Adding thin insulation to house walls (heat retention)?

topic posted Sun, May 11, 2008 - 11:46 AM by  Tanemon
Hi. I live in a 2x4 frame house with fiberglass exterior-wall insulation (built 1976). We're in plant-zone 6 and get a coldish winter (but not as cold a winter as much of the rest of Canada), and a hot mid-summer. About a year ago, I read about a highly heat-reflective paint layer that has been developed - remove your exterior siding, paint the material on the inside of the siding, replace the siding, and you supposedly have a significantly improved R value, due to reflected heat.

I don't know how true this is, about the performance of this sort of product. But it's made me wonder if there IS some thin (possibly quarter-inch) material that can be installed under siding that can significantly increase R value, without resulting in recessed window and door frames. That would be a very important consideration for me.

By the way my house was originally built with black-building paper over plywood sheathing behind the exterior siding, and with a plastic-sheet vapor barrier on the interior behind the drywall or wood panelling.

What do any of you know of about thin insulating products? I make no assumptions about the validity of these. But if such products do exist and are effective, are there down sides to using them in a house like mine? And how costly are these materials when used extensively enough in a house to be effective? Thanks.

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  • I can't imagen re-using siding, too easy to tear up when you remove it. You can of course, re-side the house with insalation under the new siding.
    • Unsu...
      I agree. It be better to do some kind of insulation that you can blow into the recesses: Cellulose Insulation or expanded foam.
      • What recesses?

        My siding is 12"-wide cedar boards, almost board-and-batten style (vertical), except both "boards" & "battens" are the same width - with about 3" of exposure of the underneath board by the two outward boards. Can you visualize it?

        Anyhow, these rough-sawn boards are 7/8" thick and pretty tough. I carefully removed about a dozen of them to install a double door onto my deck, and none of the boards were harmed when I removed them.

        But there are not enough in the way of recesses to put much blown-in insulation into. Behind the plywood sheathing (and the vertical siding that is exterior to it) are 2x4 studs with fiberglass-bat insulation. So the frame-wall cavities are filled in a conventional way. My concept is to add to this already in-place insulation.

        How about a highly insulative or heat-reflective 1/4" sheeting that I can add over the plywood sheathing, then replace my vertical siding boards?

        Know of any such material?

        • if that's the case, then removing and reinstalling the siding should be a snap. However, I don't think there are many 1/4'" products that will yield much in the way of added insulation. Perhaps the bubble wrap sandwiched between layers of foil would be an idea, but that stuff ain't cheap. Beyond that, I think you'd be looking at rigid foam insulation. I'm guessing that in order to make the effort worthwhile, you would probably need a minimum of 2" ...hopefully that wouldn't cause problems with your eaves, though you would certainly need to tweak the trim on your doors and windows.
          • Have you considered the cost vs. payback on this ?
            Being clap board, re-use is possable. but as stated, 1/4 of anything isn't going to do enuf to merit the cost and effort.
            It would probaly be easier to put the 1/4 insa. on the interior wall, with 3/8 drywall over it. you could do one room at a time. and it would all be a glue up project. ( very few nails to finish out)
            Also, because you increase mass, it would retain interior temps better.
  • Unsu...
    I have read about a paint that has micro spheres in it that the maker claims will insulate.

    It's shit. The claims are shit, the product is shit, don't spend you money on it.

    Here is the problem:
    The essential theory is flawless. The little hollow spheres should ( and would) provide a dead air space which will insulate.
    However, you'd need a few inches of 'em to get any meaningful insulation effect. A paint thin layer won't do a damn thing.

    However if you are thinking of reflecting infra red back into the house you can layer a reflective foil - under the sheetrock - that bounces infrared radiation back into the building.
    That'll work way far better than applying something to the exterior shingles.

    But the gain isn't likely to be dramatic. Hell you likely won't notice it.

    If you want the best insulation that I know of you'd need to tear out the insulation you have and inject Urethane Formaldehyde Foam into all the cavities. Of course there is all the formaldehyde that will - if not completely consumed by the chemical reaction - out gas into the building,
    UFFy foam done right does not out gas. . However "done right" infers a few factors you can't control.
    • Cliff wrote: "Adding thin insulation to house walls (heat retention)?
      I have read about a paint that has micro spheres in it that the maker claims will insulate.

      It's shit. The claims are shit, the product is shit, don't spend you money on it. "

      Yeah, you're in the right ballpark as to the type of products I've heard about. Their manufacturers do make claims for the heat-retaining value. Here is one products I found in a Web search a while back:

      If (and yes, that's a big IF) the product performed as they imply, then I'd think the effort I was describing would be worth it But perhaps the return of the radiant heat back into the house really is not significant and it would make no real difference in how the house occupants felt, in terms of warmth - hence, would not reduce my firewood consumption.

