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Attic Insulation
Old 03-19-2019, 06:08 PM   #1
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Attic Insulation

I guess I could put this under FIRE and Money, but it is only partially about the money. Background: I need attic insulation. I live in Michigan in a 1950's ranch with virtually no insulation. I've had significant ice dams in the past unless I roof rake and even then, it just moves the dam up higher on the roof. Thankfully, no damage yet. I've lived here for three winters now and I have the rest of the attic cleaned up and new mechanicals that go in the attic (ductwork and electrical) so I'm ready to button it up.

I've got two quotes so far. They both are recommended from the gas utility and have good reviews. One is quoting a basic insulation job. Come in blow in cellulose and call it a day - $3,500. The other company is a much higher end company. They intend to clear everything (not the mechanicals) out of the attic, seal all air flow from the internal walls and such and then insulate. It falls under the category of do it right. Of course, that cost a lot more - more than double - $8,000.

Here's the twist. The second guy proposes something different for $9,500. Spray foam the underside of the roof and seal it that way. Completely clean out the attic of all old insulation (what little there is) and leave me with a clean attic. The reason this interests me is that it provides me with storage space and better access to the attic mechanicals in the future.

My base plan was to get everything buttoned up in the attic, have insulation installed and try to never set foot up there again. Try not to disturb the "envelop". The spray foam insulation creates a clean attic with about 1500 sq feet of storage space. Realistically, I would only use about 200 - 400 sq feet because I'm not going to drag anything up to the attic that weighs that much or that I use that often - think Christmas ornaments, pieces of luggage, some chairs . . . This is important because I live on a slab (no basement) and limited storage in the house. We use half the 2 car garage for this type of stuff now (with plenty of room to walk around). We don't really store much up there now because it's dirty and subject to drastic temperature differences between hot summer and cold winter. The space created would be comfortable year round (chilly in the winter, not too hot in the summer). Good enough for storage and even some electronics (say I wanted to put my router or a NAS up there type of electronics).

Frankly, I never thought this was an option and getting some good storage space for the extra $6K is a good deal. My 200 sq ft shed cost almost $10K. It also allows me to work up there when needed. I still want to run a few electrical lines and just the every now and then that you need to fix something (bathroom fan) it would be nice not to have to wade through 10+ inches of cellulose insulation.

So, would you do it? More important, what things might you consider as you weigh this? Note, money is not a concern other than I'm somewhat frugal and in my mind, this was a $3-$5K budget item before any quotes so it's a bit hard to swallow. Your input, as always, is very much appreciated.
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Old 03-19-2019, 06:50 PM   #2
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Both approaches (insulating the attic floor and insulating the attic ceiling (the underside of the roof deck) will be effective to some degree. Questions:
1) How much (in dollars) is that conditioned storage space in the attic truly worth to you?

2) Do you have HVAC ducting located in the attic (you probably do, if you have no basement). Is your furnace and your AC evaporator coil located in the attic? If you have ductwork in the attic, what type is it (solid metal, "flex duct"? and how well is that ducting insulated?
3) How steep is your roof?
4) How deep are the rafters/trusses that support your roof deck?

5) The guy that wanted to spray under your roof deck: What insulation value was he quoting, and what type of foam did he say he would use?
6) The guy that wanted to insulate your attic floor with blown-in cellulose: His price didn't include sealing up the ceiling of the floor below and all the walls before he put the cellulose in? You definitely wan to do that, and you don't want to do business with someone who would think of putting the cellulose in without doing that first. How thick was the cellulose going to be (" or R-value)?


More to follow . .
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Old 03-19-2019, 06:56 PM   #3
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I don't know your market but all those quotes sound high. The spray foam a bit high. I'd be careful if you have trusses in your attic. Trusses are not made to have weight on the bottom chord. I'd also be careful on your roof deck. Some asphalt shingles deteriote under heat build up. I don't know if the spray foam would absorb heat & reflect it back to the roof shingles.

If it was me I would do the air sealing & blown cellulose. Stop the heat loss into the attic. Then insulate. And look around for more quotes
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Old 03-19-2019, 07:03 PM   #4
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Suggestion: Find out if your power company offers low-cost energy assessment. For me they did a blower-door test and identified cold spots with a thermal camera. The tech could probably give you good advice on your options.


I would be skeptical of the foam option. It leaves thermal bridging through the wood rafters, and the lack of airflow under the sheathing would degrade shingle life.
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Old 03-19-2019, 07:13 PM   #5
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Originally Posted by samclem View Post
Both approaches (insulating the attic floor and insulating the attic ceiling (the underside of the roof deck) will be effective to some degree. Questions:
1) How much (in dollars) is that conditioned storage space in the attic truly worth to you?

Not sure. That's certainly one of the main considerations. It's easily worth a couple thousand, not sure it's worth $6K.

2) Do you have HVAC ducting located in the attic (you probably do, if you have no basement). Is your furnace and your AC evaporator coil located in the attic? If you have ductwork in the attic, what type is it (solid metal, "flex duct"? and how well is that ducting insulated?

