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: 1613

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

Featured Forum Discussions

What causes a temperature plane in a home

Started by Energy Wise Solutions in HVAC. Last reply by Peter Krych on Friday. 4 Replies

Velocity Pressure Testing

Started by Horace Douglas Hunt, Jr. in General Forum. Last reply by Horace Douglas Hunt, Jr. Apr 15. 2 Replies

Videos

  • Add Videos
  • View All

Latest Activity

Gary Reed added a discussion to the group Job Board
Thumbnail

HOME ENERGY ADVISORS WANTED (NEW YORK STATE: Saratoga & Glens Falls Region)

We are currently seeking experienced HOME ENERGY ADVISEOS to join the Jack Hall Plumbing &…See More
6 hours ago
Profile IconGary Reed and Kurt Shafer joined Diane Chojnowski's group
Thumbnail

Job Board

This group is for posting jobs related to all aspects of the home performance industry including…See More
7 hours ago
Ron Sarrick liked Energy Wise Solutions's discussion What causes a temperature plane in a home
8 hours ago
Kurt Shafer added a discussion to the group Job Board
Thumbnail

Installers for Whole House Fans in Various Cities

Invisco Whole House Fan Company in Temecula CA sells the highest performance fans in history. The…See More
9 hours ago
Kurt Shafer posted a blog post

First Rooftop Whole House Fan for Homes without Attics

Eichler was one of the most famous Mid Century Modern home builders in the 50s and 60s. His homes…See More
10 hours ago
Travis Lundberg replied to angela stanzione's discussion Used Weatherization and auditing equipment for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Do you still happen to have a blower door fan, frame and fabric still for sale?  If so please…"
10 hours ago
Profile IconTravis Lundberg and Alana Barnett joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
10 hours ago
Profile IconTravis Lundberg, Ryan & Shannon Coon, Will johnson and 1 more joined Home Energy Pros
10 hours ago

Home Energy Pros

Welcome to Home Energy Pros – the unique digital community by and for those who work in the home energy performance arena.

Home Energy Pros was founded by the developers of Home Energy Saver Pro (supported by the U.S. Department of Energy) and brought to you in partnership with Home Energy magazine.  Home Energy Pros is sponsored by the Better Buildings Residential Network. Please honor our Guidelines

© 2017   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service