Zone 3 Insulation Questions

VolGalAugust 17, 2012

I am a first time poster, but long time reader of the forum. My husband and I are making final changes to our plan and hope to start the build soon. We really want to have a tight home that is as energy efficient as we can afford. We live on the edge of zone 3 - twenty minutes to the north would be zone four. We have printed and reviewed building sciences "the perfect wall," as well as many of the very knowledgable posts on this board.

Here's the preliminary plan: 2x6 advanced framing technique with blown in fiberglass, foam around windows and penetrations, and zip sheathing on the main and second floor and roof. For the walkout basement, Logix ICF's. Our main questions at this point are (1) What type of insulation in the attic? We know foam is much more expensive, should we put our money elsewhere? (2) what type of and how much insulation below the concrete in the basement? We are staining the concrete and it will be used frequently as a living space. (3) do we need foam board on the outside and if so how much? We plan on sealing well and doing two blower door tests as has been recommended on here. Let me know if any more details are necessary. Sorry in advance for my relative ignorance on the subject!

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Just a note on advanced framing. It may not be acceptable in your specific location due to wind or seismic conditions.

(1) What type of insulation in the attic?

To answer that question properly, you have to know whether there is any HAVAC in the attic and if it's a vented or unvented attic.

(2) what type of and how much insulation below the concrete in the basement?

None necessary unless you are using radiant heating or are aPassivhaus enthusiast. However, educated opinion isdivided on this.

If you haven't seen it already, you might want to look at Building Science Corp.'s Building America Special Research Project: High R-Value Enclosures for High Performance Residential Buildings in All Climate Zones RR-1005 which reviews all aspects of energy efficient design. Lots of specifics.

The US Department of Energy link below gives you Zip Code specific insulation recommendations.

Tightening up a house is probably as important as the R levels (U for windows). You really have to have a general contractor and/or trades who think the same way. For instance, extensive gasketing, sealing minute air flows with acoustical caulking where necessary and sealing around all penetrations are not things that the average trades are accustomed to doing. So either your contractor or you have to be on top of all these details.

Here is a link that might be useful: DOE insulation recommendations by ZIP Code

    Bookmark   August 17, 2012 at 9:10PM
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Thanks for the follow up! We are sold on tightening up the house and that is definitely a priority. Frankly, our concern is finding people in the rural south that understand these principles and apply them. We are trying to do lots of research on the front end so that we are at least educated enough to determine when we find someone qualified to do the work the right way.

Is there a good resource that has a checklist of all the steps to make the house tight?

    Bookmark   August 17, 2012 at 9:25PM
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Volgal - in the South, infiltration is great to control but not like in the North.

I'm in Zone 4 and our energy audit had our infiltration cost in the summer for code construction at $10 a year. Yes - the incredibly loose houses that are built only cost $10 a year for cooling cost (from infiltration). I think heating was $20 or so in my zone. Either way it was significantly less than $50 a year. So tighten to 1/2 of code and you are down to diminishing returns. I think our house wound up being 1/2 of energy star standards.

On basements, it is easiest (cheapest?) is that walls are insulated on the inside when they are framed. Sure foam on the outside is better ... but again diminishing returns. Underslab is a little overkill in our climate.

On the attic - you should keep the ducts out of there and then just blow some r-40 or so up there.

You will not find anyone in most of the rural south who will build a tight house. The priority isn't there. The overwhelming priority is window placement (that hasn't been mentioned).

    Bookmark   August 17, 2012 at 10:03PM
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Even if it serves not much purpose as insulation, EPS Type IX or XPS under the slab on top of a poly vapour barrier would still be useful as a vapour retarder.

I'm currently living in a 3,700 sf 1964 home with no foam under the basement floor or on the walls. This summer we have two dehumidifiers running 24/7 to keep the air there dry. This is twice what was necessary in our previous basement that had XPS insulated walls.

