First off, many thanks to all for the incredible source of information I have been able to access in this forum.

However, I don't seem to find any information on applying EPDM on a 1/4:12 slope SIP roof. Because of distance, I will use OSB panels so no steel SIP options for me. That said, I'm trying to figure out what to use under the membrane (I understand EPDM directly over OSB is a no-no). Should I use rigid foam insulation? I'm concerned with possibly trapping moisture and letting the OSB soak it. What are the options/recommendations for this type of roofing material?

House to be built in Walla Walla, Washington, 99362.

Any opinions or pointers to information will be greatly appreciated.

Robert

installation guidlines .............

http://technicaldatabase.fsbp.com/d...pid=808%5D

Thanks for the link, Chris–some really useful information there. However, there's no mention about using EPDM on SIP roofs, where there's no drying to the inside.

I suppose I could apply furring strips, drop sheets of OSB and apply the membrane on top. This could be labor intensive and expensive though. If there's another option, I'd love to hear about it!

Thanks again,
Robert

Robert;

wherever there is a possibility of trapped moisture, be it a OSB SIP deck or over and existing roof, the use of hi-rise mushroom cap vents would be adviseable. They are more common in commercial applications.

I would not use SIPs for a flat roof. If there is a leak by the time you find it the structural part of the SIP has been eaten away. Plywood and layers of poly-iso foam seem the safest bet to me. I say this and I love SIPs but no material does everything.

Robert,

It's been a few months and I wonder what you ended up doing? I'm in nearly the same situation.

Regards,
Pascal

Pascal, this coming Monday I'll be getting panels. Things have been moving rather slowly, but finally we'll get to start.

After much research on this and other forums, I've decided to build hybrid hot/cold roof. It'll be more work and money, but it should be a higher performance roof. A vented secondary plywood roof deck on 1x or 2x (dimension to be determined yet) purlins will be on top of the SIP roof. The membrane will be attached to this plywood, and if any leaks develop, water should runoff/dry on the WRB on the SIP. The stack would go like this: SIP, WRB, purlins, plywood, membrane.

I'm planning (actually the wife is) to start a blog to show progress and photos, so if anybody is interested, I can either post the link or provide it via PM.

Posted By rcar on 24 Sep 2010 01:56 PM
Pascal, this coming Monday I'll be getting panels. Things have been moving rather slowly, but finally we'll get to start.

After much research on this and other forums, I've decided to build hybrid hot/cold roof. It'll be more work and money, but it should be a higher performance roof. A vented secondary plywood roof deck on 1x or 2x (dimension to be determined yet) purlins will be on top of the SIP roof. The membrane will be attached to this plywood, and if any leaks develop, water should runoff/dry on the WRB on the SIP. The stack would go like this: SIP, WRB, purlins, plywood, membrane.

I'm planning (actually the wife is) to start a blog to show progress and photos, so if anybody is interested, I can either post the link or provide it via PM.

Please post them here!

IMHO the vented secondary roof above the SIP is the preferred solution, independent of roof pitch (but perhaps critical for flat or very low pitch roofs.)

No problem, I'll post the link here when available.

Dana1, thanks for your opinion. From where you see it, do you think 1x will provide enough vent space? I mean, I don't need to 'ventilate' an attic but rather provide some air so moisture is not in a vacuum, right?

You don't need to (and shouldn't) vent the attic space, but the vent space between the deck & would have a means to communicate with exterior air to purge any moisture that might leak in, but the rates of air exchange need not be super-high. Setting it up to drain away bulk-water from actual leaks is necessary, but not sufficient- even a tiny amount of air exchange will do a lot, since drying through EPDM via vapor diffusion will be impossible in any realistic time frame. If the air in the gap it's over 70% RH in the gap most of the time it'll eventually rot, even if the wood surfaces are not wet with liquid water.

Unless there's a path for the moisture to leave, it doesn't much matter if there's a gap or not. Even a 3/4" gap is plenty as long as it has some relatively unrestricted access to the outdoors even if only at one end. But designing it such that wind pressure can move air through the gap will more than double it's drying performance. Bug & varmint screens need to be on the openings to keep the gap from becoming a nesting spot. And even a 10" gap is NOT enough, if the air exchange is exactly zero.

