above sheathing ventilation (ASV) in East TX
 

I just posted in the intro forum so if you want to know more of the back story, it is there.

Anyway, we are building a house (myself) and it is just about time to put the metal roof on. We are planning on 1" thick spray foam for sealing and the R5 and then fiberglass in the house. I also have a large overhang on the front of the house that keeps the sun completely off the front south wall in the summer. We have just a few windows that face west and east and only one small kitchen window that faces north.

The house is a 1 1/2 story and I have black sythetic felt on the roof right now. IT GETS HOT upstairs even with the windows open and the fans blowing. I can feel the heat radiating from the south facing roof. (pic below). Anyway, I'm going to be using Above Sheathing Ventilation since our spray foam will be up against the roof deck (all the way to the peak). ASV is a way to keep a sealed attic cool. You basically take the ventilation path and put it above the roof deck. To achieve this, I'm going to be putting down a radiant barrier on the roof deck, then put verticle 1x2s on top of the roof rafters. Then I will put horizontal 1x4s 20" on center. The metal roof will be mounted to the 1x4s. This will easily support the standing seam metal roof and allow cool air to enter the gap between the 1x2s at the eave and allow it to heat up and run up the chanel to the peak. There are lots of studies out about ASV right now and you can read more about it via google. With ASV, I'm able to put a dark metal roof on my house and the inside is cooler than with a white metal roof mounted to the deck.

I will post pictures as it gets done.

thanks
Austin

Interesting idea. Do you have any links to info on ASVs?

You might have to post a few times to be able to post a link, that is fine. Its just spammer protection.

I would say this is a pretty good link. (if it shows up)

Cool Roof Design for Hot Texas Climate | Houston Cool Metal Roofs

If that doesn't work, I will post some pictures.

Anyway, here in TX since we don't have basements, most of our AC equipment is in the attic under a black asphalt shingle roof. Yes, the attics are vented but the attic still absorb tons of heat and just pump that heat into the AC systems. Really not the best idea. So, the first thing to do to combat this is to bring the AC into the conditioned envelope. I really don't have much attic in my build since my 2nd floor is basically IN the attic. So my insulation (spray foam) is up against the roof deck. That alone is a huge help but the upstairs will still pick up lots of heat. One way to fight that is to put on a white metal roof. Well, that is fine and good but I like the darker colors and so does the little lady. So, ASV put your metal roof about 1.5" above the actual plywood roof deck. This gap allows cool air to cool the metal from under it and stop it from heating up the plywood deck. This keeps heat completely out of the structure. The roof rafters are no longer thermal bridges to the metal roof. Also, since i'm putting verticle 1x2s down first and then horizontal 1x4s, if any water gets below the metal roof, it can drain out.

Austin