Mechanical systems

I am interested in how other people have dealt with the plumbing, heating, and electrical systems in timberframe homes. I am going to build a false subfloor over my second floor timber joists with 2x8 24" OC, with 3/4 T&G plywood over that. I will rip 1/2" OSB 4" then nail it to the joists for bearing surfaces, and place drywall between the timbers. The resulting space will provide wire and plumbing chases. If you have experience I would greatly appreciate a reply. I hate to reinvent the wheel, but I have had to do it in the past.

Installing chases for mechanical systems is a common issue in timberframes. A variety of solutions abound and the second floor build up that you describe is a common one. In your case, I think it would be easier to simply install the sheetrock over the timbers and then build the 2x8 subfloor on top of the sheetrock rather than building out both the floor (up) and the ceiling (down) into the underlying room.

I agree with Brian. In addition to extra work, expense, and materials, you reduce your useable space. That is fine if you began with 9' rooms (height) but if you started with 8' rooms, you might wind up with about 6 1/2' of useable space. You can see the problem.
Perhaps a better solution is one I recently saw in a timber frame house I was visiting. The plumbing was run across the ceiling of the first floor up aginst a beam and a chase with a mitered corner was built to but up aginast the beam on the bottom so it was the same level and was hinged with European hinges about every 3' and on the side was held in place with snap locks so it could be lowered for repair/inspection/service& cleanout.The same was done with the stacks along the wall. To make it match, a false chase was created on the opposite side of the room. It was very neat and required only a minimum of extra material and labor and kept the upstairs the same as it was. Since the beams were 6"x6", it posed no problems at the intersection where the sweep tee received the line coming across the ceiling. It looked very clean, professional, and gave the appearance that some forethought had gone into the engineering so as to widen the beam at this point to carry additional weight loads and no one even paid attention to it. Had I not been looking to see how the plumbing was handled, I would not have seen it. The water supplies were included in this same chase. Perhaps this is a cost reducing idea you could adapt for your use?

Keith in Houston

Thankyou for the input. Perhaps I wasn't as
clear as I should have been.(I'm more used to
explaning with pictures). The 1/2" OSB will
be nailed to the top of the joists, with a
1" reveal on both sides. The joists will be
4' OC allowing me to remove the edge taper
(8" total) on the drywall, thus allowing
me to drop the gypsum board on top of the
joists in the provided spaces. I think this will give me a clean ceiling, with a minimum
of taping. What I am most interested in is,
What order of construction would you use?
I plan on framing the floor without the
subfloor, (just using x-braces) then, moving
in the sub's to run electrical, and plumbing
and heating. Next I will place the subfloor
with the proper holes snake up the wire and
poly b. piping. After this I plan to
frame the second floor walls. Does this make
sense, or is there a better way? The main
problem with this plan, as I see it, is
I will have to move in the subs twice, and
there will be more work for the carpenter.