Insulating a Victoria Cottage Type House?

[sjdehner]

John,

Moving along with what we talked about earlier, and jumping straight to topic, I'm wondering if you'd be willing to discuss your opinions re: insulation in general and in particular insulating a small house, like the Victoria Cottage.

I'm curious to know if you feel that a small house like this could be too tightly insulated? Or, rather, do you think it could never be insulated tight enough, simply under-ventilated?

With less potential for air-leakage, a small house would (presumably) be easier to make air-tight. On the other hand, being so small, an air-tight state in such a house might not increase efficiency a great deal or conceivably lead to a complication like back drafting.

With that in mind, and coming full-circle, I'll return you to the opening question before posing a second.

Thanks,

Shawn

[rwanders]

IMHO the size of the house doesn't affect your ability to make it airtight----only material requirements and labor time really come into play. I also feel that "too airtight" is not actually achieved very often. It seems to me that a successful attempt to make your house truly airtight becomes self-limiting since you then need to provide mechanical ventilation to overcome what you just labored (and paid extra $$$) to get. I am a firm believer in spray foam insulation for the best way to achieve "near air tight" construction though it is somewhat expensive and not a good DIY task. I prefer closed cell polyurethane for its high vapor impermeability and found it especially good at overcoming the problems of insulating and ventilation of cathedral ceilings. Trying to achieve high R ratings in that design while having enough ventilation space, even with 2x12 rafters, is really difficult----using 11" of CC foam sprayed against the roof sheathing eliminated the need for the 2" ventilation spaces and ridge vents on a metal roof as well as a separate vapor barrier while getting at least R50 insulation values.

[sjdehner]

Rwanders:

My wife and I actually have an open-cell foam insulation (Icynene) in the house we are currently building, which has more than 2500SF of heated air space (including the basement). We also have a heat-recovery ventilation unit. It's a great combination: our energy bills are small and the house stays comfortably warm.

The HRV unit was a mere $800 plus some ducting, so the expense is almost negligible if we simply consider it as a portion of the overall cost of insulating our house. Plus it's beneficial to have an air-exchange during the winter months regardless of insulation type.

From the negative feedback we've heard locally about the closed-cell foam called Corbond (persistent odors, fading R-value, extreme rigidity, et al.), we'd not use it. Perhaps other closed cell foams are different. Whatever the case, we still think Corbond would be a more efficient choice than, say, traditional fiberglass batting, since it creates an air-barrier. And I can see why you'd like a closed-cell foam if you are looking for a vapor barrier.

But what do you think about an air-tight house under, say, 1000SF?

Shawn

[rwanders]

Some of the earlier versions of closed cell did have their problems and are still sometimes sold----not familiar with Carbond brand and there seems to be many brands marketed----a drawback to the Icynene is the relatively low R values per inch and need for a separate vapor barrier. However, I agree it is still much better than fiberglass. I don't see any barriers to building an "air tight" 1000 ft house. If the payback rate justifies the upfront investment----go for it. All the choices we make while building include compromises on many levels.

[sjdehner]

I suppose I should be more specific about locale.

The house we are currently building is on the Maine coast and our heating degree days are less than the vapor-requirement recommendation from Icyene. Northern and interior Maine are much colder and would likely install a vapor barrier.

When I posted the question about making a small house airtight I was not specific about location. I'm thinking about this small house situated in Western Washington (our home) where we experience around 5000 heating degree days.

I expect the house would still benefit from an airtight insulation but thought I'd see if I could get some other thoughts.

I really dislike fiberglass batting, which my wife and I installed on a remodel and outbuilding a couple of years ago. The batting did not work all that well (certainly not like the spray-foam), and especially so when the winds picked up (we lived on an open 1/2 acre 5 blocks off the water). We installed a formaldehyde-free batting, a plus, but they were terribly dusty, a definite minus. Frankly, when all's said and done, I just do not think fiberglass makes a good home-insulating product.

Our home town is closer to Vancouver, BC than any US city, so we had access to Canadian products like Roxul batting (slag wool). But I read the ingredients list (the MSDS) on this product and it has a high formaldehyde content, which I find unappealing, especially in a tight house.

Cotton batting is still interesting to us but it seems a risky endeavor in a wet climate like the Pacific Northwest. Built right I suppose a house should not have moisture in the walls but we do have our concerns regardless.

Closed cell foams from what we've read deteriorate rapidly over time; that is, they give off gasses to the atmosphere and suffer a decline in efficiency. Icyene is chemically inert, which I find attractive: what you pay for is what you get for the life of the product.

Another product that is popular locally is a wet-blown recycled newspaper that creates an air barrier. It's touted as an inexpensive and effective insulation (and it is both I think). However, we did speak with a retired builder who had used the product previously in Maine. He had a story - nightmare - to tell. We forget the circumstances, but the insulation got exceedingly wet (thanks to a frozen pipe perhaps?) and it was utterly ruined. Again, in a wet climate like the Pacific Northwest, this might not be the wisest of choices.

Icyene is still petrol-based, which I do not think ideal. But as you say, one has to make compromises along the way. Spray-foam is also not a DIY product, like batting or foam boards, but the end result I expect is the best thing going since you get a complete air-barrier, which will help retain the true R-value of the insulation.

Moisture too could reduce R-value, so there's an argument for closed-cell foam; but then again an open-cell foam such as Icynene is still not going to allow much moisture anyway. The company states you MAY need a vapor barrier in extreme climates, like Madison, WI, e.g. And we've not read any reports of problems associated with Icynene.

In Western Washington it seems Icynene might be a good choice. But then again we are also biased since we are currently using the product and are pleased with its performance.

If you've got any further thoughts I'd be interested.

Thanks.

Shawn

[MountainDon]

Have you looked over the information on BuildingScience?

They have approached building design from the standpoint of different needs for different climates.
Designs That Work


a note: we would have used cellulose, the blown in wet type, in the walls of our cabin if we could have found an installer that wanted to do the job (remote location, bad roads) for a reasonable price. I believe it does a great job of sealing in the corners and pipes, etc. We settled for fiberglass.

[John Raabe]

For a high-efficiency superinsulated house you need to do these things:
• high R-value insulation of 5" or thicker in walls - more in floors and roofs
• air sealing and controlled ventilation in and out. In cold climates this means heat transfer through an air exchanger.
• high R-value windows appropriately sized and oriented for use and control of solar inputs (heating and cooling)

For years doing a good job on air sealing was tricky (see my 1980's book), especially in a house (like the Victoria) with lots of corners and sloped spaces. Your positive experience with Icyenene confirms my feeling that this a a great product to combine air sealing and high R-value insulation. While it isn't a DIY product itself it can effectively seal DIY framing.

Building Science has great science but their building systems can often be simplified for milder climates.