# Attic insulation guidance



## Easy Livin’ 3000 (Nov 13, 2020)

Old stone house (1700's vintage) .  Basically a thick fieldstone and mud mortar shell, with a wood frame built inside for floors/ceilings.  Space between second story ceiling and attic floor is sparsely insulated with blown in fiberglass, no air barrier.

Plan is to fill the small, uneven space between stone walls and wood frame with spray foam, and replace fiberglass with cellulose (both blown in).  And, importantly, add a plastic sheet air barrier.

Finally my question:

Should the plastic sheet air barrier go on top of the cellulose and joists, or under the cellulose.  On top would be easier, under would require  lots of extra work, going over the plaster ceiling and wrapping each joist on the sides and top.

I may have just answered my own question, but I'd like some expert opinions on whether the air barrier should go above or below the cellulose insulation in the joist bays.


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## ctyankee (Nov 13, 2020)

Here's an article that should be helpful.


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## Easy Livin’ 3000 (Nov 13, 2020)

ctyankee said:


> Here's an article that should be helpful.


Thanks CTyankee.  I love old books and articles so much more than stuff from today.   Much more soul.  Even when reading on a small digital screen.

According to the article, the vapor barrier goes at the bottom of the joist bays.

Preferably, I suppose a vapor barrier would go up, fastened to the bottom of the joists, before installing drywall or plaster.  As that's not an option, here, I guess I need to figure on a tougher job, rolling over the top of the joists and tucking into the bays with the cellulose on top of the plastic.

A thin 1/2" layer of spray foam over the top of the plaster would make this easier.  Sure hate the cost of the foam, though.


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## BrianVA (Nov 13, 2020)

Any thought to insulating under the roof rafters with rigid foam board, rather than over the 2nd floor ceiling?  If you have HVAC duct work up there it might make sense.   It basically turns your attic into conditioned space.   I'm guessing you don't, based on the historic nature of the house.  But just thought I would throw an idea out there.


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## Easy Livin’ 3000 (Nov 13, 2020)

BrianVA said:


> Any thought to insulating under the roof rafters with rigid foam board, rather than over the 2nd floor ceiling?  If you have HVAC duct work up there it might make sense.   It basically turns your attic into conditioned space.   I'm guessing you don't, based on the historic nature of the house.  But just thought I would throw an idea out there.


Thanks for the idea, I like it and had considered it.   The attic walls, dormers and windows are way too leaky and uninsulated, and rafters are undersized, and low to the attic floor.  So it would be a way bigger job, and probably less effective once completed.


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## BrianVA (Nov 13, 2020)

Easy Livin’ 3000 said:


> Thanks for the idea, I like it and had considered it.   The attic walls, dormers and windows are way too leaky and uninsulated, and rafters are undersized, and low to the attic floor.  So it would be a way bigger job, and probably less effective once completed.


That makes sense.  Old houses are really cool, but they can be quite a challenge!


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## Highbeam (Nov 13, 2020)

The ceiling makes as good of an air barrier as you need. Air seal around the edges, tops of walls, penetrations, but dont put plastic on top, just blow in right over the ceiling.

Latex painted plaster ceiling = air seal. I tested this by putting my mouth against the ceiling and trying to blow into my attic. No luck.


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## Hogwildz (Nov 13, 2020)

I'd be putting 2" polyiso board on the bottom of the 2nd floor ceiling. Tape all the inside joints, leave a 1/2" or so gap around the perimeter and  can foam the gap closed.  Iso is approx R6 per inch, plus with foil faced, there is your barrier and air seal with the taped joints & foamed perimeter. I did that here under 1x8 T&G ciling with nothing but paper backed R30 laying ion top of the T&G. Makes for a tight seal + the added R value. can always blow in more whatever on top of the loose FG later.

Screw 1x3 lathe to the bottom of the iso, and install whatever you want to the lath. I took off the T&G, and reinstalled it to lath under the iso. The batshit showers sucked when removing the T&G.


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## brenndatomu (Nov 13, 2020)

Easy Livin’ 3000 said:


> lan is to fill the small, uneven space between stone walls and wood frame with spray foam, and replace fiberglass with cellulose (both blown in). And, importantly, add a plastic sheet air barrier.


