Insulation ideas for 2nd floor
 

A couple years ago, I bought a two story house built in '84. I've done quite a few insulation projects to keep in my precious heat during the winter. I have two heat pumps, one for the 2nd level, one for the first. I've been pretty happy with them so far.

I've been experimenting the last couple of years with the best way to run them in the winter. The first year, I just kept the house at a constant 66. They ran throughout the day, and almost constantly through the night (very bitter winter 2 years ago). The next year, I decided to start running it a bit more during the day to build up the heat so it doesn't run as much at night when the temps are typically in the high teens and low 20's. It worked well last year, but the heat pump was typically running by 2:00 or 3:00AM.

Last November, I insulated the attic. I had 8-10 inches of blown in insulation up there. I increased that to 22-24 inches of cellulose. I insulated all openings with expanding foam. The front and back sides of the house aren't that deep due to the roof slope and the need to keep adequate ventilation from the soffit vents. Overall, the added insulation has made a pretty big difference. I slowly increase the temperature of the 2nd floor throughout the day to 71. I drop it down to 63 at 9PM. With the added insulation, and the mild winter we've had, the heat rarely kicks on overnight anymore. It is typically around 65 in the morning. Pretty good I think! The main level was always more temperature "steady"....not varying as much due to outside temps (more thermal mass, no exposure to cold attic temperatures, etc). However, that has now switched. The 2nd floor now seems to suffer less from temperature swings.

Anyways, I'm looking at ways to even better keep in the heat overnight upstairs. I am planning on staying in this house for at least the next 30 years. So, although I don't want to spend large amounts of money, payoff period isn't a huge deal to me.

I feel like I've gotten most of the "low-hanging" fruit. While the windows are original, they're pretty decent wooden double planed windows, that I don't think I want to replace yet. I have weatherstripped them. I have a separate idea to build insulated shutters for the windows...that's farther down the line.

I'm thinking of two main ideas for helping upstairs. My first idea would help store heat during the day.....adding thermal mass. I've researched this a bit, and thought about adding bags of rocks to the walls. I would have to cut holes in the walls obviously, but am pretty versed in patching jobs. I was thinking of just buying rocks from lowe's, drying them, putting them in ziploc bags and dropping them in. Any thoughts on this? Would there be too much pressure pushing out on the bottoms of the walls? Could that cause any issues over time? My goal in this is to be able to only raise the upstairs temp to 67 or 68 in the afternoon (instead of the current 71). With the added thermal mass, I could possibly store the same amount of heat, without the added delta T. This should decrease the amount of heat loss to the environment, while providing the same benefits I currently get.

My second project idea is designed to help keep the heat in and reduce sound. These two goals are about equally important in my mind (we live along a fairly major street and the road noise all night bothers me). Growing up, we had 2x6 walls. My dad always raved about them, and I wanted 2x6 walls in the house we bought. Unfortunately, we fell in love with this house (the wife didn't seem interested in my insulation reasons for buying elsewhere :-). Anyways, I was thinking of adding on to the upstairs walls. Again, I've done quite a bit of research and realize there are many different options. I want to keep it simple. Let me explain my plans and let me know what you think.

I currently have a sheet of drywall on top of a 2x4 wall. Insulation is fiberglass batts. There is a plastic vapor barrier between the drywall and insulation. My first thought is to leave the old drywall up. Put a new 2x4 wall up next to the old one. I would stagger the 2x4's to prevent thermal bridging and fill the gaps with fiberglass batts (perhaps a bit overstuffed). All I would really need to do is cut the carpet back, move the tack strips (and move the electrical outlets out to the new wall thickness.

If I did it this way, do I need to remove that vapor barrier and add a new one underneath the new drywall? I have done a lot of reading about vapor barriers and the dew point, but frankly I don't quite get it.

Space isn't a huge consideration, although I really don't want to add more than 4" to any of the exterior walls. That would start to make the rooms feel a bit small.

Would I be better to remove the current drywall, and build my new wall right up to the wood of the old wall? I know there's not much insulation value in that old drywall, but I figure if nothing else it helps reduce any kind of air infiltration.

Any thoughts or help would be appreciated. Thanks!

First idea- I think the rocks idea would only work for walls heated by the sun. But if you use you outside walls it ruins the insullation you do have. If you windows are big enough and placed right, an interior wall in direct sun light might work. But this also slows the heating as much as the cooling. not sure if there would be a net-gain.

Second idea- if you intend to stay that long and you are not worried about payoff period, go all out the first time. Take down the drywall and the fiberglass. Seal the walls with an inch or more of sprayfoam. Build another 2x4 wall with offset studs inside. Finish with cellulose and new drywall. I have done just that in two of my four rooms on the main floor of my house and there is no perceivable loss of space and it's SO much warmer and quieter. I hope to do the next room this summer.