Here is a link that might be useful: Enclosures that Work: Mixed Humid Climate

    Bookmark   August 17, 2012 at 10:43PM
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Great info! Those are important points bc we do not want to spend money for diminished returns. Can hubby and I do some of the sealing ourselves (he's got DIY experience) with some good resource to go by, or should we just hire someone from a metro area in to handle this? If it is hired out, what certifications or credentials should we look for? This is probably a silly question, but do insulation subs do this or are these folks in their own category?

As far as windows, our plan (stock) fortunately has an abundance of windows on the side that will be south facing. We are hoping to take advantage of some passive solar principles just because it is seeming to work out that way anyway.

All of this is like a foreign language to us, but because it is our forever house, I want to learn all I can and have few regrets.

    Bookmark   August 17, 2012 at 10:44PM
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Where are you? A lot of South windows can be a bit overheating.

The biggest issue and sometimes hard to rectify is what SHGC to have on the windows (sometimes varying them throughout the house). SHGC- solar heat gain coefficient. A higher number heats the house more (for better or worse). Usually you want a higher number on south windows and lower on east and west but it is always a compromise.

I just want to share my house because it illustrates the difficulty of modeling. I never really knew where I lived on the zone map until I just checked - I am zone 4 with zone 3 20 miles to the south - so we are neighbors.

My energy audit based on code house with our orientation and floor plan was $1450 heating and $450 cooling. We did some things to upgrade but stayed with 2x4 walls with batts. This year we are at about $300 heating and $300 cooling. Last year was a bit more on both but the ratio was the same. What surprises me is how different the ratio is compared to the modeling. We did finish the basement over the last 2 years also and our bills only went down (weather?). I guess my point is that energy audits don't have all the answers. We have 4000 sqft and 1400 in a walkout basement - zero south windows. Our window wall is to the East with trees to tame it a little.

As far as sealing, I did most myself. The insulators did foam the windows and doors - although I had to do the basement myself when we finished it. Our insulators did it for quite cheap so it was worth it - just not pulling out the fiberglass was worth it. The other stuff I would do yourself. If you are really trying to be tight, there are some areas to foam that maybe worth paying for.

    Bookmark   August 19, 2012 at 5:52AM
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Just a note on advanced framing. It may not be acceptable in your specific location due to wind or seismic conditions.

Are you saying advanced framing possibly should not be used in high wind speed areas ? What is the generally highest accepted wind speed that you can use advanced framing techniques ? Our area is 130mph, but we tried to build our house to 150mph minimum. We did not use advanced framing, although we are considering it for the next house. Sounds like I should drop that idea for the next house ? No seismic concerns in our area.

    Bookmark   August 19, 2012 at 8:07AM
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David - nice to meet you neighbor! We live and are building halfway b/t Memphis and Nashville. It also appears that your house is within 300 sq ft of the one we are building, so your experiences are worth heeding!

I have read some about the SHGC being different on the various windows, but have a lot more to learn. Do you think it would be worthwhile to look into this issue more and price these windows? I just hate not to take advantage of all that energy that could be harnessed in the winter.

Is there a comprehensive resource that lists everything that should be sealed? What product did you use? What is you opinion on foam board on the outside of above grade walls in our climate? Waste of money?

Also in light of worthy's post regarding under slab foam and vapor barrier to control humidity, what are your thoughts? Unless you live in the south it's hard to understand the extreme heat and humidity in the summer, and how darn cold (to me at least) it can get in the winter. Being energy efficient is priority one, but a warm and dry basement is the second.

Worthy, thanks for the tip about advanced framing. I am really hoping we can do it b/c it seems to have many advantages. I had thought that wind shear was influenced more by the sheathing; I guess I misunderstood.

    Bookmark   August 19, 2012 at 9:14AM
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Windshear is a function of both sheathing and framing. You are probably far enough inland to not be a problem. I would not try and build in a 150 mph area with 24 OC. They wouldn't allow that on the NC coast for sure.

