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Old 05-01-15, 02:44 PM   #1
UNCSoc
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Question Foam versus blown insulation?

For a new construction, 1 and a 1/2 story house, we have an attic space about 50 feet long and 15 feet wide. The space is only usable for an HVAC unit or stuffing it full of insulation, since the highest point in the attic is about 6 feet.

The rafters in that area are mostly 2 X 8.

I can either use spray foam (open or closed?) or blow in cellulose or some other form of insulation, which could cover any ducting in the attic. (If not using spray foam, I would most likely not put an HVAC in the attic but in a conditioned space elsewhere in the house.)

I was advised that the spray foam, especially the closed cell foam, can create health problems and perhaps water vapor problems because it does not breath and has chemicals that may be emitted into the home over time. Any moisture that came in undetected through the roof may also create long term problems (since it is hard to detect with the foam barrier). An air exchanger may help, but is only 70 percent efficient or so. In contrast, the cellulose will allow moisture and harmful vapors to rise and escape the home.

But others said that it is hard to blow enough cellulose even into a flat space to get an equivalent efficiency since over time a thick layer of blown insulation will settle. And, they say, the foam is not a health issue. Even if it was, circulating the air or using an air exchanger could deal with any potential problems in air quality.

Which would you recommend? Foaming between the rafters or piling the attic high in insulation?

Note: I am reluctant to use fiberglass since that seems a greater threat to ones health (lungs especially!) than the blown cellulose.

Thoughts?

Thanks.

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Old 05-04-15, 06:38 PM   #2
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Your climate is different than mine in SE Alaska, but here's my opinions on the three types of insulation you mentioned.

1. Cellulose: I don't care for cellulose. It absorbs water and settles into a brick and it's mold food.

2. Spray Foam: Expensive, there are options that don't have VOC problems and they form the vapor barrier. All the designer home builders up here use it. I'd go this way if I could afford it.

3. Blown insulation: I like it and have used it. It doesn't seem to absorb water and it is easy to install yourself.

I vote for #2 or #3 depending on your budget.

Erich
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Old 05-17-15, 05:36 PM   #3
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Blown in cellulose is highly recommended if you have the blower to get a higher compression. I used it in a house in 1993 and it is still performing very well. It is also the cheapest option.

If you are space constrained, polyurethane spray is the best (high density, 2lb) and if you can afford it. My installer charges around $1/sq ft/in thick. It can be done cheaper but check the references of the installer. There are ways to cheat with this stuff.

I hate fibreglas in all its forms. Soon it will be labeled a carcinogen. The evidence is building up. ROXUL is a much better batt insulation.
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Old 05-17-15, 06:39 PM   #4
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Quote:
Originally Posted by UNCSoc View Post
...Which would you recommend? Foaming between the rafters or piling the attic high in insulation?
Your location has everything to do with how much insulation you need, what kind of insulation you need, and how it should be installed.

There is a website called degree days dot net


That will allow you to easily, and precisely calculate the Heating Degree Days and the Cooling Degree Days value for your own location. The web page will also explain exactly what it means and how it is derived.

In the previous posts, you have been given information by some very experienced people. However their experience is very much influenced by their location.

I'm just going to do a wild guess that you are in the RALEIGH-DURHAM area. Weather conditions, wind, humidity, solar insolation vary greatly even over a fairly small area, so you should not take my example as applying to you, you should re-calculate for your exact location.

For the location I guessed, your Heating and Cooling Degree days look like this:


The HDD (on the left) generally indicates how much you need to heat in the winter, and the CDD (on the right) generally indicates how much you need to cool in the summer.

Without knowing exactly what the HDD and CDD of the previous posters is, in their location, I think it is safe to guess that their heating requirements, and insulation requirements are more severe than yours. I'd also guess that their cooling requirements are less, possibly very much less, and maybe none at all.

One of the reasons this is so important is that if you lived someplace, for instance, nearer the shore, in a slightly more southerly location than RALEIGH-DURHAM and in that case lots of air conditioning will be required and a lot of moisture will condense on the outer insulation layers as it make it's way inside. So in that case moisture condensation control during the cooling season would be hugely important.

