Share your experiences with super-insulation?

mulchieFebruary 7, 2013

We're looking for some on-the-gound wisdom about super insulated homes (heating, cooling, etc.) as we move toward building a 2,000 sq ft house in zone 4b with r-40 walls and r-60 in the roof. South, Southwest orientation.

We have looked at geothermal with radiant and are now exploring ductless mini-splits which seem to get good reviews.
House will have a good air exchange system and triple pane windows.

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Thats great Mulchie. Youre way ahead of the majority when it comes to building a home with very low energy and environmental costs. Your concentration on high insulation values is a great first step and perhaps more important than that is how airtight you can get the super insulated structure.

One of the best aspects of building new is that its much easier to create an airtight, continuously insulated building envelope. This is usually much more cost-effective than most renewable energy technology especially considering there is no maintenance. Passive solar is an easy, low cost way to dramatically reduce heating costs and increase passive survive ability if you have the right site.

As the envelope gets more efficient, renewable and HVAC systems can be downsized which makes them more affordable. Geothermal is great, but paybacks can be a long time and a lot of the listed COP numbers dont include the circulating pump's energy demands.

Radiant can be more troublesome with high performance homes as there is a long lag time between thermostat adjustments. If you are in a humid climate, keep in mind that radiant will not contribute to cooling and is a very large upgrade for a highly insulated passive solar home in a zone 4 climate.

Lots of high performance homes are going with Mini-splits these days and there's a decent thread going in the Building a Home forum. Getting the building envelope right will take some up-front planning and I would suggest getting a competent energy rater and builder involved early in the process.

    Bookmark   February 19, 2013 at 11:05AM
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Hi, Brian- Thanks for your reply. I've been doing a great deal of research and everything you say rings true. We were looking at geothermal and radiant and have completely backed away from that approach in favor of... mini splits with a Zender air exchange system.
It has been a journey and we haven't yet broken ground. But you're quite right, building new allows you to really control all these decisions and design a tight envelope. We have a south-facing lot, so that maximizes our ability to use passive solar. ... I'm not sure I'd enjoy the process as much if there weren't all these variables. It's fascinating and the potential is terrific. Unfortunately, still expensive compared to conventional builds
We've got a good energy rater on board.
Where are you? You sound as though you are very experienced.

    Bookmark   February 21, 2013 at 8:40PM
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Thats great! Thanks, Iam in Western North Carolina.

I dont think its necessarily more expensive to build high performance but as you know, the details and variables are immense. Luckily, it can all be broken down and I think most of the hard work is behind you.

If you build to the minimum energy codes (IECC 2012), then you are in a way, building as cheap as the law would allow. This reasoning ignores that local jurisdictions dont adopt the broader codes but in a way, shame on them.

I feel building to this level as a minimum is a very cost-effective approach. It will make for a comfortable, energy efficient home with healthy indoor air quality. Its tough to put a price on the health benefits.

    Bookmark   February 23, 2013 at 9:08PM
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Mulchie, while I am in central NH, CZ 6 (7500 heating degree days), a lot colder in general than where you are, I have a superinsulated house, and I applaud your interest in building one. In general terms, it has R40 whole wall exterior walls, double frames and 12" cavity; attic is R60, slab and foundation walls are R20, and windows are triple pane. Heating is via ground source heat pump (aka "geothermal"); that was a good choice for us, as we were putting in a new well for water anyway, and no extra drilling was needed to support the heat pump. However, a superinsulated house loses or gains heat so slowly that almost any heating system can be used, and its operating cost will be low. In my case, size is close to 4000 sqft, and the heat pump is just a two-stage, two-ton, and slightly oversized at that for winter operation, as it keeps the house at temp easily without going to second stage. For summer A/C, it's oversized by a factor of at least two. Heating season cost is around $600, for a normal winter. In your CZ 4B, a minisplit likely would be a good choice, with good year round average COP 3 or better.

I am completely happy with the performance of the house. It is very comfortable, has no drafts, and is very quiet. For a new house, going the superinsulated, or at least very highly insulated route doesn't cost all that much more. The usual number I see is about 5% more over "conventional" construction. I see it as a good long-term investment, in terms of both operating cost and comfort.

