Attic insulation guidance

[Highbeam]

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”.

 

[EatenByLimestone]

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

 

[Bad LP]

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

That’s what I thought as well.

 

[John Galt]

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?

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.

 

[EatenByLimestone]

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 $$$$.

 

[Dobish]

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

 

[BrianVA]

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.

 

[John Galt]

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.

 

[peakbagger]

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.

 

[EatenByLimestone]

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.

 

[sloeffle]

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

 

[Highbeam]

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.

 

[brenndatomu]

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!

 

[EatenByLimestone]

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

 

[Highbeam]

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.

 

[sloeffle]

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.

 

[brenndatomu]

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?!

 

[begreen]

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.

 

[sloeffle]

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.

 

[brenndatomu]

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.

 

[sloeffle]

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.

 

[BrianVA]

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?

 

[sloeffle]

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.

 

[semipro]

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.