I’m beginning work on a new shop that will have a slab floor and radiant heat tubing. I have hired a contractor to do most of the work, but I am going to install the heat tubing myself. While laying out my shop designs, I’ve decided that I want to run a trough through the middle of the shop for dust collection and power to my jointer and table saw. I haven’t talked with my contractor about this (I’m meeting with him tomorrow) and I wanted to get some ideas on how to go about this. I plan on putting a lip on each edge of the trough and putting a cover over it.
Questions for those of you that may have been through this or might have good ideas:
1) Will it be ok to separate the slab like this? I’m guessing it could act as a big control joint. The slab will be 24×32, and I plan to run the the trough roughly through the middle, effectively creating two separate 24×16 slabs.
2) I plan on insulating the slab, should I double the insulation under the trough?
3) The radiant heat tubes will need to dive under the trough, so should I double the insulation under the trough to account for this? Should I put something on the bottom of the trough to protect the tubing?
4) For the trough cover, should I use 1″ ply or something like 1/4″ metal? Ply would obviously be easier to handle, but would require more depth in the trough.
Thanks for any advice/suggestions,
Eric
Replies
Eric,
Rather than running the tubing under the trough it would be much simpler to create two separate circuits, one in each half of the slab. There is a maximum recommended length for a single circuit and running a single circuit under a slab of that size was probably getting close to the limit anyway.
John W.
Hi John,
Thanks for your advice. I am planning on running three circuits, each between 200 and 250'. My research indicatest that 300' is the maximum recommended length for 1/2" tubing.
Even with two circuits though, at least one would need to cross the trough to get back to the heat source. But you make a good point, crossing the slab twice would be a whole lot better than crossing it 8 or 10 times! I need to redesign the tubing layout to account for the trough.
thanks again,
Eric
Eric -I did almost the exact same thing in the design of my shop floor. The utility trench or trough doesn't really need to extend from wall to wall, you can leave at least 6" clearance from one end. The supply tubing for the circuit on the far side (from the boiler) can be run directly from the boiler to that side, do the loop-tere-loop thing then run the return through that space as well.I put in a 6" lift of pea gravel and 2" of polyiso (pink styrofoam) insulation under the slab. The gravel provides a capillary break to prevent moisture migration from below - better than plastic sheeting really, and the insulation provides .... well, insulation. I used 6x6/10ga welded wire mesh throughout the floor for reinforcement. If I could have afforded it I would have prefered to use #4 rebar @ 12"oc each way but ..... If you chose to provide the clearance between the trench and one wall you will, as I did, get a shrinkage crack at that location so to control its location you might put in a strip of 3/8" expansion joint material for cosmetics. I didn't, the slab cracked minimally but I can live with it.Specify a low slump (as low as the finisher will tolerate) for the concrete to keep the water cement ratio as low as possible. This will help minimize shrinkage. When water evaporates from concrete it shrinks not unlike wood. Do insist on some kind of reinforcement. WW mesh is the easiest and least expensive to install. As soon after the floor is finished and you can get on it, apply a good concrete sealer to aid in curing............
From Beautiful Skagit Co. Wa.
Dennis
Dennis,
Thanks for all of the info! This helps quite a bit.
Regarding insulation, did you insulate around the perimeter of the slab, or on the outside of the footings, or both? I guess it depends on whether or not your slab was tied into the foundation.
From what I've read, insulating both is recommended and shouldn't be that expensive if done during construction.
thanks again,
Eric
What type of insulation do you plan to use under the concrete? I am also planning a new shop with a concrete floor and although I live in a fairly warm climate a concrete floor does get cold.
I may be using something similar to this:
http://www.owenscorning.com/around/insulation/products/foamular.asp
In a few weeks I'll know for sure, as I should be done installing by then!
Eric
EricYes, I insulated the perimeter of the slab. Sorry I forgot to mention that. Without the thermal break your slab will conduct heat to the adjacent (assumed) concrete foundation wall.It's a bit of a bummer having that strip of 2" insulation showing around the perimeter of the shop but it really hasn't been an issue. Most of the walls are covered up with either work benches, stationary power tools or storage (read junk! -grin-)My slab is completely free floating from the foundation walls. The walls are 6" concrete 3'6" high around two sides and 6' high on the other two sides. My shop is built into a sloping site thus the higher walls on the two sides.My heat source is somewhat Rube-Goldburg-ish .... consists of a wood stove with a heat exchanger piped into two hot water tanks for storage mass. I have a two circuit system. It's an "open" system meaning no pressure relief necessary, no fancy controls, just start the fire and turn on the pump. That's the reason it's an open system ..... in case I forget to turn on the pump! (hehehe)Yer on the right track!Lotsa people don't like working on a concrete floor and probably for good reason - it can be hard on the legs and knees. Forutnately I don't have that problem .....yet. I like how easy it is to sweep up a concrete floor. You need to be careful about dropping edge tools on concrete but I'd be careful about dropping edge tools period............
From Beautiful Skagit Co. Wa.
