I have an old Victorian, and I’m enlarging the third floor to add living space. So, it’s lots of roofline changes, etc, including dormers. I have a couple smaller dormers (4ft wide, 4 or 5 ft deep), gable style, that i assumed I’d spray insulation in, thinking I’d pick up one of those kits. Duh..not wise. (Should have done my research better, LOL, but this is a “Nights and weekend job”…my own stuff always gets the short stick, LOL)
Seems like the spray kits are pretty pricey, and getting a guy to come out is really over the top. Plus, I need to be careful..the house is old, insulation is lacking in other areas, and the neighborhood won’t support excessive money being poured into the house in terms of resale value…
So, it’s traditional bats and air chutes in most of the roof areas, but these dormers were built without soffit venting, and honestly, some would be next to impossible to vent anyway.
I’m thinking about solutions, and one that crossed my mind was getting foam insulation sheets,(like this: http://www.owenscorning.com/around/insulation/products/foamular.asp ), 2″ thick, and using Scotch 99 spray mount (contact cement) to mount it to the underside of the roof deck, building up the thickness with multiple layers. Any voids could be filled with the low expanding stuff from the can.
Am I missing something obvious? or does this idea have merit?
Replies
I'd look into the Mooney wall dense pack cellulose system.
http://forums.taunton.com/tp-breaktime/messages?msg=65624.1
http://grantlogan.net/
I refuse to accept that there are limitations to what we can accomplish. Pete (I am so in love with myself) Draganic
Wow. I know of the Mooney wall, but didn't consider it for the roof areas...I was going off the concept that sprayed in roofs (with foam) didn't need the ventilation to remove condensation...but is the celulose appropriate against the roof deck? I read a couple pages of the thread, but at 225 posts, I admit I skimmed some as well. I didn't see any roof comments.I only need to do about 40 sq feet or so, and headroom is a concern.Jake Gulick
[email protected]
CarriageHouse Design
Black Rock, CT
...but is the celulose appropriate against the roof deck?
Hey Mike. A little help here, please sir.http://grantlogan.net/
I refuse to accept that there are limitations to what we can accomplish. Pete (I am so in love with myself) Draganic
Dormers are notorious for valley ice-dams and resultant leaks and insulating yours without venting the roof properly won't help.
Easiest way to do it is to use rigid foam panels to not only do the insulating, but to create the ventway in each rafter bay as well. That way you get a double bang for your buck.
Assuming you're insulating from the inside (and are not pulling the roof deck itself), set a 2x2 along each side of each rafter bay up against the underside of the roof deck sheathing, and then place the first piece of XPS (or whatever rigid panel you decide to use) up against the 2x2s. Use PL300 to glue it in place; it's made for foam board.
That'll give you an inch and a half of clear vented space above the insulation. Add as many inches of rigid foam under that first one as you have room for or think you need in your climate.
Easiest soffit venting is with round vents that just 'plug in' to holes that you bore in the existing wood soffit. Check your local code and do the calcs to figure out how many you'll need. They come in several sizes, in both plastic and plain aluminum (which is handy: you can spray paint the aluminum vents to the appropriate colour while the plastic ones only come in plain white and can't be painted).
For a really small dormer that lies across the prevailing winds, you might get away with just soffit vents on both eaves, but it's better to provide some kind of ridge venting, too. I don't really like those ridge-vent gizmos, because even six inches of snow renders them pretty useless; but you could try and see if one will work for your climate. Otherwise, put a small vent in the gable wall of the dormer, and bore three ¾" holes in each rafter near the ridge (inside the vented channel, of course) to provide an air pathway from one rafter bay to the next.
Dinosaur
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foolish men call Justice....
hey, jake.....
in the thread "QuarterDeck" we insulated a cathedral ceiling (2x10) with solid dens-pak... no ventilation..... a "hot roof"
http://forums.taunton.com/tp-breaktime/messages?msg=83035.190
the BI said as long as the insulation was in complete contact with the sheathing it would comply with RI code
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Mike Smith Rhode Island : Design / Build / Repair / Restore
Edited 2/4/2008 10:08 pm ET by MikeSmith
I've been looking into your system and spray foam lately and we're not allowed to go against the sheathing here in Oregon.
Ended up with polyiso board vent chutes on the last one.
I looked thru the rest of your photos on that job. What a great building.
Do you have any more pics of your mason (s) building the stone steps? Specifically what the base/sub structure is? Just block?"Research is what I'm doing when I don't know what I'm doing..."
poured concrete footing with a block backer for the stepsMike Smith Rhode Island : Design / Build / Repair / Restore