FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Discussion Forum

Discussion Forum

Can we talk conditioned crawlspaces?

jimblodgett | Posted in Energy, Heating & Insulation on March 20, 2009 02:20am

Anyone using them?  Anyone have any experience either building, or living above one?

Thanks.

 

Reply
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Replies

  1. IronHelix | Mar 20, 2009 05:44am | #1

    Jim,

    I work as an on-site observer for a local architect and have been involved with designs and construction of conditioned crawl and attic spaces.

    The building zone here is mixed humid with 40+ inches of precip  a year, 100+ in the summer and down to zero in the winter. 

    Crawl spaces are a perpetual problem in our area....CMU crawls and basements are the worst.

    Retrofits for crawlspaces are tough..some good info in past FHB issues.

    What are your conditions/ circumstances that prompted this inquiry?

     

    ....................Iron Helix

    1. jimblodgett | Mar 20, 2009 04:43pm | #4

      "What are your conditions/ circumstances that prompted this inquiry?"

      We are getting ready to build what we hope will be an energy efficient house here in Western Washington (moderate temps, wet, moderate humidity). 

      I want to build a good thermal envelope, to keep whatever heat gets produced in the house as well as I can, to reduce the energy needed to heat the house.

      Crawlspaces are the norm here but I have never been comfortable with the way we insulate floors over vented crawlspaces.  I think an insulated crawlspace could prove to be far more efficient, even though it increases the volume of conditioned air.

      I've pretty much made up my mind to build this house this way.  I've been reading a lot at Building Science and everything in print I could find.  Just thought I'd try to stimulate some discussion here about it.  There have been many, many times over the years someone has said something I hadn't considered. 

      You just never can have too many opinions or perspectives, right?

        

      1. IronHelix | Mar 20, 2009 07:47pm | #7

        Jim,

        You certainly have been reading in an excellent source...EEBA.

        On the residences that I have been involved via the architect, there has always been a positive outcome vocalized by the client/owner.

        Some independent sites (no architect involved) tend to have materials and methods issues due to lack of knowledge or experience by the contractor, as well as the home owner. 

        Lack of reading/understanding of the manufacturer's recommended means and methods is often a point of failure.  Contractor's typical response when called out on an issue is "But, we've always done it that way and never had a problem/call-back. My retort is..."Because you have never had a "problem" doesn't mean that it done correctly!" 

        The more knowledge of material's methods & means that you have, the better you can protect yourself from potential errors and issues in the coming years after the contractor is long gone.

        Other critical areas of design are the control of rain water runoff systems and proper sloping of the lawn surface away from the building to keep water from intruding on the crawlspace area.

        Sometimes an under the  "rat slab" perimeter drain  directed to closed sump w/ pump is needed to control excessive water conditions.

        You have carpenter ants.....we also have termites and carpenter bees.

        Borate treated foam is available, as well as chemical treatment of interior & exterior soils as deterrent. Flashing details, and insulation gaps at the perimeter to serve as inspection gaps may be needed for pest detection/protection.

        ..............Iron Helix

         

        1. Snort | Mar 20, 2009 09:32pm | #8

          You know I'm a fan of conditioned crawls. Mechanicals don't have to work as hard, any thing lost through ducting isn't really lost, and utilities are much easier mess with later.The extra conditioned air isn't that much. 1 4x10 register drop and a 4" duct, dampered to the outside whenever the HVAC system is running seem to take care of around 2000sq'.One thing I'll do differently next time is to add a perimeter drain line on the inside of the crawl. I think that will get rid of a lot of water during construction that would normally take a longer time to get out.http://www.tvwsolar.com

          I went down to the lobby

          To make a small call out.

          A pretty dancing girl was there,

          And she began to shout,

          "Go on back to see the gypsy.

          He can move you from the rear,

          Drive you from your fear,

          Bring you through the mirror.

          He did it in Las Vegas,

          And he can do it here."

      2. Scrapr | Mar 22, 2009 09:06pm | #15

        Jim

         

            not sure i you have seen this site. http://www.greenbuildingadvisor.com/

        it's part of FHB. Lots of good info. Some free (quite a bit), some paid

        Lots of best practices here.

