+ Reply to Thread
Results 1 to 10 of 11

Hybrid View

  1. #1
    Join Date
    Dec 2012
    Location
    Dallas area
    Posts
    4

    Default best approach at insulation and airflow control - old farmhouse

    I have been going crazy doing research on how best to address insulating and "air-proofing" an old 1040's era farmhouse I have purchased in Dallas, which would be categorized as a "mixed-humid" climate.

    I will do my best to describe the situation I have but am not sure of the proper terminology in some cases. Sorry it is so long, I hope someone will take the time to read it.

    The external siding on the house is what I call old lap siding where the boards overlap each other slightly going down the wall.
    Inside there was old paneling nailed up, underneath that was some kind of paper mesh backed membrane. Under that are old 1X6 pine boards nailed up to the studs. Under that is nothing, an empty cavity where you can see daylight through gaps in the lap siding outside. I want to make the house more energy efficient, but do so in a way that I don't have to worry about the wall cavity getting wet and moldy. After much research and speaking to some people, I have come to the conclusion that a vapor barrier is not a good idea (at least in my area). However, it seems to me that a air-barrier (like tyvec wrap or something) that is vapor permeable may be a good idea. I am trying to figure out the best way to incorporate an air barrier and insulation. The problem with the air barrier is that traditionally that is done on the outside perimeter of the house. In this case, I do not plan on removing the siding, so that would mean installing an air barrier from the inside against the interior side of the exterior lap siding and in between the studs. To me this doesn't sound like a good idea. There is an air barrier by Certainteed that goes over the interior wall, stapled across the studs with unwrapped roll insulation underneath. Not sure if this makes sense as I am afraid there would be nothing (no air or vapor barrier) between the exterior siding and the insulation in the wall cavity. I am afraid it will get wet. After I determine how to incorporate an air-barrier (if I should), I want to put insulation in the wall cavity. Not sure what I should use. I do not have the budget to do spray in foam, I will have to stay with the old-style batt insulation. Finally, once I add the air barrier and insulation, should I simply install drywall over the studs on the interior, or should I put the 1X6 boards back up and install the drywall over the top of that? If the suggestion is to place an air barrier directly underneath the exterior siding, do I need to implement some kind of shim to leave a gap between? I am really stuck on how to proceed. Please let me know if any of you have advice. Thank you. Brad Fisher

  2. #2
    Join Date
    Jan 2009
    Posts
    14

    Default Re: best approach at insulation and airflow control - old farmhouse

    I would worry about the attic insulation first. Do you have enough there? Then, I would move to making sure windows are sealed properly. Last, I have used p2000 on my house and installed it over the similar type of wood siding on my house and sealed it with tyvek tape at the joints. Then installed vinyl siding over top of the p2000. The insulation has a good value and will allow you to then install fiberglass on the inside cavities as well. No air should be able to infiltrate if you seal all of the joints from the outside, allowing you to install fiberglass, then drywall right over the studs.
    just my thoughts.

  3. #3
    Join Date
    Jun 2007
    Location
    near St. Paul, MN
    Posts
    166

    Default Re: best approach at insulation and airflow control - old farmhouse

    You didnt say if your house is air conditioned but being in Dallas I expect you would have air conditioning. Since your exterior sheathing is so full of gaps the hot, humid air has no trouble getting into your wall cavity. When the hot, humid air hits the back of your cooler interior wall it will condense and get that area wet. With no insulation in the wall cavity it can now dry out. If you put insulation in the wall cavity it will absorb the water and stay well longer which is not a good situation. You must keep the hot, humid air out of your wall cavity. The only way to do that is to take your siding off. If you then put on a good air barrier and meticulously seal any exterior penetration and insulate from the exterior (foam board insulation, two or more layers, stagger the seams) you will keep the humid air out of wall cavity. The hot, humid air will come in contact with the foam board insulation but it will not be cold so it wont condense. Also, use a rain screen under the siding to allow any moisture that gets behind the siding a chance to dry. You then dont have to insulate in the wall cavities themselves.

    I would not put the vapor barrier on the back of the outside sheathing from the inside. Your wall studs are then in the outside environment between two sheets of plastic. They will get cold from being in contact with your air conditioned wall. They will be a place for moisture to condense. If your wall studs get wet and dont dry adequately you will have problems.