Dennis
Dennis,
Thanks again for your help! My slab will be free floating as well, and I don't think I'll mind the 2" perimeter insulation. Like you, I'll have plenty of stuff around the walls covering that up!
The system I'm designing will be powered by a normal hot water heater. It looks like I'll have 3 circuits and one zone. The wood stove with heat exchanger is a nice idea. I've looked into wood fired boilers and I decided that I don't want to keep two stoves going in the winter - our house has a high efficiency fireplace insert that I keep burning most of the winter.
A concrete floor is certainly less forgiving. My current shop has a concrete floor and it doesn't bother me too much. The easy cleanup is definitely a plus - anything to make that job easier is worth a lot!
Thanks,
Eric
Eric, I have 3/4" PW for the bridge of mine at 9" wide, and have never had one break in 22 years, and have run some pretty heavy loads across them.
This is also a good way to keep hoses and cords out of the way.
I can't tell from the wording of your question about the heat tubes, but I would suggest that you run them so that they are running back and fourth with the trough rather than crossing it. This would just cause headaches in forming the sides. It will have a wood bridge which is a good insulator, so that won't be ####big heat loss.
From an engineering standpoint, I would use the sides of the trough as a thickened edge for the two slab halves, and then lay the foam in the bottom of the trough rather than under it.
If you are poring a footing first, pore the bottom of the trough at that time, and then your foam under your slab could cross over it.
That is my two cents. Keith
My shop has radiant heat and a utility trough. My trough doesn't span the entire width of the building so I ran the heat tubes around this "obstacle." As I recall, my heating contractor insisted that no heat tube cross underneath anything that may give touble in the future. They all run through the planned doorways, away fron toilets, not under cabinets, and around the utility trough. This may be overkill, but one thing one does not want trouble with is a leaky heating system encased in concrete! You can probably avoid going under your trough by using surface piping to go around it. I'd seriously consider this even if it means another manifold.
My utility trough is big enough for a 6" duct, electric conduit, and air piping. I formed the concrete for a 3/4 inch cover thinking that I'd use plywood as a quick cover during construction then steel with shims later on. Well, later on has never come.....the plywood is still in place and works fine.
As for your slab integrity, I don't see anything wrong with what you propose. I'm assuming that the slab is free floating and does not need to contribute to the structural integrity of the building by being a continuous diaphram.
Jeff
Why a trough? Just bury 4" or 5" schedule 40 PVC under the slab just like a sewer line and bring it up through the slab where needed. Do the same thing for the electric lines. Use 2" schedule 40 gray PVC electric conduit. The electric wires can alway be pulled through and the DC lines can always be cleaned with a rotor-tooter if ever necessary. Seems to me like a trough with a cover is an unnecessary complication and total waste of time.
Just my 2 cents worth.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)
PlaneWood
Mike,
I was thinking about using a trough for a little added flexibility. I figured with a trough I could put the tablesaw anywhere along the length of the trough and have easy access to the DC and power. I was also planning on the continuing the ductwork throught the trough to come up out of the floor under the miter saw...sort of a mainline with a branch at the tablesaw and terminating at the miter saw.
I originally thought about going the route you suggested and may go back to that now that the trough may interfere with my heating plans.
Thanks for your insight,
Eric
Another thing to consider is ceiling drops for the DC and/or electrical. I have about a dozen electrical outlets in my ceiling, but I put them in at the time I sheet rocked the ceiling. Square channel on the bottom of the sheet rock would serve the same purpose for the electrical.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
Thanks Mike. I may end up putting some drops in but I was trying to avoid things hanging from the ceiling if all possible - I guess I want to have my cake and eat it too!
Thanks also Keith and Jeff! I'll definitely take your thoughts into consideration as I figure out a solution.
Eric
Eric, If it is just the TS, You may get better service wiring a pigtail into you starter, so that you can plug a shop vac under the out-feed table comes on every time you turn the saw on.
You might check with Onieda or Control Air Products regarding the most efficient method of DC and overhead vs. in-floor ducting. Seems to me when I raised this question several years ago they recommended the overhead as the most efficient method of moving chips and dust.
It is too late tonight for me to read the previous responses so pardon me if I repeat.
I did a slab with radiant floor heat and dust collection for a shop in my home a few years ago. I just buried the ductwork in the sand below the slab. It worked fine.
The duct was galvanized. At each joint I applied a bead of latex caulk before inserting one in the other, and wrapped the joint in vinyl tape. The seam of each length was always on the top of the duct, and I ran vinyl tape along all the seams, too. I used one screw in each joint on the top of the duct only (so it would not catch wood chips). The elevation of the slab was about a foot above grade in a reasonably dry area. With the sand, elevation, and frost walls there would be little moisture and oxygen in the soil there.
I also ran PVC conduit under the slab with the final portion that stuck up through the slab being galvanized schedule 40 with a box mounted a couple of inches above the floor for power for the table saw. Then pulled AWG 12 THHN conductors.
So the wiring and duct did not interfere with the radiant floor heat.
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