No announcement yet.

Radiant Barrier?

  • Filter
  • Time
  • Show
Clear All
new posts

  • Radiant Barrier?

    After having my 12 x 20 Amish-built shed for over three years now, I'm finally getting ready to insulate it and move the rest of my woodworking tools from the basement to the shed. So, insulation is the task and I recently noticed a few 'YouTube' videos pushing radiant barrier products. Sounds good, but I'm wondering about the cost and of course exactly where, if at all I should think about installing foil in relationship to the insulation.

    I had considered buying 'Roxul' for both its insulation and sound abatement advantages over 3-1/2 inch fiberglass, but both places I checked locally only sell the Roxul by the pallet (I'm still checking around though) and of course it is about twice the price of fiberglass.... still I'm leaning toward the Roxul, if I can justify it.

    The shed as a gambrel roof with lofts at each end,, which I've lengthened to five feet deep and I've doubled the joists. The ceiling sheathing is "LP TechShield" which has a radiant barrier on the underside, but I couldn't get the builder to use that for the wall sheathing too.

    So the question is, "Should I add radiant sheathing foil to the wall sheathing, and if so wouldn't that go against the sheathing between the studs before I add the insulation? A couple of YouTube video's show the barrier added on top of the insulation, like vapor barrier. My logic (perhaps wrong) tells me that you should reflect the heat before the insulation, not afterwards... but that defies what I see in the videos.

    Of course this shed is for part time woodworking. I'm not going to live out there (so my wife tells me anyway), but I do want it easy to cool (A/C) or heat; and, right now it is getting over a 100? in there.

    Any experienced suggestions would be greatly appreciated,

    Think it Through Before You Do!

  • #2
    I suggest spray foam insulation. I have seen the radiant barriers and other ‘insulation coatings”, and have tried a few myself. Check the actual R value of the film me I think you will see it is not actually an insulation. A lot of people mistakenly think that insulation keeps heat/cold out of a building. Well, it does, kinda, it still lets heat/cold through but at a much slower reared. At some time both sides of the insulation will reach the same temperature.
    The spray foam insulation really adds a lot of structural strength to a building, making the building hold up better to high winds. I wish I had been able to come to terms with the foam contractor when we built our house, but that’s water under the bridge now.
    I have a friend that has a simular size all metal building that he had spray foam insulation installed. Before the insulation It was hotter than an oven in the summer and colder than a freezer in the winter. Now he maintains a constant 72 degrees with a small 110 v window air conditioner. The higher cost of the spray foam insulation could easily be justified by the nearly nothing utility bill to heat and cool the new building.



    • #3
      I would second the suggection of spray foam insulation. We had the house done when we remodeled and it dropped our gas usage by half. That and the sound absorption is amazing. Note that spray foam is flammable so it does need to be covered.
      An ethical man knows the right thing to do.
      A moral man does it.


      • #4
        I haven't installed it yet but I plan to use a layer of radiant sheet material in my shop as part of the insulation project. Around here, building codes now require radiant coatings on the roof sheathing for new or remodel/retrofit construction. One thing about it though is there needs to be some air space against the radiant material. So, if it's stapled to the underside of sheathing, an inch or so gap needs to be maintained between the other side of the radiant barrier and any added insulation. In a typical household installation, the attic sheathing has the radiant barrier directly applied to it, or the barrier is attached to the rafters. The normal insulation is applied to the attic floor (room ceilings) so the whole attic is the air gap. But if you intend to make a vaulted ceiling or something - with insulation batts between the roof trusses/rafters - then you'll need something between the upper surface of the insulation and the radiant shield to maintain the gap. That's what I'm doing in my detached garage shop as I don't want a low ceiling. That same air gap also gives the air from soffit vents somewhere to go to reach the peak of the attic. Home centers have lightweight styrofoam panels that can be stapled to the trusses/rafters; these panels have inch high mounds in them to form a one inch thick air channel. So roof - radiant barrier - 1 inch air gap - styrofoam panel - fiberglass insulation batt - open attic space seems like a workable solution. Filling in the areas between trusses/rafters blocks airflow from one "bay" to the next however - unless there are soffit vents in every bay and the tops of every bay are vented outside or to the peak of the attic. Some airflow underneath the sheathing is necessary to avoid trapping mold/mildew creating moisture.

        Aluminum foil style radiant barrier is vapor permeable - so it does not end up trapping moisture against the sheathing. It is not a vapor barrier at all supposedly. Just a thin material that reflects 1 of the 3 methods of heat energy transfer... and adding about R-1 to conductive insulation.

        At least that's what I gathered in my research a few months ago.



