Asphalt shingles on a low slope roof
My addition to be completed this summer is to have a shed roof with a 3.6 in 12 slope connecting to a 12/12 roof. I’ve been reading about solutions to the low slope problem, and they seem to range from decreasing shingle exposure, cementing tabs, double layer of felt cemented together to using an adhesive membrane as an underlayment, which is evidently the best approach. I’m in coastal Maine, moderate snow load.
What are your recommendations?
Replies
EPDM or standing seam metal? Or does it have to be asphalt?
jt8
It's better to light a candle than to curse the darkness. --Chinese proverb
This will be just my third DIY roofing experience, and although I feel pretty confident with shingles, I truly have no idea hoew to install a metal roof (although they do look good). Also, I don't like the look of EPDM on a visible roof. (Is that like the stuff that comes in a roll and you melt down?? I've done that on proch roofs.) But thanks for the suggestions.
I've never done (or sub'ed out) a standing seam metal roof. From listening to greencu and others, I suspect it isn't so much that its hard to install but rather that the required tools are rather pricey.
And I agree with ya. EPDM isn't very attractive (just black). 3-4 in 12 is probably visible, so probably not the best esthetic choice. But on a flat roof that isn't really visible from the road, it works like a champ. It comes in rolls and you adhesive it down (that's also what flexible pond liners are made out of). IMO the two tricky things about EPDM is having a good substrate to glue it to, and getting the edges done right.jt8
It's better to light a candle than to curse the darkness. --Chinese proverb
http://www.certainteed.com/NR/rdonlyres/68B200A2-0892-4510-B27D-E5C6FC88F0B4/0/SAMv7_ch15_Laminated.pdf
Hey Mister Sushi, you forgot to cook my fish.
"Am I dead or alive? What's this? Linoleum? I must be in hell." -The Salton Sea
I don't consider that slope to be requiring anything special unless it is in a location where a tremendous pile of snow drift or ice can be expected to pile up, then just use ice and water shield under it.
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3.6/12 isn't "low slope" ...
most manufactures recommend tightening up the standard 5" exposure to 4" when U approach 3/12.
below 3/12 is still possible with full manufacturer honors with full ice shield and venting.
3.6? go with a 4" exposure and get on with it.
Jeff
Depending on which side of the house this sets and the wind direction,you could possibly have a real snow trap situation.So in addition to protection to the low slope you should make sure of the weather tightness of the pitch change juncture if the 12/12 roof won't be reshingled along with the new work.
I like the idea someone had for standing seam roof or if the add. is not facing the street maybe use EPDM.
I plan to run the new shingles up past the junction. It will probably look a bit strange, but who cares?
By "full ice shield", you mean a membrane on the entire roof, not just at the eaves, right?
Yup ... covering the whole deck with the ice and water.
But .... not till we're below that 3/12 ...
like start wrapping the whole thing at 2.5/12.
With the full wrap ... U need increased ventilation.
The original Q was about a 4/12?
I'd just double up the felt (just to make myself feel better) and shorten the exposure.
Jeff
Jeff, where he is he's gonna get eight times the snow and consequent ice-damming that you do in pgh. I've lived in a place with a 4-in-12 with no stick-down membrane under the eaves; every spring I had to go up and chop the ice dams out of the way or stick a bucket behind the head of my bed....
One row of standard ice-and-water membrane at the eaves edges oughta do it. After that, shingle away, standard exposure, don't worry it'll be fine....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
I agree with your last paragraph ...
but first ... I don't know where he lives ... but our freeze/thaw leads to tons of ice dams ... pleasures of our unique Pgh weather pattern ... don't like the weather? Just wait 5 minutes ... it'll change .... We get the Lake Erie Effect ... plus the Canadian effect .. plus ... the southern winds blowing up ... and every now and then ... a good ol' Nor'Easter blown thru ...
and ... second ... ice dams aren't a function so much of the roofing as they are poor insulation. The ice guard does just that ... "guard" from farther damage ... proper insulation/ventilation does the "preventation" ... Philly/ Erie/ Cleveland/ Columbus get the snow ... we get the ice and potholes ...
While we're on the subject ... where's he live? Now I'm curious!
But we agree ... just roof the damn thing ... we're still not talking "low slope" ...
Jeff
Man what you doing up as late as me? And I gotta go quote a roof before lunch today, too.
