Can we talk conditioned crawlspaces?
jimblodgett
| Posted in Energy, Heating & Insulation on
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Replies
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
"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?
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
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."
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.
I have conditioned crawspaces only. Never do them vented, ever. No problems either.
But I've seen many problems with unconditioned crawlspaces.
Jeff
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.
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.
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
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.
"Any remedy, of an organic nature for this?"
You mean carpenter ants?
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
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."
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."
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."
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.
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.
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.
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
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.
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
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."
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.
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
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?
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
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?
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