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  • Above grade basement needs insulation only-help

    I finally got the fireplace going great, it is heating main floor great as our heat source. I use a small fan to drive the excess heat down the stairway to the basement and also use the furnace fan occasionally to distribute heat to the basement. On a cold winter night of 15 deg. so far the temps in basement are 55 deg. It may get colder as ground gets colder? On the outside I have no snow next to the basement walls as it melts from the heat loss.

    The house is a ranch with cinder block walls in basement and the base of the walls leak in summer so I am not finishing the walls. THe water actually enters near the top of the blocks, but that is another project.

    NOW: I need to insulate the sill area better than the minimal fiberglass the builder installed with no vapor barriers even.
    Does the sill area between the joists get fiberglass insulation with a vapor barrier on the interior surface, not against the wall in other words? I do plan to seal joints with foam sealant also prior to installing the fiberglass.
    Since the builder in 1989 did not use vapor barrier it may have been since kraft paper is burnable? So can I just use no facing insulation?

    There are solid 8 inch cinder blocks above grade sitting on top of the normal hollow core below grade blocks.
    I want to insulate the solid cinder blocks only at this time, since they are only 4 inches deep and hollow blocks are maybe 8 inches. Solid blocks are also the only blocks that are exposed to outside cold air. I only need about 10 inches wide to cover these solid blocks and sill plate. Covering the sill plate and blocks will cut down the sealing with foam any air gaps. The rest of the exposed wall is between the joists.

    Question: Do I use foil faced extruded polystyrene or polyisocyanurate and then fiber glass insulation?
    There will be no drywall and no studs.
    Or just insulation applied to the foam with some reflectix double reflective foil insulation which is rated class A Class 1 fire rating applied to interior surface of insulation?
    Any other suggestions? Foam with the reflectix?

    I am not doing the whole wall just the top section that is above grade and I need it cheap as possible but I do not want pipes to freeze. I do not care what it looks like, the basement is just a huge storage bin anyway. Our freezers should at least be working less anyway.

    The house is air conditioned in the summer. There is a sump pump. There is also a workroom if a person can get to it.

  • #2
    The basement shouldn't get too much colder than ground temperatures which hover around 52-55 F.
    Snow melt directly around the base of a house is reasonably normal, building products like cinder blocks etc... will warm up much faster than the ground.

    There is little point insulation the top section of the basement if that's where the water comes from, you'll create much bigger problems for yourself with regards to mold etc... You need to fix the water problem first.

    The floor joists (basement ceiling) should have at least R13 insulation
    NON faced if the basement is not heated by way of furnace vents then it should have R19 non faced. Your right if the insulation is not going to be covered your not allowed to use faced insulation because of the fire risk, it is very dangerous to leave the paper face open.
    NOW....if the basement is NOT heated you can install R 19 faced insulation but the faced side MUST face the heated area and in this case the heated area would be upstairs above the basement so the paper would be against the floor boards and not exposed.

    Unless there are large holes in the band board (between joists) and there shouldn't be, there is no point spraying foam in this area then installing insulation, fit the insulation all the way in between the joists all the way up to the band board, you can bend down the end of the insulation to cover over the band board and sit on the sill plate.

    There is no point at all in trying to insulate the cinder blocks, this will without a doubt become a bigger problem (especially since you already have water problems), the above ground blocks are not sealed or have a vapor barrier on them so they will "wick" moisture from outside to the inside, by adding any sort of insulation directly to these blocks will allow mold to grow between the insulation and block. It is much wiser to leave this open to air movement.
    If you have gaps between block and sill plate that you feel cold air coming in, seal these with a good quality caulk, to stop air infiltration.

    I assume your furnace is in the basement, in my opinion it would be much wiser and cheaper to seal any air infiltration gaps with caulk, reinstall fiberglass insulation to cover the band board area and make sure you have working vents in the basement. For over all air quality of your house the basement should have working vents. This doesn't mean trying to heat your basement like the rest of the house, it means adding a controlled air environment and remember heat rises, any heat you put in the basement will warm the rest of the house.
    Even with no working vents in the basement the basement should never get cold enough (32F) to freeze water pipes.
    Last edited by pushkins; 12-24-2009, 09:08 AM.
    Little about a lot and a lot about a little.
    Every day is a learning day.

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    • #3
      Thank you for your quick reply.
      Water enters the hollow core bricks about 2 bricks down below the grade level, not at the grade level. We have the outside wall painted with roofing tar completely surrounding the house and glass block windows are inset into cement within the above grad portion of the basement wall. So would the water still wick in from the outside to the inside if we just take care of the above grade portion? We could also put the foam board on top of the now open top of the hollow core blocks. That would also keep stuff from falling into the wall cavities and never to be seen again.
      It sounds like we can use R19 in the joist area and put the facing upwards to the floorboards thus solving the exposure problems.
      Still unsure insulating of the solid block area though since the outside of wall is painted with roofing tar to seal from water penetration.
      Our furnace is in the basement and we have 2 hot air vents also in the basement. Also all ductwork is exposed. Water heater is insulated as are all water pipes.
      It is nice to know temps should not go much below 52 deg. but that is awful cold for uninsulated floorboards and to walk downstairs for laundry.

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      • #4
        We were going to attach some waterproof material along the wall above the grade and then spread it out several feet beyond the wall to prevent water from getting anywhere near the house where the leak is occurring. The leak is only at a few cement seams of a couple of blocks a few feet from ground level. I can see the leak when looking down from top of wall through the cavities in blocks.

        WE had planned this last summer but a row of shopping carts pushed into my already injured back sealed the end of that fix as well any other fixes for the rest of the year.

        I just have to convince my nephew to do some digging along a short length of about 10ft for me.

        There are no leaks along the rest of the walls.

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        • #5
          Unless the entire exterior of the basement is sealed (obviously not by your leaks) water WILL wick back up all the blocks, they may not feel wet but they will be damp in some way, so again, it would not be recommended to add any direct contact insulation to the block walls above or below grade, even in a brand new sealed basement wall home, contact between any insulation and the block wall is not recommended and prohibited in many cases. Air movement across block basement walls is paramount in all finished basements for mold issue reasons.
          As for the cavities in the top of the blocks (there shouldn't be any, the blocks are filled with cement with anchor bolts and then the sill plate sits over that with the bolts up through it, normally the sill plate is treated 2x8 which should cover almost all of the top of the blocks) anyway, poke some crunched up newspaper down them just a few inches (6") then spray foam on top of the paper, use low expansion foam (blue tin) to avoid over filling.

          If you add R19 to your basement ceiling you will notice a dramatic change in the floor temperatures above.
          Little about a lot and a lot about a little.
          Every day is a learning day.

          Comment


          • #6
            It sounds like we will not be spending any money except for the joists area anytime soon. If we were to insulate the basement ceiling then no heat would be transmitted to the basement from main floor via the floor at least. It would be difficult to do with all the cross braces,pipes and ductwork,lights,wires anyway.
            The hollow core cement blocks are hollow, the solid block sits on half the hollow block and the sill sits on the solid block. At least .5 of the hollow block is open at the top and if one were to shine a flashlight and crane your neck between the floorboards and the cement blocks you are able to see all the way to the bottom row of the blocks. The only cement that was used are in the joint seams.

            We painted roofing tar on the original waterproofing stuff they had applied below grade and also applied it above grade all the way up to the siding. I will try to post pics later this weekend if possible.

            Thanks for your replies, you are the expert I am not , I am trying to explain and clarify the situation.

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