I am covering a concrete fresh-water cistern with a shed. (Two birds, one stone) The cistern is basically a 12 x 16 concrete “basement foundation” for purposes of discussion. Because this cistern is for drinking water, I do not wish to use treated lumber as the sill plate. I’ve been thinking of redwood but have worries about it being too soft – lots of sapwood in our area stores. I’ve also thought of Polywood but am naive about its nail-holding abilities. And then the is tropical woods which always seem to be cost competitive on Saturday-afternoon, Bungle-It-Yourself, home shows but never with my suppliers.
Please, “What say you?”
TIA
Edited 8/25/2003 2:20:55 PM ET by ADGUSTUM
Replies
Trex
Kevin Halliburton
"I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity." - I.M. Pei -
trex would still need some framing underneath.
JeffBuck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
He's talking sill plate right? As in bolted directly to the concrete foundation.
It certainly wouldn't be the first time I missed something, if I missed something, but I'm not sure what framing you are refering to.Kevin Halliburton
"I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity." - I.M. Pei -
For clarification, I am talking sillplate - bolted directly to the concrete foundation. Lays flat and is structurally and fully supported along its entire length by the concrete.
One answer always spawns more questions. Next step: the floor joists are fastened to the sill plate. Typically, this is done by toe-nailing the joists to the sill plate. Does Trex hold nails? Or should I call the Trex representative for this application?
Ok, a bit more info... Talk to a Trex rep but I wouldn't use Trex as the only base plate material. I was talking about using 1x Trex as a separator between your sill plate and the concrete. What you end up with is a double plate with the Trex underneath acting as a barrier between the concrete and a standard stick of lumber that you nail into.
This came up in a thread on base plates for Structural Insulated Panels recently and I thought it was a good idea.Kevin Halliburton
"I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity." - I.M. Pei -
There is going to be a lot of moisture on the underside of whatever you use for a floor structure over that cistern. I would think that would be as much if not more of a problem than your sill plates.
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shake makes an interesting point, will ventilation be adequate? also it seems to me a vapor barrier separating wood structure from water? i would not want sap from untreated wood in the water. a metal flashing or maybe even a bituthane flashing on concrete should keep regular framing material from rotting as it isolates it from concrete.
what about building with steel studs, i have been looking into using steel for a house, just checking the availability and costs etc., and found a supplier that makes a steel joist system that are like the studs, but oversize and rated for spans. a plastic vapor barrier over the top of joists and then plywood subfloor, and build as normal above. supplier was dietrich industries, wwwdietrichmetalframing.com
my fault....I thot we were talking about building something to span over .....
had the pic of my buddy's well in my head.....just had a design/beer session at his place on Sun .....my fault.
my buddy's gotta put a regular size manhole cover over a hole about 6 ft across...that's what I was picturing....something that needs a "deck" built over it.....
JeffBuck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
They make sill material out of plastic that I use for replacement on rotted sills the stuff nails up and cuts like wood and won"t rot. I buy it at lowes or home depot.
ANDYSZ2
I MAY DISAGREE WITH WHAT YOUR SAYING BUT I WILL DEFEND TO THE DEATH YOUR RIGHT TO SAY IT.
How about a row of block or a cast stem wall?----add aluminum flashing, then skip the treated, use standard lumber to frame, lap the siding a full inch+ on the stem wall, and leave the interior unfinished for wet/rot inspection.
JAT...............................Iron Helix
A couple of options come to mind;
There is a new treated lumber called ACQ that doesn't have arsenic or chromium in it. That might be all you need. I think as long as you didn't soak a piece of this stuff in your drinking water, it's probably safe.
Trex is not suitable for any structural application. It's a decking material.
Typically, a building code will call for treated lumber or a naturally rot-resistant lumber in contact with foundations. If redwood isn't an option, cedar or black locust or something similar might be, depending upon what grows in your area.
The issue of "direct contact" is sometimes addressed by simply putting down a metal flashing and a foam sill sealer between the concrete and the ordinary lumber plate. This one depends upon your climate and comfort level with that approach. Some places this works fine, other places it wouldn't be such a good idea.
There are also some pretty good water-based acrylic sealers you can treat your own lumber with, assuing no exterior exposure or ground contact.
DRC
Any reason why you aren't going with a traditional reinforced concrete lid to your cistern? Or am I missing something?
I'm going to try to catch all the questions. So here goes:
Why not a convential concrete lid? Major reason is cost and effort to form it up. Remember it is 12' x 16'. Also, I want insulation so my water won't freeze in the winter. Yes, it is below grade some and the earth will insulate some but there are days it could freeze, especially when the water level is low. Therefore, I would have to build a wooden structure for the insulation that would look a lot like a floor. So I'm skipping one of the two and choose a wooden floor (lid for the cistern) for my above-cistern shed. Yes, I could depend on the insulation in the shed walls and ceiling to hold heat but I only want to heat the smaller air space directly in the cistern.
Why concern for the sills and no concern for the underneath of the floor? Well, we all agree the sills are important since they rest directly on concrete. But the floor?; plans are that the bottom one-third of the floor joists are to be primed and coated with a two-part epoxy paint. The upper two-thirds of the joists and the bottom of the floor itself will be encapsulated in polyurethane foam insulation. Thus, no raw wood is exposed to the highly humid air of the cistern.
Trex is a decking. True. Which is why in my initial post I inquired about Polywood which IS structural. Although I seem to think Trex would work as a sill as it is asked only not to crush under the load of the floor joists. But maybe it cannot perform in that application. That is why I call on the experience of the people who come to Breaktime.
Edited 8/28/2003 10:44:10 AM ET by ADGUSTUM
Another alternative is Kodiak preserved wood.
http://www.kodiakwood.com
1-800-K-Kodiak
It's redryed after treatment, and not classified as hazardous waste material.
I've had a piece of this stuff exposed to the weather for three years now and it still looks good.
DRC
Osage orange and Black locust have been used as fence posts, in direct contact w/the earth for years. I think they contain natural fungicides so they don't rot. Not certain if they could be considered toxic, tho.This jobless recovery has done more to promote the consumption of exquisite chocolate than the finest chocolatier. Cost be damned.