      But that's why I started this thread here in DIY Tribe... to get a discussion and learn something.

      • If you'll buy that, I made some nano wires in college that you could wire your house in. They work on the concept of surface plasmon resonance meaning ideally nil resistance.

        You could pay me a lot of money to recreate those wires and they would be loaded with nano technology, but they couldn't carry the load for a house or even a light bulb. Also when they do blow or break you wouldn't be able to find them.
      • Yeah I find it interesting that they carefully avoid giving actual hard figures on the performance of their product. They carefully discount means of measuring the performance. Definitely smell a rat.

        • Yeah, that's why I wanted to check around. Every so often, there's a product that hits the market that's based on a simple but heretofore unutilized principle, and it actually works... and gets known and is then put into widespread use. But there are lots of gimmicks and half-baked things put on the market, too. I almost never buy stuff I don't have experience with unless I check it out with people who've used it and who seem to exercise good judgment. With this company's product, I thought possibly it was one of a number of similar products put out under different brand names - but still I know no one who's given it a whirl to see what happened.

    • Jon
      offline 0
      Hi Cliff,

      I have heard considerable doubts expressed over nano-paints but care is needed not to generalise this type of reasoning to all nano-insulation - for instance take a look at aerogels.

      Conventional thermal insulators and nano-insulators cannot be compared by the type of reasoning that applies to dead air space and thickness of that layer of dead airspace. You are right to look at depth of insulation as a primary consideration for conventional insulators, you are probably right from what I hear on the paint issue but the argument you make does not extend itself to nano insulation technology in general. The physics at the nano-level is radically different.


      It has remarkable thermal insulative properties, having an extremely low thermal conductivity: from 0.03 W/m·K[8] down to 0.004 W/m·K,[5] which correspond to R-factors of 14 to 105 for 3.5 inch thickness. For comparison, typical wall insulation is 13 for 3.5 inch thickness. Its melting point is 1,473 K

      You may already know all of this of course, I just want to make sure that arguments aimed against the paints are not mis-interpretted by folks so that they think nano technology is a load of hogwash because it is not - NASA would not be spending their time messing around with this stuff otherwise.
  • I'm no rocket scientist and I don't know the thickness of the existing insulation (R value - do you have full walls ? or only 2" ??) but you might think about these ideas.

    1) If you have a electronic stud-finder, locate the stringers/cleats in the wall and then cut a hole thru the drywall (inside wall) just below them and the top plate and blow in Styrofoam beads like they use in bean bag chairs to fill in the voids in the wall. You could use the same blower as for cellulose insulation.

    2) You can use Radiant barrier insulation (foil and Mylar film) any where under sheeting or siding, roofs - walls - etc. and it is suppose to reflect 80%+ heat. Think survival blanket it's the same product !

    3) As already suggested you could use foil backed bubble wrap, same as above but with bubbles but way more pricey.

    4) Adding an extra layer of drywall to the inside of every room is a good idea too, and you can do one room at a time as money permits. The thicker the better. You could even put a layer of sheet styrofoam under the new drywall and use thinner drywall if need be.

    Nothing will work as well as ripping off all the siding and putting 1" of styro on and a complete re-wrap with vapor but that's alot of work.

    Dry wall would be the cheapest - Good Luck !
  • DJ
    offline 0
    Reflective Coatings are best used in Sunbelt areas (about 20% efficiency gain yearly in those conditions).

    What Canadians need are 2 in 1 (Heat Box/Solar Water heater) to save on energy costs year around. Wouldn't be surprised to get your return within two years on a home built model.

    The best use for coatings in your area will be the use of sustainable coatings... (reflective colors, 30% more solids than normal house paints, 20% I.R. efficiency in direct sunlight, and will keep dirt and debris off like rain-x). They are expensive but the best architectural coatings available to date. I would only spend the money on areas where the sun is ripping at the house (South and West sides).

    As far as insulation concerns.... it would be ideal to trap the attic floor with a double sided reflective barrier while foam sealing the perimeter of the attic which will help immensely.

    I would think your best bet is to 1) seal the attic floor first 2) create an air sealed radiant barrier wall on the coldest sides of the house 3) start on the homemade 2 in 1 (Heat Box/Solar Water heater) and gradually earn it back -more so- than the idiots making Green sound like a million dollar adventure.

    With the 3rd option you can pump the heat with a 12 v inline fan straight into the areas you spend most your time. Some people prefer pumping straight into fured floor joists where they spend most their time.

    My up coming project is to insulate a crawl space using scrounge materials and tyvak to stop the moisture. I've decided to buy a slow burning wood stove to place in the basement and will make an underground channel to loop 16 ft of piping under the crawl space @ 15 degree incline before entering the exhaust stack.

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