It is not as easy as it sounds to move the electric to the new wall if you leave up the drywall. You will likely need to extend the wires, that means unaccesable junctions in the old boxes, that is against code and bad form.

I think that because they would be slowly gaining heat throughout the day, the rocks would still work. They have 8-10 hours to collect heat, even if not from direct sunlight. I know most thermal mass material you read talks about having it in the sun, but obviously that's not always possible. Some of the rock filled walls would get some sun, but not all. And no, I was not going to use an exterior wall :) I think the only reason there would be an overall gain is because I use heat pumps. If I was using a gas furnace, it runs at the same efficiency day or night, and it likely wouldn't make much difference. However, my heat pump is far more effective during the day than at night. My overall idea is to build heat up during the day and be able to keep it through the night. This makes my heat pump run less frequently, and is easier on it by running it more during higher outside temps.

I do like your wall idea. However, I was planning on doing each room individually over the course of a couple years. So, doing spray foam would be hard, as would blowing in cellulose (renting the machine each and every time, etc). Wondering if I could use XPS foam, cut slightly smaller and sealed on the edges with canned spray foam. I know I've heard this technique for sealing rim joists. Would that work if I pull out the old fiberglass?

In doing this, are you renting a machine each time? What about the spray foam?

With regards to the electric boxes, I am reasonably sure that the wire in and wire out both go up to the attic for each of those boxes....although now that I think about it, maybe I'm wrong....seems like it would be a waste of wire. Assuming that is the case, moving the box out would not be hard at all. It would just be an inch or two higher on the new wall. I still have to investigate this more to make sure. Otherwise, I could just put in extra outlets and move the position of the current ones. This would of course require taking out the drywall, like you suggest. Now that I get to thinking, removing the old drywall is sounding better and better. It would allow me to put in the foam (increasing my r value for those first 3.5 inches), not worry about wires, tie my new wall directly to the old one at top and bottom, etc.

Any idea about how good XPS is at reducing sound compared to cellulose or fiberglass?

I would never hide a junction box. Had several of those in my old house and it made me quite angry!

"Last November, I insulated the attic. I had 8-10 inches of blown in insulation up there. I increased that to 22-24 inches of cellulose. I insulated all openings with expanding foam. The front and back sides of the house aren't that deep due to the roof slope and the need to keep adequate ventilation from the soffit vents. Overall, the added insulation has made a pretty big difference." Awesome to know. I've got 7 inches or so of cellulose (R25) and am looking to 16-20 inches(~R60-R75) and it's good to know it's very noticeable. I figured it would but it's nice to hear of a good confirmation that it's not just a small barely noticeable difference.

The wall inside a wall sounds like a ton of work. Moving the electrical outlets out isn't easy because the wires are too short and I wouldn't want a whole pile of wire splices in my house's branch circuits, that's a whole bunch of twisties in junction boxes to trust. My own opinion on the matter instead of tearing down this drywall or constructing new stuff would be to install a 2" layer of rigid foam on the outside of your house. IMHO that's easier because it is less invasive, can be done when you are doing your siding anyway, and also cuts the thermal bridging and you can seal the gaps between the rigid foam sheets and create a more airtight enclosure that way.

Rocks in the walls, not sure you'll get that much thermal mass doing that, usually thermal mass is done with huge chunks of concrete fashioned into the house, such as a kitchen island. I'm not saying rocks in the walls won't make a difference but it might not be as nice as you think.

Best of luck, you've got a great start.

Id suggest looking into the mooney wall concept for your exterior walls, it eliminates like 98% of thermal bridging in a wall and drastically increases effective R values.

It works great when you are remodeling and is very cost effective.

I believe builditsolar.com has quite a bit on the subject.

Good luck!

I like the sprayfoam method over the foam sheets because there is little to no waste. I buy a 600sf fast rise kit from Tigerfoam for each room and after all the prep. I just keep spraying until the tanks are empty. I think it works out to equal or even cheaper than all those little cans to seal around the sheets.

Renting the cellulose machine from the nearest box store usually costs $20 or less and I can return it the same day. I know SF will disagree but I've had good luck with getting a nice dense fill on my walls.

I could save more money by doing two rooms at a time as my rooms are small and I end up with about 4 inches for sprayfoam on the walls. But I am happy with the results.

MN: You live in minneapolis and only have 7 inches?!? Woah!

Not ready to replace the siding, so I didn't want to do the foam on the outside. The house is pretty big, so new siding would add a huge cost to the project.