    Theres no easy way around this. If you dont do this right you will trap moisture in your wall cavity which will cause you problems probably big problems.


    Check out this presentation by Pat Huelman from the University of Minnesota on exterior insulation.
    https://www.eeba.org/conference/2012...t-Overcoat.pdf

  4. #4
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,710

    Default Re: best approach at insulation and airflow control - old farmhouse

    Sherry brings up some interesting points that apply to many areas along the gulf coast, but do not apply to the Dallas/Ft. Worth area. Dallas has a subtropical humid climate, but not humid enough for condensation to form inside the wall cavities of an air conditioned space, unless the AC is turned down very low. For the normal recommended interior summer temperature, condensation will not form.

    This is a link to historical temperature and humidity data for Dallas.

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

    You can see in the charts that as temperature rises, RH (relative humidity) drops. On a hot day of around 100F, the RH is around 40%. The temperature record is around 113F with a heat index of 117F which would indicate a very low humidity on that day.

    This next link is to a chart for temperature, RH, AH (absolute humidity), and dew point. Dew point is the temperature where condensation occurs when the the air temperature and RH are at various values.

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

    The chart is from Europe so the temperatures are in centigrade. For comparison to Fahrenheit, use the following:

    15C = 59F
    20C = 68F
    25C = 77F
    30C = 86F
    35C = 95F

    So on a typical hot day in Dallas with 95F and 40% RH, we look on the chart and see that the Dew Point for 35C and 40% RH is 18C which is between 59 and 68F. Unless you set your AC below 68F, you will not get condensation inside your walls.

    The bottom line is, leave the outside alone. If you have removed the interior sheathing of the stud bay (the lath and plaster) then you can insulate this house the same way you would in most of the US, vapor barrier on the room side.

    The AH inside your house will be higher that the outside in winter. The greater danger from moisture and condensation will come in winter if the warm moist interior air migrates into the stud bay and condenses on the colder surfaces. Putting a vapor barrier on the inside will block most of this moisture, and what does get out will mix with cold dry air and not be a problem.

    I'm pretty sure your house wasn't built in the 1040's and since the 9 key is next to the 0 key, I'm guessing 1940's era. That means the studs are probably on an even spacing, i.e 16" OC. For this, my recommendation is standard faced batts, but do not staple the batt wings to the inside face of the studs as most commonly done. Instead, staple the wings to the ends of the studs and overlap the wings from the batt in the adjacent bays. Any air gap between the batts and the finished surface should be on the outside of the stud bay, next to the pine boards and should be flush to the interior wall (sheetrock). This will keep the insulation dryer and it will work better.
    Last edited by keith3267; 12-05-2012 at 02:39 PM.

  5. #5
    Join Date
    Nov 2012
    Location
    central pa
    Posts
    98

    Default Re: best approach at insulation and airflow control - old farmhouse

    i think you should put tyvek on the inside mainly because you aaid you can see light between the clapboards. this will let water and air in wich will bring moisture and get your new insulation wet causing rot mold and lots of other problems

  6. #6
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,710

    Default Re: best approach at insulation and airflow control - old farmhouse

    I may have misunderstood the wall construction. Are the 1x6's on the interior side of the studs? I was thinking that they were under the clapboards on the exterior side of the studs. If the clapboards are nailed directly to the studs, then you might need to address the "daylight issue. A lot depends on whether water gets on the inside of the clapboards. If the gaps are such that any water is shed down to the claps below, then the gap is not an issue, but if water can blow into the cavity, the it needs to be addressed. Just seeing daylight is not always a problem.

    If there are only a few gaps, you may be able to fix the problem with small pieces of Tyvek or similar product. If it is the butt ends of the claps that is the cause of the gap, then some type of flashing can be used. What ever you do, any water that gets behind a clapboard must be directed back to the exterior. Just sticking Tyvek behind the claps will not fix the issue. The water must shed like water off a ducks back.

  7. #7
    Join Date
    Nov 2012
    Location
    central pa
    Posts
    98

    Default Re: best approach at insulation and airflow control - old farmhouse

    i totally agree that the claps need fixed but covering the back with tyvek is a good temporary fix till the siding issues can be addressed. not sure about weather in texas but here in pa if you can see light through the siding you will get water for sure

Posting Permissions

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