but have 3:12 trusses coming tuesday. 2 fixed skylights will be installed one on each side of this gable style addition. Soffits, baffles and ridge vent planned.

Thanks in advance !

Id use some type of flat roof material. Epdm or granualated modified maybe.

“snap lock” standing seam (metal roof) would be another opt

do not use architechual or demensional shingles.
use 3tab only.
theese shingles shed water much better on low slopes.


you shouldnt use any shingle on a 3/12.epdm fully adheared,youll have no proplems for many years

I have to agree, I don’t like to put shingles on anything less than a 4/12 pitch and then its on a 4" exposure. A 3/12 pitch is ideal for a modified or whatever fits your budget, and will be more practical than shingles on a flat roof.

GAF liberty cap sheet nailed under each lap 6" you won’t even need the mid-ply


The roof should be resolved before you start to build.

More important then the type of roof material, is what type of skylights are you installing. This will dictate the roofing material.

Depending on the skylights you have, you may be better off throwing them away and ordering a better skylight.

I had downloaded a .pdf file for a GAF Elk shingle, just to find mfr. info on what slopes would be allowed with architectural style shingles, here is a portion …

Underlayment: Low Slope 2/12-4/12 (167mm-333mm/m)
Application of underlayment and eave flashing: Completely cover the deck with two
layers of underlayment as shown. Use only enough nails to hold underlayment in place
until covered by shingles. Use blind nailing for eave flashings. At eaves and where ice
dams can be expected, use one layer of GAF Weather Watch®, StormGuard® or other
GAF-Elk Leak Barrier. Eave flashing must not overhang the roof eave edge by more
than 1/4" (6mm) and extend 24" (610mm) beyond the inside wall line. Where ice dams
or debris dams are not expected, install 2 plies of Shingle-Mate® underlayment.

Our brand new Velux skylights also are allowed on 3:12, I won’t be throwing them out Lefty :slight_smile:

[quote=“bctile601”]I searched the board before posting with 3:12 pitch, low slope, and low slope shingle, and also went through the first ten pages looking for a similar previous conversation, but didn’t find one

Hi Brian, I think the pros are playing it safe, 3:12 pitch has probably been found to be troublesome over their years of experience.
I’ve got 3:12 on part of my house and it worked fine for 25 years with three tab shingles. I’m re-roofing with Certainteed Landmark 30 year now and expect it to be fine still. I put double lapped titanium under it and storm guard in the valleys.
I think the key is what type of weather where you live. I’m in mild coastal ca. in a wind sheltered area with no nearby trees to cause leaf problems so it is not hard for the water to get off my roof. If I lived in a place where it snows and freezes I’d probably add a layer of storm guard or other stick on water barrier under the whole 3:12 roof just to play it safe. I have some skylights on raised curbs and find them reliable, I’d keep the width as narrow as possible to minimize the potential water along the top flashing area.
Bottom line is the best approach would be to talk to the best roofers in your area and get proposals from them or if you want to do the work yourself pay them for some consultation and see what works best in your conditions.
Regards, DaveB

I like to treat a 3 pitch as a flat roof but there are exceptions where its neccesary and within code to shingle it.The old way was double felt the new way is to I&W the whole area with Grace “don’t use the cheaper brands”. you also have to be careful with your flashing details and nailing pattern. We almost never use three tabs in this area anymore.


We had to make sure you were using a good skylight. Talking about shingling with a junk skylight is a waste of time.

Half laping the felt is good. This gives you the double protection.

Three tab shingles are the best for this slope. Timberlines will work fine also.

Mobile homes are 3/12’s. They are all over the country working just fine. They also use junk skylights. So you should not have a problem.

most cost effective thing is definetly GAF liberty cap sheet nailed it’ll be cheaper and better than ice guard with shingle the cap sheet costs 60 per sq iceguard is about 30 per sq than you have at least 60 to 70 sq for shingle plus nails etc… so just use the GAF liberty and put butterfly patches on all your corners and if you want lap seal the selvage edges you can’t beat it faster install too quality and it’ll be perfect with snow sitting on it no manufacturer likes 3" pitched roofs they never say its totally recommended and dimensionals yeah they could work, but try that on a 20’ rake and it’ll leak… i don’t even see why your debating it truthfully thats what self adhered roofs are for small residential flats and low slopes they tie in to shingle no problem either i’d never use epdm on a residential roof for nothing especially if your tie’n into shingle epdm just looks bad goto GAF and read up on installing liberty it’ll be a snap and i’ve never had a problem with it only thing i do is i make sure i custom make the dripedges so they go all the way into the gutter and when i hem the front edge i make it an 1" past the fascia so their wont’ be any rolling back of the water

Cost effective would be felt and three tab.

how it still would cost more i only pay 60 sq for liberty 3 tabs are about 60 now and well i use shingle mate so i dont know nails etc… its either the same or the 3tabs are more and the liberty will definely go down faster

liberty is faster. Felt and nails are cheaper then the base. For our area the shingling the roof would cost less in material.

thank you daveb,

“I’ve got 3:12 on part of my house and it worked fine for 25 years with three tab shingles”.

3tabs are specifically made for low slopes.


I have done some 3/12 pitches with shingles because the contractor that signs my check said thats what he wants and he did let me put them on a 4" exposure, but he knows that I do not warranty shingles on a 3/12 pitch. If there aren’t any dips in the roof it will work, but still no guarantee and no warranty.

I’ve done Winterguard and Landmarks on a few 3/12’s with no issues but the biggest section of roof was only a couple squares.

Got a large roof with about 60% at 2.25/12. The three tabs currently on the roof have been on there for about 12 years with no evidence of soft spots.

Thinking torch down if the insurance company opts to buy the roof.

haha…3 tabs are running me $75 vs. $72 for 30 year.