Insulation + vapor barrier (new Seattle home)


Lots of good posts in this newsgroup but could not find the answer. Here is my question:
Considering our Seattle climate, where the temp outside the house is below 70F for some 5 months of the year and above 70F during the other 7 months and humidity is fairly moderate, what would you recommend for the optimum insulation material and how would you deal with the vapor movement (one local insulation contractor suggests no vapor barrier within the wall but rather on inside of the sheetrock; he also suggests staying away from spray-foam saying that air movement is very much needed)?
I am definitely considering installing a Heat Recovery System to ventilate the house as much as needed. Other than that I am for installing a system which works well and has value (good bang for the buck). I don't mind spending extra if I can recover the cost (by lowering energy bills) in 5 years or so. Fiber bats and spray foam are my choices (as I don't like the duct-effect of blown-in very much).
This new 2-store house will be on crawlspace, will have 2X6 exterior walls (per local code) and a combination of attic and cathedral ceilings. I will have radiant heating floors on both floors and AC installed only on the second floor via attic (lots of open spaces for the cold air to drop down).
Any suggestions would be appreciated.
Thanks much.
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First, don't post in html.

Second, Seattle is mostly cool. NREL says the average yearly temp is 52.0. August is the warmest month, with an average 65.2 F and a 75.2 F daily max. So I'd put the vapor barrier on the warm inside, or use SIPs.
Third, you won't save much with an HRV box, compared to an exhaust fan, IMO. If a 2000ft^2x16' "airtight" US house naturally leaks 0.5 ACH, ie 0.5x2000x16/60 = 200 cfm, enough for 13.3 ASHRAE standard full-time occupants, you will rarely need mechanical ventilation. How many days per year have no wind and equal indoor and outdoor temps for more than an hour or two?
HRVs seem economically iffy even for R2K houses. Maybe an IDEAS house...
Nick
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And what do you gain by running an HRV with equal indoor and outdoor temps?
Nick
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Sorry about html. Good suggestions. Thanks. SIPS are unfortunately not in my picture as: - the structure of the house is complex (turrets, roof, ...) - many subs in the area are unfamiliar with the product and will bump up the price of their work - SIPs themselves will cost me much more than 2X6 frame
The main purpose of HRV was to ventilate out the bad air and bring fresh (basically a more sophisticated whole-house-van). I guess I don't care much about the HR factor but I would want a good ventilation. My current house (remodeled 1950) has many new walls, insulation, etc. and rooms that don't have cold air return and are closed for some time seem to have a bit unpleasant air in them.
Thank again.

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2x6 walls with R19 would be adequate.
Your only rooms without cold air returns should be bathrooms, the kitchen etc, there should be returns in hallways to compensate for this.
If you are going to be thoroughly sealing the house, then an HRV scheme sized roughly for 0.3 air changes an hour would give good IAQ, without creating drafts or depressurizing the home.
Martino wrote:

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Quite useless compared to an exhaust fan for a US house, IMO.
Nick
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I would like to hear why you think it is useless.
I am keeping windows open throughout most of the year in my bedroom but in winters and during really hot summer days the rest of the house has closed windows. The new house will be even more sealed due to the more careful construction process and either spray foam or sealed (for vapor barrier) sheetrock. I cannot imagine only removing air from bathrooms and kitchen; it seems to me like a source of fresh is not only needed but also a must. There will be an AC fresh air inlet but A/C will be installed only on the second floor + I will only use it some 4 weeks of the year. HRV seems like a good contender here.

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1. ASHRAE says each occupant only needs 15 cfm of fresh air, so a family of 4 in residence 50% of the time only needs 30 cfm, ie 30x60/(2400x8) = 0.094 ACH for a 2400 ft^2 x 8' house.
2. An average US house naturally leaks about 0.7 ACH. An Energy Star house might leak 0.3. A few SIP builders guarantee 0.2. Building a US house with 0.094 ACH would be painstakingly heroic and very expensive, IMO.
3. If natural air leaks supply 2-3X the ventilation required, a mechanical ventilation system will be mostly unemployed, except on days with no wind and equal indoor and outdoor temps.
5. With equal indoor and outdoor temps, an HRV will save no energy, compared to an exhaust fan.
Q. E. D.
Nick
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In Canada, they routinely build houses to code with natural air change rates of 0.35 per hour or less.
If your contractor is incapable of building a well sealed home, then you will not need special mechanical ventilation to control indoor humidity in the winter, in fact you may need a humidifier.
If you are building an air tight home, an HRV or perhaps even an ERV is the best way to go.
I base my comments on my experience with 100s of homes -old, new, even those built to the R2000 and higher standards. These homes are in a climate colder than Seattle, however similar codea and systems to what I am accustomed to are in effect in Vancouver and Victoria BC.
1) A 30 CFM ventilation rate for a 2400 sq ft home is bad advice.
2) It is truly sad that they cannot seal a home in the USA. If the house is that poorly sealed then buy a humidifier. Nick will suggest you flood your basement floor in the winter to keep your drafty home humidified.
3) Nick still uses an outhouse with free natural ventialtion.
No 4) to comment on
5) Nick has a case for stating the obvious.
snipped-for-privacy@ece.villanova.edu wrote:

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IIRC, that's the current ASHRAE standard for a house with 4 occupants in residence 50% of the time. For many years, it was 5 cfm/occupant.
Nick
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For many years the building envelope of a home had the integrity of Swiss Cheese.
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The 5 cfm standard came from 19th century mine ventilation... a productivity enhancement--below 5 cfm, coal miners fell asleep.
Nick
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Have you studied the Building Science Corporation web site? They have reports on several test houses and reports on various aspects of building.
How are you dealing wtih the crawl space? A closed, insulated crawl space is worth looking at.
How are you dealing with duct work? Keeping it within conditioned space is worth looking at.
TB
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Good pointer. Thanks.
The crawls-space will be as closed as it can be but insulation is something I might think about. Are you thinking sides (like ICF) and bottom (instead of just a foil on the soil)?
No duct work in crawl-space: radiant heating floors and AC only on the second-floor. Crawl-space will allow me to access plumbing only. Slab might be an option but there is some elevation difference within the footprint of the house (some 10' on the 90' distance).

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Have you studied the Building Science Corporation web site? They have reports on several test houses and reports on various aspects of building.
How are you dealing wtih the crawl space? A closed, insulated crawl space is worth looking at.
How are you dealing with duct work? Keeping it within conditioned space is worth looking at.
TB
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