This is an offshoot from Hal's thread on the need for better classification of radiant barriers: http://homeenergypros.lbl.gov/forum/topics/different-classification...

I didn't want to drift on his, so I have started new.

Using the sciences to our advantage.

I have a camp in the planning stages (similar to David Meiland's question on the cost of rigid foam insulation), on posts and enclosed on the bottom.  Here's David's http://www.linkedin.com/groupItem?view=&srchtype=discussedNews&...

Mine is a heating dominant climate as well, in Maine and close to water, thus the posts will provide a better view and some protection from seasonal high water on rare occasions.

Having a living space over a cold space is a frequent problem in cold country and often results in cold floors.  Overhangs, porches, a bedroom over a garage and yes, my proposed camp are all examples.  But all of these have one design consideration in common, the warm is stacked over the cold, a configuration that does not support convection.  IMO, warm over cold needs some careful consideration.

Of the three modes of heat transfer, radiant, convection, and conduction, any time we can shut one or more down, we have reduced some major paths for heat transfer.  Now, picture the floor of my camp design, foil under the flooring, I-joists, and air sealed cavities with no insulation.  That's no insulation.  There will be some conduction via the bridging and some radiant transfer from the upper portion of the I-joist (which could be detailed with some foil as well), but no conduction through the cavity, virtually no radiant transfer, and because the warm is stacked over the cold (almost) no convection.  Add to this that any heat that does migrate down and warm the cavity air, the resulting convection would move the warmer air back to the top of the cavity.  It's ironic, but filling these cavities with fiberglass could increase my heat transfer as air is a very poor conductor of heat.

The benefits of warm over cold are not new as our cooling climates benefit from it when the ac is running.  Warm attic air does not migrate down to displace the cool air buried under our insulation.  In a heating climate, that cold air we vent into our attics goes directly to the lowest point it can access and pushes any warm air it finds up and away. 

Instinct says the floors will be freezing, but I can't identify the heat loss path.  And if there is any benefit to adding a radiant barrier to the underside of these floors, even with just a small air gap and lots of insulation, I'd like to be able to calculate it.

All comments are welcome, I think.

Bud

Views: 1189

Reply to This

Replies to This Discussion

Bud, I don't think you will get anything close to your R-23. For one thing, the increase in total R with depth of cavity is non-linear with quickly diminishing returns. For another, it's impractical to expect much value from a layer of foil on the bottom facing upwards as it will become covered with dust or condensation (unless the space is perfectly hermetically sealed in a dust-free, dessicated environment and impervious to water vapor diffusion). The thermal bridging will be substantial because of the large surface area of the TJIs facing the air space. And there's a reason that most of the R-value claims of the radiant barrier industry have been debunked - they have very limited value in the real world. 

Unless you can create a perfect vacuum in those joist cavities and turn the floor into a thermos, you're going to need some kind of insulation to make it energy efficient. There's no getting around it.

RSS

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

David Eakin replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"I mis-spoke - I was referring to the Midori House in Santa Cruz. Have an in-depth discussion with…"
36 minutes ago
Profile IconScot Davidson, j jarvella and Michael joined Home Energy Pros
7 hours ago
Kaushal Bharath Raju replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Hi David & Bud, $400/sqf > $300 sqf. The latter is the minimum cost of new construction in…"
8 hours ago
David Eakin replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Kaushal, There was a deep energy retrofit upgrade project (to Passive House standards) in San Jose…"
10 hours ago
Kim Tanner updated an event

Beyond Residential Testing at The Energy Conservatory

May 14, 2014 to May 16, 2014
The Energy Conservatory (TEC) is hosting a Beyond Residential Testing event. In addition we are…See More
12 hours ago
Casey Gesell posted a video

Super Attic - Attic Insulation System

http://www.drenergysaver.com | 1-888-225-6260 The new Super Attic: Advanced Conversion System -- converts your attic from a vented attic into an unvented at...
12 hours ago

Casey Gesell just added their location.
(via Member Map)

14 hours ago
H.O. Electric posted a video

H.O. Services, Generator, Electrical, Plumbing, Heating, Cooling, Belmont, Lexington, Arlington, MA

H.O. Services is your residential Electric-Plumbing-Heating-Cooling Specialist. We are an electrical contracting company providing homeowners the best Electr...
15 hours ago
Jim Gunshinan's blog post was featured
15 hours ago
Luis Hernandez posted a discussion

Air Source Heat pump or mini-split efficiency

Greetings everyone!    I have a technical questions I hope I could get some feedback! I understood…See More
16 hours ago
Jim Gunshinan posted blog posts
yesterday
H.O. Electric posted a photo

about us-team

H.O. Services is your residential Electric-Plumbing-Heating-Cooling Specialist. We are an…
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service