I am not a builder by trade, but building my own house and shop. These are located in the phoenix metro area.
I am getting ready to set trusses and sheath the roof on the shop. We will be using a tile roof. I am looking for feedback on people’s choice of underlayment. The roof does not have any valleys, but it does have a couple of sections where the roof plane abuts a knee wall on a taller section of the building.
I am building this for myself and have every intention of being here for a long time. If the underlayment fails in 20 years I’ll be the guy fixing it most likely. And like most of us here, I want the absolute best possible product – without breaking the bank…
I have spent a little time reading on this subject here at Breaktime. The choices seems to boil down to two: 30 lb felt or Ice & Water. The downside of Ice & Water besides the cost is the rated lifespan of the product. The downside of felt is that it does not self seal around nail holes, etc.
Since this is in the desert, we don’t have an ice dam issue. We do have long HOT periods to dry stuff out. We also can get a couple of inches of rain in an hour with driving wind – occasionally.
I have read where the felt should be doubled. I saw one description that the doubling is achieved by starting with a 19″ half strip at the eaves and then overlaping each run by that much. That versus running one full covering of felt and then start over again at the eaves and running the second.
Any advantages, theories on combining the two products. Since I don’t have any valleys, would there be any benefit of using the I&W at the roof/wall intersection? The building is being made from Rastra (ICF material) and the flashing at this intersection will be kerfed into the Rastra block. So any I&W run up the sidewall will be no taller than the flashing.
I have not priced either approach yet. Can someone give me a rough price comparison for any sized roof for felt vs. I&W?
Thanks for the great feedback.
-dch
Replies
I suggest you follow the instructions from the manufactor. I know I almost signed up as a preferred installer back in the 80's and they had rules to follow.
What brand/type of tile? Some manufacturers have a proprietary underlayment which is typically a re-branded I&WS.
Here's what we typically use:
http://www.interwrap.com/titanium/udl_30_main.html
Not sure how it would last in your climate, but I've not had any problems with it.
doubling is achieved by starting with a 19" half strip at the eaves and then overlaping each run by that much. That versus running one full covering of felt and then start over again at the eaves and running the second.
The advantage to double lapping vs double layers is that if any water penetrates the 1st layer, it theorectically gets brought back to the surface of the underlayment. If water penetrates the top layer of a double layer, it remains between the two layers until it finds a hole in the 2nd layer.
We do have long HOT periods to dry stuff out.
I'm unsure of how that affects I&WS. The main enemy to I&WS is UV rays, so if the "open" time is limited, then that might be your best choice.
The old tile roofs around here used a hot mop underneath.
You didn't specify the slope of the roof. That would also influence my decision.
would there be any benefit of using the I&W at the roof/wall intersection?
Won't hurt, might help. I've heard of Rastra, but have never touched it. Don't know about it's water turning abilities. If it absorbs much, then you're probably in trouble if you haven't thru-flashed when the wall was laid.
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like seeyou, we're using all 2d generation roof underlayments... including the titanium
we use felt under our siding, but haven't used felt on roofs for almost 10 yearsMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
Roof pitch is 12:4.
Rastra is not waterproof. The Rastra is not on the knee wall yet - Rastra makes a flat panel that does not get grouted. I am using this for the gable ends and the knee walls. The Rastra gets covered in Stucco.
Your recomendation on the flashing is to run it up the framed knee wall and then put the Rastra over it. That would work, but would be impossible to remove later. My thoughts on "kerfing" the flashing into the Rastra would mimic flashing mortered into a brick chimney.
I have attached a sketch of a cross section of what I have in mind.
Thanks for the input.
Looks like the attachment didn't come through.... Here it is
In Maine, I just installed some IWS. The box says NOT recommended for the Desert Southwest. That would be you.
http://www.tamko.com/ProductDisplayPage/tabid/53/ControlType/productDisplay/itemid/1575/Default.aspx
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traditional is a dual ply of 30# installed by lapping 18"
For a step up, use Rooftopgaurd II which is toughr and has limited selfsealing at nails. It goes on fast too, being 5' wide, and will handle turning up that 18" at kneewalls well. A good compromise between the 30# and the bituthene
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Just a Thought, I used a product like this under 56sq snap lock standing seam, easy to work with and was impressed with how water tight the project was during instalation of the roof.
http://www.energy-innovation.com/files/file/StrongSeal%20Roofing/StrongSeal%20SA%20Technical%20Data_12_07.pdf