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| I was hoping that someone could give me some advice about the insulation on our new build. We have not started construction yet so anything goes. We are in the northeast so the winters get pretty cold.
Our specs give us 12" R-38 for the ceilings, 6" R-9 with poly vapor barrier for the exterior walls, 4" R-11 for the foundation walls. All that I know is that this is fiberglass insulation. Should we be looking for anything else? Thanks... |
Follow-Up Postings:
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- Posted by AnnieDeighnaugh (My Page) on Thu, Jul 19, 12 at 17:21
| Depending on how much $$ you want to spend, I would suggest you investigate closed cell or at least open cell spray foam insulation. Closed cell is the most expensive, but you save on not needing a vapor barrier with it. It adds structural rigidity to the house and our house is also very quiet as a result. When we were looking into building green, all of the advice we got said put your money into your insulation as, regardless of how you generate a BTU, the longer you hang onto it, the more you save. We live in the northeast as well. |
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- Posted by energy_rater_la (My Page) on Fri, Jul 20, 12 at 13:48
| there are less expensive ways to make walls perform. payback for foam in walls is very long, and we can build walls air tight fairly easily. your best savings would be to clad the house relying on foam for structrual integrety visit buidingscience.com and read building if you use foam, use it to create an unvented here in the south we use open cell, but if closed R-value for your area still has to be met. foams shrink. they are installed in wrong places here is an fairly comprehensive article on the http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/25546 /4-Pitfalls-of-Spray-Foam-Insulation educate yourself and make informed decisions. you'll best of luck. |
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- Posted by Karen.1288 (My Page) on Fri, Jul 20, 12 at 15:22
| thanks for the advice. energy rater what do you mean by "R-value for your area still has to be met. Thanks |
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- Posted by energy_rater_la (My Page) on Fri, Jul 20, 12 at 16:19
| you have to have enough foam to meet code requirements. if your code requires R-38, then the inches of foam the 'average' 3-4" of foam that 'performs' like R-38 R-value and air tightness are two different things. foam companies can't invent their own values best of luck. |
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| I design insulated and super insulated structures all the time. Trust me, do not waste your money on spray foams. As ER said, there are far better ways to achieve a tight shell. With the right materials and fairly simple methods, you can get a tighter shell, higher r value, and guess what, it will cost less then foam. What ER is meaning is a lot of foam guys will claim that, since spray foams perform better then fiberglass batts (meaning, they are more air tight) then therefore you do not NEED to put in as much thickness as code requires. This is not true. They know they have an expensive product, so they are trying to be more competative in pricing. |
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- Posted by hollysprings (My Page) on Fri, Jul 20, 12 at 19:32
| Your proposed insulation levels would not meet code here in the warm South, much less in the cold north. At a minimum, you need to be looking at 2x6 construction to get the code mandated minimums. And a heck of a lot more attic insulation. |
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- Posted by AnnieDeighnaugh (My Page) on Fri, Jul 20, 12 at 21:24
| The problem with these other methods is they are very dependent on the diligence of the installer vs. spray foam which covers all openings and places where materials come together without a lot of effort. But with spray foam, be prepared for a chemical smell which will take time to dissipate. |
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- Posted by david_cary (My Page) on Sat, Jul 21, 12 at 7:23
| lzearc - do you think zip sheathing with foam taped on top is a bit of overkill? And in a lot of the NE, with a decent southern glazing, wouldn't an HRV not be cost effective. I'm sure it depends on your heating fuel, but getting that tight and then ventilating is obviously ideal, but may not be a reasonable ROI. If someone is really concerned about costs, HRVs are expensive. What you are telling the OP to do is spend $7k on the walls and then $3k on the HRV. Sure they will save $500 a year and be more comfortable but few people stay in their houses 20 years. Obviously the numbers are fictitious and maybe $1000 is a more realistic savings but you get my point. |
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| Annie- what does spray foams do to address thermal bridging? what does spray foams do to address leak prone areas at top and bottom plates? Spray foam places the air barrier inside the walls, my recommendations (and many building scientists) place the air barrier on the exterior of the wall. While there is some diligence required by installers, by using sheathing from top plate to basement sill plate, you now have a continuous exterior air barrier. |
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| David as I mentioned above, I like to detail and exterior air barrier. Having a solid, rigid nailed continuous barrier is what I prefer as I am more confident it will last longer. Foams can move, shrink and pull apart opening up cracks for air movement. I use foam as a thermal bridge reducer, never as my air barrier plane. (and IECC in our area requires it for framed commercial walls, soon for residential) On the cost of ZIP, from the projects I have done, it has been a wash with the contractors compared to properly installed Tyvek and typical 1/2" OSB sheathing. Infact most prefer using ZIP after they have used it. We all know how easily Tyvek can get ripped or snagged and is flapping in the wind. A contractor can lean a ladder against it and rips a big hole in it. They rarely return to patch and tape it... It is next to useless at this point. SO no, ZIP + foam sheathing is not overkill IMO especially since we really are not seeing an increase in cost for contractors who have used it before. (I will say I am not sold on the roofing ZIP and that does cost more then a 5/8" deck with synthetic felt). The HRV recommendation was not to save energy, but to provide the mechanical ventilation a tight home requires, assuming of course there is a blower door test completed and it tests out below 2 ACH@50 pac. My project specs are typically 1.5 or below, averaging closer to 1. It could be an ERV as well assuming zone 4 or 5. Again, some of my findings could also be more localized as far as costs, but then again very few residential contractors use or have used foam sheathing either in my area, but I have yet to have a single one refuse. Most are very open to it, are sceptical at first, but when its done they admit it was much easier then they thought. |
