Just put on metal roof, rigid foam and spray foam

[gtojohn]

Are you installing house wrap inside your rainscreen? I've been looking for a good rainscreen illustration but haven't found one.

[dablack]

Hey John,

I was on hardie website the other day trying to get a good hold of exactly how I want to do it. They have a download on best practices.

The question I always have is where do I put the Z-flashing. Originally I was planning on putting the foam right to the window opening. Then put window trim on top. Does the flashing go above the window trim and on top of the foam? Doesn it go under the foam? I really started chasing my tail on that one.

Finally I decided that the foam would not go under the window trim. I will just put on some thick window trim and the z flashing can go on top of that. I'm doing it like this. Just like what I found in the hardie best practices.

[AC_Hacker]

Originally Posted by dablack

Don't want to deflect this thread, but the "gap" in the above photo is a really important concept.

When I was building my Mini Loo, I left a gap at the bottom of the wall, where the tile shower wall & tile floor pan meet, for exactly the same reason, so that water would not 'wick' up the wall, into the grout and possibly the backer board.

Also, a friend showed me some poorly performing Hardi plank where he neglected the gap, too.

Gaps are good.

-AC

[creeky]

Be careful you don't end up with two vapour barriers. If you foam inside make sure the sheathing outside can breathe and vice versa. the point of failure is when moisture gets trapped. hence the gap for the hardy board.

My camp build 2012 | Off grid tips, cartoons, paths taken

is my camp build where I used what is now called the cool roof on my washroom. the diagrams (of the highest technical specification, snort) are about 1/2 way down the page.

in 2012 it was a pretty new idea. but i used the ridge vent and 1" foil covered polyiso sheathing. 2013 was a record hot summer for us. and even tho 1/2 the roof faces due south the washroom never reached more than 1 degree above ambient. which. if you've ever been in a tin clad building on a hot sunny day ... you know is pretty amazing.

if you want solar powered cooling it is an excellent technique to use.

google buildingscience "perfect wall". they have done some excellent research in this area.

[dablack]

The foam in the wall is open cell so it doesn't act as a vapour barrier. Here in the south, we have to make sure we are able to dry to the inside if the wall gets wet. No internal vapour barriers for us.

The external rigid foam, is right next to the house wrap. The foam will be taped so it will act like a vapour barrier.

Austin

[creeky]

we're in the same boat here in humid ontario. we get the best of both worlds. freezing cold. and hot and humid. so there is considerable debate over where to put the vapour barrier.

I hope you don't mind, but I'm not the most experienced construction guy so I like to double check stuff. and there is good research out there showing that many of us are better off leaving extra breathing room on our rigid foam installs. (that's my story

the roofing install that I show in my blog comes from research I did in 2010 and is my second and improved version.

my second roof (the one illustrated) puts the air movement outside of the sheathing.

and while you put your rigid insulation between your purlins on top of the roof water proofing I used purlins or strapping over my insulation and attached the metal roof to that. interestingly that gave me the air gap now recommended.

this roof design really does remove solar heat gain very efficiently. kind of a solar chimney really.

for other people looking at this. there is research showing the metal foil covered insulation helps improve heat removal also.

you have a real nice build going there. congrats.

[dablack]

Hey Creeky,

What you are talking about is called ASV (above sheathing ventilation). We discussed it in this thread as well : http://ecorenovator.org/forum/renova...tion-help.html

It is a great way to go. I had to work with what my roofers were comfortable doing. Get them out of their comfort zone and the price goes way up and the quality usually goes down.

Also, I'm at the top of a hill with high winds. I really wanted my metal roof attached directly to wood. Putting the wood on top of the foam wouldn't have given me that. With the silver metal, rigid foam and then spray foam underneith the sheathing, I think I'm doing ok.

Now that I'm about to start putting on my hardi siding, it looks like they will let me nail through foam and into the studs as long as the foam isn't more than 1" thick. I haven't decided if I'm going to go with one or two layers of rigid 3/4" foam. I would really like to nail directly, so I might just do one layer of 3/4". Then I can do the window and door trim on TOP of the foam.

I will take lots of pictures of that too.

[creeky]

as far as I know the concept originally came from an aid worker in Africa trying to help people keep their houses cooler. he used two sheets of tin roofing. nothing like the materials we have access to here.

i hear your concern about wind. kind of one of my biggest concerns with metal roofing. you know. giant sheets of metal flying through the air. here in Ontario tho, as I mentioned we're pretty safe. but on my "arctic wall" build I screwed my purlins into the joists with 8" screws. better safe for sure.

it is great to see how fast and how far things have gone towards smarter more energy efficient builds.

look forward to your build and pics.

[rvCharlie]

I did something similar when we renovated our early-50's era ranch about 15 yrs ago. Since I'm too cheap to buy anything new if I can find it used or salvaged, I used metal/foam 'door cores', the waste left when a foam core exterior metal door has an opening cut in it for glass. Obtained them locally from a local door mfg company. The existing shingle roof was covered with the metal/foam/metal sandwich, and metal roofing was screwed down on top, with screws reaching through to the original 1x6 roof decking. The walls were covered with the same material then wrapped with house wrap, then fiber cement siding applied using a framing nail gun and 3 1/4" galvanized framing nails that went through the siding, insulating panels, and into the original 1x6 sheathing.

This is a hip roof with soffit vents & passive ridge line vents.Winter insulation is basically ok (wasn't that careful about sealing up the 50 yr old house), but summer in MS it's magic. Attic temps in August (typically 140-160 in MS) are only 10-15 above outside temp.

Charlie

[dablack]

Charlie,

That sounds really cool! I like that! I would love to see pictures if you have any.

thanks
Austin