Ducting is in the attic, not the equipment. That's in a mechanical room in the garage. The duct work is mostly flex duct with a main trunk line(s) running down one side of the attic. All well insulated, all new.

3) How steep is your roof?

Not very steep at all. In fact, this is the main reason this is not an easy decision. One cannot stand in my attic. Of course that makes the storage less valuable and certainly less utility. Still, with no basement, it is storage that I don't have and would be better than the attached garage I'm now using for much of what I would put up there.

4) How deep are the rafters/trusses that support your roof deck?

I'm pretty sure they are 2x8's. I'm not worried about the load of storage because I would not be storing a lot of weight and with this configuration, I could spread it out very well.

5) The guy that wanted to spray under your roof deck: What insulation value was he quoting, and what type of foam did he say he would use?

Open cell. Seven inches.

6) The guy that wanted to insulate your attic floor with blown-in cellulose: His price didn't include sealing up the ceiling of the floor below and all the walls before he put the cellulose in? You definitely want to do that, and you don't want to do business with someone who would think of putting the cellulose in without doing that first. How thick was the cellulose going to be (" or R-value)?

I realized that sealing would be best, but that quote was a bare minimum situation for me to consider. Though, he never did mention sealing. Basically, it would get rid of my ice dams and save me some money on my heating and air conditioning bills. He claimed my current R value was 13 (swag) and my ending R value would be 51 (I doubt it). I knew from my research that the second company did higher level work. My original goal however was to solve the problem and see if I could get a reasonable payback. The spray foam idea brought in a completely different dimension.


More to follow . .
See above.
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Old 03-19-2019, 07:17 PM   #6
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I'd be careful if you have trusses in your attic. Trusses are not made to have weight on the bottom chord. I'd also be careful on your roof deck. Some asphalt shingles deteriote under heat build up. I don't know if the spray foam would absorb heat & reflect it back to the roof shingles.
I do not have trusses.

Thank you and Manerac for the thought about the heat reflection and impact on the roof deck and shingles.
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Old 03-19-2019, 07:25 PM   #7
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FWIW, I recently did >both< of these approaches in one house (a home I am working on for my daughter). It is a Cape Cod style 1 1/2 story house, and due to the way the HVAC system is installed, I blew cellulose on the floor of the attic on one side, on the other side I insulated under the roof deck. Both are working fine.
For your project:
Insulating the underside of the roof deck with spray foam: This can work well. I do think it increases the chance of the roof deck eventually rotting and failing due to moisture in the plywood or OSB. All roofs eventually leak, and if closed-cell (low permeance) spray foam is sprayed against the deck it will>not< have an opportunity to dry toward the inside. Also, since the underside of the roof deck can no longer be seen directly, >finding< the leak can be very hard, and more extensive damage is likely to result before the moisture is detected. You won't have a ventilated roof anymore, you'll effectively have a cathedral ceiling with all the woes they can bring.
There is another way to insulate under the roof deck: put vent troughs under the deck (between the rafters) from the eaves to the peak. Then stuff the bays with fiberglass hold it in place with insulation board screwed to the underside of the rafters. You need to get the right kind of board (fire-rated and approved for exposure to the inside of the attic). Thi s the approach I took on one side of my daughter's house. The R-value will not be as high as with solid sprayed-in foam, and I can't directly inspect the roof deck, but the materials were much less expensive (about $2/ft), I could do the work myself, and gaining access again to large areas of the roof deck is not hard.
If you take any approach that insulates the underside of the roof deck, please don't believe that attic space will be comfortable in the summer. It will be cooler than what you have now, but it will still be quite warm unless you add registers to the area and actively push cold air into it (and have returns so air can get back to your HVAC system). You'd have to treat it just like another room if you want it to be comfortable. Without dedicated registers, the hot air from inside your house will collect there, and in the summer the temps will be somewhere between your downstairs temperatures and the temperature outside.

Insulating the downstairs ceiling with blown-in cellulose: This will be the least expensive approach. It also leaves the underside of your roof deck exposed so you can see and fix leaks rapidly, and so your roof deck can dry to the inside. If you add an attic floor over the cellulose All over, or just in places you'd find convenient for storing things), you can have storage space in the attic that is easy to use. Everywhere you don't add a floor, you'll retain easy access to any electrical, HVAC, and communication cables laid in your attic (just push the cellulose out of the way).

Be >sure< to do a good job of air sealing every opening/gap of your downstairs envelope/ceiling before blowing in the cellulose. It will be much harder ever do this in the future once the cellulose is in the way.

Insulating ducts and (if possible) the HVAC air handler is important if you choose to insulate the ceiling of the living spaces. If the ductwork is on the floor of the attic--GREAT! Just make sure it is well sealed and then mound the cellulose over it.