    Bookmark   March 3, 2013 at 7:06PM
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Thanks for sharing your experience. I'm very encouraged by how much you enjoy your new house. Could I ask what window manufacturer you settled with and why? That's a difficult part of the process, for sure.
We believe we'll be fine with a single mini split, but we are building in the capacity for a second in case this seems insufficient. We've done all kinds of projections and moved away from geothermal as a case of classic overbuilding. It's daunting how many details interrelate! But it's great to hear you are so happy with the outcome. Thanks for your reflection.

    Bookmark   March 4, 2013 at 3:51PM
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I used Thermotech Fiberglass (Canadian). They are a mix of mostly casements and a few fixed glass. They certainly are well made, but maybe the most expensive. Since I selected them three years ago, some other decent ones have appeared in discussions on and the building science forum of I don't recall the names of the newer ones that seem to be liked. One builder of double wall houses in Maine spoke of problems with after sale service from Thermotech Fiberglass.

    Bookmark   March 4, 2013 at 6:50PM
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For the last two years, I've been super-insulating with 4" and 5" sheets of polyiso a 1917 1600 sf house on the coast in the Pacific Northwest with r-50 attic and r-30 walls.

What I have learned so far is to be obsessed about air infiltration. Seal, fill, plug everything! Make sure air can't be exchanged between inside and outside unless you control it. even pin sized holes must be addressed. Be careful how you do vapor barriers. In my climate, you want indoor moisture to migrate out but not so that it can condense inside your walls. The only VB will be the paint on the walls. The polyiso is not foil faced in order to avoid trapping moisture inside the walls. The siding is vented behind it to provide extra drying during the rainy season and to provide air to the housewrap to help wick moisture away.

The house started out with ZERO insulation, aluminum single pane windows, and vinyl siding. So far I have replaced the roof, siding, windows, two of the three doors, and insulated the attic and a small part of the outside walls. I'm now gutting and upgrading room by room and expect to finish in another three years. The results have been pretty dramatic already. Even now, the house actually stays cool during our rare summer heatwaves and there is no draft anymore during the winter. My heating bill has not dropped dramatically yet due to no wall insulation but the house is much more comfortable at the extremes of weather. I'm very happy with how the project is going and expect to cut my energy usage by half by the time I'm done. When completed, the insulating and weatherizing aspect of the project will pay for itself in about three years as I'm doing all the work myself.

    Bookmark   May 27, 2013 at 9:14PM
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Be careful with spray foam. The practice of putting it on the underside of the roof decking has the potential to cause serious rotting of the deck and trusses down the road. All roofs will eventually fail. Many fail while still looking good. Regardless of what they say about the foam being permeable, I have never seen a foam sample that water will pass through. A roof leak will trap the moisture between the foam and the wood to do it's mischief unnoticed. Regular insulation will let the leaky roof announce itself with spots on your ceiling, much cheaper to fix than wholesale rotted decking and trusses.

    Bookmark   July 29, 2013 at 7:43AM
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Agreed. Foam does present its own problems. I would not spray foam directly to the underside of any roof. On my house, only the bottom sections of the roof has foam between the rafters and that is gapped 3/4 inch directly underneath the sheathing (the roof itself is 12/12 pitch). The upper half of the roof is open attic with the foam sheets lying on the ceiling joists. Any leaks on the lower half of the roof will hopefully be dried by the air moving from the soffit vents into the attic. My roof is two years old and has no leaks, so I would not be too concerned for quite a few years.

It is, however, a potential problem that needs to be considered. One option I have considered is buying or renting a fiber optic camera and periodically checking each rafter bay for leaks, perhaps every two years or so. I don't see too many other options to make sure the roof is not leaking in those parts that cannot be directly visually inspected.

    Bookmark   August 5, 2013 at 1:00AM
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Windows on Washington Ltd

In high efficiency type homes, I like the ideas of above deck venting or at minimum, some sort of SIP design to the roof deck to eliminate the thermal bridging.

    Bookmark   August 17, 2013 at 10:06AM
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