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Rusty 07-04-2006 10:10 PM

add a non-supporting concrete "skirting" under log house
What a great site!

I have a owner-built log house, 30 yrs old, 16" concrete posts down 6' on 15' centers (so I was a recreation director, not a contractor). There are similar sized cedar posts (now rotting) located between the concrete (we were on a budget).

I didn't leave enough crawl space under 30% of the house and I am concerned the insulation is lacking for various reasons and I can't reach it without raising the house or digging out.

So, I thought I would pour a concrete skirting wall under the logs and around the house with vents, etc. and maybe put a small heater for winter (remember we are in the Rocky Mountains). My thoughts so far are to use styrofoam insulation as the concrete form on the inside (and leave it there) and wire a removal plywood form for the outside.

- does the above form idea seem reasonable?
- Will this method suffice to keep the floor warm?
- How should I seal between concrete and sill log?
- any other helpful hints?

thanks for your feedback.

Square Eye 07-04-2006 10:27 PM

Foam is going to be hard to work with. The concrete will be hard to contain with foam. Whatever you use to support the foam will have to be really massive (solid backing) or really close to the floor (short span). If you do figure a way to use the foam, you may consider termite proofing the foam before pouring the concrete. Termites could possibly find their way up between the foam and the concrete. Foam is being used behind foundation walls commonly here, but the forms go on right over the foam. OR, the foam is added after the pour.

Vents by USA code have to be 1 per every 150sqft of living space. I have no idea what Canada requires. With the vents closed in the winter, you will notice a difference.

Sealing the top of the wall to the sill log?

Chink chink chink.

Newer log homes don't use chinking. You will have to do something. Maybe flexible foam backer rods then caulking. The answer will come to you when the time comes. If not, feel free to discuss it with us!

Kimberton 07-05-2006 08:49 PM

Have you checked out - they don't have detailed answers like that online, but they do post phone numbers and their web site is very interesting.

inspectorD 07-07-2006 07:28 AM

Welcome rusty,
Square Eye is right about the foam not being able to hold back concrete. Not unless it is going under a slab should it be used as a form.
Something else to consider is to seal the ground under the crawl space. A 6 mill or better plastic will work to keep down the moisture after you seal it up.

My opinion would be to hire a reputable contractor to evaluate just what should be done. I would recommend some digging out of areas to gain future access to head of future problems you will not be able to see from the outside.
This being a log cabin it is a different animal than a stick built home. The potential to hold large amounts of water in the logs from not having the correct moisture levels in the crawlspace can make for some very interesting gaps in the logs.

Remember that the home right now breaths underneath...when you seal it up it sweats it out.
Call someone in to manage the will pay in the long run.

glennjanie 07-07-2006 09:49 AM

Perhaps you could fill in the missing parts of the foundation with stone. If you could get a truck-load of 6" limestone (what we call rip-rap) and lay it using mortar to fill the voids in the stone you would have a solid foundation that you put in yourself and you know its right.
You would still need the 6mil poly ground cover, dig a trench and start the stone at least 1' below grade, put an aluminum moisture barrier on the bottom log (also a termite stop) and still use the foundation vents and a metal access door.

Rusty 07-10-2006 11:04 PM

thanks to all for the information and ideas. Nice to see the great support.

I am still wondering about the negative reaction to the foam for the inside form? Are you suggesting it will leak concrete between pieces or it just won't be strong enough? How about wireing it like a regular form to the outside form? By the way, at the greatest height it will only be 18 inches, some places 6 inches.
Digging out for future problem solving ease would actually be a major undertaking. But if I have to .....
The poly-barrier on the ground is a good idea. I originally had poly down but the cats and dogs destroyed most and the rest eventually disentegrated. At least the new "skirting" will keep the animals out.
A couple of you mentioned termites - I remember termites in the states but haven't seen any up here (not that they don't exist). Could it be too cold for termites?
thanks for the rock wall idea glennjanie. I think I will at least eventually rock the outside surface. The aluminum moisture barrier between the bottom of the bottom log and the new "skirting" sounds interesting.
And Kimberton - I will be checking out a few log builder sites. thanks

Square Eye 07-10-2006 11:36 PM

Foam isn't very tough structually. Even at 18" it would be risky to use it as a form. 6" may be OK. Corrugated metal would hold up if you fastened it top and bottom, then you could put foam over that and pour concrete against it.
Corrugated metal can be found used. And CHEAP!

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