Reuben's Home Inspection Blog

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Before you insulate your foundation walls, start with the rim space

Have you ever noticed how snow will melt around the foundation on older houses?  This will happen at any house with unheated foundation walls, and it's a great visual indication of how the house is losing heat.   When there's no melted snow up against the house, we can rely on thermal imaging to figure out where the heat loss is occurring.  In the image below it's right at the rim space; that's the part that shows up as the brightest orange / yellow.

Heat loss at rim joist

While houses usually act like chimneys, sucking air in at the bottom and exhausting air through leaks at the top, the photo below is a perfect example showing how it doesn't always work that way.  The frost that has accumulated against the siding is all coming from air that's leaking out of the un-insulated, un-sealed rim space.   It was about -15 degrees outside when I took the photo below.

Frost on house

To cut down on basement heat loss, an obvious place to start at is the rim space.  I mentioned this a couple weeks ago when I wrote my post about how I had my entire basement re-insulated, but today I'm going to focus on the rim space alone and discuss the different options for insulating and air sealing this space.

Rim joist

The old way of insulating rim joists was to use fiberglass batts.  As I've mentioned many times in previous blogs, fiberglass batts are a poor choice of insulation for any project... but they should never be used at the rim space because it's nearly  impossible to install a proper vapor barrier here, and fiberglass batts will allow for a lot of air leakage.   Without a vapor barrier at the rim space, you'll have relatively warm, moist air passing through the fiberglass insulation and then condensing at the rim joist.  This can create mold or rotting.

There are only two ways that I ever recommend to insulate the rim space: rigid foam or spray foam.

Using spray foam at the rim space is just about the only thing that is ever done on new construction houses in Minnesota today; while it's expensive, it's worth it because it can be applied quickly and does a perfect job of both insulating and air sealing the rim space.  Wires, faucets, pipes... they're no match for spray foam.  All of the penetrations get sealed.

Spray Foam at Rim Space

While spray foam is supposed to be covered by an approved material to prevent the possible spread of a fire, the rim space is one exception to this rule; this exception can be found in the Minnesota Amendments to the IRC, sectionR314.5.11.  Here in Minnesota, up to 5 1/2" of foam insulation can be sprayed at the rim space and left exposed.  The only downside to using foam insulation is that it's relatively expensive.  You can buy do-it-yourself insulation kits for fairly small jobs, such as a rim space, but I would personally just hire a professional to do this.  It wouldn't cost much more than a spray foam insulation kit.

The alternative to having spray foam applied at the rim space is to install rigid foam insulation.  Installing foam insulation at the rim space takes a long time, but it's not a very difficult project.  Basically, pieces of rigid foam boards get cut to size, placed at the rim space, and caulked or foamed in place to help prevent air leakage.

Rigid Foam at Rim Space

While writing this post, I came across a great blog written by a handy homeowner, showing how he insulated his own rim space with rigid foam.  You can view it here - rigid foam at rim space.

The one thing to remember when making a house tighter is that you'll have less air leaking in to and out of your house, which can create other problems, such as a backdrafting water heater or excessive moisture in the home.  The Minnesota Department of Commerce Energy Information Center has a great handout that specifically addresses this topic, which you can download here - Combustion & Makeup Air.  

Post edit: Check out Charles Buell's post from today about tighter houses.  This is exactly the stuff I'm talking about in the paragraph above.

If you don't have any insulation at your rim space, add this project to your list of 'to-do' projects.  It's not as critical as attic insulation and it takes more time, but it's a good thing to do.  Just don't use fiberglass.

Reuben Saltzman, Structure Tech Home Inspections

        

Comment balloon 49 commentsReuben Saltzman • December 13 2011 05:57AM

Comments

Reuben: One picture is truly worth a thousand words. Sounds like the spray insulation is the way to go. Happy Holidays!

Posted by Anne M. Costello (Weidel Realtors) over 6 years ago

Hi Rueben,

Bandjoists have always been neglected in older homes.

the foam application is a greatway to "air seal" just adding insulation to the band joists will not stop most infiltration/exfiltration.