Blue: I've looked into the mooney wall, and think it's a great concept.

I really like the idea of taking out existing fiberglass, and doing a couple inches of foam on the back, against the outer wall. This would give me the airtight seal, but leave room for cellulose or fiberglass. That would only leave me about 5 inches to blow in cellulose. Would I be able to pack it well with only 5 instead of 7 inches? I know you dense pack it, but does anyone worry about settling over time? It looks like in the mooney wall they have a depth of around 5 inches. Do the horizontal 2x2's in the mooney wall help to prevent it from settling? I don't want to do all this just to realize there's not insulation in the top foot a few years down the line!

hamster: So, do you dense fill with cellulose on top of your spray foam? If you put in 4 inches of spray, how many inches of cellulose do you have?

Thanks for the ideas guys. I'm starting to narrow down my options!

I do the best I can at dense pack with the tools I rent from Lowes. We do worry about settling, that's why we try to dense pack. I leave a little gap between the outer original studs and the inner new studs so I get 3-4 inches of foam and 4-5 inches of cellulose. > R40

In one of the other threads SF told us how to use mesh netting to hold the cellulose, before the drywall goes up. I will try that next time so I won't have to patch new walls were the cellulose goes in. I am confident that I got firm, continuous fill with the cellulose but the mess would make it easier to be sure.

If I were doing an inner wall, I would take the old drywall and insulation down for several reasons:
1. I could inspect for rot, air gaps, etc.
2. I could install tyvek or similar air barrier.
3. I could pull staples on wiring to move sockets to the new wall.
4. I could get rid of the old vapor barrier and any potential complications from it.
5. I could choose to use foam insulation, or could at least use fresh, insulation.
6. I could install insulation properly--I have seen a lot of badly installed stuff.

A couple extremely important things to remember when making a double wall in a retrofit: You will still have band joist issues. If you have decent replacement windows you will still have more air leakage through the band joist than in all windows combined (usually). Also there is the enormous thermal bridging issue there as it a band of 8"-10" wood wrapping the house on all sides. You also have one of these under the first floor which brings along the same kind of air leakage and thermal bridging issues. This is one of the main reasons that outsulating has become so popular. It's dead easy in a retrofit. To properly insulate and air seal in a retrofit from the inside you would need go gut the house. Or at least gut one part of the house at a time.

I'm not for the rocks in the walls, they will also retain the cold.
I would use stucco/plaster walls as the last wall covering, then it is in constant contact with the inside heat,as opposed to being sandwiched in the middle somewhere.

I think insulating the outside walls, from the outside of the house, under the siding would be more effective. You would get that tight seal you want out there to keep the summer heat and winter cold out of the framework/walls.

With your tips and other research, I think I have decided on doing the following:

1. Tear down the old wall and take out the old fiberglass.
2. Install 2 inches of XPS foam in each cavity. I will cut it a bit small and use canned expanding foam to get a good seal around the edges.
3. Build another 2x4 wall inside the first one. I will stagger the vertical 2x4's to reduce thermal bridging. I may even leave a 1/2 inch gap between the two walls to almost completely eliminate wood-wood contact (the top and bottom plates) and allow another 1/2 inch of insulation area.
4. Put up netting and then blow the remaining gap (~5-5.5 inches) with dense pack cellulose.

I have run the numbers, and this is the cheapest option (besides reusing the old fiberglass). It will run me about $275 (just for insulation, not wood or drywall) for a 240 square foot wall.

In regards to adding the foam to the outside of the house, I like the idea, but there are several problems:
1. I don't want to replace the siding at this time.
2. We have a walkout, so the top of the siding on the back and side of the house is about 30 feet in the air. Probably not a job I'm comfortable with. Adding in labor (even if just taking down then putting back up the old siding) would add too much cost to the job).
3. At least half of the reason for this job is to decrease outside noise infiltrating the wall. From my research, it seems dense pack cellulose is the way to go. The XPS doesn't decrease the sound much from what I understand.
4. When the siding does need to be replaced, I will still have the option of adding more XPS at that time.

My only question is: do I need to put up a plastic vapor barrier on the front face of the new 2x4 wall? I understand that the XPS is a vapor “retarder”, but I don't know if I need an actual vapor barrier on the inside part of the wall. I plan on sealing the new drywall pretty well, so I don't know if that would be good enough. I also have read some things that it's not good to have cellulose "sandwiched" between two vapor barriers. Any moisture that gets in there doesn't have a chance to escape. Any words of wisdom?

Thanks!

