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Attic insulation- Balloon frame cavity insulation

Attic insulation- Balloon frame cavity insulation

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  #1  
Old 01-30-15, 04:24 PM
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Attic insulation- Balloon frame cavity insulation

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I have a few questions that are related because I was talking to the moderator Bud about attic stair insulation in another thread and he got me thinking about additional insulation across my whole attic. I live in NJ and currently have R30 Batt insul between my attic joists although I was told that because its only 6" depth of Fiberglass, the R rating that is says on it is inaccurate and its much less?
I was told that minimum R40 is code where I am so what do I need to do to get the higher R value? Is the diy blow in cellulose from Home Depot quality stuff? Would I just add that right over top the existing fiberglass and does that carry any weight where it would compress the fiberglass?
Also, I live in a two story house that is balloon frame construction built in 1940. I recently sealed up my basement rim joists when I realized how much draft was moving in the walls between attic to basement. So today for the first time I looked into those same wall cavities from the attic end, and I discovered there is insulation running all the way down as far as I could see with my light. Its not very thick, only 3 inches but I was surprised to see it because I have been worried about my Hot water radiator pipes(which are in the walls from the basement up)freezing at some point, especially since I sealed off all warm air coming up from the basement. My question is, would they have put paper faced insulation in the wall cavities in 1940 when the house was built? I see no other way it could have been added to the extent that I see it, but that rests my mind a bit that I don't have complete open drafty walls from bottom to top. Another thing I also noticed from the attic end was blocks of 2x wood horizontal between the wall joists(fireblocks?) They are not in all of the cavities, more on one end of the house then the other and but are more than a foot down from the top of the attic joists so I don't see how they could have been retro-fitted. But a true Balloon frame construction would not have them correct? They were not thinking of that in 1940. Thanks for your thoughts on this.
 
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  #2  
Old 01-30-15, 05:03 PM
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The cellulose insulation is heavier than fiberglass. There are variations according to the density of fiberglass batts but in general, the standard density fiberglass batts come in at about 1/2 to 6/10 pound per cubic ft. Cellulose is generally going to fall in the 1.25 lb. to 1.5 lb. per cu.ft.. Again, that number is subject to some variables but can be looked at as an average application.

Are you sure that your existing material is fiberglass, the material in the walls seems like it MAY be rock wool which was commonplace in the days of construction you are referring to. Rock wool also came with a facing material.

The top of your wall cavities should be closed off as well as possible, not only as a fire stop but also as a means of controlling air flows up the wall cavity. Your picture shows the gap between the back of the perforated gypsum lath and the batt material caused by the plaster keys. This gap allows the warm air at the inner face of the batt to escape upward to the attic.

The blocking you show can certainly be of original construction. Although you have balloon framing, that doesn't negate the possibility of someone placing blocking as a firebreak, an added nailing surface or for some other reason, even in 1940.

If the ceiling insulation is fiberglass and you want to add more, you should probably stay with that material. If you are removing the underlying material then you could do a premium job of sealing air leakage paths at wires, soffits and partitions and light fixtures and vent stacks. If the fiberglass is in reasonably good shape and clean, you could reinstall it. Frequently, fiberglass batts may not reach full loft unless you give them a few shakes when you place them. This helps in developing the air cells between fibers that give it insulating value.

The issue of adding additional insulation is one that has to be approached with caution. Review appropriate ventilation procedures and look at the back of the roof deck to see if you have any areas that exhibit signs of condensation. Adding more insulation without reviewing other issues can increase the level of condensation since the attic will be colder.
 
  #3  
Old 01-30-15, 05:41 PM
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In fairness to the workhorses here, I'm not a moderator, just a volunteer.

The r-40 I mentioned was a ballpark guess. Here is a link to let you pick your location and code insulation values. NJ happens to be divided between two zones, but remember, the code requirement is a minimum. Looks like you would be r-38 to r-60, but local codes can vary.
Recommended Levels of Insulation : ENERGY STAR

Pipes inside a poorly insulated exterior wall should still be a concern, especially as you make energy improvements that will require the heating system to run less. Not sure what to recommend.

