+ Reply to Thread
Results 1 to 10 of 10
  1. #1
    Join Date
    Oct 2007
    Location
    Louisiana (Cajun Country USA)
    Posts
    143

    Default Attic insulation questions

    Hi guys.......Happy New Year!

    Well, it's been quite a while since I've dropped by here. Been busy with life.

    I'm going to need to insulate my attic soon and had a few questions. At some point in the distant past, my house was rewired from the old knob & tube wiring. When they ran the new wires, instead of running them along the rafters and dropping down where needed, they just ran them along the ceiling joists and stapled them down. Now that it is time to insulate, I will have no choice but to pass the insulation underneath said wires, which will compress the insulation at that point. Everyone knows you are not supposed to compress insulation. What can be done?

    In addition to that question, what do you do when putting the insulation at the outer walls of the house? You are not supposed to go all the way, right? There is that small air space that I can see when I look down into the space where the wall meets the attic floor.

    Also, is there any benefit whatsoever to putting insulation above my porch areas?
    peace,
    Sophie

  2. #2
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,503

    Default Re: Attic insulation questions

    Sophie,

    Are you trying to put insulation on the under side of the roof?

    Is the attic a heated / cooled space?

  3. #3
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,418

    Default Re: Attic insulation questions

    I take it that you are using insulation that is thicker than the joists are tall. I.e. maybe your joists are 2x8 and you are using 12" thick batts. If so, when you come to the wires, use a pair of scissors to cut down 4" and sip the wire into the groove. If the wires were run as a group so that you have a 6" wide section of wires, then you can peel up the fiberglass at the cut, slid the 8" section of the fiberglass under the wires and then lay the 4" section on top.

    Personally, if it isn't much more expensive, I would use batts that match the height of the joist. Then put a second layer over it, but offset so that it covers the joist and the batt edges meet in the center of the batts below them. Most people recommend that you run the second layer perpendicular to the rafters but I prefer to go parallel with an offset. I maybe the only one here who prefers it that way.

    At the edges, you should be seeing the top plate of the wall. If not, when you look down, you may see a gap. Unfortunately, most of the time, if you can see the wall insulation, the gap will be between the interior wall surface and the insulation instead of the exterior wall sheathing and the insulation. It is unfortunate that even many local codes require that the wall insulation be improperly installed like that. Wall insulation works best when it is absolutely flush with the interior wall and there is a slight gap between it and the exterior sheathing.

    I see by your location that you might be in an area where the traditional vapor barrier against the interior wall might not be the best choice for you. Read my reply to this thread about humidity and vapor barriers.

    https://advice.thisoldhouse.com/showthread.php?t=122263
    Last edited by keith3267; 01-01-2013 at 04:00 PM. Reason: add link

  4. #4
    Join Date
    Oct 2007
    Location
    Louisiana (Cajun Country USA)
    Posts
    143

    Default Re: Attic insulation questions

    Quote Originally Posted by HoustonRemodeler View Post
    Sophie,

    Are you trying to put insulation on the under side of the roof?

    Is the attic a heated / cooled space?
    No, putting insulation on the attic floor. Attic is not heated/cooled.
    peace,
    Sophie

  5. #5
    Join Date
    Oct 2007
    Location
    Louisiana (Cajun Country USA)
    Posts
    143

    Default Re: Attic insulation questions

    Quote Originally Posted by keith3267 View Post
    I take it that you are using insulation that is thicker than the joists are tall. I.e. maybe your joists are 2x8 and you are using 12" thick batts. If so, when you come to the wires, use a pair of scissors to cut down 4" and sip the wire into the groove. If the wires were run as a group so that you have a 6" wide section of wires, then you can peel up the fiberglass at the cut, slid the 8" section of the fiberglass under the wires and then lay the 4" section on top.
    My ceiling joists on the original part of the house are 2x4. On the addition to the house, they are bigger. I think they are 2x6 there. That suggestion makes sense, just alot of added work for me. It would be nice if my joists were taller, but they are what they are.

    Quote Originally Posted by keith3267 View Post
    Personally, if it isn't much more expensive, I would use batts that match the height of the joist. Then put a second layer over it, but offset so that it covers the joist and the batt edges meet in the center of the batts below them. Most people recommend that you run the second layer perpendicular to the rafters but I prefer to go parallel with an offset. I maybe the only one here who prefers it that way.
    That is also an option to think about. This one will give me twice the work.

