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Discussion Starter · #1 · (Edited)
I want to insulate my roof deck (soffit + ridge vents) from the attic, there is currently no insulation there. I don't want to mess with baffles+batts because distances between the rafters vary and there are some more rafters added (someone messed up the framing) so baffles wouldn't work. I watched a video on Youtube (can't find it anymore) showing a guy cutting a foamboard (pink ones from Home Depot) into strips and nailing (glueing?) them alongside both rafters (making room for air flow), then cutting a foamboard to fit between the rafters and attaching it to the strips.

Anybody ever heard of this technique?
 

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http://www.finehomebuilding.com/membership/pdf/021192086.pdf

Here you go. Read this in FHB years ago. I think you're wasting your time ripping every piece of foam to fit between rafters that are different distances apart. Also you'd have to stack a lot of pieces of foam on top of each other or add other insulation on top in order to get any real insulating value which would make the waste of time add up significantly. I vote block the vents and pony up the money for someone to spray it.


Tom
 

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well good intention. remember this if you trap moister in that system, many more problem will occur! hot roof systems is a bad thing. remember the ship that sunk well the same applies you can not stop the moister from entering the system. it will fail at one time or the other!!. a house must be able to control the moister. condition space is what it mean.
 

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Comfort,
I do agree that trapping moisture is a bad thing, but my understanding of it is that spraying closed cell foam should prevent moisture issues as it is a vapor barrier. Any moisture in the roof deck can breath to the exterior.

I also am not fond of the idea of hot roofs, but haven't actually seen any failures due to spraying foam against the roof sheathing. I have used this method a number of times and still try to sell it in many situations. I do not think it is worth the time and effort to spray foam and add a channel for ventilation (which I guess would be the best way to air seal and keep a cold roof).

I am by no means an expert though, and would like to know if I have caused problems by spraying like this in the past.
 

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Thw
well with out getting into a pissing match. i had the the bird eye view of what happen in these systems. I get the Please help us calls. the system will work until it fails many problem are not of what we do but of what happen in the life of the home. lack of up keep is number one. i hope this help you understand why we need to build smarter not faster.
 

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Thanks comfort,
In no way was I trying to say you didn't know what you're talking about. I have no doubt you have witnessed failures involving foam. I was merely relating my experience with it and my limited understanding of the system. I still think that spray foam is a viable and even preferable alternative in many situations.

I guess mos should do a lot more research to decide it if is for him.
 

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HI THW
not only Foam i'm referring to the system. that is the house performance. is where we including myself could do better. I've been in places that the system was so bad that it would rain in the attic. most condition attic system don't have Havc system in place to control the space.
 

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Sean
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Wow not to call complete BS, but a location & knowing what type of insulation you install might be nice - yes I have seen failures also & not just with hot roof systems (oh & HVAC is not required with a hot roof system)

A hot roof system works & works well if installed properly, just like baffles & batts / cellulose but it all comes down to doing it right based on your climate

As for venting & encapsulating an attic - those can be a little tougher but work well also - I would rip strips from 2" foam board to use as battens (about an inch thick) & then apply as many layers of 2" boards as you need for your climate. No worries on a perfect tight fit & in fact would probably recommend cutting them a fraction narrower & using foam to seal up all the edges & with the right type - to each other. The final layer should be full sheets if possible attached to the rafters - no air gaps

You will still need to do some air-sealing & make sure you deal with the interior moisture issues - i.e. bath fans vented outside, etc...

For more on what it takes & options: http://blog.sls-construction.com/2011/what-is-a-hot-roof
 

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Hi SyS
not saying if the work is done correctly. i'm referring to the life of the project. many project are going to face thing like maybe having the cable guy add a line or a rodent enjoy making a new home i could go on but you must by now understand what i'm talking about.
that's what i meant by the sinking ship it will happen. my point is what can we do to plan for this?
 

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Discussion Starter · #10 ·
Wow not to call complete BS, but a location & knowing what type of insulation you install might be nice - yes I have seen failures also & not just with hot roof systems (oh & HVAC is not required with a hot roof system)

A hot roof system works & works well if installed properly, just like baffles & batts / cellulose but it all comes down to doing it right based on your climate

As for venting & encapsulating an attic - those can be a little tougher but work well also - I would rip strips from 2" foam board to use as battens (about an inch thick) & then apply as many layers of 2" boards as you need for your climate. No worries on a perfect tight fit & in fact would probably recommend cutting them a fraction narrower & using foam to seal up all the edges & with the right type - to each other. The final layer should be full sheets if possible attached to the rafters - no air gaps

You will still need to do some air-sealing & make sure you deal with the interior moisture issues - i.e. bath fans vented outside, etc...

For more on what it takes & options: http://blog.sls-construction.com/2011/what-is-a-hot-roof
Thanks for the info. What should I use to attach strips and boards to the roof deck? Also, should I use a regular spray foam (the one for use with windows and doors) to seal my boards?
 

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Sean
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Go to your local insulation supply store (not HD / L) but an actual store & see what they have on hand & there recommendation - I have used all types including Great stuff & most of that was due to what was available at the time down where I was at. I can also say some newer & better products have popped up since then

For the foam to boards - prefer screws through a specialty plastic washer that holds it tight - attach through side for first one closest to roof
for foam on foam - they make a special one piece plastic push in one that works great
For the final layer over the rafters - a long enough screw & similar washer used in the first one
As for foam there are numerous brands & they are all good - as I said see what the store recommends based on your application & buy the gun to go with it - it allows for better control & less waste as compared to disposable cans
 

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Can't believe this DIYer hasn't been taken out yet..
 
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I recommend that you contact an insulation contractor, not just because you're not a contractor, but because it's a very competitive business, and they generally offer fantastic value. As long as you hire a reputable one, they'll also do the job much better than you will. Getting the details right is crucial with insulation.
 

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Capra Aegagrus
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