The XPS is a vapor barrier. You can't have another one in the wall anywhere. Once you go down the road you're talking about you can't put foam on the outside as it will create a vapor barrier sandwich and your sheathing will never be able to dry. You will end up with a rotten house. This is the #1 reason I never recommend people to put foam in their walls. Once you do it you are committed to foam and you can never put foam on the outside or eliminate thermal bridging at the band and rim joists. When you gut the bottom floor you will be able to foam the band joist from the bottom but there will still be appreciable thermal bridging through the joists connected to it.

I have foam as an outside sheating (looks to be about 3/4-1 inch). I have metal cross bracing instead of plywood. So, right now I have siding-foam sheathing-2x4 wall.

I am planning on putting the new xps just on the inside (butted up against) of the current exterior foam sheathing. Then I want to blow cellulose on the interior side of the xps.

So, if I'm understanding you correctly, I should still be able to do more foam on the outside in the future, correct (because I don't currently have plywood sheathing)??

I guess it seems weird to me to NOT have a vapor barrier on the inside, but you think I'll be ok?

Ahhhh. Foam sheathing and metal let in bracing. You'll be OK. Just make sure the cellulose doesn't bulge the foam sheathing out. You also have to remember that you need at least 40% of your R value to the outside of the wall in the form of the foam or you may have condensation issues. And NO. You can not install a poly barrier under the sheetrock. Again, vapor barrier sandwich. Also you have a ton of plastic in your wall already. I personally wouldn't want to live in a plastic box if I could help it.

You only get a vapour barrier when the XPS foam is 1.25" or thicker and well sealed. Somewhere I have an article from the Building Science Corp that shows a couple of inches of closed cell foam on the outside followed by either mineral wool (roxul) or cellulose. A vapour barrier is still needed on the inside. Note that the entire cavity needs to be well sealed because rot comes from continuous fresh moist air. If you don't use the foam on the outside a standard air barrier (tyvek) would be needed.

Also, on the inside, I put a radiant barrier over the studs (and over the vapour barrier), then 2x2s horizontally on 16" within which goes all the electrical. That way there is no opening at all in the barriers. Drywall goes on after that.

If you do EPS on the outside, it will need to a lot thicker to be considered a vapour barrier

Everything I've read about how a radiant barriers work is that they require an air gap. I'm not certain that adding the foil layer did anything for you.

Ahhhh, good sir, but there is an air gap....1.5" between the radiant barrier and the drywall....

The situation you describe is a code violation in MA. 1" of XPS is a class 2 vapor barrier and the foil is class 1.

I'm not familiar with the MA code. What is the definition of a class 1 and 2 vapour barrier in MA. And why would a radiant barrier be an issue (or maybe it is not, by itself)?

The sandwich, I expect, is the problem so if you have a semi permeable outer skin and a proper barrier on the inside, is the code satisfied?

Ok, color me confused. I'm hearing both sides. So....vapor barrier on the inside or not?

No. No VB on the inside. You already have one on the outside. When moisture gets into the wall, how is it going to dry out? Not only is it a code violation, it's a recipe for rot and IAQ issues.

Check out these articles:

Do I Need a Vapor Retarder? | GreenBuildingAdvisor.com

All About Wall Rot | GreenBuildingAdvisor.com


@ mikesolar, the first one describes the various classes of vapor retarders. In it there is also a link to a BSC paper on the subject.

To do the outside of the house 2nd floor at that would be time consuming EXPENSIVE did I mention expensive.. I know I suggested it..
I have suggested for someone else not to do just for that reason, who has 30-40 grand to toss at an insulation project, Not many people, I can Vouch for that.
Just tear drywall off , extend the inside wall by a 2x6 width, extend the window sills and take 6 inches off the ceiling drywall. Stud it up like a normal wall. Put netting up, blow in Cellulose and dry wall it. Less Painful for the wallet. Doable by any home owner with a good back and basic carpentry skills.
No need to vapor barrier it. Its under the siding already to keep the wet out.

Just thinking The R value of Cellulose is lower than Fiberglass, unless they have better Cellulose then the bag I have.
So roll in fiberglass instead of blowing in cellulose is my thought.
Other people who posted here know much more than me on insulation choices... They would know what is good bang for buck.

That works if you don't mind all the new electrical work, cable, phones, paint, trim, possibly moving the stack to stay warmer, plumbing, toilets, and anything else that is now squished by a moved wall.

The outside insulation can look like a bargain if done right, and your inside life is not disrupted.

Not disrupted aside from window details. ;)

Really IMHO it's better to go with a cellulose retrofit. It is more expensive to accomplish the same initial results though. In a retrofit you really need to build a new wall beyond the existing wall to compete with the common DER foam outsulation. We have two major obstacles and we can't tackle one without addressing the other: Air movement through penetrations and energy movement through materials.