        • #5
          I remember many years ago when sheath foil became the rave, there were door to door salesmen pushing the stuff all over the place. I listened to several of their spills myself. A report came out comparing a house with a thermostat controlled electric attic vent fan and the same house with sheath foil. The results were the fan help reduce the house inside temperature better than the foil sheath without the fan did. Roxul advertises that it reduces the temperature of the attic 50%, what it doesn’t say is after how long of a heat exposure. It reduces the heat load on your primary insulation that is piled on your ceiling, just like the attic fan does.

          I doubt that R1 insulation is worth the time to install. Corrugated cardboard has an approximate R4 value, the higher the R-value, the better the insulation. In fact, if the R-value of insulation is doubled, the heat going into (or out of) your house is cut in half. So... if you have to climb up in the hot attic and install it yourself you might be better off getting several corrugated cardboard refrigerator boxes from an appliance store and staple them to the rafters and save yourself the cost of the foil. I can’t imagine foil would be easy to install in an attic.


          • #6
            Thanks everyone,

            I just wasn't wrapping my head around "aluminum foil" as a heat barrier. Everywhere else I've used aluminum has been for it's heat conducting properties... like electronic heat sinks, cooking foil and utensils, etc. I do believe that it's reflective qualities might be beneficial; but so would be painting my shed white, instead of the dark green that it is. The fact is, "radiant barrier" ISN'T on the sunny side of anything in such applications... so, it did leave me wondering.

            A mentioned earlier, my shed is 12 x 20 (maximum the city would allow me to have) and that is fine for the amount of work I do or have time for. I barely get eight hours a week to spend there and so I don't need to dump a pile of money into insulation. Foam I think would be way too expensive, but I'll check. Right now I'm having trouble justifying even Roxul, as it is twice the price of fiberglass. Biggest obstacle there is that around here I can only buy Roxul by the pallet and one pallet is slightly too little I think, and two pallets are way too much.... especially because the last time I checked, it was $600 a pallet. I do like it though, as it has better sound abatement than FG.

            Does anyone know the R-value per inch of styro foam? We can't dump that around here and I have a growing stock of styro foam packing (big pieces from tool and furniture past purchases.) I've just been stuffing it in the back of the garage for now, as my only other choice is to cut it up into small chucks and stick it in the city garbage bags for putting in the landfill (I don't like dumping such things in the landfill). I don't have enough to do the whole shed, but could probably handle the sunny-side walls if there was any advantage to it.

            Thanks to everyone for the assistance. Right now, it looks like sticking to plain old fiberglass with a paper moisture barrier.... conventional and cheap!

            Thanks again to everyone,

            Think it Through Before You Do!


            • #7
              I thought about what you said about your styrofoam packing cutting up and using it for insulation. My google search wandered to styrofoam peanuts, kinda close to cut pieces of packing. It said..

              The very reason why plastic peanuts work well as packing makes them a bad choice for wall insulation. ... Moisture passing through the walls could makeyour insulation dissolve over time. In addition, a supplier told me that most plastic peanuts are not fire-resistant.

              The R-value of polystyrene is about 4.0 per inch. But the problem with using packing peanuts for attic insulation is that, while the individual peanuts may have an R-value of about 4.0 per inch, the peanuts have large air spaces between them which allows air currents to easily flow through a layer of packing peanuts.

              I’m of the belief that if you have a shop that is comfortable to work in, ie. Comfortable temperature, well lighted, reasonably dust free, easy access to the house and inviting to your wife and friends you will enjoy being in the shop. Whether you are working on a project or planning future projects of just tinkering with something you will really enjoy a temperature controlled shop. My wife spends a lot of time in OUR shop when I am working on my projects, she will be painting her little do dads, using colored pencils on her adult coloring books, balancing the checkbook, reading and all matter of googling. Neighbors often drop by to see what’s being built and we all sit around and talk about the kids and whatever. I’d say insulate the building, install a window air conditioner and enjoy it, your shop time might go from 8 hours a week to 40 hours a week. You are not guaranteed tomorrow, and you can’t carry the money you save by not insulting the shop with you when you die.



              • #8
                Thanks Cap,

                You make some great points, all well worth the consideration.

                I wasn't thinking in terms of "peanuts", as I have a significant about of thick long pieces as well as several sheets of stryrofoam that could be cut to fit in behind electrical boxes, into the tight corners behind the studs, over windows and doors, etc. In many areas it would provide seamless fill of the voids, etc. On the other hand, it might also trap moisture as it surely doesn't breath like normal insulation, so I might just as well not consider using it.

                I do agree about making the shop as comfortable as possible though... who know, if I take to spending too much time out there, I might have to sleep there too!

                Think it Through Before You Do!


                • #9
                  Sleep in the shop? Thought of that! It is our (my wife and I) power outage plan. My generator will not operate the house air conditioner/heat pump through the transfer switch but it will operate the shop air conditioner/heat pump so we will sleep and hang out in the cool or warm shop during power outages.