Maybe I misunderstand the plan here, but spray foam is an air barrier, why add the plastic?
I'm hearing that this is getting to be a somewhat common practice, a thin layer of spray foam to air seal, then obtain the rest of the R value with cheap cellulose.


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## Corey (Nov 13, 2020)

Highbeam said:


> ... I tested this by putting my mouth against the ceiling and trying to blow into my attic. No luck.



Same rule as for Isaac - pix or it didn't happen!    

Um...well, on second thought....NM


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## hockeypuck (Nov 13, 2020)

brenndatomu said:


> Maybe I misunderstand the plan here, but spray foam is an air barrier, why add the plastic?
> I'm hearing that this is getting to be a somewhat common practice, a thin layer of spray foam to air seal, then obtain the rest of the R value with cheap cellulose.


You will have to check with the actual company that makes the foam product, but I think it takes 2" of foam for an official vapor barrier.  But I think we are splitting hairs.  1" would probably do it in my book.


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## brenndatomu (Nov 13, 2020)

Corey said:


> Same rule as for Isaac - pix or it didn't happen!


Just don't ask him for photo documentation of how he does his OPE winterization!


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## John Galt (Nov 13, 2020)

Seems like there are two things happening- walls and ceiling. The foam was for the walls, plastic for an air barrier in the ceiling?

1" of closed cell foam is considered a vapor barrier. I've never seen it sprayed directly on a stone wall but I don't live in that region. Blowing cellulose would require a permeable sheeting to hold in the dense pack, not plastic, since you don't want two vapor barriers with insulation in between. The wall has to dry to the inside or the outside. A wet pack cellulose might work. I think that forms an air barrier and then plastic is stapled inside as a vapor barrier, no foam required.

The ceiling shouldn't need a vapor barrier assuming the attic is vented. Highbeam is right, paint is an air barrier so is plaster. Sealing up light fixtures, outlets, and other penetrations to avoid a stack effect will help more than a plastic sheet under the insulation. The water vapor has to go somewhere, you don't want it condensing in a place where it won't dry.

 With a house that age the worst thing you can try to do is attempt to seal it up. You'll never get an air tight house and you could cause some serious rot and mold issues.


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## Easy Livin’ 3000 (Nov 14, 2020)

brenndatomu said:


> Maybe I misunderstand the plan here, but spray foam is an air barrier, why add the plastic?
> I'm hearing that this is getting to be a somewhat common practice, a thin layer of spray foam to air seal, then obtain the rest of the R value with cheap cellulose.


Air barrier + cellulose for R value, just as you said. 

It's either plastic sheet or thin layer of spray foam, I wouldn't do both.  I'll probably go with the plastic because it'll be much cheaper, even though it'll be more work.  The joists will be under the air barrier, but I think that'll probably be ok.

EDIT:. I'll probably forget the plastic all together and add another layer of paint to plaster ceiling and foam around the perimeter.


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## Easy Livin’ 3000 (Nov 14, 2020)

Highbeam said:


> The ceiling makes as good of an air barrier as you need. Air seal around the edges, tops of walls, penetrations, but dont put plastic on top, just blow in right over the ceiling.
> 
> Latex painted plaster ceiling = air seal. I tested this by putting my mouth against the ceiling and trying to blow into my attic. No luck.


I've been wrestling with this in my head.  I think you are right.  I'll just put another layer of paint on the ceiling, it needs it anyway, and forget about the plastic or foam.  That cuts the job by more than half.


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## Easy Livin’ 3000 (Nov 14, 2020)

Hogwildz said:


> I'd be putting 2" polyiso board on the bottom of the 2nd floor ceiling. Tape all the inside joints, leave a 1/2" or so gap around the perimeter and  can foam the gap closed.  Iso is approx R6 per inch, plus with foil faced, there is your barrier and air seal with the taped joints & foamed perimeter. I did that here under 1x8 T&G ciling with nothing but paper backed R30 laying ion top of the T&G. Makes for a tight seal + the added R value. can always blow in more whatever on top of the loose FG later.
> 
> Screw 1x3 lathe to the bottom of the iso, and install whatever you want to the lath. I took off the T&G, and reinstalled it to lath under the iso. The batshit showers sucked when removing the T&G.