         

         

  2. User avater
    Jeff_Clarke | Mar 20, 2009 06:21am | #2

    I have conditioned crawspaces only.  Never do them vented, ever.   No problems either.

    But I've seen many problems with unconditioned crawlspaces.

    Jeff

  3. drapson | Mar 20, 2009 02:16pm | #3

    Not only conditioned but insulated the outside of the CMU foundation to provide heat sink. No problems and I used this on Habitat houses in the past.

    More mass on inside of house the better, I feel.

    1. jimblodgett | Mar 20, 2009 04:47pm | #5

      We have carpenter ants here in the Great Northwest.  I agree that insulating the outside of the foundation would add thermal mass, but I plan to insulate inside the walls/under the slab/above the pier pads.  I just think there are long term durability/bug issues insulating outside the building envelope. At least here. 

      1. User avater
        BarryE | Mar 20, 2009 05:02pm | #6

        sure we can.... unless you're looking for consensus. ;)I've done vented and unvented. I think the unvented worked much better.We used icynene on the interior walls and rim joists. The icynene was sprayed with firefree 88 to comply with code. This was an addition to a full basement so we vented heat in from therewood floor above with walls being floor to ceiling glass curtainwall. Clients say the floor stays nice and warm

        Barry E-Remodeler

         

      2. drapson | Mar 22, 2009 05:32pm | #9

        Good point. Any remedy, of an organic nature for this? Just wondering that I might use here on next project. I can research myself, just asking I you have any greenies you are talking to!Thanks, dan.

        1. jimblodgett | Mar 22, 2009 07:20pm | #11

          "Any remedy, of an organic nature for this?"

          You mean carpenter ants? 

          1. drapson | Mar 23, 2009 12:22am | #16

            Yes, and other pest. We do get some of the ants here. But not many. However with the changing weather I believe we will get more not less. And the lessening of lumber quality this will also contribute.I am also into alternative building methods so I love this forum. thanks,
            dan

      3. User avater
        shelternerd | Mar 22, 2009 07:11pm | #10

        We've been using the American Polysteel ICF forms to build our crawlspace walls. Some of this was prompted by sloppy work from our block layers. I have my trim crew set them up and pour them and the accuracy is phenomenal. sealed and insulated and the Polysteel forms have borate in them for insect resistance so it's a great solution tot he termite/ant concern. we still cap them out with galvanized termite barrier over sill seal and caulk the termite barrier to the foam with Bostik low VOC adhesive before. Stucco over the exterior and it's a pretty good solution.------------------

        "You cannot work hard enough to make up for a sloppy estimate."

        1. Snort | Mar 22, 2009 07:22pm | #12

          Hey Michael, how's the stucco hold up? And, how do you detail it? I've only seen one Poly Steel job, and it was atrocious, outside and in. Is Not Dead Yet playing today? Bob oughta be pretty rested, he didn't have to help Roy coach too much yesterday.http://www.tvwsolar.com

          I went down to the lobby

          To make a small call out.

          A pretty dancing girl was there,

          And she began to shout,

          "Go on back to see the gypsy.

          He can move you from the rear,

          Drive you from your fear,

          Bring you through the mirror.

          He did it in Las Vegas,

          And he can do it here."

          1. User avater
            shelternerd | Mar 22, 2009 07:35pm | #14

            Ive been stapling spiderlath to the polysteel and two coat stucco on that. Tempted to try one coat of Surewall surface bonding cement and then then the topcoat of stucco but haven't been brave enough yet. the Spiderlath is pretty cheap insurance. The key with ICFs is to take the time to lay them up with care. I've seen some sloppy work myself but it's a great system if you take the time to get it right and it's tha bomb for insulated radiant slab edges. We played yesterday bass and two guitars and today they are working through some stuff with the drummer/singer without me because I'm taking a new design client on a house tour. They are doing a gig at the Bean and Barrel next weekend without me because I need to be in Connecticut. m------------------

            "You cannot work hard enough to make up for a sloppy estimate."

        2. jimblodgett | Mar 22, 2009 07:33pm | #13

          I'm not a big ICF guy.  I can see why they are popular and there are applications where I might condier them, but for the most part I still use plywood/snap ties/cleats and whalers. 

