finalizing my attic insulation plan...

[OhioBurner©]

So I've got some advice from here in the past, and did some reading online for what to do with these cape cod upstairs. I think I have a better idea now, and my week off is fast approaching (week after next) so I wanted to run it by you all one final time. I still think this is something I can do, and looking forward to the experience since I'm pretty handy but haven't really ever tried major home renovations. I plan on moving sometime in 2-10 years, this is not the home I want to stay in forever. If I was planning on staying I'd gut the walls take off siding, whatever, and use the best stuff. But what I am looking for now is just a quick best bang for buck upgrade to at least make the upstairs bearable.

A quick review of my home. A small 1900 cape with a large full 2 story addition in 1990. The upper level of the cape has 2 rooms. 1 room had been renovated prior to me moving in 2008. It has sheetrock walls and fiberglass batts. The other room has uninsulated walls/ceilings (plaster and lath) with only fiberglass on the floor of the crawl space behind the knee walls. Nothing is air sealed either. The sloped wall/ceiling is built right on the roof rafters.

Here is a to scale sketch I made of the upper level:

The two rooms are different widths right now. The area along the outsides of the 31' edge and the crawl spaces behind the knee walls.

Here is a shot from inside the knee wall attic on the side with uninsulated plaster wall/ceiling...


There is no ventilation. That is what caused me to change direction recently. I had planned to add ventilation but in this house it would be nearly impossible and cause other problems. I've read this is typical problem with cape cods. For one thing I have no eaves. And only one gable end is exposed, and not really enough exposed space in the crawl space to put a decent size vent in. And the one bedroom that's more recently remodelled I'd have to tear out to ventilate and I don't want to do that (FG between drywall and roof, only way to ventilate would be to tear down ceiling and remove FG, and still no good way of bringing fresh air in). Some reading revealed the unvented approach can be ok... http://www.energyauditingblog.com/unvented-attics/


The cape cod half of the house. I drew red lines to show where the knee wall attic space was. Doesn't leave enough room to put a decent size gable vent to draw air in, and no eave vents. The front of the house the eave end adjoins the porch roof, on the back side its the same curvy white metal trim with rain gutters.

I thought about just trying to add insulation but it would be too difficult to get it in the very small cavity between the angled plaster wall/ceiling and the roof (less than 4"). So here is the plan. Going to tear down the plaster walls and ceiling. If I can't ventilate properly I've read I should do the opposite and seal/insulate the outer envelope... along the roof and the eave and gable ends. I'll expand the floor over the whole width (removing the FG on the floor). So the whole space will be bedroom - I may add a similar 'knee wall' but it will be on the interior of the room and turn the sides into storage space that within the conditioned area.

I'm going to seal best I can. I'll have to remove most all the insulation first and seal everything up with spray foam on the eave and gable ends, then insulate. I was just going to use FG batts but should I look into something else? What about those rigid foam boards? Could I do FG between the rafters and then a thin layer of foam board on them and then drywall on the foam board? The roof rafters measure 2 3/4" wide and 3 1/2" tall. 2' on center (actually they seem to measure 24 1/4"). I was wondering if I could maybe add a couple inches to these using 2x2's to get deeper cavity but I suppose if I use that rigid foam I could add thickness to the insulation without needing to use the cavity right? There is a stairway (unused) down one side that I will remove and cover up. Right now it bisects the knee wall attic and creates a section that is inaccessible. Plus I'd like the extra space in the laundry room below it.

I plan on getting this stuff for my air sealing:

More expensive than the $3 cans of Gaps and Cracks but I hear the gun gives you a lot better control and results, and a lot less waste. I also bought a respirator and tyvec suit for working in that nasty dirty dusty moose poop covered knee wall attic. Anything I'm missing or other recommendations?

 

[semipro]

You may want to read this thread if you haven't already. https://www.hearth.com/talk/threads/spray-foam-gun-recommendation.73362/

 

[Highbeam]

I also bought a respirator and tyvec suit for working in that nasty dirty dusty moose poop covered knee wall attic.

How did the moose get into your attic!