Very nice post. What type of blower door do you use. I have a dg700 digital.

Thanks for sharing the information. Have a great Holiday Season ahead. Best for 2012. 

best, Clint McKie

Posted by Clint Mckie, Desert Sun Home, Comm. Inspection 1-575-706-5586 (Desert Sun Home, commercial Inspections) over 6 years ago

Great post and I am happy that a home inspector takes notes of this, thanks

Posted by David Popoff, Realtor®,SRS, Green ~ Fairfield County, Ct (DMK Real Estate ) over 6 years ago

Anne - foam is definitely the way to go.  As I'm sure you know, I'm a big fan :)

Clint - bandjoist, eh?  ;).  I think that's a Southern term (or maybe rim joist is just a Northern term).  

I don't own a blower door... yet.  Some day, maybe.  When I google dg700 digital, I come up with pressure gauges, not blower doors.  What's up with that?

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

David - thanks.  I'm glad I've finally written a post on this topic, so I can include a link to this information in my inspection reports :)

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Reuben-That was a great article. The photo was an outstanding illustration. We don't have the tough winters like you have in your area, but summers here are pretty hot. So I can see this application being used for checking on conditioned air loss in summer.

Posted by Wayne Johnson, San Antonio REALTOR, San Antonio Homes For Sale (Coldwell Banker D'Ann Harper REALTORS®) over 6 years ago

Yummie, 15 degrees and snow...  Say it ain't so Joe!

So, should I double up on that fiberglass bat I have all around my rim joist?  Will that help?

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

Wayne - thanks.  You're right, insulation is a good thing for any climate.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Jay - Fifteen degrees?  No way.  You're thirty degrees off!  :)  

That was negative fifteen.  

Have you ever pulled the fiberglass batts away from your rim joist to check for condensation on a cold day?

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Reuben, great article, very informative. There are so many ways to save money with insulation. I just mentioned it in a post of mine.

Posted by David O'Doherty, Clayton NC Homes, Raleigh, NC (Raleigh Realty Inc) over 6 years ago

UGH Reuben,,,

MINUS fifteen? That's too cold even for me. Love the thermal shot, it says more than any amount of words!

Posted by Richard Weisser, Richard Weisser Retired Real Estate Professional (Richard Weisser Realty) over 6 years ago

David - when it comes to saving money, it's all about how much you're losing and how much you'll spend to stop losing.  The rim space ranks pretty high on the list of potential returns on investment.

Richard - That was too cold for me too.  I'm pretty sure I have permanent nerve damage in my hands from being exposed to that kind of weather for too long.  

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Reuben, the photo says it all. I spent a little time in Duluth a while back. That's why I now live in Virginia. Good information.

Posted by Michael Setunsky, Your Commercial Real Estate Link to Northern VA over 6 years ago

Reuben...Great post.  Nothing gets a homeowner's attention like a picture using  thermal imaging.

Posted by Howard and Susan Meyers (The Hudson Company Winnetka and North Shore) over 6 years ago

Uh, OK, silly question time.... I'm guessing the furnace is in the basement and as the heat is rising to the next level this photo shows it is escaping thru the rim space as described?  My furnace is in the attic (Texas) so my photo would be reversed? With the heat escaping along the roof line... between the floor of the attic and the ceiling of the first floor (in a one-story house)? or thru the ridge vents in the roof? For my type of design/construction, what areas of my home would be indicative of a similar problem needing attention? (God forbid I ever live again in neg 15 degrees. Freezing is 32 deg. When the pork chops in my freezer are warmer than I am -- I figure I'm living in the wrong dang place!)

