Replies

1. 
   patrick_mccombe | Apr 05, 2013 11:02am | #1

   If you go with ice and watershield, you'll want one suitable for high temperatures. Like this:

   http://www.na.graceconstruction.com/underlayments/download/GIWS-210E-GIWS_HT_2.pdf

   I'd use 30-pound felt--much less expensive.

2. 
   Mike_Mahan | Apr 05, 2013 12:40pm | #2

   I've put metal roofing right over composition shingles without removing them. They were in good shape but it was a low pitch and they grew moss to easily. We just pressure washed the roof to remove the moss and put the metal right over the existing shingles. This was in a mild but wet climate.

1. 
   seeyou | Apr 06, 2013 06:43am | #3

   That's a really bad idea. The expansion/contraction of the metal panels causes friction against the shingle aggregate and will rub the finish off the back of the panels. They'll rust out from below. It's also hard to torque the screws properly. The common practice is to add furring strips over the shingles if they're not removed.

1. 
   Mike_Mahan | Apr 06, 2013 12:05pm | #4

   Furring strips.

   I forgot to mention the furring strips. I used metal channels.

1. 
   oldhand | Apr 06, 2013 04:40pm | #5

   another way...

   The metal roofing install instructions from some authority or the other I forget says you can put metal over shingles with felt between to lessen the abrasive issue. Lath being not strictly required.

3. 
   catfish | Apr 21, 2013 06:37pm | #6

   Standing seam is going to oil can.  Nothing you can do is going to stop it.  I & W is SOP for some systems, T-panels being one.

   5-V is junk anyway, so its going to leak.  You can be sure when he prices material he will use the 5-V from Lowes.

1. 
   finefinish | Apr 23, 2013 09:39pm | #7

   Hey Catfish, Agreed standing seam is going to oil can.  It can look awful or be barely noticeable too and a lot of that in my humble opinion is what's underneath it and how it's fastened.  The rosin paper over the Grace and backer rod is cheap enough and if it helps a bit then to me it's worth it.  The 19" wide standing seam panels on my house were done this way and show no oil-canning.  I know this is rare however.  

4. 
   gbaune | Apr 29, 2013 11:01am | #8

   Slipping is Good

   The backer rod idea sounds good, what size of rod do you normally use??

5. 
   IdahoDon | Apr 29, 2013 11:14am | #9

   Read the fine print as not all ice and water is rated for use directly under metal roofs - the extra heat that's transfered to the ice and water dries it out and it crumbles like dust.

   I love ice and water and wouldn't use anything else on a project, however, under a metal roof I'd cover the ice and water with a double layer of 30 lb felt.  It provides a surface the metal can slip on, and just as important provides some insulation from the extra heat generated by the metal roof.

6. 
   perkerk | Apr 29, 2013 09:03pm | #10

   re: Metal roof advice

   Don't use rosin paper! I hope you mean felt instead, and if not, then use 30# felt (asphalt-impregnated), overlapped shingle-style.

   Why not do it right since you're going through the effort? Remove the old shingles and underlayment, replace it with a new felt layer, put down horizontal furring strips as purlins (1x4's work fine) and install the metal roof panels over that? This will keep the metal roof panels from being in direct contact with the shingles. In a wet and hot climate like yours, that's a bad combination.

   And if you really want to do it well with just a little extra effort and cost, create yourself a convection roof.  Instead of putting purlins directly on the felt, first put down vertical 2x4's over the new felt to create a air convection layer and then install the purlins on top of them. Also be sure to install continuous soffit and ridge vents (sized appropriately). This allows the heat that builds under the metal panels in the space created by the 2x4's to rise, drawing cooler air from the soffit vents and exhausting through the ridge vent. To truly get a convection engine (which will draw the hotter air from the space between the felt and roof panels), the rise from soffit to vent needs to be at least 5', but even without that the roof will vent and exhaust moisture effectively.

   Yes, like others mentioned, metal roof panels witll tin-can. But the seals used now are pretty good, and even with tin-canning (which implies movement), the seals are really minimize water intrusion. If you use the 2nd approach described above (the convection roof), this is the best of all worlds IMO. Some water will get in in the harshest condition regardless - the convection roof provides the best approach at allowing a way for that water to evaporate and exhaust out the vents.

   Eric