Arguement that breathable underlayment makes no difference


since shingles are essentially a vapor barrier.

If this was true, a vapor barrier underlayment like Titanium would NOT have printed warnings that structure has to have proper ventilation, (And there are posts that confirm this.)

And old homes with no ventilation have been without issue when felt and shingles are used - they way it’s been done for 50 years.

NOTE: originally I believe 1by and shingles was the earliest config, then felt was added, they plywood substituted for the 1by, and then VB substituted for felt - the evolution was to completely seal the roof. But problems were discovered with old homes w/o ventilation.

Any thoughts on this?


Work on 100+ year old slate houses on a regular basis with the double 30# still in tact over the 1x or t&g decks. When you pull some slates for replacement and have to take some felt off to replace a pipe collar or something the deck is beautiful. If 30# asphalt saturated felt has done its job that long imo there is no reason to switch to something relatively new and unproven.


Old houses are/were drafty and leaked air all over the place so any moisture had a chance to dry out, they were made with real wood as opposed to engineered wood products also.

When asphalt shingles came out I suspect that they were marketed as the new high end roofing material that would solve all of the problems with cedar shingles.

People took these asphalt shingles and installed them over the top of cedar shingles, this changed the physical dynamics of the roof assembly dramatically.

With asphalt shingles over the cedar shingles the roof could no longer breath so this lead to massive ice build up and leaking.

Now that the house doesn’t have the air exchange that it used to the moisture from leaking didn’t get an opportunity to dry out, leading to rot & mold.

It seems like it took a few decades for people to figure out what was happening and the underlying cause.

This is the result of a vapor barrier on a building that wasn’t designed to be air tight.

Nowadays and even for the last couple of decades we have been building domiciles that are more air tight and require a different approach than homes of 100 yrs ago.

If you have a newer home or a home that was designed with ventilation in mind it matters not whether your underlayment is a vapor barrier or not because the building is designed to handle it, if it is working correctly as a system.

In some specific cases this is very important but for the vast majority of sloped roofing rooftop vapor barriers make no difference.

If it is an older home that originally had cedar shingles on it there needs to be a proper cedar to asphalt conversion done, this would include the installation of a roof ventilation system.

I personally prefer asphalt felt also but felt that meets the minimum standards doesn’t exist in my area, the only asphalt felt available to me is complete junk.


Know all about junk felt axiom. We were using tamko blue label for years and recently haven’t been able to get every has been substituting with junk. One of the good suppliers stocks warrier brand and it is a good 8-10lbs a roll than anything I have seen in the past 15 years. We started bringing pallets in it and using it as our standard.


Axiom, May I ask what synthetic product do you use? Also, I saw another one of your posts that mentioned working on a home by Lake Michigan. May I ask are you located in Michigan? If so, whereabouts?


I primarily use Certainteed DiamondDeck and Malarkey Secure Start Plus.

I service Northwestern Michigan, primarily the Leelanau, Grand Traverse, & Antrim counties but really anything south of the bridge, West of I-75, & North of M-55.


I’ve always liked the Certainteed 30#, we get mostly IKO felt nowadays.


I’m using Deck Armor but looking into the SIGA products which are supposed
to not hav any problems with rain of any kind.

Hummm… Never any Michigan references with me. Must ha me confused with
someone else?


I have a friend who does slate roofs and he is Old School all he way. No
ice & water guard for his jobs.


I would hate to ventilate my curent project: 24x28f 7in12 hip roof w/4ft ridge and 4 dormers as wide as possible - two of them intersect the hip rafter.

Ventilating that house would be a nightmare so I’m keepig it Old School although I’ve put a triangular gable vent in he downwind dormer (the gable vent becomes the entire dormer gable so calling it a “gable vent” is misleading.) I might add 1 or at most 2 more of these but none on the upwind dormer.