Posted by Judith Sinnard, The SMARTePLAN Lady (SMARTePLANS; Houston, Texas) over 6 years ago

Reuben,

GREAT post!  The temperature in the Florida Keys very rarely drops below 70 degrees.  If the weather dips to those frigid temperatures it's only for a day or two, but the same principles apply in the American Caribbean where we are trying to keep the extreme heat out.  So thank you so much for sharing your expertise!  
Maya

Posted by Maya Thomas LLC, Broker, Key West FL Historic Old Town Estates, Bungalows (Key West, Key Haven, Geiger, Sugarloaf, Cudjoe, Summerland) over 6 years ago

You cant stay dumb on ActiveRain...you just cant! thank you Reuben

Posted by Richie Alan Naggar, agent & author (people first...then business Ran Right Realty ) over 6 years ago

Reuben~Could you use fiberglass over the rigid foam to increase the R-factor, or still not a good idea. This is something I have to do, but don't want the expense of the spray foam if I can avoid it. Thanks!

Posted by Michael S. Bolton, MN Appraiser (Michael S. Bolton,Inc.) over 6 years ago

What an excellent post! I'm definitely going to be checking around my house after our first snow!!

Posted by Lori Cain, Midtown Tulsa Real Estate Top Producer (eXp Realty) over 6 years ago

Reuben, that first picture is awesome.  We do not get to see that obvious air leakage around here.  Our posts are kind of related today.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 6 years ago

Rueben, very informative!  I have been doing research on foam insulation lately.  I am going to be finishing a basement and think it will be the way to go.  I think I am going to use your rim joist option!  I love being able to do things on my own. Thank!

Posted by Jo Olson, HOMEFRONT Realty @ LAKE Roosevelt - Stevens County (HOMEFRONT Realty) over 6 years ago

Reuben, thanks for the detailed post. It gives me just a bit more knowledge to mention to clients

Posted by Paula Bradfield, Your Salida Colorado and Nearby towns Realtor (Keller Williams Performance Realty) over 6 years ago

This type of home improvement is probably one of those jobs that most homeowners would never really think of, getting this knowledge is extremely valuable.

Posted by Morgan Evans, LICENSED REAL ESTATE SALESPERSON (Douglas Elliman Real Estate) over 6 years ago

Reuben,

Great post and a you and Charlie are on the same wave length. I can not agree more with you observation and recommendations.

I sure wish fiberglass would go away, but that is my opinion ; )

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) over 6 years ago

I like your post. Very well written and extensively documented and illustrated with great photos.

Now, one last thing. What is snow?

Posted by Jon Quist, Tucson's BUYERS ONLY Realtor since 1996 (REALTY EXECUTIVES TUCSON ELITE) over 6 years ago

This is an excellent post and now with energy being considered for the buyer's qualification, this is a great way for the homesellers to improve their energy efficiency which will keep that buyer on the table!  Great illustrations.

 

Posted by Maggie Finegan (Keller Williams Preferred Realty) over 6 years ago

Great post Reuben.  Shows the power of infrared.

Posted by Stephen Gaudet (Gaudet Inspections) over 6 years ago

Michael - no further explanation needed.

Howard & Susan - thanks.

Judith - not exactly.  My basement is part of the same 'thermal envelope' as the rest of my house.  In other words, the basement is warm and the house is warm.  The attic is outside the thermal envelope, so the temperature in the attic should be pretty similar to the outdoor temperature, even if you have a furnace up there.  

Without being familiar with the way houses in Texas are built, I'm not a good person to ask about which areas could probably use attention. 

Maya - I don't want to hear about it ;)  Glad to help.

Richie - good stuff, thanks!

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Michael - I suppose adding fiberglass over the rigid foam probably wouldn't hurt.

Lori - let me know what you find.

Charles - definitely.  We should have discussed this first, and I could have included a link at the end of my post to yours.  Come to think of it, it's not too late.  I'm going to do that as soon as I finish writing this comment. 

Jo - foam is the only way to go.

Paula - thanks.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Morgan - most people aren't in to spending much time in their basement, and when they do decide to insulate it, it's almost always fiberglass batts.  Yuck.

Donald - I completely agree with you.  I just added a link to Charles's post :)

Jon - what is snow.  Huh.  Ignorance really is bliss :)

Maggie - definitely.  This stuff certainly helps.

