Spray Foam Question

[timswi]

Don't want to start a war like I've seen on other forums, so here goes:...I am finishing the 2nd floor of my house, a true Cape Cod style with 2 bedrooms and a full bath...I had the spray guy come out due to the notorious difficulty of HVAC in capes...I have the ductwork stubbed up there already.

His suggestion, and it's not new so I find out, is to open cell spray the roof deck, seal the soffits and ridge vent. Obviously this violates traditional thinking but is beginning to make sense the more I research it. I am concerned about moisture etc although that may be moot.

In essence, no interior walls will be insulated, just the outer shell.

Anyone here done this or know someone well who has? This is a very permanent and expensive proposition so I'd like some advise.......Thanks.

---This is in Southwestern PA if climate is a question.

 

[Rustyiron]

Not sure on what other forums you've seen, there seems to be a bunch of smart folks not selling anything on GreenBuildingTalk - Green Building Forums on Insulating Concrete Forms (ICF), Structural Insulated Panels (SIP), Radiant Heating, Geothermal Heat Pumps, Solar Power, Green Construction Projects
This stuff gets very scientific, but I think if you have at least 3", you'll move your "dew point" in your wall/roof out to the point where it will do no harm. There is a concern with the roof(ing). I think that some asphalt shingles may not warranty this application. I'm hung up on the differences between open & closed cell. I believe the closed cell has a higher "r" per inch cost more and is waterproof. The open cell (I think) can absorb water and might worry me to be certain it is the right material for a roof vs. a vertical wall.
Spray foam is good stuff, I think that there are a lot of things/decisions that matter for a good job, I don't know your answer but I'd keep doing your homework until you are confident to make that (proper) selection and expense.! Let us know what you find out!

 

[boggen]

while other folks would have an attic space above the main floor, you built the attic up some, to have a couple bed rooms and a bathroom inside the attic in a sense.

a regular attic, with just a main floor, relies heavilyl, on air movement, to remove excess heat / cold. along with moisture.

but you on other hand, there is no space for air movement. everything is getting dry walled for most part.

a open cell foam, lets air move through the foam. (basically a sponge) wood needs to "breath" to let excess moisture in/out along with keeping air from getting to hot and expanding like a balloon, and in that open cell foam lets the air move through things so things do not expand.

=============
not familier with your actual house style beyond above, so exiting that part... about closing up ridge vent and softit vents. i can understand wanting to close them up, but not real up to speed in how closing them can be good or bad.

=============
i would suggest if you have a little bit of cash insulating interior walls. more so if you plan on closing doors, and turning off heat and/or a/c to the given room. an uninsulated wall, can create a wind current in rooms. simply by convection. warm air rises, cold air goes towards the floor. it basically kinda like a slow moving tornado on its side in a room for a wind current. laying in bed, you might consider it a slight draft. this draft can be enough, to cancel out closing off the room from heating and/or a/c. the same goes for the floor of 2nd floor and ceiling of below. get some insulation in there. or you will have kinda like a heat sink, were warm air goes straight up in summer, and all the cold air coming straight down in winter.

above comes more from family / friends homes, and staying over the night when a kid. and trying to find the warm or cold spots in the room, and getting a good night sleep, with type of house ya wanting to do.

 

[SPIKER]

Closed cell foam is what you want on the roof for at least 2" thick, you can cover additional layers of open cell to reduce costs. The R value is about same but any leak or seep in the roofing will ruin the roof & insulation from top to bottom.

Mark

 

[Coyote machine]

Works in theory, but I'd use closed cell, making sure there is no air infiltration from anywhere. AND you need to bring in outside air to properly feed your furnace/boiler, or you'll be sucking out your breathable oxygen from your indoor air space. You will have to exhaust all stale/moist cooking/bathing air to keep the indoor air quality acceptable. You could also save money by doing flash and batt in the roof deck area by spraying 2+ inches of foam and filling the rest of the rafter cavity with Roxul.

 

[timswi]

Thanks for the info given so far...more data: 5" of open cell on the roof joists and 3" on the gable ends and dormer walls. They want to put a thin sheet of foam board down at the soffits and fill the gap with foam...The open cell is giving me some pause as has been said here. The company says it's no issue--gonna call the manufacturer tomorrow.

The interior of the knee walls and collar ties will be drywalled, heated and air conditioned. I have a heat pump with an electric backup furnace so no fuel burn issues...All mechanicals are in the basement.