If my ceilings weren't 6' 5", and I wasn't 6' 2",  I'd agree.  This old house has small dimensions.   Plus, your solution is expensive, every sheet of polyiso is $40 around here.  I splurged for one sheet to make the hatch to cover the walk-up attic opening, but even that hurt$.  

Plus my heat is free, I just want easy 80° rooms in the dead of winter.


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## Easy Livin’ 3000 (Nov 14, 2020)

hockeypuck said:


> You will have to check with the actual company that makes the foam product, but I think it takes 2" of foam for an official vapor barrier.  But I think we are splitting hairs.  1" would probably do it in my book.


I misspoke previously.  I meant air barrier, I actually don't want a vapor barrier.  I've considered using tyvek or the like, but I think Highbeam is probably right, the multiple layers of paint over the thick plaster should be enough, coupled with some cans of foam around the perimeter.


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## Easy Livin’ 3000 (Nov 14, 2020)

John Galt said:


> Seems like there are two things happening- walls and ceiling. The foam was for the walls, plastic for an air barrier in the ceiling?
> 
> 1" of closed cell foam is considered a vapor barrier. I've never seen it sprayed directly on a stone wall but I don't live in that region. Blowing cellulose would require a permeable sheeting to hold in the dense pack, not plastic, since you don't want two vapor barriers with insulation in between. The wall has to dry to the inside or the outside. A wet pack cellulose might work. I think that forms an air barrier and then plastic is stapled inside as a vapor barrier, no foam required.
> 
> ...


Thanks, agree with everything you said.

I am only worrying about the ceilings for now, the walls are actually only the thickness of furring strips, lath, and plaster.  The only air gap is the thickness of the furring strips.  I will slow the air through that space with foam at the top and bottom, wherever I can get access.


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## johneh (Nov 15, 2020)

Easy Livin’ 3000 said:


> Plus my heat is free, I just want easy 80° rooms in the dead of winter.


Good thing you don't live here the cost to have my home at 80
would bankrupt most also we would be down to our tightey whities. 
65 to 70  is warm enough but then I live in the Great White North


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## Dobish (Jan 7, 2021)

i just tore out all of the insulation above my dining room, and removed the insulation and the drywall above my living room in prep of replacing the ceiling. My house used steel wool insulation.. I was going to just toss it, since it is pretty dusty, but I decided since it is in bags, and I am already up there, there was no point in just blowing in more. I am going to spread it around on the other part of the ceiling that has R-19 Insulation in it. I have gone around and sealed up everything outside (for the most part) and am looking forward to a much nicer R-38 faced batt, with some blown in insulation above that. I think the biggest problem is that the upstairs gets a lot more solar than the downstairs (with south an west facing windows), so I might have to move the thermostat 

I hate working with insulation, especially old stuff!


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## Dobish (Apr 13, 2021)

we decided that instead of just replacing the ceiling, we were going to vault it. It also provides us access to the crawl space a bit more efficiently. After tearing down the ceiling and vaulting, I went with an R-38 Insulation on the vault. We still need to blow the insulation back in the crawl space over the main house, but I wanted to finish up the duct work for the swamp cooler and the electrical related stuff before blowing back in.

Even with just the 1 room sealed up, a door over the crawl space it is a lot more comfortable!


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## BrianVA (Apr 13, 2021)

Dobish said:


> we decided that instead of just replacing the ceiling, we were going to vault it. It also provides us access to the crawl space a bit more efficiently. After tearing down the ceiling and vaulting, I went with an R-38 Insulation on the vault. We still need to blow the insulation back in the crawl space over the main house, but I wanted to finish up the duct work for the swamp cooler and the electrical related stuff before blowing back in.
> 
> Even with just the 1 room sealed up, a door over the crawl space it is a lot more comfortable!


Looks great!  Glad you're happy with the results.  

I'm having 3" of closed cell spray foam (R-19) installed on the roof deck in my attic to seal it up and better insulate.  My HVAC for the 2nd floor is up there, so it makes sense to "encapsulate" the whole attic.  The leakage from the ducts will be sufficient to semi-condition the space.

What's interesting is that I intended to have 6" of closed cell which would be R-40 (2x8 rafters), but the sales guy literally talked me down to to 3" (R-19).  He said I would get all the value of the foam at 3" with no need for additional insulation.  I told him I was willing to pay extra.  He said if I really insisted on it that he wanted me to talk with one of the building scientists at Icynene (the manufacturer of the product they spray) so that I could here the facts from them before I spend additional money for no reason.  Pretty powerful coming from the sales staff who would obviously get a higher commission if I spend more.

Do any of you have any knowledge or experience with this?


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## Dobish (Apr 13, 2021)

You are going to get better air sealing with the spray foam,  so you get a lot less air movement.  Especially if it is really an attic space,  you will have a second layer to keep that space consistent.  Insulation is only part,  but the seals make the difference


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## Dobish (Jun 13, 2021)

Finally got around to blowing some insulation in the crawl space! Man, it is amazing what a few feet of insulation and air sealing will do!  Between that, and the swamp cooler installed, it has not gotten over 80° in the upstairs yet!  When it was cold, and I didn't have the fire going, the furnace only kicked on once or twice a day, instead of every 20 minutes or so!


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## BCC_Burner (Jun 13, 2021)

Dobish said:


> Finally got around to blowing some insulation in the crawl space! Man, it is amazing what a few feet of insulation and air sealing will do!  Between that, and the swamp cooler installed, it has not gotten over 80° in the upstairs yet!  When it was cold, and I didn't have the fire going, the furnace only kicked on once or twice a day, instead of every 20 minutes or so!



Just for clarification, you're referring to your attic, correct?  I've never heard anything called a crawl space except below grade areas with ceiling heights less than 65 inches.


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## Highbeam (Jun 13, 2021)

Dobish said:


> Finally got around to blowing some insulation in the crawl space! Man, it is amazing what a few feet of insulation and air sealing will do!  Between that, and the swamp cooler installed, it has not gotten over 80° in the upstairs yet!  When it was cold, and I didn't have the fire going, the furnace only kicked on once or twice a day, instead of every 20 minutes or so!



Added a “few feet”? I blew r50 cellulose in my shop attic and I think it was only 15 or 18”.


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## EatenByLimestone (Jun 14, 2021)

I'm thinking the few feet refers to square footage, as in ceiling square footage.


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## Bad LP (Jun 14, 2021)

EatenByLimestone said:


> I'm thinking the few feet refers to square footage, as in ceiling square footage.


That’s what I thought as well.


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## John Galt (Jun 14, 2021)

BrianVA said:


> Looks great!  Glad you're happy with the results.
> 
> I'm having 3" of closed cell spray foam (R-19) installed on the roof deck in my attic to seal it up and better insulate.  My HVAC for the 2nd floor is up there, so it makes sense to "encapsulate" the whole attic.  The leakage from the ducts will be sufficient to semi-condition the space.
> 
> ...


Closed cell foam doesn't have a high R value compared to other insulation. Generally they do a "flash and batt" where 1" of foam is sprayed and then the rest of the rafter/wall is filled with fiberglass. You get all of the benefits of air sealing foam and a higher R value with the fiberglass - I think around R-36, but I don't have the specs in front of me. Spraying open cell foam on top of the 1" closed cell is another option if you have the all foam desire.


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## EatenByLimestone (Jun 14, 2021)

Closed cell foam is around R7/in

Open cell foam is around 3.5/in, as is fiberglass.  

The only reason to flash and batt is $$$$.


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## Dobish (Jun 14, 2021)

Yep. Meant attic.  Feels like a crawlspace....


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## BrianVA (Jun 15, 2021)

John Galt said:


> Closed cell foam doesn't have a high R value compared to other insulation. Generally they do a "flash and batt" where 1" of foam is sprayed and then the rest of the rafter/wall is filled with fiberglass. You get all of the benefits of air sealing foam and a higher R value with the fiberglass - I think around R-36, but I don't have the specs in front of me. Spraying open cell foam on top of the 1" closed cell is another option if you have the all foam desire.