          I really don't like giving critters a concealed runway between exterior foam and concrete, plus we get earthquakes often enough that I'd like to be able to see at least part of the foundation wall on a regular basis.

          And to be honest, I don't like the fact that ICFs have to be bought new every job.  I've been using the same plywood forms for...geez...maybe 15 years now.  Every once in a while I buy a few new panels as replacements or for special applications, but I really like reusing those same forms over and over again, just seems more conservative somehow.  

          1. davidmeiland | Mar 23, 2009 12:28am | #17

            Jim, any chance you want to build 100% slab on grade, with no crawl space? I finished a house last year on a slab and would definitely do it again. The hassles of a crawl space are completely eliminated (as is easy remodeling of the underslab plumbing, electrical, etc). May be worth considering.

          2. jimblodgett | Mar 23, 2009 07:28am | #18

            Yeah, slab floors are definitely on the increase around here what with the hydronic heating craze.  I did give that some thought, but I really like elevating the floor a bit above grade and that's tough to do with a slab. 

            Plus, I've never been a big fan of concrete floors.  I like a wood subfloor and the ability to make changes over the life of the building.

            Even typing that seems like rationalizing...just stuck in my ways, I guess. 

          3. seeyou | Mar 23, 2009 11:06pm | #20

            Jim - I've done one retrofit on a rental property I have.

            It has block stem walls and the crawl space was damp, stinky, and muddy when I bought the property.

            We got the source of moisture controlled by repairing the gutters and put down plastic on the ground when it dried out and added 2" of polyiso to the inside of the stem wall and the band. The major difference is that the musty smell is gone. We also added a foot or so of cells in the attic as well as some other weatherizing measures at the same time, so I can't vouch for what change if any it made to the heating bills. http://www.quittintime.com/      View Image        

          4. jimblodgett | Mar 24, 2009 06:28am | #22

            Seems like it's a common practice in the humid southeast.Very rare here. So rare that when I asked the local plans examiner about it he had to think a minute and ask an ex inspector, who did give me the name of a local contractor who had used them. My main interest is improving the insulation values in the floor and the ability to keep all duct work and plumbing within the conditioned envelope. 

          5. seeyou | Mar 24, 2009 02:05pm | #24

            Seems like it's a common practice in the humid southeast.

            Not that common here, but the majority of houses here have basements or are built on slab. Crawlspace construction is kind of rare here.http://www.quittintime.com/      View Image        

          6. Snort | Mar 24, 2009 03:18pm | #25

            Most homes here are on crawlspaces. Conditioned crawls have been accepted, just recently. Code requires a termite inspection gap, I think it's 2". Rat slab is accepted. No flexible barrier to get torn up, but rough on the knees. I'm not sure how cold it gets in Yelm, but the crawl walls are the only thing I've seen insulated here... nothing under the slab perimeter or up piers. Saw a job where they ran the vapor barrier after the perimeter foundation went up, but before the piers... no cutting or taping up the piers. The con is the sheeting can get torn up during construction.If an insulation company does the job here, they usually want to get in before the floor system.... sissieshttp://www.tvwsolar.com

            I went down to the lobby

            To make a small call out.

            A pretty dancing girl was there,

            And she began to shout,

            "Go on back to see the gypsy.

            He can move you from the rear,

            Drive you from your fear,

            Bring you through the mirror.

            He did it in Las Vegas,

            And he can do it here."

          7. jimblodgett | Mar 24, 2009 04:49pm | #26

            How do you deal with access?  Seems like you'd want the walls in a conditioned crawl to be as airtight as possible.  I had a building once with crawl access through a closet floor and I don't like that idea.  What do you do?

            It's not real cold here but I was thinking if I insulate under the slab it will cut down on heat radiating into the ground, even if that's a small part of the heat loss picture. I'm pretty sure it's required by our building code; but even if it's not I think it's a good practice because that slab will be the edge of the conditioned envelope. 

  4. User avater
    jonblakemore | Mar 23, 2009 10:29pm | #19

    What are you going to use to insulate the walls?

    In our area we need R-10 continuous insulation on the crawl walls. If you use foam, you need to be concerned about treating for vermin, inspection for termites (usually a gap near the top for a visual inspection) and a thermal barrier. We can get EPS that meets these requirement, but you would want to check for a local supplier.

