Ice on roof edges even after adding insulation?


#1

Ok I have 1ft overhangs, roof has 3ft ice and water with Archet shingles ( 30 yr) the roof is a 4/12 hip roof with a Southern gabled addition on the back so i have 2 valleys total. I always get ice on either valley side in the back ( South ) This Fall I added additional insulation and baffles to the rear addition and I have full run vented soffits all along the whole length of the house and addition which gives me about 160 ft of vented soffitt and about 80 ft of ridge vent or more. , I have more than enough ventilation i would think and about 18" of insulation. Why do I still get the ice ?? It goes up the roof about 6" and gets about 3" thick at the edges. I put the heat wire up 2 yrs ago and it works very well but it still seems I shouldn’t have ANY ice at all. I get some in the fron above my bow window but most on both valleys in the rear. When they did the roof 11 yrs ago he ran ice and water up the valleys 6 ft wide, then metal then rolled roofing and ice and water 3ft up around the whaole house. I havent had water ever come inbut Im nervous I may ???


#2

on some houses you will just get ice no matter what. the insulation/ventilation is a formula and is not guaranteed to work because every house is different. mas long as the ice isn’t hurting anything just let it be.


#3

Ok is 3ft enough ice and water ?? I know everyone uses 6ft now . I dont know if its worth tearing off an 11 yr old roof jsut to put own more i&W


#4

Normally 24 inches inside the warm wall does the trick. If you have a 1 foot overhang then it will not be inside the warm wall. I would not worry about unless it leaks.


#5

wait a minute, if its 3ft wide and I have 1 ft overhang doesnt that leave 2 ft ? Also wouldn’t the water or ice still have to go back 3ft to get under the I & W ? My ice usualy is about 5" back about 2" thick at the edge on about a 20ft section of the roof ? Ok or not ??


#6

It code states it must be 24 icnhes inside the warm wall. Basically look at the wall facing outside and then it must be 2 foot past that wall. If you have a foot overhang then you will not have 24 inches iside the warm wall. Hope that makes it easier to uunderstand.


#7

??? The ice and water is 36" wide, the overhang is 12" to the outside wall so that leaves 24" from the wall up the roof, whay do you say I dont have 24" ??? I must be missing something. It goes from the drip edge up the roof 3 ft and again the overhang is 12" in my book that leaves 24" past the overhang onto the roof so I should have what you say code is right ?? Thanks


#8

Your exterior wall is probably more than 6" thick.
So, from your eave to the inside of your exterior wall is at least 1’ 6"…
Horizontally.

The Ice & water shield is supposed extend a MINIMUM of 2’ (24") beyond the interior wall line.
Vertically.

The Ice & water shield is going on a slope so in order to get 2’ past the interior wall line you will need an additional 1’ or so, to meet the minimum.
How much you need on the roof to get past the interior wall line varies according to pitch.

If you want to be picky and do the bare minimum you can use the pythagorean theorem to figure out exactly how much you will need.
Or you can do what roofers all over do, use either 1 1/2 courses or use 2…
There is a line down the middle of most Ice & water shield that you can use as a guide to cut it in half.

2’ beyond the interior wall line is a minimum, it is frequently advisable to exceed this specification.
I have consistently found that to do a roof correctly in my climate requires approx 1/3 of the roof to be Ice & water shield.
Most of my roofs are cut up though.

If you ask nicely maybe Ranchhand will draw a nice picture for you.


#9

If you have snow on your roof especially a 4/12 you are going to have ice if certain weather conditions are in place no matter how much ventilation & insulation you have installed…Mother Nature will make sure of that,you cannot control the outside elements,a little bit of sunshine,slight rise in temp. the snow starts to melt,wind blows over the roof,the sun goes down,the temps fall,the ice starts to form at the edges and will continue to build up as long as these factors are in place…the heat tapes can help prevent ice damming,if it gets to bad and starts to leak you have to go onto the roof and remove the snow & ice,just have to be careful not to puncture the valleys ect…IWS will help with melting ice back up under the shingles…With the ventilation and added insulation you have helped keep the roof deck cold in the winter and may have eliminated some of the ice damming/build up but it is not a total cure due to the climate we live in.It can be a pain if you have water entry,but it can all be fixed & replaced, I think you have done all that you can… Take care


#10

Axiom, I think he gets the idea by now… no sketch needed.

But I do appreciate your thinking of me. :smiley:

By the way; for HornFans.com, I did a sketch recently of me & Vince Young roofing. I hope y’all like it.


#11

first try at art work
good-times.webshots.com/photo/25 … 3997TXkWBf