Refer to the post above by EatenbyLimestone.  The product I'm having sprayed is R7 per inch.  No other insulation product provides an R value this high.  If willing to pay for spray foam there is no reason to use fiberglass batts.


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## John Galt (Jun 15, 2021)

BrianVA said:


> Refer to the post above by EatenbyLimestone.  The product I'm having sprayed is R7 per inch.  No other insulation product provides an R value this high.  If willing to pay for spray foam there is no reason to use fiberglass batts.


That's what happens when you try to go off of memory early in the morning without enough coffee.  I agree that the closed cell is higher than fiberglass and open cell. $$$ is the reason most people don't do full closed cell.  I have seen pictures of uncured foam when it is sprayed thick but I assumed it was installer error.


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## peakbagger (Jun 15, 2021)

I know of a super insulated ranch being built near me. Its 2 by 6 walls covered with 1" iso board on the outside with 1/2" iso board overlapping the 1" with an air gap and then siding. The plan for attic is about 2.5 feet deep of cellulose. Its got a crawl space underneath with about 2" of foam on the inside foundation  walls (overlapped sheets) iwith the same treatment as the walls on the outside. And 4" in the floor with a good vapor barrier. He went with a standard double pane window (mostly casements or fixed glass) but his glass to wall ratio is fairly low. No doubt it will require an air to air heat exchanger.  He is also incorporating lots of thermal mass (barrels of water in the crawl space). The steady state heating load will be very low but getting it up to temp will take awhile. 

A friend had an older home sprayed full depth with foam for 4" thick walls on an older building gut. job. It was 2 foot on center rough cut studs. After spraying they run a special milling machine to mill it smooth on the interior before the drywall goes in. Its tight but his basement was not insulated which ups his heating load. Strangely,  sound transmission suffers with full depth spray foam, the foam adheres tight to exterior and propagates the sound inside like a drum. The structure definitely feels more solid.
Flash and Batt is supposed to be better for acoustics as the fiberglass batt decouples the exterior wall from the interior so more noise gets "lost" in the fiberglass. Note flash and batt needs to take into account dewpoint, the flash needs to be thick enough to keep the interior face of the foam above the dewpoint.


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## EatenByLimestone (Jun 15, 2021)

They will grind down open cell foam.    Closed cell is taken down with a curry comb.    If you hate your helper, you can really make his day miserable.


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## sloeffle (Jun 15, 2021)

peakbagger said:


> A friend had an older home sprayed full depth with foam for 4" thick walls on an older building gut. job. It was 2 foot on center rough cut studs. After spraying they run a special milling machine to mill it smooth on the interior before the drywall goes in. Its tight but his basement was not insulated which ups his heating load. Strangely,  sound transmission suffers with full depth spray foam, the foam adheres tight to exterior and propagates the sound inside like a drum. The structure definitely feels more solid.


In my house addition I have R60 in the attic, and 2x6 walls that are sprayed full of open cell foam. Studs are 16" on center though. I was going to do flash and batt, but the spray foam guy got a little carried away so I told him to just go ahead and spray them full for an agreed up price. Band board has about 2" of closed cell foam on it down to the second course.  

When I was painting the closet I had to turn the halogen lights off because it got so hot in there. First world problems


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## Highbeam (Jun 15, 2021)

Those high watt halogen work lights are serious heaters. Burn like heck if you touch them too. I’m too cheap to upgrade to led until the halogen bulbs break.


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## brenndatomu (Jun 15, 2021)

Highbeam said:


> I’m too cheap to upgrade to led until the halogen bulbs break.


Too cheap to let the LED's start paying for themselves...keep feeding those halogen pigs!


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## EatenByLimestone (Jun 15, 2021)

Eh, if the job is in the winter, you've just heated your room, AND got free light!    Bargain!


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## Highbeam (Jun 15, 2021)

brenndatomu said:


> Too cheap to let the LED's start paying for themselves...keep feeding those halogen pigs!