For reference, here's an outside picture so you have an idea of the style..12/12 pitch etc

 

[Coyote machine]

Your pic shows heat loss at the interface of the gable end wall(s) and roof, and at the ridge line.
Have you had an energy audit done? Blower door test, to see how many air exchanges/hr?
I would have those done before any of the work you plan to do to show a base line and then where they hopefully make improvements in the building envelope.
Is the attic living space? If not then the alternative, less costly method is to super insulate, (R-50) the 2nd floor ceiling/attic joist bays and keep the soffit vents/ridge line vents, gable vents. Then the cold air area above the heated living space is not problematic.

 

[timswi]

Your pic shows heat loss at the interface of the gable end wall(s) and roof, and at the ridge line.
Have you had an energy audit done? Blower door test, to see how many air exchanges/hr?
I would have those done before any of the work you plan to do to show a base line and then where they hopefully make improvements in the building envelope.
Is the attic living space? If not then the alternative, less costly method is to super insulate, (R-50) the 2nd floor ceiling/attic joist bays and keep the soffit vents/ridge line vents, gable vents. Then the cold air area above the heated living space is not problematic.

At the time of that picture, there was "utility insulation" on the floor and stairwell in addition to an uninsulated door at the top of the steps...Also, we had 3 feet of snow the night before and the outside temp went to almost 50 the next day, so oddities all around in that picture as far as snow melt.

Edit--The picture also is showing the north side of the house, the sun and warm temp had already melted the south side...There was no drywall etc up there at the time, just some insulation on the ceiling of the first floor...The sun would warm it up pretty good, even in the winter due to the pitch and size of the roof.

 

[boggen]

would never really believed it, but the hard board insulation you can get in 4' x 8 ' sheets and local hardware stores (menards, lowes, homedepot), the foil face insulation. that foil, can add some major benefits. at least it has here in a cabin, and in a shed. the reflectiveness of the foil. not light, but reflecting heat. what use to be 100 plus degree sona stepping into cabin in summer, is now can be colder in summer than outside temps, 2x4's in the ceiling "rolled insulation" then 1/2" thick double foiled face hard board insulation, then 5/8" decorative plywood (kinda looks like a log cabin the plywood does) the walls just have 2x4 studs, with rolled insulation, and the 5/8" decorative plywood.
and in winter. it is warmer in the cabin than outside air temps. this is without any sort of heating or cooling.

it took a few months to get ceiling done, so there was a couple months that the double foil faced hard board insulation was not up. and just the rolled insulation in the ceiling. the major difference immediately showed up, after the 1/2" thick double foil face hard board insulation was put up. it was a complete night and day difference. i would like to say there might of been some air leakage before the hard board insulation went up. but used "great stuff red can, closed cell spray foam" along with some calking before anything went into the ceiling or walls. (more to keep bugs and mice out) with that i don't think it was air leakage.

the cabin is 20x24, gabel (not attic) much like your second story will be for a ceiling.

 

[dstig1]

No no no no no! Open cell foam is going to cause you major trouble down the road in this application. Go read the last couple pages of my thread in the Projects forum (it's on page 2 of that forum now). Any insulator recommending open cell in that application is a serious fool and does not know his trade. That would scare the crap out of me, and I would look elsewhere for someone with a clue.

The key is to keep the temp of the condensing surface above the dewpoint. In this case the condensing surface is the roof sheathing. Open cell is not a vapor barrier so it allows moisture through. That moisture raises the humidity which causes the dewpoint to increase. If the dewpoint at that surface increases above the temp of that cold surface in winter, you will get condensation and then mold and rot. You have to keep the surface dry and warm. When you use closed cell foam, it is a vapor barrier so you move the condensing surface to the face of the foam. Since the foam is insulating the roof deck, the face of the foam is now much warmer and thus the dewpoint there is lower. Surface Temp above dewpoint =

The basic principle of what you are describing is fine, but the selection of materials, and the workmanship are critical to making this work. Closed cell foam or XPS/Iso foam sheet, sealed at ALL the edges with closed cell (or canned) foam is necessary. What your guy is proposing is house suicide. That really scares me that an insulator in your climate would propose that.

I had a former coworker (long since retired) who was convinced into using open cell foam in his house in a similar fashion. Winter year 1 he was able to squeeze water out of his insulation in the attic, and it went downhill from there. There is sound science behind my explanation above. Beware!