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- Posted by david_cary (My Page) on Sun, Jul 22, 12 at 7:42
| Except who uses tyvex when you have foam sheathing? And how much air is coming through 2 layers of staggered foam taped and then OSB? I understand that air sneaks in thru very small paths but when there are panels where seams don't line up, it is hard to imagine the air movement. My last build, I told my builder to use Zipwall if it was less than $1000 (2100 sqft) and we went with Tyvex (no foam sheathing). |
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| no one uses Tyvek over foam sheathing that I know of. Nor did I say to use it over foam. I said I did not trust a foam layer to be my air barrier and hold up over the years compared to a rigid nailed sheathing layer. If you apply 2 layers of overlapping foam with joints foamed and taped...yes, you can get it very tight. However the labor costs do increase with this method as well. One can also air seal standard osb sheathing if they prime the joints and then tape it off. Then use Tyvek over top and you will achieve about the same thing as ZIP sheathing. |
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- Posted by Renovator8 (My Page) on Sun, Jul 22, 12 at 10:59
| You probably meant r19 for walls and foundation insulation would be foam But to advise you about insulation I would need to know what town and how the walls would be constructed. There are too many ways to build and insulate a house. |
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| Investigate flash and batt. A thinner layer of spray foam is used to seal ad provide the outer layer of insulation, and then batts are used to achieve the balance of the R-value at less cost than foam alone. |
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- Posted by energy_rater_la (My Page) on Sun, Jul 22, 12 at 14:33
| note that all my comments are on common practices and materials I see in my 10+ years in the efficiency business. this is not to say one product is superior over another, just itrw here in La. concerning flash & batt: also note that I've never recommended foam sprayed never seen flash and batt on attic side of here we don't do fiberous insulations against rooflines I wonder why would a foam company make multiple trips now if it was for a bulider with several projects I try to be that bridge that brings homeowners and Davd cary & lzerarc here we have hurricanes. solid sheated walls with osb here is a link to my utility co-op's energy efficiency pay special attention to the exterior wall composition. in general: trades people should seal holes they make as they make them. in a perfect world. continuing education for everyone! LOL! best of luck. |
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- Posted by david_cary (My Page) on Sun, Jul 22, 12 at 20:24
| lezarc - what I heard was you arguing that zipwall doesn't cost more than tyvex. Right? But when you are using foam sheathing, you don't use tyvex. So of course, zipwall costs more. I see your argument about durability, I am just not sure I agree. Of course a second layer is better than one. I just don't see if you glue and nail the foam to OSB and the seams don't line up that there is much air movement at all there. And if there isn't much air movement, then the cost of a zipwall is wasted. We can agree to disagree and given a good argument, I would change my mind. I've really come around to your double wall in a cold climate so you never know. |
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| tyvek, with a k ;) What I was arguing was, from my experience and local area, zip wall does not cost more then osb and tyvek from people who have used zip wall before. I thought you were meaning Tyvek over foam. So yes, zip wall plus foam would cost more then osb plus foam if you do not put tyvek over the osb. Like I said, foam moves. it shrinks, shifts, etc. the wood walls are shifting, shrinking and the foam doesnt always go with it. I just dont trust it, and that is based on experience of seeing foam opening up. But even if it were 500-1k more...and it helps insure a better air barrier for a longer period of time...why would it not be worth it? on a 250k+ home? that is half a percent of the total cost. The OP asked what people recommended, and I am sharing what I have found to work great. Its not always the cheapest option. People do not batt an eye at dropping 20-40k on custom cabinets when Ikea are arguably just as good for under 10k. Everyone has their areas to spend the money on...most times things you dont see are not as important in the budget unfortunately. but since you brought it up....I have found the double stud wall to be cheaper then thicker foam walls, details are easier, etc. However you do lose some square footage, and very few people jump at the higher r wall option mainly due to that. The couple double stud wall projects I have done cost the same as a 2x6 wall with 2" of XPS with close to 2x the insulation and nearly 100% thermally broken. If designed right, one can completely eliminate a ducted furnace system instead using a single mini split. Mitsubishi hyper heat units can product 75% of their heating output at -13, and 100% at 5. Most mean temps in zone 6 are above 5 degrees in the winter, with design temps pushing -10 to -17, however they last for a very short amount of time. A tight, highly insulated structure can ride out the dips in temps easily for several hours with only a few degrees lost. Obviously many are very skeptical of this method and are sold on over designed, multistage ducted hvac systems bc that is what hvac guys are pushing these days in order to obtain comfort. A tight, highly insulated home does not have temp differences from room to room. So your insulation and shell increases by a few k, but you cut the hvac and ducting, so you drop 10k or more depending. So yes, i think the double stud is the best for zone 5 and above. However I typically do not go there first since its a hard sell. Hell getting people to upgrade from batts to a blown product is hard enough sell sometimes! |
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