Side Attic Insulation Question


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Old 02-26-15, 05:17 PM
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Side Attic Insulation Question

Hi All,

Long-time lurker, first-time poster.

Background Info:

I have a 1 1/2 story house built in 1942. Situated in British Columbia, it is in temperature zone 7 - meaning there is snow in the winter, and 30 degrees Celsius temperatures in the summer.

I bought the house five years ago, and paid to have the side attic covered in spray foam insulation, meaning it is a "hot" attic - unventilated, a part of the conditioned space of the house. The choice has been the right one for me - there are no visible problems to date, and stored items are better protected from the elements.

My Question:

My house was extensively remodelled around 1960. Specifically, the main floor ceiling was lowered from a 9-foot ceiling to an 8-foot ceiling. At that time, insulation was placed below the side attics in the new, lowered cavity. This means that the joist space immediately below the side attic floor is empty. This empty joist space runs from one side of the house to the other, going from side attic to side attic underneath the upstairs bedrooms.

1. Would there be any benefit in filling this joist space with insulation? If so, what type of insulation is recommended? Would there be any negative effects in further separating the side attic from the heated space downstairs?

2. Does the spot where the joist space meets the outside wall of my house need any special attention?

3. Some of the joist spaces have 1940s electrical run in it. I believe this wiring was abandoned in place around 1960, and checking with a non-contact tester seems to confirm this. Because these cables run to places I can't reach (finished walls), I believe it is best to leave them in place?

In short, I am looking for thoughts to continue to improve the insulation in my side attic. Have I done all I can reasonably do, or would putting some sweat equity into the floor cavity be helpful? I'm attaching pictures to help your understanding.
 
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Old 02-26-15, 05:37 PM
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If I am understanding you right, right now you have a space between two floors all the way around the house that is not insulated? you will definatly want to insulate the exterior of that space all the way around. Getting the spray foam guys back in to do that area would be the best option.
 
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Old 02-26-15, 06:41 PM
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The link below shows an illustration of a roof rafter fill like yours (I like your foam fill better) with the joist cavity below having a foot or so of insulation out next to the exterior end. Your description indicates this joist cavity is empty with the insulation below the joists on top of the new ceiling.

Like Keith said, this exterior end, both ends and both sides, needs a good fill of insulation. How you access that will probably help determine how you insulate it.

The front and rear of the house will have a cavity the full width of the house and you may not want to open the floor in those finished rooms. Cellulose could be blown in from one or both sides. Not experienced with foam so not sure if they could fill from the ends.

But definitely, the space needs the exposed perimeter insulated.

Bud
http://www.finehomebuilding.com/pdf/021230088.pdf
 
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Old 02-27-15, 04:14 PM
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Bud and Keith:

Thank-you for your replies; and Bud, the link is most helpful.

So, my plan is to fill the joist space along the exterior of the house with insulation. My understanding is that spray foam is preferred where possible, and that blow in could be used where spray foam would not work.

Questions:

1. Would buying a few dozen cans of spray foam be appropriate for this job? Its such a narrow strip that lacks insulation.

2. Is blow in do-it-yourself friendly?

3. Is Styrofoam board insulation or batt insulation a possibility for any component of this job? They would be easiest for me to work with, I think.

Again, thank-you for your time,

Graham
 
  #5  
Old 02-27-15, 05:21 PM
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Spray foam in the can would not really be economical except to fill any obvious gaps of air leakage you have to the outside.

Blown-in is do it yourself friendly, but requires at least two people. Most places that sell the blown-in will rent the machine to you.

If you are albe to get at least one layer of 2" styrofoam all the way around the perimiter, and seal the gaps with spary foam in the can, that would be great. Fiberglass in addition to that could be done, but not really nessicary.

Fiberglass on its own will work, but it is best to get some sort of air seal in there, which is why the rigid foam or spary foam is the best option.
 
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Old 02-27-15, 10:24 PM
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From the pictures I'm not sure what you will do for access. Is that a board floor that will need to be removed to add the new insulation?

If there will be boards above the new insulation it will be important to ensure the air sealing from the outside includes paths up through that flooring.

As mentioned, the single part can foam is not for large areas. They do make DIY foam packs but reports are you have to have everything ready and move quickly. They are not inexpensive, but in some cases the large foam companies won't come out to do small jobs or charge extra. But, it never hurts to ask, get a quote.

Bud
 
 

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