Yeah, I remember the 'wait-five-minutes Lake-Erie-effect' from when we lived outside of Cleveland. But this guy lives in Maine, and coastal, too, he said. He's gonna get a three-foot snowpack on that roof plus whatever drifting does to him. And that transition from 12/12 to 3/12 is like the curve in a traditional Québec farmhouse roof: it'll collect snow in a nice deep drift if it happens to be facing the prevailing winds. That deep snow will keep that roof nice and warm, heh, heh, heh. (Which was why the old farmers designed that curved roof style: Deep snow on the roof kept heat in the house in the days before insulation existed.) Still, you gotta see a foot-and-a-half-thick ice dam with a foot of water behind it waiting to hit ya in the chest when you chop through it some day. It's a genuine great white north experience....
A bad insulation job will definitely exacerbate ice damming. But good ventilation can ameliorate that somewhat. But interestingly enough, sometimes just direct southern exposure to strong sun in the spring can cause an amazingly thick ice dam on a relatively well insulated and vented roof.
There are guys here who earn their living all winter doing nothing but shoveling roofs. But they are getting rarer as ice membranes become more popular. I generally stick down a single course of membrane on anything under 5 in 12 just for peace of mind. It's cheap insurance. What the heck is another 65 bucks in a $5000 job?
Nighty-night....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Not that much difference in climate between Jeff and Javier
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Not that much difference in climate between Jeff and Javier
That surprises me, having had some experience of Jeff's climate. I must be overestimating the snow in coastal Maine? I don't have the US codes here so I can't look up the snowload for that area. What kind of snow depth would you expect to find on a roof in that area? This is what I'm used to (snow load factors Ss=2.6/Sr=0.4; design temps 2.5%=-27 / 1%=-30; 5300 degree days below -18):
View Image
This photo was taken mid- to late March, IIRC....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
I don't know about ccodes, but I have lived within fifty miles of both locations. Either can look like your photo on a short term basis.here on the coast. a storm can dump four feet in a couple of days, but it doesn't stay around forever because of the warm gulf current so the snow turns to ice or water.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I have lived within fifty miles of both locations. Either can look like your photo on a short term basis.
Whatever; my place looks like that pretty much all winter. At least if we're lucky, LOL....
In any event we're not arguing; Javier needs a course of I&S membrane and then he can go to town with the shingles and a clear conscience....
Me, this pm I'm estimating a roof that I saw this am two different ways; owner 'would love' cedar shakes...but wants the price diff on asphalt shingles. This is an established client; no problem with charging for the DCA. But I haven't done shakes in a while ($$$!!!); gotta refresh my memory and double my initial enthusiastic guess as to how long it's gonna take me....
He has one shady side that will dry slowly and that's an issue we have to discuss, but I think I'll propose stripping the roof to the deck (which has at least one hole in it that we can see right through the shingles), repairing it, then laying on a course of I&S membrane and 30# before building a ventilation lattice of vertical 2x4s on the flat topped with 1x6 skips. I'll want to interleaf the shakes with 30# too. This is gonna be a major re-roof; what's up there is only 17 years old but it's a cathedral ceiling with minimal insulation and not too great ventilation. I'll want to keep that new roof nice and cold and cribbing the shakes ought to help do that.
Now all I gotta figure out is how to get a container up near the house; access is by a home-made RR-tie 'bridge' across a 10-wide X 4-deep creek--it holds my truck okay, but I don't wanna make any guesses about a loaded 30-yard container on an 18-wheeler. Gotta get the container guy to drive out and take a look-see on Monday. If I gotta hire somebody to do nothing but haul the scrap out by wheelbarrow over the bridge, it's gonna double the labour bill....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
That would make it worth investing in a dump trailer.Given the cathedral cieling, you could also think about adding a ply of foam XPS over the sheathing and under the rails for your skip sheathing.
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I'd have to check out rental on a dump trailer. I don't know who's got them around here....
I did suggest exterior foam boards to boost the insulation, but that probably won't happen. The heating bill for that place is high but not completely off the wall. It'd probably take them 10 years to recuperate the investment. I could run the calcs, but I think he'd prefer to invest in the shakes than in additional insulation. I don't think he's ready to pay for both....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
It is less the insulation and more the preventive insurance re condensation that I was thinking of.I bought a dump trailer about 18 months ago. Don't know why I waited all these years. It saves an hour of labout on every dump run, so just the labour savings have made it pay for itself ( c. $3000 new) alreadyPlus, it is larger than either a PU bed or my other trash trailer, so there are fewer dump runs to make for the same volumne. large dumpsters are not available on site for me.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
It is less the insulation and more the preventive insurance re condensation that I was thinking of.
If I lay those shakes on top of skips spaced 1½" off the existing roof deck, they're gonna stay cold. I'll have to vent the ridge and the rake boards, but there'll be enough air moving through the space between the two roofs to keep things dry. That's the way I figure to propose it.
