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  1. #1
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    Default 2x4 walls and no insulation any suggestions?

    I have a 100+ year old house in North Idaho. Winters here can be pretty rough and I need to insulate big time. I am fighting with ideas on how to fix my insulation problem. Quick rundown of walls from exterior to interior. Insulated aluminum siding over original clapboard over 1x6 ship lap to 2x4 studs to 1x6 ship lap. I have already looked into spray foam applications but it is insanely expensive here due to the lack of contractors available, so that's a no go. I have considered just using standard fiberglass batts but I want more r value. With the standard batts in place I am considering placing the original ship lap back up also. Another idea is to add 2x3 framing to the exterior walls to add more depth to existing framing cavities. With this idea I would use 1/2" solid core foam boards to seal off the airflow from the exterior then use 5 1/2" fiberglass batts over that then sheetrock.

    Any ?'s, comments and suggestions will be helpful. Thanks.

  2. #2
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    Default Re: 2x4 walls and no insulation any suggestions?

    I often warn people that the will not get the expected payback with wall insulation that they may expect, but in your case, even if you don't get what you expect, the savings can still be significant.

    Typically, when you start with an uninsulated house, you are looking at the following percentages of heat loss: roof 30%, walls 20%, windows 20%, floors 10% and infiltration 20%. Those percentages vary widely because of design and other factors, but without an energy survey, they are a good starting point.

    Your walls are currently about an R-4 to R-5. Adding fiberglass batts will bring that up to a total of R-12 to R-13. so you are looking at a savings of about 2/3rds of that 20% for walls. If you add additional insulation and bring it up to around R-20, then you reduce that 20% portion of your bill by 75 to 80%, not much different, but since your heating bill is probably pretty high, it might be worth it.

    First, you need to locate any wiring and water pipes that might be in those exterior walls. The wiring isn't too much of a problem, but if you open the walls, depending on what is in there now, you may want to upgrade your wiring. Water pipes are a big deal. If you insulate between the pipes and the interior of the house, they will be more likely to freeze. You will need to deal with this before you put in any insulation. The best thing is to bring the pipes to the innermost part of the wall so that all the insulation is behind them.

    I would put in unfaced fiberglass batts, then put 2" foam boards, tape all the seams of the foam boards, seal around any outlets with minimally expanding foam, then sheet rock over all that. That should yield a wall with about an R-25. The walls will also be warmer as you will have a thermal break over the studs, which tend to conduct a lot of heat from the interior.

  3. #3
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    Default Re: 2x4 walls and no insulation any suggestions?

    Thanks for the reply Keith. I have already decided to replace all of the wiring through out the house.

    As for the water pipes they are currently ran up along the chimney (all Interior walls and the chimney is used as the exhaust for our oil furnace).

    I am a bit confused on your suggestion about the unfaced fiberglass batts and 2" foam boards. Are you suggesting that I do that with the idea of adding the 2x3 framing to extend the depth of the cavities? As the walls are now they are 2x4 framing. The additional 2x3 framing would give me an overal depth of 6". Is there 4" unfaced fiberglass batts available? I have only seen 3 1/2" and 5 1/2" locally. I love the idea of the unfaced batts and foam board combination. With the sizes I have seen locally wouldn't a 1" foam board and 5 1/2" batts sightly compressed work best or should I go with the 2" foam board, 1/2" foam board and 3 1/2" batt. That would give me full depth with out compressing the fiberglass batts. And what type of tape would you suggest? Thanks again, looking forward to hearing back.

  4. #4
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    Default Re: 2x4 walls and no insulation any suggestions?

    I am suggesting that you forgo the 2x3 studs. You only need one vapor barrier so use unfaced 3.5" batts. Then use 4x8' sheets of 2" thick foam. then tape the seams to form a vapor barrier with the foam. The sheetrock will need extra long screws that will need to go through the sheet rock and the 2" of foam. That would be a 3.5" screw.

    If you decide to do a double stud wall, offset the studs. Wood only has an R-value of about 1.25 at best, so a 3.5" stud would have an R-4.4 at best. This makes a low resistance path for heat around the batts. The foam would make a thermal block between the sheetrock and the wall studs, about R-6 per inch of foam. You can accomplish the same thing by making a 2x3 stud wall inside the exterior wall with the studs offset. Then use 3.5" batts in each, but use faced batts or a vapor barrier on the inner wall. either way results in a super insulated wall.
    Last edited by keith3267; 01-21-2013 at 08:50 PM.