    If you're not planning to use foam, what is your approach?

     

    Jon Blakemore

    RappahannockINC.com Fredericksburg, VA

    1. jimblodgett | Mar 24, 2009 06:19am | #21

      I am planning to use rigid foam, Jon. Inside the walls, over the piers and under the (rat) slab.Tell me more about this inspection gap. Is it continuous? How wide...an inch maybe? 

      1. User avater
        jonblakemore | Mar 24, 2009 07:58am | #23

        Many of the pest control companies won't warranty the job if there is not a gap showing the foundation on the inside so they can perform a visual inspection.I would talk to your local termite guy to see what he wants to see.I don't really like slab on grade (I think I probably share some of your irrational complaints), but I will say there are some challenging elements with crawlspaces that you avoid with SOG.

        *Edit- I just saw that you were planning on using a rat slab. I wonder if this will eliminate some of the challenges of a conditioned crawl. How high will the crawl be? Is a full basement an option? 

        Jon Blakemore RappahannockINC.com Fredericksburg, VA

        Edited 3/24/2009 1:06 am ET by JonBlakemore

        1. jimblodgett | Mar 24, 2009 04:53pm | #27

          Yeah, I could use a full basement, but I'm not sure why I would.  Seems like a lot of concrete and expense.  24" tall stemwall on 8" footing is standard practice on a flat lot out here.

          Do you see a reason to go deeper? 

          1. User avater
            jonblakemore | Mar 24, 2009 05:57pm | #28

            If your lot is flat enough that you can use a 24" stemwall then I think a crawl is the ticket.I see some houses out here that have crawl spaces that are 7'6" tall at one end. Since you're already pouring a rat slab, if you had a lot sloped that much I would consider the extra cost of a full basement. Of course then you want to add a walk-up, nice exterior doors, a few 2/8x5/0 windows for daylight, etc. etc. and it does add up. 

            Jon Blakemore RappahannockINC.com Fredericksburg, VA

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Video Shorts

Categories

  • Business
  • Code Questions
  • Construction Techniques
  • Energy, Heating & Insulation
  • General Discussion
  • Help/Work Wanted
  • Photo Gallery
  • Reader Classified
  • Tools for Home Building

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |
View More Create Post

Up Next

Video Shorts

Featured Story

Podcast Episode 684: Masonry Heaters, Whole-House Ventilation, and Porch Flooring

Listeners write in about fireplaces and ask questions about whole-house ventilation, traditional porch flooring, and gutter sealants.

Featured Video

A Modern California Home Wrapped in Rockwool Insulation for Energy Efficiency and Fire Resistance

The designer and builder of the 2018 Fine Homebuilding House detail why they chose mineral-wool batts and high-density boards for all of their insulation needs.

Related Stories

  • Podcast Episode 684: Masonry Heaters, Whole-House Ventilation, and Porch Flooring
  • FHB Podcast Segment: Repairing an Old Home While Maintaining Its Integrity
  • Tools and Gear for the Moms Who Get it Done
  • An Easier Method for Mitered Head Casings

Highlights

Fine Homebuilding All Access
Fine Homebuilding Podcast
Tool Tech
Plus, get an extra 20% off with code GIFT20

"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Fine Homebuilding Magazine

  • Issue 331 - June 2025
    • A More Resilient Roof
    • Tool Test: You Need a Drywall Sander
    • Ducted vs. Ductless Heat Pumps
  • Issue 330 - April/May 2025
    • Deck Details for Durability
    • FAQs on HPWHs
    • 10 Tips for a Long-Lasting Paint Job
  • Issue 329 - Feb/Mar 2025
    • Smart Foundation for a Small Addition
    • A Kominka Comes West
    • Making Small Kitchens Work
  • Issue 328 - Dec/Jan 2024
    • How a Pro Replaces Columns
    • Passive House 3.0
    • Tool Test: Compact Line Lasers
  • Issue 327 - November 2024
    • Repairing Damaged Walls and Ceilings
    • Plumbing Protection
    • Talking Shop

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, in your inbox.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 81%

Subscribe

Enjoy unlimited access to Fine Homebuilding. Join Now

Already a member? Log in

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data