    Quote Originally Posted by keith3267 View Post
    At the edges, you should be seeing the top plate of the wall. If not, when you look down, you may see a gap. Unfortunately, most of the time, if you can see the wall insulation, the gap will be between the interior wall surface and the insulation instead of the exterior wall sheathing and the insulation. It is unfortunate that even many local codes require that the wall insulation be improperly installed like that. Wall insulation works best when it is absolutely flush with the interior wall and there is a slight gap between it and the exterior sheathing.
    I can't "look down" as you say. I can't fit into that area of the attic, there just isn't enough room. My roof pitch is about 5 or 5 1/2 on 12. I can tell you that my house was built in the 20s and there is no insulation in the walls.

    Quote Originally Posted by keith3267 View Post
    I see by your location that you might be in an area where the traditional vapor barrier against the interior wall might not be the best choice for you. Read my reply to this thread about humidity and vapor barriers.

    https://advice.thisoldhouse.com/showthread.php?t=122263
    Are you talking walls, attic, or both here? I ask because I have the walls open in one of my bathrooms and I have put in some insulation on the outside wall. I installed in paper side facing towards the living area as this is how I thought it was supposed to be. When I do the attic, I was planning to put it paper side towards attic floor (living area). Right now, it is paper side up away from the living area and I always thought that was wrong. Yes, I do have insulation in the attic right now and yes I am taking it all out. It crumbles when you try to pick it up. It has been trampled so much when my house was rewired, and it is all broken to pieces. I'll check out the link you provided.
    peace,
    Sophie

  6. #6
    Join Date
    Oct 2007
    Location
    Louisiana (Cajun Country USA)
    Posts
    143

    Default Re: Attic insulation questions

    Keith.....I read the other thread you posted a link for. It is still unclear to me whether or not I should be putting paper side of insulation towards living or away from living in both walls & attic.
    peace,
    Sophie

  7. #7
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,418

    Default Re: Attic insulation questions

    "There is that small air space that I can see when I look down into the space where the wall meets the attic floor." This why I thought you were looking down into the wall from the attic.

    As for your area, you first need to find a link to the historical averages of temperature and humidity. I don't know exactly where you live so you will need to do this for yourself. You need the averages for the summer months. You look at the average high temperature and the humidity at that temperature. Do not mix the highest temperature with the highest humidity unless they occur together.

    Often the relative humidity (RH) goes down as the temperature goes up during the day. What is important is the dew point, which usually stays relatively the same all day and night. If the dew point is higher than the temperature you plan on using inside your home. There are very few areas in this country where that is the case and most of them are right along the gulf coast. That doesn't affect the whole gulf coast though.

    You might also get this information from your local TV station weatherman. If you do live in one of these areas, sometimes the best bet is to not use a vapor barrier at all. Treat those exposed studs with a sodium borate solution to prevent mold and rot. Search for Timbor or Boracare.

    You don't need a vapor barrier in the attic, it should be well ventilated. Walls aren't as well ventilated, thats why they usually need a vapor barrier.

    Example, if your average daily temperature in the Summer is 87F with 80% RH, your dew point would be around 78F, which would call for the vapor barrier on the outside, however it would need to be on teh inside for the rest of the year, so in this case, I would not use a vapor barrier at all.
    Last edited by keith3267; 01-01-2013 at 09:32 PM. Reason: add example

  8. #8
    Join Date
    Oct 2007
    Location
    Louisiana (Cajun Country USA)
    Posts
    143

    Default Re: Attic insulation questions

    Quote Originally Posted by keith3267 View Post
    "There is that small air space that I can see when I look down into the space where the wall meets the attic floor." This why I thought you were looking down into the wall from the attic.
    Ahhh I see what you were thinking. My poor explanation led you to that conclusion. If I were at the center of my house looking over towards the exterior wall and I see the roof rafters sloping down towards the wall, that is what I meant. The air space I am referring to is the top most piece of clap siding, it is actually cut to fit between the rafters. There is about a 1" air space there above that piece of siding. I'm assuming that I don't want to shove the insulation all the way and block that off, right?

    Quote Originally Posted by keith3267 View Post
    As for your area, you first need to find a link to the historical averages of temperature and humidity. I don't know exactly where you live so you will need to do this for yourself. You need the averages for the summer months. You look at the average high temperature and the humidity at that temperature. Do not mix the highest temperature with the highest humidity unless they occur together.