Air sealing as Calvert mentioned is a high yield improvement.

Bud
 
  #4  
Old 01-30-15, 07:14 PM
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Calvert and Bud, thanks again for your advice. Calvert, I want to respond to your individual points.
"Are you sure that your existing material is fiberglass, the material in the walls seems like it MAY be rock wool which was commonplace in the days of construction you are referring to. Rock wool also came with a facing material". The material in the wall is clearly rock wool and you said it was commonplace in the 40's but was it actually used in homes walls regularly? The R30 on my attic floor IS Fiberglass because I put it in myself. That's why I was afraid of possibly compressing it and destroying its R value by adding blown in cellulose over top of it'. So you recommend adding additional Batt insul. over top of it at this point and I imagine it should be completely unfaced correct?
Your picture shows the gap between the back of the perforated gypsum lath and the batt material caused by the plaster keys. This gap allows the warm air at the inner face of the batt to escape upward to the attic. So are you saying this gap between the Plaster and the batt is clearly a bad thing right? If I was to rent the DIY cellulose blower and blow cellulose into those gaps as far down as possible, would anything be wrong with that?
The blocking you show can certainly be of original construction. Although you have balloon framing, that doesn't negate the possibility of someone placing blocking as a firebreak, an added nailing surface or for some other reason, even in 1940. If I can see these fireblock 2x's in many of the cavities from the attic side, what are the chances they put them further down as well because this eases my mind(slightly) after reading about fire disasters with these style homes.
Adding more insulation without reviewing other issues can increase the level of condensation since the attic will be colder. Calvert, this attic of mine cant get any colder. I've got open gable vents on both ends so the wind crosses through at full speed. All the more reason to bring my Insulation to code or above code. Thanks again.
 
  #5  
Old 01-30-15, 08:31 PM
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Hi Dale, adding additional insulation would probably be best done with one of the high density unfaced fiberglass batts like 5-1/2", R-21. The slightly higher density helps to keep cold air from infiltrating the material below, (R-30), yet is not so dense that it will impact the thermal performance of that material by compressing it appreciably.

Rockwool is an old form of insulation and I have advertising for it from 1879. It was originally used on flat roof decks under the layers of hot mopped roofing felts. When first used in walls it was sold as loose material and hand packed into the wall cavities before lath or sheetrock was installed.

Although it was available for residential application in batts in the 1940's, and perhaps earlier, the application was still an option, decided upon by the builder on a local basis. You may want to view it as a sign of a conscientious builder in your case.

You can certainly install the blown in cellulose in the gap between the rockwool and the gypsum lath in the walls. If you are renting a machine at HD or Lowes you have to make sure you understand the proper settings for doing a constricted space like you have or you will end up very frustrated with clogged hoses. The important last step in upgrading the performance of the walls is to cap it at the lower edge of the ceiling joists and try to make that seal as airtight as possible.

If you are seeing the blocking in the wall cavities, I would be somewhat surprised by there being multiple levels of blocking in the cavities. Again, the codes were very localized then and more than likely did not require it so if a builder put them in, it was likely someone who was forward thinking, not a bad quality for a builder. I would not get too paranoid about the fire issue. I have seen fire spread significantly slowed by just having fiberglass batts in walls, so if you get your walls insulated as well as you can you will add considerable protection to the assembly. You also have gypsum lath and probably sand aggregate basecoat plaster, both of which contribute well to fire resistance.

With regard to your last point, I'm happy your attic has good air flow but I assure you if you do the measures to increase thermal performance and decrease air loss from the living space...you will make the attic colder.
 
  #6  
Old 01-30-15, 10:56 PM
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To add to the point of a colder attic, being colder by itself doesn't necessarily increase the moisture issues. In winter, it is the inside air leaking into the attic that provides the moisture. Better air sealing, balloon walls interior and exterior, electrical and plumbing penetrations, and around any chimneys, for examples, will greatly reduce that moisture.

Gable only venting does rely heavily upon the wind, so if you have the wind you are fine.

Roxul would be another high density batt insulation to consider.

Bud
 
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