Power is quite cheap here and the lights don’t get used much anymore. I did upgrade the shop t8 tubes to led when just one ballast died. Much better light and half the consumption.


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## sloeffle (Jun 16, 2021)

brenndatomu said:


> Too cheap to let the LED's start paying for themselves...keep feeding those halogen pigs!


I don't use it enough to justify paying $100 for a new one. I can buy a lot of electric for $100.


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## brenndatomu (Jun 16, 2021)

sloeffle said:


> I don't use it enough to justify paying $100 for a new one. I can buy a lot of electric for $100.


You have $100 bulbs?!


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## begreen (Jun 16, 2021)

brenndatomu said:


> Too cheap to let the LED's start paying for themselves...keep feeding those halogen pigs!


In a closet, no problem. These are not lights that normally are on for more than a few minutes. I have only replaced bulbs that are used for extended periods of time. The others can wait until they burn out.


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## sloeffle (Jun 17, 2021)

brenndatomu said:


> You have $100 bulbs?!


I guess my original post wasn't very clear. I was using a halogen tripod light to help supplement the crappy CFL light I had in there. That is what I meant by "I don't use it enough to justify paying $100 for a new one. ".  Aka - replace the halogen tripod light with a LED version.


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## brenndatomu (Jun 17, 2021)

sloeffle said:


> I don't use it enough to justify paying $100 for a new one. ". Aka - replace the halogen tripod light with a LED version.


Oh, yeah, definitely not. Would only make sense for lights that actually get used a fair amount.
That's a fight I've had with my employer in recent years...they want to spend big bucks to replace _everything_ with LED...my stance has been that they will NEVER pay for themselves when many of these lights run between 0-5 minutes per day. Now, if a light fails and needs something more than a bulb (flourescent) to fix it, then that's a different story.


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## sloeffle (Jun 17, 2021)

brenndatomu said:


> Oh, yeah, definitely not. Would only make sense for lights that actually get used a fair amount.
> That's a fight I've had with my employer in recent years...they want to spend big bucks to replace _everything_ with LED...my stance has been that they will NEVER pay for themselves when many of these lights run between 0-5 minutes per day. Now, if a light fails and needs something more than a bulb (flourescent) to fix it, then that's a different story.


I agree completely. When LED lights first came out, a friend of mine spent hundreds of dollars replacing all of the light bulbs in his house to be more "eco-friendly". Doesn't seem very "eco-friendly" to me when you just threw away a bunch of perfectly good working CFL lights bulbs for no reason. 

Unfortunately we are a country of consumers, and some of us want the latest and greatest of everything.


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## BrianVA (Jun 30, 2021)

sloeffle said:


> In my house addition I have R60 in the attic, and 2x6 walls that are sprayed full of open cell foam. Studs are 16" on center though. I was going to do flash and batt, but the spray foam guy got a little carried away so I told him to just go ahead and spray them full for an agreed up price. Band board has about 2" of closed cell foam on it down to the second course.
> 
> When I was painting the closet I had to turn the halogen lights off because it got so hot in there. First world problems


Wow, that's a really well insulated addition.  Are you able to feel a difference compared to the rest of the house?


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## sloeffle (Jul 7, 2021)

BrianVA said:


> Wow, that's a really well insulated addition.  Are you able to feel a difference compared to the rest of the house?


Sorry it took me awhile to get back to you, I've been on vacation in West By God riding UTV's.

The "original" part of the house has 2x6 batt insulation and R40 in the attic, so it isn't horrible to heat and cool. Yes, the house addition is easy to heat and cool. If I were to build a house I'd do the spray foam insulation again in a minute. It's money well spent IMHO.


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## semipro (Jul 7, 2021)

peakbagger said:


> Strangely, sound transmission suffers with full depth spray foam, the foam adheres tight to exterior and propagates the sound inside like a drum. The structure definitely feels more solid.


One of those unintended consequences that tend to haunt us.  I would not have thought of that.  I will now.  

It reminds me of when I replaced all the HVAC flex duct in our 1st level to improve flow and prevent mouse damage only to find out that air handler noise travels much better through rigid duct than it does through flex duct.


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