 

[johninwi]

I bought the gun for the greatstuff pro cans, very happy with it. You can set it down for a week come back and it works fine, it does need to be reshaken but it's not a big deal. The gun will work upside down till the can gets mostly empty then it sputters some. I saved an area where the the gun is right side up or can upside down and it empties the cans better. It also eliminates the question of "will i empty the can or waste half of it" routine that alway's seemed to get me.

And wouldn't the moose be happier in the basement.

 

[OhioBurner©]

Oh I'm definitely getting the gun, actually went ahead and just ordered it and the pack of 12 cans to make sure I get it in time. I have plenty of air sealing to do in the basement too.

The part I am less sure on is the insulation. If I use FG batts between the roof rafters, do I need to use plastic or some kind of moisture barrier, or if I decide to cover it additionally with an inch or so of rigid foam board? Or should I do the entire thing in rigid foam board for maximum r-value in the small space? That would be a lot of cutting and sealing.

 

[semipro]

The part I am less sure on is the insulation. If I use FG batts between the roof rafters, do I need to use plastic or some kind of moisture barrier, or if I decide to cover it additionally with an inch or so of rigid foam board? Or should I do the entire thing in rigid foam board for maximum r-value in the small space? That would be a lot of cutting and sealing.

I'd suggest you read this article (http://www.energysmartohio.com/blog/how-to-insulate-and-ventilate-knee-wall-attics) and then move on to sites like energy vanguard, building science corp, greenbuildingadvisor etc. and do some more reading.

 

[OhioBurner©]

Yeah I've read a lot that is where I have got most of my info from, that energysmartohio link was one of the first ones I've read, though it barely even mentions an unvented attic and doesn't go in to much detail about insulating against the roof and FG versus rigid foam, etc. I was originally going to do very similar to what it says, insulating the knee wall but decided against it after reading others like http://www.energyauditingblog.com/the-problems-with-attic-ventilation/ I'll keep reading though. For now I am thinking insulating the roof and making the entire upstairs conditioned space with no attic. Should be easier/simpler. Especially compared to trying to air seal under the knee wall and all the nooks n crannies. Now I just have to spray foam to air seal along the eave ends I assume. R11 fiberglass batts between the roof rafters, ~1" thick rigid foam over the rafters with sheetrock on it. Should give me R15-17 depending on what foam board I buy (or more if I go thicker). How to 'seal' all the foam boards though? Do you leave a gap and then spray foam between them all?

 

[Swedishchef]

Do you have a budget to spray foam the entire thing? I am PRO spray foam. It worked well for me. No worries about mould, vapour barrier, etc.

IF you use FB batts, VB must go on the warm side.

Andrew

 

[OhioBurner©]

I thought about it, and would consider it more if i was going to rip out the entire upstairs and spray foam the whole roof. But since I'm only tearing out one room, I only have access to that half plus the knee wall attic on the other side. So if I am going to half ass it, I'm going to half ass it with the cheap stuff, not the most expensive lol. I've already got most all the materials now and plan on getting this done next week (I have it off). My plans changed a little from the initial thoughts, and I wanted something more rigid since I didn't have any roof sheathing (and I hear you shouldn't have the open face of FG exposed to air) so I am putting a thin layer of 3/8" foil faced EPS in the rafter bays, spray foamed around the edges to air seal, with foil face out. Then R13 fg batts in the rafter bays, then 1.5" eps foam panels over top the rafters (air sealed) and drywall on that. I probably should have just done the whole thing layered EPS instead of throwing the fb in the mix but thought I'd get sick of all the cutting and trimming.

 

[Swedishchef]

Did you buy your FB yet? Maybe consider Roxul..I love the stuff. It's much easier to work with, is considered a fire wall and is very waterproof/ water resistant.

Just my 2 cents...and with our current exchange rate, it's not worth much at all

Andrew

 

[OhioBurner©]

I've got the FG batts, EPS sheets, sturdi-floor, studs, case of spray foam & gun, can lights, sheetrock, primer... all ready to go tomorrow so a little late to change now. Tyvek suite, respirator, and dumpster for the demo. I should have pretty much everything I need except baseboard, finishing paint, and floor covering. I'm sure I'll find a few more items I forgot about along the way though, no biggie. I'm not going to replace the old nasty carpet until my dog passes.