Rebar OK for ACQ landscape timbers?
Crackshot
| Posted in Construction Techniques on
This is regarding building a rectangular-shaped “window well”, which is basically 3 retaining walls for a basement egress window.
I have purchased a load of 6×6 inch landscape timbers, ACQ treated for ground contact, and haven’t installed them yet. My plan is to secure the bottom-most timbers with #4 rebar pounded through a pre-drilled hole in the timbers, and into the ground about 2 feet deep below the timbers. Recently, I have learned that ACQ corrodes steel, so I am rethinking this approach. Thanks in advance to all of you for your helpful expertise and ideas.
P.S. The other fasteners to be used throughout the rest of the retaining walls are 10-inch galvanized spikes.
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A: The gravel drain bed has a narrow section at the wall the extends down to the tile. The timbers of the Well are two layers deep into the gravel.
B: Is a water spigot and the Well section under it is filled to a convenient height.
C: The bottom two timbers were set in place and gravel backfilled and compacted on both sides to their top. The next timber (stairstepped) was set on the gravel and pinned to the next lower timber. Backfilled and compacted to its top. Each stair timber is resting on compacted gravel.
The timbers parallel to the wall are also stairstepped. All timbers gravel under and behind. All gravel has geotextile silt fabric under it. Only the top 4"-6" of any part of the Well will be in semi-direct contact with soil, there will be geo fabric between.
SamT
SamT - thanks for the fast response. The photo shows a very similar application of landscape timbers, a lot like what I'll be doing. I'm hesitant to dig any deeper downwards into the dirt, as I'm basically at the level of frost barrier needed, versus where the footings are. Or, if I pile up enough gravel in the bottom of the well to provide effective resistance to lateral movement of the bottom-most timbers, then the base of the well gets too high, versus the window sill. That's why I was planning to use the rebar. I know of someone who's done that before, but I don't know if it a) will pass inspection "to code", and b) will stand the test of time. I am trying to learn more about the corrosive effects of ACQ on steel, particularly from people who have actual experience and observations, rather than info from books and other theoretical sources. For example, if I could find a 30" long galvanized spike, I would just use that. Or, if I could coat the rebar or fill the pre-drill hole with something that would retard corrosion, I might do that. Thanks again.
The "new" landscape time bolts are suppose to be approved for ACQ.I think that they are called Timberlock or something like that. They are advertised in FHB.The have a hex head and self drilling point on them.
Benny,
a simple 1/2" rod doesn't provide much (a few pounds only) resistance to lateral forces.
Have you considered drainage? It is important for moisture control in the basement walls.
Unlike you, I was replacing the footing drains and finding and fixing a 1 1/2" hole in the wall when I put those Wells in.
The minimum I would do in your situation is to excavate a trench 1' wide by 6" deep next to the wall. Post hole dig a hole down to the footing drain gravel. Fill the posthole with gravel in a tube. Lay a timber in the trench 6" from the wall as a side to side brace for the Well walls. Fill the remainder of the trench with gravel on geo fabric. Add 2"-4" topsoil over all for plantings.
SamT
>> will pass inspection "to code", <<
I'd be surprized if there were any code specs pretaining to this. I know there are not in the area where I live...
Matt
I don't really know either, but was wondering if you could bore the holes a little oversize and either sleeve them with a piece of pvc or fill between the rebar and the timber with epoxy?
Danno - that's a brilliant idea. Thanks. Have you ever done it, or know anybody who has?
Benny, if I recall correctly, 1/2" steel is supposed to be ok to use with ACQ because the surface forms a protective layer. If I were you I would use Timberlocks though--those things are amazingly easy to drive. Where the timber meets the foundation wall can you run a leg back alongside the foundation wall to keep the base secured?
Mike
No, I haven't done it--just seemed like it might work. Another post mentioned that you can get rebar that is epoxy coated. But someone else mentioned that 1/2" might not be very strong. If that's true, maybe something like allthread might be stronger (I don't know about that either--just seems that it might be available in different strengths since its application is different than rebar).
Better than a PVC sleave would be HDPE or XPE. Like 3/4 or 7/8 or 1" radiant floor tubing. At least if you can buy it by the foot. It is vastly more temperature resistant than PVC which I have shattered at 40F. Whereas Iditarod musher run dogsled on polyethylene runners at -50F.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Danno,
1: It's not that rebar isn't strong enough, it is that soil isn't. The application mentioned, rebar as a a lateral brace against soil pressure, requires the soil to resist the movement of the rebar thru the soil.
Assume for the moment that the soil pushes with a force of 1 lb per square inch. That the wall of the Well is 30" wide by 24" tall. That is a force of 720 lbs. If one used 3 1/2" rebars, that would be 240 lbs each. Most of the 240 lbs would have to be resisted by the top 6" of soil to prevent bending the rebar. 6" long by 1/2" diameter of the rebar means each square inch of soil has to resist 80 lbs of force. That is almost 6 tons per square foot! Soil can't do it.
2: Rebar is designed primarily for shear strength, which is what this application requires, whereas allthread is designed for tensile strength. 1/2' allthread will bend and break much sooner than 1/2" rebar.
Three #8 rebars long enough to reach into 3' of soil under the sill timber would probably work because the #8 will not bend under the appied forces. Considering the bottom 6" of the rebar as the pivot 'point' of the lever gives us 30 square inches of rebar trying to move thru the soil. That is only 8 lbs square inch, which is still high, 1152 lbs/sqft.
SamT
SamT
Epoxy coated rebar is standard at large suppliers.
I was thinking the same thing about ACQ when I joined 6X6 together for treads in an exterior stair.
Use a copper ground rod or galvanized allthread?
The Morphine s eems to do no good at all..I'd run all the way if I would not fall...
galvanized pipe... 1/2"..