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Mudball · 06-02-2006, 05:02 PM

I have had two separate roofers say that they would build me a roof using the trusses and then 1X4 laths across the trusses and then lay down this bubble foil over the 1X4 lath and then screw the metal roof directly over and next to (on top of) the bubble foil.
In all the information I can research on the web I can only find where it is important to have some kind of air gap between any type of foil/bubble/insulation and the roof.
Any thoughts and/or suggestions on this procedure ?

**inspectorD** · 06-02-2006, 07:57 PM

I have never heard of this....hmmmm....time to do some research.....I love research!!
I am guessing it is to let the roof expand and contract in the temp differentials....hmmmm....
I'll get back to you....

Mudball · 06-03-2006, 04:54 AM

Thanks for your interest inspectorD. I have been searching for information on this issue for quite some time now. I was doing it again this morning and I finally found a site (the first and only one Ive found) that shows what I believe is the same application that my potential roofers has described.
Can I post a link to companys advertising web site on here ?

**inspectorD** · 06-03-2006, 06:56 AM

Whenever we find some info about something we go ahead and share the news. As long as it is not spam....then the sheriff shows up and runs it outta town.

Mudball · 06-03-2006, 12:23 PM

Thanks again. I actually found a few different sites. My problem with my search was I forgot two important words..."post frame"..ect...
Anyway this following link is one of the better examples. Please read the description in combination with the top middle picture and tell me if this is not what I described the roofers said they were going to do ?
It looks to me in the picture that I see the trusses then 1X4 lath and then the foil radiant barrier...correct ?
Also one roofer said (after I asked) that he turns the foil face toward the metal roof. I think thats what he said but from what Ive read so far all the sites say that the foil sides all go toward the inside.
Sorry for all the questions

http://www.radiantbarrier.com/post_frame_new_construction.htm

Square Eye · 06-03-2006, 12:53 PM

I get confused just reading this thread.

Bubble wrap insulation with a foil face is it's own vapor barrier. The link you have provided shows it being used that way, directly against the metal.

Think of a cold can of the drink of your choice. If it's not sitting in one of those fancy can-coolers, it collects moisture that had been previously lingering in the air. This humidity will collect on just about any surface that is cooler than the air. Then the process of evaporation makes the surface even colder, drawing that much moisture until the temperatures equalize and then evaporation slows and you're left with a wet mess.

Your metal roof is the same way. In the evening when the sun goes down and the metal loses the heat built up from the day's sun light, the nature of the metal makes it slightly cooler than the air around it. The moisture in the evening air collects on the surface and if it has access to the underside, it will collect there. If you have an air gap under the metal, the water collected there will have nowhere to go because of the vapor barrier built into the insulation. The insulation will make it even more difficult for the temperature to rise enough to help evaporate the water and eventually it will build up enough to find an escape path or to make an escape route by destroying the wood that it has contact with.

The last thing you need to put on the roof right before the metal goes down is the bubble wrap with the foil vapor barrier facing away from the metal. This will keep as much moisture away from the metal as possible with a sheet type of insulation.

Want something better? Have it sprayed with a closed cell foam insulation after it's installed. No airgaps at all with that stuff. It's been used for years in commercial applications and it works great, it costs a lot, but it works great.

Mudball · 06-03-2006, 08:40 PM

I certainly didnt mean to confuse anyone. I think most of the confusion comes from my lack of education and experience building period...not to mention terminology. I guess thats why Im hear to learn. Im now confused at this point. I will have to do some more research and reading so I can further confuse myself

Thanks for the advice Square Eye even though I dont fully understand it. Are you saying that the roofer I talked to should not face the foil (shiny side) toward the metal or not ? The product that he mentioned (bubble foil) also had no "R-value". I dont believe the spray type you mentioned will be used for us because of the cost factor. Please tell me your procedure if it was your house and you had nothing but truss, lathing, bubble foil (R-value or not), and metal roofing material.
Thanks

Square Eye · 06-04-2006, 12:06 AM

Part of the reason I'm confused is that, the radiant barrier type of bubble wrap used here, has foil on both sides.

Radiant Barrier (bubble wrap) does not have an R-value because it's intended purpose is to slow radiant heat and is not intended to reduce conducted heat. Although it may actually have a low R-value, R-values apply to conducted heat and would be misleading when comparing radiant barriers. The air gap that is mentioned in your link is intended to separate the the radiant barrier from the regular insulation. The radiant barrier is still a vapor barrier, so it needs to be directly against the metal. Then an air gap, then the fiberglass insulation or foam panels can be used.

So, having said all of that, in my home, I would do this.

On top of your perlins, nail plates, lathes, whatever the lang is in your area, put the radiant barrier on top. Then fasten the metal directly on the radiant barrier (bubble wrap).

If you want to insulate the ceiling for an R-value, I'd put foam panels under the lathes, or perlins, or nail plates, or whatever you want to call them.

More insulation? Put in a ceiling and insulate with fiberglass. Leave the bubble wrap against the metal.

If there is a foil face only on one side, I'd turn it away from the metal. Where the vapor barrier should be.

glennjanie · 06-05-2006, 03:11 PM

Hi Mudball:
I have a structural comment for you. I would want the lath on the trusses to be 2x4s standing on edge. You can pick up a piece of metal roofing by the sides and the middle will bow way down but if you pick up a piece by the ends (3' or 4' long) you will not notice any bend. Your trusses are probably spaced on 2' centers (I have seen them as far as 8' on centers); would you rather stand between trusses on a flat 1x4 or a 2x4 standing on edge? I would prefer the 2x4s on edge. The trusses run up and down the roof, the lath will lay across them long ways, and the metal will go up and down.
Glenn

Square Eye · 06-05-2006, 04:24 PM

Hey!

Dad made an interesting point. I have read that the manufacturers of steel specify that 2x4s be used on edge for purlins. This allows the expansion of the steel without elongating the screw holes. This will make your metal last longer and leak-free for longer. The screws will also last longer.