I Don’t know about no ice and water on a new slate install. I use I&w on the eaves on slate to prevent ice damming and meet code, but then put layor of 30# over it to prevent the slates from sticking to it making repairs impossible. Do the same with metal work and metal valleys, but use a layor of rosin paper over the I&w to act as a slip sheet and allow for proper expansion/contraction.


Phew, I thought I was the only one that still believes in good ole 30# or 15# felt instead of the new underlayments. Ice and water on the eaves and valleys and felt over the rest of the roof. Works every time…


Regarding slate and lead flashing:

I did the counter flashing on my chimney cricket in lead sheet that was laying around the shed for at least 60 years.

If you ever worked with lead, you’d never want to use anything else. No Port-O-Brake - just a couple pieces of wood to slap it, an edge of wood, and your hands.

What is unique about lead is that it’s modulus to mass ratio is so low, you can perfectly straighten a piece of bent up lead by “spanking” it onto a flat surface. And I mean it will be perfectly flat. This works because the mass is so high that it “self dollies” itself if you are familiar with auto body dent repair.

There are so many things that have to be just so for a sealed and ventilated house:

And what no one mentions is that the basement has to be totally dry which is NOT the case of even new homes when they get 10-20 years old. Lots of new homes do not have proper shedding landscaping so they install French drains which work only for 10-20 years until they clog. Then you have moisture finding its way into the basement and if finished, you can count on black mold behind the paneling or plaster.

And if there are any environmental issues like radon, formaldehyde, or some new one that is not known at this time, you will be in trouble.

The only place a true VB works nicely is in tents.

NOTE: If I used I&W on my little hip w/dormers, there would only be about a 3x3’ patch of exposed sheathing on each side of each dormer - in other words, 100% I&W would be the result. The only place that should be considered is in hurricane country - but then, shingles shouldn’t be used there. The old 50’s homes had low slope roofs, parapets, and gravel roofs. Not pretty but strong as a pillbox in a 'cane.


There is nothing like the smell of good asphalt felt on a sunny morning.


I like the way it sounds when you roll it out!
That constant sticky sound
of it unsticking from itself.

If you can hear your feet unsticking from it,
Even better!


I agree, I tried drying in a house by myself with a synthetic underlayment, didn’t like it , to hard to keep wrinkles out . But with #15 or #30 lb. Felt it goes alot smoother for me cause I work by myself. Might get your knees and hands a little dirtier but to me easier to work with


Edgar, another Solo roofer! that’s a tough occupation.

When you tear off and felt, do you start at the top?

I had lots of 1by sheathing repairs and was flirting with rain. So I would tear off about as much as I thought I could get done before the next rain. I’d felt each portion so when I reached the bottom of roof, it was felted.

I do like the idea of 30# felt because it is very cheap and is no big deal if I waste some doing some temp work to beat rain that will be tore off after the weather.

I HATE tarps. The good ones are too heavy and even the cheap ones are a PITA for one man.

On the way up the roof, I would shingle and if I did not reach the ridge, I’d tape the top edge of the shingles to the felt with 3in Gorilla tape. (A thinner tape with just as much adhesive would be better - eve if rolled, it tough to get a really good bite in shingle granules.


Without ventilation there will be no manufacturer’s warranty in effect. This idea that felt paper lets the roof breath is absolute Bs.


So accustomed to getting complicated a stuff tight with felt, such as bending a fold and sliding up behind the crown molding and fascia/sofit on dormers. If you try the same thing with synthetic it’s impossible.

I normally have crew of 4, towards end of the day 2 guys felt, 2 do cleanup… no problems. Every time I try synthetic ends up being windy, all 4 guys end up on roof, more kickers/ planks are needed colored to walking felt, and really seems like it takes 4x the labor.


To Mrcreosote Question, I usually don’t do whole roofs I mostly do additions,mod. Torch, repairs. But yeah I have started some steep jobs shingling from the top down in months when it is hot to keep from scaring up shingles. 3 tabs not deminsionals.