typical hi RH-winter, here

[cem-bsee]

at 6am, dry bulb= 23F, wet= 21F = ~95%RH
so,
sealing attics & crawlspaces prevents sucking in moist air;
probably best to forget vapor barrier --

this hi RH will typically be until 10am --

so,
don't make firm statements that one should draw in outside air;
unless
it is conditioned --

[motoguy128]

It's 95% RH... the key term is RH. That amount of moisture at the indoor temp of 70F, is only around 25%RH if I read my Psychrometric chart right.

A <25F dewpoint is still pretty dry.

Maybe I'm understanding your statement wrong. As a pro, I'd think you'd know this already. The saturation point of air it terms of how much moisture it will hold decreases as temeprature decreases. So saturated air at 20F, hold 1/4 the amount of moisture as air at 70F.

Ideal conditions of 40-45% RH at 70F is a dewpoint of around 45-50F. So to better understand this, if the home is an idea 45% RH at 70F, then any indoor surface that is <50F will have moisture on it. This is why windows have moisture at low outdoor tempratures.

[beenthere]

I could be wrong.

But, at 23°F DB and 21°F WB the RH is 75.1%, 13.0588 grains per pound of air.

At 70°F DB and the same 13.0588 grains of moisture, it would be 12%RH.

According to my Carrier chart.

[Shophound]

I could be wrong.

But, at 23°F DB and 21°F WB the RH is 75.1%, 13.0588 grains per pound of air.

At 70°F DB and the same 13.0588 grains of moisture, it would be 12%RH.

According to my Carrier chart.

You are correct on both counts.

cems-bee wrote:
so,
sealing attics & crawlspaces prevents sucking in moist air;
probably best to forget vapor barrier --
this hi RH will typically be until 10am --
so,
don't make firm statements that one should draw in outside air;
unless
it is conditioned --

Beenthere (along with motoguy) is correct again, in that drawing in air under the conditions you gave is still dry air, and will lower indoor RH levels if not humidified (or if indoor moisture generation is low).

Any vapor barrier, to my understanding, should be on the drainage plane of a wall (behind the siding or cladding, in front of the sheathing), not on the interior. Housewraps are air and liquid moisture barriers, but allow vapor diffusion (allowing a wall cavity to dry to the exterior as well as to the interior).

[ampulman]

You are correct on both counts.

Any vapor barrier, to my understanding, should be on the drainage plane of a wall (behind the siding or cladding, in front of the sheathing), not on the interior. Housewraps are air and liquid moisture barriers, but allow vapor diffusion (allowing a wall cavity to dry to the exterior as well as to the interior).

How about fiberglass insulation w/paper vapor barrier, applied to the sill (not sure if this is the correct term, but is first wood above grade on top of cinder block).

The barrier is on the inside face of the insulation.

Thanks.

Amp

[Shophound]

How about fiberglass insulation w/paper vapor barrier, applied to the sill (not sure if this is the correct term, but is first wood above grade on top of cinder block).

The barrier is on the inside face of the insulation.

Thanks.

Amp

Do you mean something like this, where a framed stem wall sits on top of the basement wall or crawl space wall? :



In the drawing, notice the lack of a vapor barrier to the interior, and why. The interior plane shows drywall painted with latex, to allow drying of the wall cavity via vapor diffusion to the interior.

If you're speaking about a different configuration (such as an above grade block house) please specify where this is found in the house.

[ampulman]

Do you mean something like this, where a framed stem wall sits on top of the basement wall or crawl space wall? :

Yes, this is a basement w/10 ft cinder block walls. The cinder block extends about 1.5 feet above grade. There is an attached crawl space which has the same treatment.

In the drawing, notice the lack of a vapor barrier to the interior, and why. The interior plane shows drywall painted with latex, to allow drying of the wall cavity via vapor diffusion to the interior.

The basement is unfinished; hence no interior walls.

Would I assume correctly, that my 'configuration' doesn't pose any problem?

Thanks.

Amp

[Shophound]

Yes, this is a basement w/10 ft cinder block walls. The cinder block extends about 1.5 feet above grade. There is an attached crawl space which has the same treatment.



The basement is unfinished; hence no interior walls.

Would I assume correctly, that my 'configuration' doesn't pose any problem?

Thanks.

Amp

The fiberglass batts...are they attached to the basement wall, or the crawl space wall? Is the basement wall exposed block, or does it have a framed wall in front of the block to contain insulation? The crawl space...is it ventilated? Is the floor over the crawl space insulated?

[motoguy128]

I could be wrong.

But, at 23°F DB and 21°F WB the RH is 75.1%, 13.0588 grains per pound of air.

At 70°F DB and the same 13.0588 grains of moisture, it would be 12%RH.

According to my Carrier chart.

That's probably right. I just "eyeballed" a chart I found on google that wasn't specific to HVAC. The Carrier chart is probably a little more precise (easier to read). I had to convert from celcius as well.

[ampulman]

The fiberglass batts...are they attached to the basement wall, or the crawl space wall? Is the basement wall exposed block, or does it have a framed wall in front of the block to contain insulation? The crawl space...is it ventilated? Is the floor over the crawl space insulated?

The basement wall (cinder block) is below grade, with the exception of about 1.5 ft. On the top block (above grade), there is an approximately 2 x 5" board laid flat, on which 2 x 8 joists are placed. At the top of joists is the first level sub-floor. This (8") is the space which contains the (kraft paper inward) faced fiberglass. This is all open to the basement.

The crawl space is basically the same, except that the joist level is split (lowered) from the main (first floor) about 8". The crawl space is under a section of house which has no second floor, and contains heating ducts, pvc furnace vent pipes, and plumbing.

There is fiberglass (about 1") board on the walls; some thick material on the floor. The space is open to the basement and is not vented to the outside. It is on the cool side.

Thanks.

Amp

[cem-bsee]

read about vapor barriers at BUILDINGSCIENCE.com

so, I did not carefully note my dry bulb, I focused on the wet bulb & RH%.

nevertheless, every thing I have heard or read from the health 'experts' is that RH% should be kept between 35 & 55%.
No body stated that it was dependent upon temperature.
so, maybe my bdrm @ 57F does not have much moisture per cubic ft, but it is still on the high side [60+ percent], especially during the early morning --

[beenthere]

If you know WB and RH, you can find/determine DB.

[cem-bsee]

why look-up or calculate when I can just read my instrument?
I suspect that I did my first look-up in 1961 --

again, what is your 'take' on RH% needed ID for good health, even at 57F?
at 67F?

[beenthere]

I said calculate it, because if you only keep records of WB and RH, you can use them to know what it was in those years that you didn‘t track DB..

I don’t believe there is one set range of RH for everyone.

If in the heating season, you wake up in the morning, and your throat is dry and scratchy. Your RH is too low for you. And that is unhealthy.

Same way, if you wake up and your sweating, its to high, or the temp is too high for the RH.

If you set your humidistat at a setting that both keeps the dust down, and your throat from drying out. Plus your not condensing or frosting up your windows. That’s the RH that is probably best for you, and your home.

[teddy bear]

read about vapor barriers at BUILDINGSCIENCE.com

so, I did not carefully note my dry bulb, I focused on the wet bulb & RH%.

nevertheless, every thing I have heard or read from the health 'experts' is that RH% should be kept between 35 & 55%.
No body stated that it was dependent upon temperature.
so, maybe my bdrm @ 57F does not have much moisture per cubic ft, but it is still on the high side [60+ percent], especially during the early morning --

Here is what we are all tring to tell you. You need a little some of that 23F, 95%RH air in your to get you bedroom below 50%RH. When home have high %RH during cold weather, they are not getting enough fresh air to remove the moisture generated by the occupants. You need an air change every 4-5 hours to pruge the indoor pollutants. That would make your home dry when the outside dew point is below 32^F, 100%RH.
Its about the water content of the outside air. A plastic bag of 32^F100%RH, 32^F dew point warmed upto 57^F is 40%RH.
You are not getting enough fresh air into your home remove the moisture. A couple in a +2000 sqft. home will with an air change every 5-6 hours will be a little on the dry side, <35%RH with a 23^F outdoor dew point. Generally, homes that are getting enough fresh air during cold weather are dry. You know the rest of the story. Homes that are getting enough fresh during wet high dew point weather are wet, unless they have 30-70 lbs. of moistue removed per day (a/c or dehumidifier). During 65^F outdoor dew points, a properly venitlated home needs +30lbs. of dehumidification per day. Regards TB