Stephen - thanks.

 

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Excellent post Reuben with great illustrations!  Thanks for keeping us educated.  I just learned something new.

Posted by Lisa Dunham, Associate Broker, Alexandria Virginia Real Estate over 6 years ago

Great information.  many peopel cold save a lot of money with just a bit of effort.  Much of what you show doesn't even cost all that much.

Posted by William Feela, Realtor, Whispering Pines Realty 651-674-5999 No. (WHISPERING PINES REALTY) over 6 years ago

Thanks Reuben, and I am going to go back into mine and provide a link to yours and especially that "Combustion & Makeup Air" article.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 6 years ago

I did a lot of these things last year to my home and I saw a noticable difference right away.

Posted by Vern Eaton, Realtor 651-674-7449 over 6 years ago

Adding this to my favs to work on. My 100+ old house can use some of this.

Posted by Dora Griffin, NMLS 6380 (D A Griffin Financial.LLC) over 6 years ago

Lisa - thanks!

William - you're right, this is a pretty inexpensive upgrade, and it's not all that difficult to do.

Charles - good chatting today, thanks for calling.

Vern - good to hear. 

Dora - some day, right?

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

I was being facetious, you silly you.  And I did not see the - !  Now I am the silly for thinking that it was that warm where you are!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

Great post. I recommend foam for the rim as well. Funny you mentioned about excess moisture. I noticed more moisture in my house since installing the new high efficiency boiler. The oil boiler was drawing air for combustion from inside the house. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) over 6 years ago

Btw here is a rim shot I took not long ago. 
Rim Joist

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) over 6 years ago

Reuben and Jim, these rim joists could be referred to as "reverse radiators" :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 6 years ago

Thanks for the training. I definitely learned a few things from your post.

Posted by George Bennett, Inactive Principal Broker, GRI (Inactive) over 6 years ago

Jay - yeah, I know :)  But I'm assuming you really do have fiberglass at your rim space, don't you?

James - not only combustion, but also dilution air.  I wrote a post about that same situation a couple years ago - http://activerain.com/blogsview/1128601/moisture-problem-caused-by-high-efficiency-furnace .  

Nice rim shot.

Charles - It would be nice to have reverse radiators in the summer.

George - glad to hear it, thank you.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago
Reuben: thank you for this informative post! I learn so much from my AR inspectors!
Posted by Joni Bailey, Your Huntsville / Lake Livingston Area REALTOR® (Berkshire Hathaway Home Services - Anderson Properties) over 6 years ago

Good post I recently spoke about this same topic to someone. In your diagram it also shows a little insulation over the sill plate. This is important to help stop the cold from coming up from the concrete foundation. We sometime call them band joist here but the band joist is really the same as a rim but on the 2nd floor.

Posted by Rob Ernst, Reno, NV-775-410-4286 Inspector & Energy Auditor (Certified Structure Inspector) over 6 years ago

Two great posts on the same subject in one day. I love it. Always something to learn more about. Thanks Reuben>

Posted by Marshall Brown, BSEE, CHI (Mid America Inspection Services, LLC) over 6 years ago

Of coursa!  House fourteen years olda!  Rim joists leaka!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

Reuben,

It looks like you are going to make me watch the rim of my house... boring... but... I suppose I better do it!! lol

 

:)

Posted by Marzena Melby, Realtor, Twin Cities Minnesota Real Estate (Coldwell Banker Burnet Realty) over 6 years ago

Joni - thanks!

Robert - thanks for the explanation of 'band' vs. 'rim'.  

Marshall - good timing, huh?

Jay - yeah, what else could it be, right?

Marzena - It was good to meet you yesterday, thanks for coming!

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Great information Reuben.  Every body (OK, most people) insulates roofs, but we often neglect the floor...

Posted by Chris Smith, South Simcoe, Caledon, King, Orangeville Real Esta (Re/Max Chay Realty Inc., Brokerage) over 6 years ago

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