You could have an enclosure with R-1,000,000 walls and screen for all materials aside from insulation and you could have an enclosure like a vacuum tube with no R value but it's perfectly air tight. Neither will work properly for a living space.

I'm on the quest for vacuum tube tight (for moisture management) and R 1,000,000 (because no amount of conservation is ever enough.

Let us know when you find it....lol

I won't need to let anyone know because it will start raining lotus petals and there will be universal goodwill toward man.

Then the oil/pharm/war/whateverelse institutions fail.

I'm not going to sleep tonight because I am waiting for it to come.:D

I think Your right, it may be cheaper to do the outside..
The outside insulation would be much more convenient.
Good points, especially about the fixtures toilets etc. Kitchens would have to get pulled, what big Job it's turning into. I think it would be a nightmare for living conditions, would have rent a motel or whatnot.


Renting Professional scaffolding would make less daunting.

The house has thin insulation out there now, I know they do that under Vinyl siding , I am guessing that what it has now.
So a vinyl siding job as opposed to drywall/mess house gutted and losing 6 inches of elbow space in each room, especially the bathrooms, they could take a big loss in space.
It would not work very nicely to insulate inside for my house, the toilet is tight in a corner behind the bathtub/showers back wall Same with basement with no real option short losing a fair bit of the small space they have now.
Which does not help resale at all.

No disrespect to your advice S-F !
it has merit as well.

The original poster asked about the second floor. This likely only has a bathroom and some bed rooms. These probably need renovation anyway, mine sure did. When I did mine, I looked at it as a chance to do new electric, fix the heat, seal everything, etc... Sure all those things cost, but pay back in efficiency and peace-of-mind.

If the inside is nice and functional and you have sufficient roof overhang the outsulation may be the better option. if the inside needs renovation, a gut and fix job is better. Room by room as possible.

In the long run outsulating is almost always cheaper due to the previously mentioned reasons. The problem with it is that you're using a ton of foam, which I personally find distasteful. Basically a good DER using no exterior foam involves a complete gut renovation and usually also something on the outside to deal with all the thermal bridging.The Larsen truss is pretty interesting though. It's a TON of work but you can still go all cellulose/no thermal bridging.

This is exactly what I intend to do, although probably only 2x4 new wall instead of 2x6.

In regards to losing space, moving all kinds of plumbing, etc, none of that is a concern. Every wall I want to extend is a bedroom or a bathroom. I will not have any plumbing to move, or anything else major. The only thing I will have to move is electric. And since I'm taking off the old drywall, this will be quite easy. It also is nice because I would like to add some extra outlets. I had not wanted to do this before because I didn't want to disturb the current drywall. Now I have an excuse :-)

The R value of cellulose is said to be in the mid to high 3's. I believe fiberglass is in the mid to low 3's. When you factor in the fact that fiberglass is impossible to install perfectly, the cellulose seems the clear winner in by book. In addition, one of my main goals is to reduce outside noise. It seems that cellulose is much better than fiberglass at this.

I don't have that much extra overhang for soffit ventilation if I were to put 4 inches on the outside (at minimum what I would want to get the same effect as my inside plan). Plus, that foam probably wouldn't help too much with sound deadening that is at least half the reason for the project.

I am planning on one or two rooms at a time, so definitely a doable job.

Now I'm almost thinking of possibly JUST using cellulose and not putting the 2 inches of XPS. I originally wanted to do that because of the increased R value and air sealing properties. However, if I do 7 inches of dense pack cellulose, would that be pretty good at stopping any air movement? Or should I still stick with the XPS idea?

I feel , with the outside seal in place, stay away from the interior Xps.
From what I have picked up, it pretty much dictates to using the more the breathable choice/cellulose.

At least cellulose is people friendly /lung and skin as opposed to fiberglass.
I am unsure of Cellulose's lifespan with its rated R-value, I know The Expandable Foam they inject in refrigerators starts to lose its R-value in 10 years or so.
fiberglass all though nasty may hold out for the long run, a pure guess on my part.
Worth further investigating never the less..

Foam looses R Value because it outgasses. Cellulose doesn't rely on non air gasses for it's R Value so it doesn't ever loose it.

As long as it is dense packed. In a loose-fill attic floor application, the settling causes the R-value loss proportional to its thickness.

Yes this is true. But when cellulose in installed (at least around here) the settled density and R Value is what's calculated. So for 12" or R 38 (the code depth for attics) people usually blow to 13" - 14" in anticipation of the 1.5" settling.