Insulation + vapor barrier (new Seattle home)

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

HRVs seem economically iffy even for R2K houses. Maybe an IDEAS house...

Nick

And what do you gain by running an HRV with equal indoor and outdoor temps?

Nick

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

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

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 ma>

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).

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.

Mart> Sorry about html.

Quite useless compared to an exhaust fan for a US house, IMO.

Nick

I would like to hear why you think it is useless.

I am keep>

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

1. 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

1. 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.
2. With equal indoor and outdoor temps, an HRV will save no energy, compared to an exhaust fan.

Q. E. D.

Nick

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.

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.

No 4) to comment on

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

For many years the building envelope of a home had the integrity of Swiss Cheese.

The 5 cfm standard came from 19th century mine ventilation... a productivity enhancement--below 5 cfm, coal miners fell asleep.

Nick