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bobinphx 08-06-2012 07:21 PM

concrete tile roof underlayment recommendations??
first off, I am a way over zelous diy home owner. I do my own plumbing, electrical, hvac, contruction and roofing (flat and shingles).

with that said, I have a 30 plus year old concrete tile roof that needs new underlayment. Research on the net shows that just about anything from 15 lb felt to synthetic underlayment to self adhesive, self sealing SBS is available.

I am in phoenix az, where temps can reach 120 degrees and the attic has gotten as hot at 200 degrees (yes, I log attic temps... LOL).

I just completed a spray on radiant barrier for the underside of the roof. Note that the underlayment has been brittle for about 4 or 5 years, so the radiant did not accelerate the underlayment getting to the point where it needs replacement.

So, now the question, what to use for underlayment. I am leaning towards a very thick SBS self adhesive type underlayment. Then I want to used painted or treated wood, with drainage grooves as battens. I have used self adhesive under shingles an my shed, which has worked great for the last 3 years. but thats a shed, not the big house!!!!

given the heat, given I want the underlayment to work for 30 years is self adhesive proven?? or would a 30 pound layer (or maybe 2 layers) be better??? what type of priming is suggested for self adhesive (I used a liberty product on the shed which required priming with asphalt emulsion.

Thanks in advance.

Windows on Wash 08-06-2012 11:42 PM

200 degrees in the attic? :eek:

What color roof was it and is it vented?

bobinphx 08-07-2012 07:21 AM

yes, 200 degrees. Directly under the plywood roof. about 190 halfway down and 185 at the insulation (r19). ventilation is only two site built gable vents that are way undersized. no eave vents. Once its cooler out, I will be adding vents this winter. the roof color is dark red ceramic paint on the concrete barrel tiles. so, yes it gets hot on the roof. after that will be insulation removal and ceiling sealing with mastic, can foam and caulk. Then we will add insualtion to get to about r30.

side note, my bother had less vents in his house and we added screen vents on all eaves and then 7 hood scope type vents on the roof and he now runs, at max 20 degrees above ambiant.

roofnron 08-07-2012 10:35 AM

You are right to want a heavier underlayment. You want the roof to not leak a drop before the 1st piece of tile makes it to your roof. I would never use 15lb or 30lb or synthetics for this.

Check out the They have a ton of info that may help you out as well as pdf installation manual you can download. You should consider the counter-batten system that is detailed. This method will leave the underlayment roof more watertight because the battens will be fastened with waterflow. Also you can incorporate details to allow for above the deck ventilation.

Windows on Wash 08-08-2012 07:27 AM

+1 to roofnron.

You absolutely need to add in some ventilation and air seal and insulate. If you are putting in loose fill, go over R-30 as it is cheap and you might as well go R-50 if you are already up there.

Make sure the battens don't block water flow as discussed and they actually make battens that are designed to allow water to pass through as well.

hotrod351 08-08-2012 09:04 AM

im in mohave valley, 12 miles from bullhead city, and have done a few hundred tiles roofs here. you want to use #40 pound and use simplex nails on the seems. #15 is a joke, ive only heard of that being used once, #30 was ok until i found out after 7 or 8 years the felt buckled on the overlap, even if it was nailed with simplex nails, it would just tear. the #40 seems to actually stick to itself. anyway thats what i used on homes for years and never had a call back. if you were loaded you could go with torch down, id say #90 pound but its almost as expensive as torch down. might also be time to figure on installing a couple dormer vents. i know letting the hot air out is a big thing here in arizona.

bobinphx 08-09-2012 09:06 AM

Guys, I totally agree that the attic is way to hot. I am looking at a full on attic vent plan!!! eave vents (full screen type), sheet metal insulation hold back / air troughs, More gable vents and even looking at roof venting on the roof deck. I also am planning on pulling all the insulation when its cooler. I want to air seal the ceiling, then put in about 3 inches of blown in, then lightweight plywood and then fill in to about r40 or so and then a radiant barrier paint on the underside.

but first is the roof...

if what I am reading here and else where, the tile roof should be considered almost a decorative element. Yes it will shed water, 100 percent (if installed right), but it will have leaks give the right wind direction and amount of rain. This makes the underlayment the real roof that keeps the water out of the house.

sbs makes sense to be because it seals around the nails. selfadhesive also makes sense, since torch down is a skill and cold applied is a mess.

so I guess that sort of settles it.. sbs selfadhesive, with a counter batten system under the tile. This will provide water drainage and air flow, along with an almost leak proof roof that should be good for about 20 to 30 more years.

sound like a plan?????

roofnron 08-09-2012 10:03 AM

Sounds good to me. Make sure to you good material for your metal flashings. (NO coil stock) Copper if you can. This roof will last more than 20 or 30 years, the flashings will be the first things to go.

hotrod351 08-09-2012 10:17 AM

the tile isnt really decorative but it does let water in in extreme cases, thats why the battens are suppose to only be 4', for water run off, and the bird stop has a hole in it every foot or so to let water run out. shakes are more decorative then tile, considering that the shakes protect the felt and the felt is what is water proof. most of the time water gets under the tile by improper flashing installation and the hips and ridge isnt cemented, so water blows up under it. they actually have a metal, or plastic, that is designed for the hip and ridge to keep 99% of the water out, ive never used but have seen it, a lot easier than carrying cement up the ladder to cement everything. so at least a #40 pound underlayment, or if money provides then plain surface torch down, which you dont have to torch you can just over lap and nail the seems. but #40 will last here for at least 20+ years.

roofermikeinc 08-14-2012 10:20 PM

Power up!
Power up those gables! Slap a gable fan on the inside blowing out. Consider a white tile. Check out Polysyick TU Plus underlayment. Takes the heat pretty well. Very popular with Miami roofers. Pretty hot here...

Roofer Mike

...AND LIKE ROOFER MIKE!!! :thumbup:

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