Your house will be a lot more comfortable once you are done with this, no matter which approach you choose. It sounds like you should get more estimates. Yes, check with your utility company(ies) to see about rebates, but also don't let the tail wag the dog--sometimes these "preferred" companies charge a more because of the rebate they know you'll be getting. If you find a reputable company, don't be dissuaded from getting their estimate just because they aren't on a list of companies who can get the rebate.
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Old 03-19-2019, 07:34 PM   #8
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Like others, I wouldnít choose the option where they spray to the underside of the roof sheathing. The shingles may not like it. And it you ever need to have some roof sheathing replaced - there goes the insulation.
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Old 03-19-2019, 07:47 PM   #9
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Yes, check with your utility company(ies) to see about rebates, but also don't let the tail wag the dog--sometimes these "preferred" companies charge a more because of the rebate they know you'll be getting. If you find a reputable company, don't be dissuaded from getting their estimate just because they aren't on a list of companies who can get the rebate.
Thanks for the thoughtful reply.

The rebates are available regardless of the contractor. I just started with contractors that the energy company listed on their web site and had good overall reviews. Unfortunately, unless you understand this, what does a review mean? They were nice?
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Old 03-19-2019, 08:02 PM   #10
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Ahh, open cell foam, okay. Well, even at 7 " thick, there would be some ability for the roof deck to dry to the inside IF you don't put a vapor barrier on the inside.

In your situation, I think I would favor the approach of insulating the floor of the attic. Getting the air leaks from downstairs plugged and blowing in cellulose is certainly the best bang-for-the-buck way to get the top of your home insulated. A floor up there (over the cellulose) gives you good, easy-to-use storage. Add good ventilation at the eaves and ridge and it will help a lot to reduce temps in that storage space. I even put some reflective barrier material on the south side of the roof under the roof joists to reduce temps a bit.

Anyway, getting a lot of ventilation of the attic (intake at the bottom and exhaust at the top) is as important as the insulation to eliminating those ice dams in the winter. Keep that roof deck frozen until the eaves thaw--ventilate the attic well.
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energy savings
Old 03-19-2019, 08:41 PM   #11
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energy savings

I can't imagination a house in michigan with little attic insulation - the heating and AC bills gotta be high now.

I would insulate the attic floor and cover it over in sections for storage. Either way as others have stated, you have to keep a lot of open ventilation or you'll have moisture / frost problems inside your attic. Having said that, if you do the spray foam, you'd basically be heating and cooling a barn (your attic). Insulating the floor is going to save you a lot in energy bills and make your living area more comfortable to boot.
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Old 03-19-2019, 08:43 PM   #12
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OP - you must have some insulation in the attic already, probably fiberglass batts between the studs ?

15 yrs ago, I had a similar thing, the house was built in the 1960's, I had insulation blown in AFTER they shoved some attic eaves vent channels in place so the attic would get great ventilation.
This type of thing in photo.

Total cost was $900

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Old 03-19-2019, 08:51 PM   #13
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OP - you must have some insulation in the attic already, probably fiberglass batts between the studs ?
Seriously, I can see the ceiling from the attic in some places. Thereís something fluffy in between some of the joists, but nothing more than a couple inches. Can see the tops of all the joists.
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Old 03-19-2019, 09:00 PM   #14
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I can't imagination a house in michigan with little attic insulation - the heating and AC bills gotta be high now.
I donít know. Not sure what to compare it too. Iím all natural gas. Hot water, cloths dryer, stove, heat. Even during the polar vortex, our bill didnít go over $200 for a 1700 sq ft house. That makes this even harder. The payback period will almost certainly be more than 5 years. The expensive alternatives I mentioned above donít ever pay back in any reasonable timeframe. 10+ years.
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Old 03-19-2019, 09:01 PM   #15
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You are not going to get to the required r-value with blown in and have storage on top of it.
I sealed up all bypasses, ceiling light penetrations and cables in my home and blew in two feet of cellulose in my 1870ís MN home. With that amount Of blown in could probably have foregone sealing stuff up as there would hardly be any paths for air leaks.
You could also spray foam your attic floor instead of the roof deck. I donít think we are allowed in our city to spray foam the roof decking without proper vent channels.
If you choose to use spray foam on the floor you would have a very sturdy surface, but it would donít be very even for storage.
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Old 03-19-2019, 09:28 PM   #16
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With that amount Of blown in could probably have foregone sealing stuff up as there would hardly be any paths for air leaks.
I think that was the strategy of the first quote. Fill it and it will be good enough. Havenít fully ruled that out yet but it collides with my ďyou must do things rightĒ gene. I hate that gene. Itís cost me a lot of money over the years.
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Old 03-19-2019, 09:51 PM   #17
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You are not going to get to the required r-value with blown in and have storage on top of it.
DOE or state/local codes may specify/recommend R50-R60 in Michigan, and that would be great. But, like many things, there are diminishing returns with adding insulation. If he's got very minimal insulation right now and his gas bills are just $200/mo in the winter, then adding 6" (settled depth) of cellulose (approx R19), is going to make a big difference, going much thicker will not make a very big difference as far as monthly bills or comfort. Adding another 8" (14" total, for R50) only reduces heat flow a comparatively tiny additional amount.
(Graph below from this piece).


As far as air sealing: blown in cellulose does do a better job of blocking air than fiberglass, but it's still not great. Caulk, spray foam, and (for large chasms over soffits/dropped ceilings, etc) rigid board foam is really needed to stop airflow.


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