There is a good resource on sealing but I forget where it is.

Foam board on above grade walls is not a bad idea, it just is a little overkill with 2x6 walls. Partly depends on your heating fuel as far as ROI. I think my return on a 2x4 wall was about 15 years. On a 2x6, it would be more like 25 years. If you have a good southern exposure, of course the return is even greater since you are using free fuel more of the time.

SHGC is really tough issue to get right. Sometimes building codes limit how high you can go even if it helps in the winter. Certain windows are not sold in the South because the heating load is so low. It takes a lot of patience and research to see what is available in your area. Energy star certification prevents you from doing any higher SHGC windows because they don't account for orientation and varying SHGC throughout the house.

    Bookmark   August 19, 2012 at 2:12PM
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Great advice above. Someone has to bring up the permanence of the building envelope so it might as well be me. Building envelopes are the most permanent part of the structure, hardest to correct and improve once complete and will influence the energy use of many families and generations to come. While ROI is certainly important, being mindful of rising energy costs and the future impact of your decisions is important too.

The difference in energy performance between advanced and typical framing is so small that its usually not worth the trouble in my opinion. Insulative sheathing, SIPS, ICFs and some pre-cast concrete panels (that come with foam sheathing) however can have a huge impact on energy costs. I think their increased benefit has as much to do with their air-tight properties as better insulation. Youre right that sheathing plays a bigger role in strength than advanced framing which is one of the many reasons I prefer SIPS.

Insulating under slab in Zone 3 is a tough one. I would tend to think its not worth it but would look to energy modeling to influence this decision.

Passive solar design is absolutely worth including in your location especially if you already have a good site for it. If you do it right its free, increases passive survivability(comfort during power outages) and better daylighting and contentedness with nature. Free, clean heating is tough to beat and pay very close attention to your overhang details to combat overheating.

Here is a link that might be useful: Green Building Advisor article; Cost Effective Passive Solar Design

    Bookmark   August 19, 2012 at 2:57PM
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Would like to add that Occupant Behavior is a huge factor in energy modeling. David gets some pretty low energy bills probably in large part because of his energy awareness. A different family in the same house could easily have 3x the energy costs.

    Bookmark   August 19, 2012 at 3:03PM
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David, was this directed to me ? Windshear is a function of both sheathing and framing. You are probably far enough inland to not be a problem. I would not try and build in a 150 mph area with 24 OC. They wouldn't allow that on the NC coast for sure.

Our house we built last year is oceanfront. Our zone is 130mph, but for the most part we built to 150mph (or better). There were several things we did to achieve that ... all stainless nails & fasteners, hurricane windows, special nailing patterns for framing and roof deck, entire roof deck has self-adhering (peel & stick) underlayment, higher mph shingles & siding, hurricane ties, strapping that wraps over the roof rafter trusses all the way down studs and wraps under the lowest horizontal foundation truss, foundation trusses bolted to foundation pilings, wall sheathing to create shear walls and impact resistance. That's all I can remember off the top of my head.

We hopefully will be building again one year from now, so I am on the search again to expand my knowledge of building standards. Good to know advanced framing is not allowed on the coast, I can cross that one off my list.

By the way, we have an oceanfront lot we own with my mom & stepfather who have now divorced. So, we have it on the market for a great price if anyone is in the market they can email me from 'my page'.

    Bookmark   August 19, 2012 at 5:18PM
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The old Occupant behavior - makes a huge difference. I will say that the wife and I sleep at 66 degrees - in the summer and a bit lower in the winter. So we are not perfect.

The flip side to future energy costs is that they could actually go down... One never knows. The other issue is that there is a lot of energy used to make foam. In the right climate, it can take 50 years to recover that.

And then global warming can make a lot of that insulation seem like overkill.

But structure is definitely long lasting and in general it is not built well enough.

As far as occupancy behavior, no amount of air sealing can make up for leaving windows open...

    Bookmark   August 19, 2012 at 9:40PM
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