    Often the relative humidity (RH) goes down as the temperature goes up during the day. What is important is the dew point, which usually stays relatively the same all day and night. If the dew point is higher than the temperature you plan on using inside your home. There are very few areas in this country where that is the case and most of them are right along the gulf coast. That doesn't affect the whole gulf coast though.
    OK, that just confused the heck out of me. Where I live and where my house are happen to be two different cities. The house in question is in Lafayette, LA. I live further south from there.


    Quote Originally Posted by keith3267 View Post
    You don't need a vapor barrier in the attic, it should be well ventilated. Walls aren't as well ventilated, thats why they usually need a vapor barrier.
    As I mentioned earlier, there is insulation in the attic right now. It is installed paper side up. I thought it was wrong simply because it states "install with paper side facing living area". But you're telling me I don't need paper at all?! This is a little sketch I did of what the roofing system was like before I had my roof changed.





    When my roof was redone in October of 2011, they removed material down to the slats. They went directly over the slats with plywood, then underlayment, then metal standing seam roof.

    As for the wall, I remember reading in that other thread you linked to about the walls and I think I remember reading someone say that the clap siding should not be nailed directly to the studs. That is exactly how mine is. When I took the walls down in my bathroom, which is 11" wide 3/4" thick boards, there was the stud and directly on the other side of that was the exterior clap siding. Is the fact that I added insulation in the wall paper side facing in a bad thing?
    peace,
    Sophie

  9. #9
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,418

    Default Re: Attic insulation questions

    I can get the climate data for New Orleans and that is a very border line area.

    Summer http://web.utk.edu/~archinfo/EcoDesi...TempRH7-12.gif

    Winter
    http://web.utk.edu/~archinfo/EcoDesi.../TempRH1-6.gif

    Table
    http://www.tis-gdv.de/tis_e/misc/klima.htm

    I finally got the search engine working again, here is an interesting report if you are interested in some light reading, it has some good charts though

    http://docs.lib.noaa.gov/rescue/mwr/...93-02-0113.pdf

    Looking at the maps in this document, it appears that throughout most of the year, your dew point is below 70F but July and August are a problem. The dew point during these months is above 70F. I can't tell by how much. If you are setting your summer time temperature inside your house to 78F or higher, then you should not have a problem with condensation inside your walls, so having the vapor barrier against the interior side of the walls should be no problem. So what you did already is no problem.

    The attic would also not be a problem with the vapor barrier against the living side, but up there, you really don't need a vapor barrier as long as you have good ventilation. That gap you mention is your ventilation and it should be there. It would be nice to have a screen over it to keep bugs and critters out though.

    The reason that nailing clapboards directly to the studs is that it doesn't provide any structural support against racking. But there are other ways to prevent racking. Racking is where the house falls over to one side. One way to add structural rigidity is to use a 2x4 inset into the studs at a 45 angle. Other ways are to use boards on the interior side under the plaster that are at a 45 angle.

    Many old houses in New Orleans were made from very wide boards from the barges used over a century ago. Wide planks, even if they are not placed diagonally against the wall will provide a lot of racking support. But plywood between the claps and the studs is one of the most common ways to keep the structure upright and not leaning to one side.

    You said that your bathroom walls were 1x12 (3/4 x 11.5) on the inside. Were these horizontal or vertical? Did you put them back? These may have been your support for preventing racking and if you put up sheet rock in their place, you could have a problem. If you only did the bathroom, you will probably be OK, you just need to be aware of this before you take down any more of these boards in other rooms.

  10. #10
    Join Date
    Oct 2007
    Location
    Louisiana (Cajun Country USA)
    Posts
    143

    Default Re: Attic insulation questions

    Quote Originally Posted by keith3267 View Post
    You said that your bathroom walls were 1x12 (3/4 x 11.5) on the inside. Were these horizontal or vertical? Did you put them back? These may have been your support for preventing racking and if you put up sheet rock in their place, you could have a problem. If you only did the bathroom, you will probably be OK, you just need to be aware of this before you take down any more of these boards in other rooms.
    Sorry for the long delay. Yes, the boards that I took down in order to insulate the exterior wall went back up. They were placed horizontally on the wall. No sheetrock is going up on any wall in the house.
    peace,
    Sophie

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •