Does air tightness trump R value to some degree?

[Dutchman]

I ask because I'm living through the evolution of my house and am at the stage where it's getting tighter, but the r value is still not where it "should" be.

I finally have all new windows, (400 series, nothing special...all awnings and casements, pretty tight but not perfect) and at the beginnings of a PERSIST detail which is now at the point of 90% completion of the building wrapped with peel and stick.

What I'm noticing versus last season at this time (not all windows replaced, not fully wrapped) is a dramatic difference in heat demand and loss when it is used (just turned it on last week actually) and the actual "feel" inside.

The temperature is roughly the same inside as last year (65), but it's a different 65...it's quite comfortable. The humidity is very consistent at 35% and there are no noticeable cold spots in the house adjacent the old clunky vinyl double hung windows that are now replaced.

I completely agree and understand that we need thermal resistance in our walls (in any climate, and I'm headed that way) but I'm seeing a dramatic difference in the building with the simple effort of air tightness.

Are we putting too much emphasis on insulation when it's more about leakage?

In this model (because they are all different):
1. Coastal Maine, VERY windy in the winter
2. Cold, yup, got that one.
3. Wet, yup, just had sideways rain for 12 hours two days ago, maintained 35% RH inside.
4. Still has a clunky fireplace with no damper...the damper is a hunk of cement board taped over the opening when not in use with some Gorilla tape..leaks like crazy in reality.
5. Uninsulated basement floor, incomplete spray foam on basement walls....much to do.
6. Window detail on the inside: Drywall returns, zero air leakage after foaming or caulking window in place and then mudding it in...very tight other than the 400 series units that leak a wee bit.

I'll be monitoring my energy consumption as usual, but suspect that the air tightening will have a huge impact. After outsulation, badabing!

Have at it fellers!

[Mark Parlee]

Re: Does air tightness trump R value to some degree?

Dutch

Air tightness is critical to the performance of the wall assembly. If you have a wall that allows air to entrain the insulation this will seriously devalue the “R” of the wall because it diminishes the value of that insulation. We do need the thermal resistance in our walls but we want it to be actual value and not a value that is degraded to who knows what due to sloppy sealing of the wall cavity.

Give me a tight house with lees R value and it will outperform a home where you have a lot of insulation but the envelope is loose and allows a lot of infiltration.

[davenorthup]

Re: Does air tightness trump R value to some degree?

What Mark said. That's been my observation as well.

[dgbldr]

Re: Does air tightness trump R value to some degree?

Yup. Pretty simple and intuitive physics. If you give me a house insulated all the way around and let me blow frigid air in through a hole, it doesn't really matter what R value you insulated to.

[CASHCOW]

Re: Does air tightness trump R value to some degree?

R-Value is a measure of convection, one of the parts of heat transfer along with conduction and radiation. When you heat your house hot air wants to convect to colder outside air. Dry air is a good insulator, and if you fill the wall cavity with a material that creates small air pockets in it, these pockets are more efficient at reducing heat transfer by convection than the big air cavity. If the material is fiberglass or cellulose and it gets wet it becomes less efficient at convecting air or reducing heat transfer. They greatly reduce what is known as your walls' U value - which is a measure of how quickly they lose heat. The lower the U value, the slower heat transfer - and the less energy you need to keep your home warm. Good idea to keep the u value of your windows low too depending on what climate zone you’re in. Conduction is also reduced by dry air. Radiation such as foil on foam sets up a heat barrier to reduce moisture infiltration.

Outside of a reduction in cold spots the other thing you should notice in an air tight house is a reduction in air quality and stuffiness. There are codes based on how much air changes per hour (ACH) based on a blower door test. Both the 2012 IRC and IMC require mechanical ventilation when the air infiltration rate of the dwelling unit is < 5 ACH when tested with a blower door in accordance with the 2012 IECC provisions.

Some of it can come from range hood, in-line, bathroom, utility, etc.. fans depending on their CFM per watt efficiency. At some point to keep the air quality healthy you’ll need a forced ventilation system is required in houses with a natural infiltration rate less than 0.35 ACH if you ever get there. This is typically accomplished with heat recovery ventilation or exhaust fans running constantly or periodically. ASHRAE Standard 62.2.

[johnny watt]

Re: Does air tightness trump R value to some degree?

Let me be the first to answer the question.
Yes, yes it does.
In fact, not only does infiltration trump R-value to some extent for the most popular insulation/wall assemblies, it can easily trump it to a large extent.

This is especially aggravating in my area, where the arbitrary and capricious energy code is enforced for R-value but not for infiltration (other than to require sill seal).

But the good news is that this year electricity prices keep breaking record highs, coal industry is on the ropes, oil prices are climbing and natural gas is not being fracked in my state. So looks like reality may someday catch up with the ROI calculated in the "modeling software" that supports some of these home energy practices.

[Ted S.]

Re: Does air tightness trump R value to some degree?

Here's what I know. Attached is an average new home to be built. You can see where the loads are. Pretty compelling case, but sometimes I stand back and say to myself, is what the software says the same thing as reality?

Scan007.pdf

[dgbldr]

Re: Does air tightness trump R value to some degree?

R-Value is a measure of convection,

No it's not.

It's the reciprocal of the thermal conductivity of the material.

Radiation such as foil on foam sets up a heat barrier to reduce moisture infiltration.

No again. Foil is a radiant barrier and "heat barriers", whatever that may be, have nothing to do with moisture infiltration. Moisture infiltration is reduced with water barriers and/or vapor barriers.

Cashcow, you're new here and I appreciate your contribution. But you have been posting a lot of "science" stuff that contains a fair number of gross errors. Please post less and check your facts more.

[dgbldr]

Re: Does air tightness trump R value to some degree?

Attached is an average new home to be built.

Ted, your 3d biggest hitter is "Ducts". Does that mean you have ducts in unconditioned space? Pretty easy one to fix if you ask me :)

[Ted S.]

Re: Does air tightness trump R value to some degree?

Yes, dg. You are correct. I will say these houses are set to code minimums so that we are not relying on overly tight ducts and envelopes to pass on test day, typically 1-2 days prior to the closing. Not much time to fix things.

Many builders still have ducts in unconditioned spaces, although they are getting better about it. Keep in mind, these are every bit production houses, nothing fancy there.

It would be interesting to see this load summary with 2009 vs 2012 code minimums, maybe I'll do that if I get a moment and that will really shed light on Dutch's question.

[CASHCOW]

Re: Does air tightness trump R value to some degree?

No it's not.

It's the reciprocal of the thermal conductivity of the material.

No again. Foil is a radiant barrier and "heat barriers", whatever that may be, have nothing to do with moisture infiltration. Moisture infiltration is reduced with water barriers and/or vapor barriers.

Cashcow, you're new here and I appreciate your contribution. But you have been posting a lot of "science" stuff that contains a fair number of gross errors. Please post less and check your facts more.

I do alot of research before I post, not the best writer or speller in this difficult communication medium. If you don't find my post accurate or informative please stop reading them. I have alot to accomplish in a short time and will take the liberty as you and everyone else to post as often as I like. I read the rules not violation there, new or not.

If you read this you can debate R-Value with alot of folks out there if you want I'm not interested and have bigger fish to fry.

http://www.cellulose.org/HomeOwners/WhatR-valueMean.php

If you read this you find foil as a vapor retardant, again I am not interested in a debate have fun!

http://www.naima.org/insulation-know...retarders.html

[Ted S.]

Re: Does air tightness trump R value to some degree?

Actually foil would typically be considered a Class I Vapor Retarder provided it has a permeance of 1 Perm or less. However, many foils would have less than 0.01 Perms and therefore be referred to as a "vapor barrier"

[CASHCOW]

Re: Does air tightness trump R value to some degree?

Actually foil would typically be considered a Class I Vapor Retarder provided it has a permeance of 1 Perm or less. However, many foils would have less than 0.01 Perms and therefore be referred to as a "vapor barrier"

Got it! Least your nice to noobs that make there best efforts to research something new and may not get all their facts right, thank you for that you have been a great help to me and I appreciate it. As you know I come from a different world many of you might struggle with but I have and would always help.

I've never looked at foil this close except yesterday with a turkey on it....I don't what R value it had but it sure was gooooooD! :)

[Ted S.]

Re: Does air tightness trump R value to some degree?

Its always tough being the new guy, stick around, you'll fit right in.

[CASHCOW]

Re: Does air tightness trump R value to some degree?

Its always tough being the new guy, stick around, you'll fit right in.

Thanks for welcome. I tried CT at first, bunch of kids trying to impress one another. Every time I go there some immature bash is going on. I found a more mature crowd here. I been around forums a long time, always interesting the ones that sit back so afraid to write a lot or post at all in fear someone will rip on them. It’s always easy to sit back wait for someone else to post then throw darts, there is NO intelligence or effort in that or doing some cheap goggle research you don't fully understand, and it does not promote open dialog from some talented posters or a good enviroment for such, a lot of people can throw darts at post easy! I must say I seen it all and can smell it 1000’s of miles away. Goggle some of personalities known behind post, very interesting and accurate assessments out there these days. You and few others the good ones I can tell, a wealth of knowledge you are willing to share without the big head.

I took thermodynamics a long time 30 years ago in engineering school, been through all the Q calcs validated by lab results, been around a lot of heat transfer since. If I wanted to I’d post the numbers and probably confuse most, but that throw this tread off track and I got better things to do. As far as I know it is a "science" section for posting scientific info so if you think you know it all(not u Ted) DG post some q-calcs of a basic wall to back your theory then validate it by test results. Help me it's been a while :) Don't goggle it either you never know what you'll find out there. :) You should know the basic Q formula off the top of your head as most "experts" do.