  5. #5
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    Default Re: 2x4 walls and no insulation any suggestions?

    Ah ha, I get it now. Thanks for the clarification. Will strongly take your suggestion in to consideration. Thank you very much. I will post what I decide to do.

  6. #6
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    Default Re: 2x4 walls and no insulation any suggestions?

    Let me add this, two inch thick foam boards are about the thickest that you can use without some additional studs for support, additional studs would be counter productive. But 2" may not be optimum. By that I mean that as you go thicker, you costs go up linearly, but your savings increase at a decreasing rate. Just using batts will cut your heat losses through the walls by about 65%. That leaves on 35% available for further savings.

    To me, the issue with just using batts in a very cold climate is that sheetrock or plaster has a low R value. If they are attached directly to the studs that go completely through the walls to the exterior sheathing, the lower R-value of the studs combined with the lateral conduction of heat by the interior surface will leave you with a cold wall surface. Even though the total heat loss will be less, a cold wall will make the room feel colder because it will cause a greater exchange of heat between your body and the room.

    Even as little as a half inch of foam over the studs will break this conduction and the interior surface will feel much warmer, This will be more comfortable with lower air temperatures in the room. A half inch foam board will add about an R-3 to the wall so now your total savings will be about 75%. Thats about a third of the remaining 35% so the payback is pretty good in both economic terms and in comfort level. Using 1" foam instead of 1/2" will add another R-3, but the payback will be less, it will be closer to a total reduction of 80% or only about 5% more of that original 35% left. Going with 2" foam will double your costs for the foam or the 1", but the payback will be even less.

    In economics, this is referred to as the point of diminishing returns. You will need to determine just how much additional cost will be justified by the savings. Plan on some future energy cost increases. You can expect energy costs to triple over the next 20 years, but even with that, too much additional insulation may not have a payback.

    BTW, I hope you are looking at you total insulation package. You should have at least 50% more insulation in your attic or roof as you have in the walls. Your windows and doors account for as much energy loss as your walls so don't ignore them. There are ways to increase their efficiency without replacing them.

    The floors also need some insulation, but doing them is very different that walls and ceilings. check out some of the posts on floor insulation.

    While you have the walls exposed, look at caulking the sill plate to the floor. A lot of air can seep in under the plate and that can make the floors very cold, even if they are properly insulated.

  7. #7
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    Default Re: 2x4 walls and no insulation any suggestions?

    Sorry about the lack of User profile. I live in the northern pan handle of Idaho. So certainly more heating then cooling in these parts. Still not sure about that paper material though. Like I said there are several layers of wallpaper then the cloth material used to adhere the wall paper to the walls, then there is the mystery stuff over the top of the ship lap. Thanks.

  8. #8
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    Default Re: 2x4 walls and no insulation any suggestions?

    Directly over the shiplap was nailed a now yellowed gauze type gauze.

  9. #9
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    Default Re: 2x4 walls and no insulation any suggestions?

    OK so I was wrong on the levels of crap I need to remove. Wallpaper on top of wallpaper on top of the thick mystery material then ship lap on exterior walls of the room. Interior walls of the room are the same except instead of the mystery material there is the gauze stuff over the shiplap.

  10. #10
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    Default Re: 2x4 walls and no insulation any suggestions?

    You have what is called a "balloon frame" house. Now that you have opened up the wall, you have essentially opened a can of worms so to speak. To comply with modern codes, and for your own safety, you should put in fire blocking between each floor. Without this fire blocking, if a fire were to get started in this house, the wall cavities would act like chimneys spreading the fire very quickly.

    The last TOH project house was a balloon framed house. You can view selected episodes on this web site to see how they tackled it. Your biggest problem here is that modern dimensional lumber is smaller that the dimensional lumber used in your house, so every piece of blocking will have to be custom ripped to width as well as cut to length.

    For batt insulation, I would suggest that you get the 24" batts and cut them to size using a chef's knife. Try one of those ceramic knives you see advertised on TV, you can get them at Walmart now. I learned the hard way not to use one of those to cut Brownies up into squares in a Pyrex baking dish, they cut right into the glass, so they should be good at cutting insulation. A steel knife has a very hard time cutting glass.

    Use the left over strips for cavities around window and door frames and/or in the attic.
    Last edited by keith3267; 02-03-2013 at 12:58 PM.

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