Think of the size of the weep & vent holes in a masonry wall. It's not much cross sectional area, but it protects the wood on the other side of the wall cavity by giving moisture both a drainage and air-transport path out. In the masonry wall there is a convection-assist to keep the air moving that a vented flat-roof doesn't have, which means you'll need more vent area than the masonry wall, but the principle is pretty much the same: In the absence of a good vapor-diffusion path for drying, providing an air-transport mechanism can do the trick. (Getting vapor-diffusion through wet brick never works. The large amounts of moisture that gets IN through brick via wicking through the porous material is the problem that the cavity & weep/vent holes solve.)

rcar, thanks for the reply and I'm glad it's sparking some more discussion, this is very pertinent to my own project as well.

Care to share some details on how you plan to finish and trim the eaves of the assembly and the rafter vent as well? I'm going to be setting up scaffolding next week to begin my re-roof project and whether or not I actually go with SIPs if undecided as of yet but the layering / assembly of your project is exactly what I'm thinking of doing. I need to move all of my insulation outside the deck so I can reveal the 100+ year old beams and planks as the ceiling of the house.

Cheers,

Dana1, thanks again for your post—great information. I'm thinking of having 3/4" gap with ventilation on both ends so hopefully that will work.

Pascal, it sounds like you'll be working a great remodel project. As far as of actual details, I don't have any. No one locally can even imagine this kind of detail. So, after searching online, I found the Cor-a-Vent products that have inspired me on a solution. Check out http://www.cor-a-vent.com/s400.cfm. The top photo shows exactly the sort of detail at the edges that might work on my situation. Whenever my roof is done, I'll have photos available (I'll be getting roof panels on 10/12, so sometime after that I suppose), but it might be too late for you. If you come up with any ideas, please post them here.

And for all of you that care to look at some photos or follow our project, my wife made the blog live last night: http://modwalla.blogspot.com/

Robert

Robert;  nice looking job

Thanks Chris!

Dana1, just finished the last posts on the House Wrap discussion. For my situation being a flat roof, would you use Tyvek on top of the OSB? Or would a different product like Hardie Wrap be better? I can't seem to find what will work best.

This shouldn't be this difficult, should it?

Thanks again,

Robert

Posted By rcar on 30 Sep 2010 06:36 PM

Pascal, it sounds like you'll be working a great remodel project. As far as of actual details, I don't have any. No one locally can even imagine this kind of detail. So, after searching online, I found the Cor-a-Vent products that have inspired me on a solution. Check out http://www.cor-a-vent.com/s400.cfm. The top photo shows exactly the sort of detail at the edges that might work on my situation. Whenever my roof is done, I'll have photos available (I'll be getting roof panels on 10/12, so sometime after that I suppose), but it might be too late for you. If you come up with any ideas, please post them here.

Very interesting, thanks for the link! It's basically just a thicker assembly of corrugated plastic. Not a bad idea at all! I'll be checking out your blog, thanks for the link!

Posted By rcar on 30 Sep 2010 07:56 PM
Dana1, just finished the last posts on the House Wrap discussion. For my situation being a flat roof, would you use Tyvek on top of the OSB? Or would a different product like Hardie Wrap be better? I can't seem to find what will work best.

This shouldn't be this difficult, should it?

Thanks again,

Robert

A roof isn't just a tilted wall.  Use whatever the membrane manufacturer recommends for the slip surface between the membrane & outer OSB decking. With a membrane roof over it, there's no point to putting a layer of housewrap on the SIP skin, but DO seal the seams of the SIP from air leakage.

A roof isn't just a tilted wall. Use whatever the membrane manufacturer recommends for the slip surface between the membrane & outer OSB decking. With a membrane roof over it, there's no point to putting a layer of housewrap on the SIP skin, but DO seal the seams of the SIP from air leakage.

Dana1, the idea behind the Tyvek was to provide a bit of protection to the SIP skin in case of leaks and still allow it to dry to the vented space. Wouldn't the Tyvek's water resistive feature help by sheding water instead and reducing the chance the skin would soak the moisture.

Regarding the sealing of SIP seams, yes we'll be applying SIP tape on the panel's warm side (interior). This is what the manufacturer recommend. I'm also tempted to spend a little more and tape all wall seams as well.

Thank you for your perspectives

Are you going to adhere or ballast the membrane?

Bruce

Are you going to adhere or ballast the membrane?

Planning to adhere the membrane. Does it make any difference?