awatson72
Registered Users
Posts:5
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| 08/19/2008 10:00 AM |
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I live in a northern climate, and am designing the walls for an addition. One method I'm considering is to use a traditional 2x6 framed wall, insulated with fiberglass or maybe cellulose, with OSB sheathing, and the departure from tradition - a 1/4 inch radiant barrier, (a product called Microvent), over the sheathing instead of house wrap, then the vinyl siding. Can anyone talk to the effectiveness of using a foil radiant barrier product to combat thermal bridging, instead of using the more common approach of rigid foam board? If there are no major drawbacks, I'm thinking this could be an effective way to build the exterior walls.
Thanks for any insight
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Alton
Registered Users
Posts:314
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| 08/19/2008 12:35 PM |
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| Do you plan to have an air space between the vinyl siding and the radiant barrier? |
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Alton C. Keown
Residential Designer and Construction Technology Consultant
Auburn, Alabama
334 329-0957 AT&T Cellular |
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awatson72
Registered Users
Posts:5
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| 08/19/2008 12:47 PM |
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| I don't think so, unless it would be advantageous to. The vinyl would be attached such that the fasteners would not compress the 1/4 inch of radiant barrier. |
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PanelCrafters
Registered Users
Posts:1329
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| 08/19/2008 1:27 PM |
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| A Radiant Barrier and Insulation are 2 different Animals. They are not mutually exclusive. Also, a Radiant Barrier needs an air space on one side to be effective. If you are in a Northern climate, during the winter, I don't really see it's purpose. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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awatson72
Registered Users
Posts:5
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| 08/19/2008 1:50 PM |
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Here is a website with information about this product. It claims to be designed to be installed under vinyl siding.
http://www.barrett-inc.com/microvent.html
Now I'm really confused, since I've also read elsewhere that a radiant barrier needs an airspace on one side to be effective. So where's the airspace if the vinyl siding is on one side, and the sheathing is on the other side?
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Jack Costantino
Registered Users
Posts:3
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| 08/19/2008 3:07 PM |
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| It might be worth your while to use 4 1/2" SIP's with XPS at R20 and combine that with a product called rain-slicker under the siding. Search "rain-slicker". We use MURUS SIP's, but there are several brands available. I'm also associated with a company who is beginning fabrication of completely framed and bio-foam insulated walls. The stick frame is 2x6 on 24" centers with 3" of pre-applied foam. All door and window rough openings are complete. Just another way to go. |
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Timber Frames Unlimited, LLC
Jack Costantino
100 Old Farmers Road
Long Valley, NJ 07853
201.230.6429 |
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ReadyToRetire
Registered Users
Posts:195
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| 08/19/2008 3:34 PM |
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Vinyl siding has the advantage that the voids behind the "planks" allow drainage. Those same voids would provide an air space to permit the radiant barrier to work -- assuming that you're not using the foam backed siding.
Larry
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awatson72
Registered Users
Posts:5
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| 08/19/2008 4:04 PM |
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OK, well that explains why the product is marketed for use under vinyl siding. The benefits of that seem obvious in a warmer climate where I imagine the goal must be to reflect heat away from the wall before it permeates, but I wonder how useful a radiant barrier installed over the sheathing, and under the siding would be in a cool climate, where the primary design goal is to keep heat from escaping the building...
Another way of presenting the question - is a radiant barrier important in a wall in a cool climate, and if so, should it be on the outside or inside of the wall?
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PanelCrafters
Registered Users
Posts:1329
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| 08/19/2008 4:50 PM |
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Posted By awatson72 on 08/19/2008 4:04 PM
Another way of presenting the question - is a radiant barrier important in a wall in a cool climate, and if so, should it be on the outside or inside of the wall?
My opinion is:No! I think that you'd be better served with a High R-value/Low Air Infiltration wall assembly. As the other jc indicated, SIPS are great for that application. ICF's, and double wall(2x4) will also work. I designed this for those that are looking at that method:
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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GRStock
Registered Users
Posts:2
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| 08/19/2008 8:18 PM |
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| I wold look into Icyonene spray in insulation. It's pricey but you will not have any air infiltration nightmares. I recommend it to all my ICF buyers. |
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Glen Stockinger
Insulating Concrete Forms LLC
918-437-2425 |
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wes
Registered Users
Posts:376
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| 08/20/2008 7:54 AM |
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The old adage in my part of the world is: Never use foil faced sheathing under vinyl siding.
This has nothing to do insulation values or anything so interesting.
Simply put, the foil reflects so much heat that the vinyl siding expands and contracts so much that it will not stay attached to the wall, and falls off. I've seen this happen several times over the years. On jobs installed by qualified and meticulous contractors, so its not bad technique causing the problem. When the foil faced sheathing is replaced with non foil faced, no more problems. |
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Wes Shelby
Design Systems Group
Murray KY
wandr@ainweb.net |
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Jack Costantino
Registered Users
Posts:3
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| 08/20/2008 10:37 AM |
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| awatson...is it necessary to use Viny siding. We have used only fiber cement for some time, i.e., Hardie Plank. I build custom Timber Frame homes with 4 1/2" R20, SIP exterior walls, a layer of rain slicker, fiber cement siding and Kleer PVC trim. There is zero wood on the outside of the house, but since all the traditional wood trim profiles are now available in PVC the appearance is indistinguishable from a properly trimmed wood home. |
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Timber Frames Unlimited, LLC
Jack Costantino
100 Old Farmers Road
Long Valley, NJ 07853
201.230.6429 |
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Mark Fleming
Registered Users
Posts:188
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| 08/20/2008 5:56 PM |
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My experience is that radiant barriers work amazingly well in an amazingly few number of situations. If you are using it above traditional ceiling insulation to reflect heat out of the conditioned space, they work great. Unfortunately, it radiates the heat back towards your composite roofing, which deteriorates in direct relation to the amount of heat cycling. You have lower cooling costs offset by needing a roof every 25 years instead of 35 years. An attic fan would be more effective. A solar attic fan if you want to be green.
I don't know what heat does to vinyl siding. I do know that I wouldn't bother with a radiant barrier siding on the north side of the house or anywhere not directly hit by the sun.
And the list goes on for radiant barrier sort of working.
I'd go with 2 inches of spray foam and the rest traditional fiberglass insulation. If the design was simple, I might look at SIPs (I like the concept but have never had it pencil out). Window awnings in the summer and shutters in the winter will do more than any of the new whizbang insulation products.
Mark |
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awatson72
Registered Users
Posts:5
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| 08/21/2008 8:26 AM |
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Thanks for the insight. I'm not going to use the radiant barrier material, it just doesn't seem to make sense. What I will end up with is a combination of high density fiberglass and isocyanurate rigid foam board. Of course, if money was no object, I'd use the sprayed in foam, but where I live, it is still extremely expensive. Perhaps worth the expense if building a new home, but the fact is that I'm adding onto a home that is rather poorly insulated, and I'd like to have some fundage left over after the addtion is built to improve the existing insulation. I'm currently researching whether to put the foam board on the inside or outside of the walls. Both seem to be done regularly. As for siding, I'm assuming vinyl, but if I can find accomodation in the budget, I'd go with fiber cement in a heartbeat.
Andrew |
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