To insulate in addition, I'm looking at 3" polyiso boards, which is a custom order, and means I have to mount the 2x4s on edge as a crib. So in addition to the cost of the foam boards (not cheap) there's the labour to drill all those 2x4s and lag them to the roof deck, plus the labour to install the polyiso. Figure right there we're looking at 48-60 extra man hours plus the extra materials. Then, to keep the new fascias and rake boards from making the house look like a kid that schmeared lipstick from her nose to her chin--and to vent the rake--I'd have to tier them in two cascaded layers. I wouldn't mind selling it, but I don't think he's gonna buy.
This roof has a 12/12 section and a 8/12 section plus a couple of dormers and two chimneys, so 6 valleys and some step flashing which may or may not be in good shape after 18 years. (It was aluminum.) Access is easy for most of three outta four sides (second floor wrap-around deck puts the eaves at waist height), but the fourth one is gonna need 12 sections of scaffolding set up 4 levels high x 3 wide. He's gonna be in for a decent sized bill no matter what option he chooses....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
I just bought a dump trailer this week (6x12). We kept having too much trash at the end of a job to fill a p/u, but not enough to bring in another container. Plus, it's mighty nice to pull up next to those poor fools unloading a p/u or trailer by hand at the stinky transfer station, open the gate, hit the button, and wave goodbye.Hey Mister Sushi, you forgot to cook my fish.
"Am I dead or alive? What's this? Linoleum? I must be in hell." -The Salton Sea
Also, if you find any goodies to take home for recycling, you can haul more of them, LOL
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Boy, we can't have any fun at our landfill. You can't scavenge, either (I saw some pretty nice mattresses out there the other day, too).Hey Mister Sushi, you forgot to cook my fish.
"Am I dead or alive? What's this? Linoleum? I must be in hell." -The Salton Sea
I found the best dump a coupla years ago ...
the containers are 10 ft down a drop off ...
they always have two sitting and waiting ...
they dug the area out so U just back up to it ... and take a dump!
when the two containers get full ... they drag them out to the big yard and empty.
Works great for both dump trucks/trailers ...
and Vans/pick ups.
Back the van as close as possibloe so I still have room to stand ...
and start grabbing and rolling.
I box/bag everything cept for lumber ... so I don't have muc brooming to do.
Roofers with pick ups just unload about half the bed by hand ...
then push broom the rest down and into the containers.
Plus ... the office has "dump cats" ...
Big day going to the dump .... if I can arrange it ... I'll wait till Fri afternoon ... pick the boy up early from daycare ... and head off to the dump!
Jeff
When unloading some trash once I saw a guy pull in with a regular pull behind with two foot sides full of old shakes.
He had a system worked out with the guy working there where he backed the trailer up, hooked a chain to something and drove forward.
Had a tailgate of some kind up against the front side of the trailer so when he drove off the tailgate with the chain attached to it dragged all the trash of the bed of the trailer.
Worker threw the chain and tailgate into the trailer as the driver waved and drove off.
Whole thing was done really quick and he was out of there.
be thinking
"I can't say I was ever lost, but I was bewildered once for three days."
I've used that trick, too. Trucker delivering a 30-foot steel I-beam to one of my sites a few years ago showed up alone expecting me to have an excavator or backhoe available to unload the beam.
As it happened, I only had Wingnut the useless helper and my dog with me that morning. So I had him back up right over where I wanted the beams dropped, and I hooked a rope to the beam and made it off to the foundation. We slipped a few pieces of 2" galvanized pipe under the beam as rollers and had the truck drive away.
Worked like a charm.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
We can't do that around here anymore. We used to put an empty pallet at the front of the trailer (or truck bed) with a chain hooked to it hanging out the back. The landfill bulldozer would hook up to it and drive away pulling the load out.
A couple of years ago, someone used some aircraft cable instead of chain and it snapped and shot back thru the window of the truck, seriously injuring his small son. There're signs posted everywhere saying "PULLOFFS" are not allowed now. Hey Mister Sushi, you forgot to cook my fish.
"Am I dead or alive? What's this? Linoleum? I must be in hell." -The Salton Sea
If you can't get the container or the dump trailer across the bridge, how about a Bobcat? It's a whole lot faster than a wheelbarrow and a jacka$$...and lighter than a 30 yarder.
I rebuild alot of porches that were 4/12 or so. I actually make the slope a little lower because in the old days they put the second story windows very close to the porch roof. I like to lower the roof to give some more room between the roof and windows.
So that means a pitch lower than 4/12. I`ve read that asphalt shingles shouldn`t be used below a 4/12. Therefore I use an ice and water shield as underlayment and never have had a problem.