Bituthene and “breathing” houses
Finishing first part of a roof rebuild. 1963 ranch with a 4:12 pitch, 7,500 feet in snow country, several feet of snow for several months at a time. Rebuild prompted by soft 5/8″ decking (now 23/32″), 2×6 rafters on 24″ centers (now sistered with 2x8s), and three layers of shingles with leaks and condensation problems (increased the soffit venting, tripling the ceiling insultation, considering an exhaust fan for the gable vent). Last winter, we even had a second ice dam several feet above the eave’s ice dam!
Many of the flatter pitched roofs up here use a full coverage of bituthene (Ice & Water Shield) and that’s where I’m leaning (the first four of six courses are laid). Naturally, I’ve bent the ear of everyone I know with a truck and a nail gun, and it has led to a couple of questions.
The majority of the people agree with 100% bituthene, even if some say it’s overkill. However, one roofer was adamant that I should still put a layer of felt on top of it. Any big advantage or disadvantage to this?
I did have one contractor insist that 100% bituthene would not allow the house to breathe and that I would still have condensation problems. Seems to me that if the attic is cold and ventilated, the breathability of the roof should not be an issue. Am I missing something?
Thanks,
Curtis
Edited 8/7/2002 12:50:48 PM ET by BADDOGLT
Replies
Curtis,
Increasing the strenght of the roof will go a long way to ensuring a long life to whatever products you install up there.
100% bituthene would probably be overkill but I'm not familiar with your conditions.
Felt over bituthene would be a total waste of dollars and time.
The roof membrane does not need to breath, suck or blow.
Good luck with your project, it seems on track.
Gabe
house breathing depends more on your total ventilation package. Bituthene is nolo contedre.
It used to be that felt was required over the bituthene. One reason was walkability and saftey. He might, like myself, have once had the unpleasent experience of sliding off due to slippery bitch.
Another reason had to do with looking into the future and being able to remove or replace shingles. If they are stuck to the membrane, they are stuck to the membrane!
Now, think like a drop of water.
Suppose you get through the shingles in a wind driven strom near the peak of the roof. You are now under the shingles and over the bit. Gravity hooks up with you and you begin traversing the slope like a slolum skier until you come to a point within three feet where that lttle beaded edge of stickum at the bit lap has a shingle stuck to it, making a bag and stopping you from going further down the slope. A few of your wet little friends find a way down maybe but several others join you and eventually you get a touch of frost and puff yourselves up. That frost pockeet doesn't do the shingles any good.
a layer of felt can help prevent that from happening. Overkill maybe, but not wasted effort, either.
Meaning no disrespect but how can the glues strips between the shingle layers glue the shingles to the substrate?
Felt has no use over bit. Safety or anything else.
Gabe
No dis taken.
The sticky bead I was refering to is on the edge of the bit. About a quarter inch of the gummyness is exposed. unless it is hit by dust for awhile before shingling, the back of the shingle sticks to it.
I'm not arguing for or against but there are some advantages to having the tarpaper if you want to go to the trouble. Mostly, I was explaining the probable reasoning of the roofer who wanted to do it. Historically, if you go back twenty years, you find that it was required when the stuff first came into regular use.
You used to have to use a roler and apply a nasty primer to the sheathing too. This kind of product came into being to replace what we used to do, which was to hot mop a sheet of tarpaper over a ply nailed down. Try that with a hot mop on an 8/12 three stories up sometime for thrills if the whitewater ever gets too boring for you.
;)Excellence is its own reward!
Yes there is a edge to the bit. but being shiplapped water could never penetrate and that small of an exposure to the sticky side of bit. wouldn't have any real effect on shingles sticking to the substrate any more than any other product would.
Don't need any other thrills, thankyou. I just finished inspecting the outer caulking on the outside of the 18 story roof parapet on a swingstage with a healthy wind. Getting too old for this kind of ####.
Gabe
"Getting too old for this kind of ###"
Awww, come on now! You gotta admitt - it keeps the blood from all settling into your feet, or butt.
:)Excellence is its own reward!
Sounds like time to go fishin'.
Anytime, anywhere, any weather, any river, any lake, any species...is a good time to go fishing.
Gabe
Puts the whole scheme of life into bite size pieces.
Gabe and Piffin,
Thanks for the replies. Sounds like the felt _may_ be a wasted expense, but with no real downside. Shingles get delivered tomorrow, we're pounding on Saturday, so I still have three days to decide.
Curtis