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ceebizzle

1" insulation - is it worth it?

ceebizzle
9 years ago

I'm renovating a 100+ year old rowhouse and I've got an exterior wall where I ripped off paneling to find furring strips over the original plaster, which was done directly over masonry. There's wiring in the wall so I can't just go back to the original plaster like I've done in most places. So I'll hang drywall on the furring strips, which are 1x3s. With that 1" to work with my insulation choices are limited to foam boards. So far the best choice I can find within several decision making parameters is an R3 product that will run about $100-$150 for the room. The masonry and plaster have a decent insulating effect of their own and from what I understand the new drywall and the airspace between it and the old wall will have an additional insulating value. Any thoughts on whether or not this is worth it?

Comments (15)

  • klem1
    9 years ago

    I think the 1" dead air space is close to what the foam would give you. I vote no foam unless the labor is real cheap.

  • jakethewonderdog
    9 years ago

    Wow, Klem isn't correct on that. Neither is the brick and plaster a very good insulation. Google R Factor of brick and you will find R-factor of many construction materials.

    So, a common 4" brick has an R-Factor of 0.8. If your walls are 2 bricks thick, that' 1.6 Add 0.45 for drywall and a little bit for plaster and 1.0 for the airspace and you have a wall with an R factor of 3.5 or so.

    Where is this rowhouse located (city?)

    Use R-Max or similar product and get as high an R-factor as you can for the space you have. A 1" board of R-Max has an R value of 6 - almost double your current R value. Your wall would then have an R-value of about 8.5 - still very low, but much better than where you were.

    Keep in mind that energy prices will continue to go up and you aren't going to open up these walls again. Take the opportunity to do it right now.

    Here is a link that might be useful: R- values of building materials

  • kudzu9
    9 years ago

    jakethewonderdog is absolutely right in his analysis. I spent years working as an engineer in the energy conservation field and one of the sayings is: "The first inch of insulation is the most important." I won't go into the thermodynamics of why this is so, but suffice it to say that using the space you have to put in the highest R-value foam board will make a huge difference, and pay off quickly from an energy savings standpoint. Jake is also right about the insulating value of your the walls: brick and plaster are solid, but they are terrible insulators and suck heat away quickly. Put in the foam.

  • rwiegand
    9 years ago

    Good advice from jake and kudzu. Use the foam.

  • energy_rater_la
    9 years ago

    1" foam sheathing can be higher than R-3
    look into extruded poly for R-6.5 per inch.
    tape all seams, caulk at top and bottom of sheathing
    to top & bottom plates of walls. also...caulk bottom
    plate to floor.

    make sure your location allows for interior vapor
    barrier.

    best of luck.

  • ceebizzle
    Original Author
    9 years ago

    Thanks for the help all. I'll go ahead with the heavy duty 1" foam. A question about the vapor barrier though -- is that needed when I've got 1" of plaster and then brick on the other side? If a vapor barrier were used, where would it go, between the plaster and the insulation or between the insulation and the drywall?

    Thanks again for all the helpful comments.

  • energy_rater_la
    9 years ago

    the foam sheathing is a vapor barrier.

    in my hot humid climate vapor barriers on walls
    are to exterior (ambient).

    thus the still unanswered question of your location.

    best of luck

  • bus_driver
    9 years ago

    From one whose expertise with insulation is just lots of observation. the 1" is far better than nothing.
    In my childhood, many in my area tacked flattened corrugated boxes onto the walls for insulating effect. It did help a great deal but was a significant fire hazard.

  • energy_rater_la
    9 years ago

    I've seen old homes where the interior of the exterior walls were the same boards. no 2x framing...just 1x's on flat.
    between 1x's on interior..layers of newspaper.
    as the homeowner had more money...they would cover newspaper with wall paper.

    not much insulation value...but I think they were just
    trying to stop air flow between boards!

    back in my weatherization days I busted the insulator we used for saying he insulated the walls...but there was no place for him to insulate as the walls were as described above!

  • ceebizzle
    Original Author
    9 years ago

    Thanks all... I'm in Philadelphia where we have pretty moderate humidity outside of the summer months. I measured again before buying anything and those 1x are really 3/4 so I'll be limited to a 3.7 or so R value from what I've seen but of course it is better than nothing. I'll just have to stick around long enough to make sure it pays for itself in gas bills.

  • jakethewonderdog
    9 years ago

    Fir the nailers out a 1/4 inch and go with 1".

    This is very minimal insulation at a minimal cost... don't short change it. It will pay for itself in energy savings and in comfort.

  • dkenny
    9 years ago

    refletex insulation..
    only 1/4 thick..and R13..

    -dkenny

  • homebound
    9 years ago

    Philly? "Moderate" humidity? Ha. I would rate them "fairly oppressive".

  • kudzu9
    9 years ago

    dkenny-
    !/4" thick and R-13?...not remotely true. I'm not sure where you get this, but the Reflectix web site seems to indicate that the benefit is substantially less than this. For example, to get an R-14 value in a 2X4 exterior wall, you need to use Reflectix with an R-13 batt! Or you need to use the product in one or two layers with large sealed air spaces. None of these apply to the OP's situation.

    Here is a link that might be useful: Reflectix specs

    This post was edited by kudzu9 on Thu, Jun 26, 14 at 2:09

  • SaltiDawg
    9 years ago

    homebound,

    "Philly? "Moderate" humidity? Ha. I would rate them "fairly oppressive"."

    You've obviously lived a sheltered life. Charleston, SC, or Savannah, GA, now that's "fairly oppressive." Philadelphia, not so much.

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