This exact kind of problem would be a much greater worry than Alaska.

But there, the exact opposite, condensation forming on the inner layers of the insulation during heating season.

So you need to consider the dominant weather, and if it were me, I would ask around to several local installers to see how they handled things, and also see if your state or local government has information specific to your local conditions.

And then I'd go on-line, look at lots of info, to find out for myself what the optimum arrangement would be for your locale.

Best,

-AC
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Old 05-17-15, 08:43 PM   #5
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It would be wise to do a lot of homework on your home exergy before filling your attic space with an arbitrary amount of insulation, just because it will fit. A 50 x 15 ceiling is just a number that is one factor of many.

Since your home is new, the people who built it should be able to tell you anything you might want to know about it. If you had a hand in the design, you should know what choices were made in material selection and energy efficiency options. For example, if the attic was intentionally not insulated, were the walls and basement also under-insulated? If so, insulating the attic might not help so much.
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Old 05-17-15, 09:22 PM   #6
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"Fiberglass" means a lot of things. Loose blown fiberglass, with no binder) can cause health issues, especially for the one installing it. I used a fiberglass blow in that was blown in with a resin binder. It does not compact, does not mold, is not friable and is not expensive. Netting was installed first, a slit cut and the material blown in. A slight roll to have it conform to the wall studs and that was it.

If the home is appropriately ventilated (thing ERV or HRV) then build up of toxic off gassing is a moot point (or very nearly so).

As AC correctly points out, you are in a mixed zone with both heating and cooling degree days. You are almost the same latitude as I am in central Oklahoma and a very similar heat/cool situation. Your issue is far more humidity in the summer than we have here.

The humidity issue is key as you have to decide where you put the vapor barrier. In far north (Madison, Fargo, Duluth, etc.) , the barrier is put on the warm side (underneath sheet rock), where in hot humid situations (like Miami, Houston, etc), you put the vapor barrier on the outside wall. The key is to prevent a critical dew point drop and condensation.

But a mixed climate is tough. In your humid situation, I would go for an insulation that does not degrade with moisture and has a barrier in it. For those reasons, I chose a resin impregnated loose blown fiberglass.

Think about R40 if you can . . . .

Not a perfect solution, but there is no "perfect" when it comes to insulating.

Steve
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Old 05-18-15, 08:20 AM   #7
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Need to add that the resin blown fiberglass is best done between rafters. That way you get some insulated space up there for storage. The least cost is to put R-40 on the attic floor covering the ducts. Less cost as the floor is flat and the roof pitch creates more surface area.

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Old 05-18-15, 11:26 AM   #8
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Continuing on the idea that non-local, general insulation advice should be questioned, and your insulation should be determined by your own micro-climate, I came across an easy to use tool that can assist you in making a more intelligent decision:


...as you see, the climate characteristics for your state vary considerably.

Also, this wonderful map is "clickable", so you will be able to find precise data for your own home. When you click on the map you will find a large amount of very useful information. Which will show you, for example, that the state recommends ceiling insulation R-values that vary from R-30 to R-38, depending on your precise locale, and not a general R-30 for your state, a state that is so rich in topographic and climatic diversity.


And here is another lovely gem of a document:


...this little ruby has obviously been written by forward looking North Carolinians, who want to go beyond code and see substantial energy reductions in your fair state.

A quick scan revealed that they are pushing for ceiling insulation levels of R-42 minimum... interesting!

This paper also goes into fairly rich detail on other energy reduction benchmarks that could be wise to meet or exceed.

I don't think a man can have too fast a horse, too much money, or too much insulation.

Best,

-AC
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Old 07-18-15, 07:51 PM   #9
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One bonus for blown in is burying your hvac ducts. Spray foam in my opinion is better used in walls. The foam advantage being the greatly reduced infiltration. Other options to consider...what kind of roof? Metal? Consider rigid foam under the metal to start with. You could do mineral wool batts in between the rafters. Beyond climate recommendations budget and time can be huge factors. Are you going for super tight super insulated uber efficiency or decent budget minded don't shoot myself in the foot design? Theres no kill like overkill bu I'm too cheap and in too much of a hurry for super tight construction.

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