Woodworking Shop Buildout
I am planning the buildout of a wood shop in my “new to me” home, and I would appreciate input from the forum. Goals for the project include insulation for thermal control, soundproofing to reduce machinery noise migrating to our living spaces, and of course there are a few special requirements for the shop. Thanks in advance for any advice, and for slogging through this lengthy post!
The house itself was built in the 20’s, but the shop space is the lower level of an extension built on our home roughly 20 years ago so it’s fairly modern. I have some demo work to do, but here is what I can tell about the construction. The space is roughly 17 feet square. The walls are CMU construction, and transition to 2x4 pony walls after 9 courses of block – roughly 70” off the floor. The exterior is a single course of veneer brick. One wall is shared with the house, and strangely is also CMU to the same height. There is a large opening in this wall, maybe 60” wide which connects to the house. I plan to install a thick set of doors in this opening. The ceiling is roughly 10 feet tall, so I have a little headroom to work with. Ground level gradually slopes down from the highest spot, so that there is a pair of French doors to the exterior on one wall, and several windows on exterior walls. The sill of the doors is roughly 15 inches above the slab, with a small step. There is evidence of water infiltration in the past around the room, but I am fairly confident that recent upgrades to the gutters and grading on the exterior have minimized this issue. There are no interior or exterior drains that I know of. Tests with small sections of poly taped to the slab were dry after several days.
FLOOR: I found some great information in other threads on this forum, and developed my flooring plan accordingly. First, a layer of 6 mil poly sheeting was applied to the slab and roughly 6 inches up the walls. I temporarily caulked the edges to hold them in place, but this has worked loose so I am planning to go back with duct mastic and seal the edges of the poly to the CMU walls. Next came a layer of ¾” XPS. I used Foamular 150 which was all I could find locally, though I would have preferred a little extra compressive strength since there will be some heavy machinery in the room. On top of the XPS, I put down 23/32 T&G Advantech subflooring fastened with tapcons every 24”. Truthfully, this is still in progress as time got a little tight before moving in so there are still some fasteners to be installed. This will be used as the finished floor as long as this room is a shop, and I will likely paint the floor with a durable type of porch/floor paint. In the future, some other flooring can be added fairly easily if needed.
CEILING: My biggest concern here is trying to prevent the noise from the shop from going straight up into the living room directly above, though I want to get the insulation details correct also. The ceiling above is standard dimensional lumber, nothing fancy like I-Joists or anything. There is an existing layer of ½” drywall, but I plan to demo this so that I can improve the soundproofing details and likely the insulation also. I would of course seal all penetrations in the floor above and the rim joist areas with caulk, though I don’t yet know if I need to splurge for acoustical caulk or whether there is a cheaper alternative. I guess I’ll insulate the rim joists with XPS, but I’m unsure of the thickness. I have access to ¾”, 1” and 2” locally. After the caulk, XPS, and more caulk on the rim joists, I’ll fill the remaining cavities of the framing with unfaced fiberglass batt insulation as a cheap improvement before closing up the ceiling. I’m assuming for now that the ceiling above is framed 16” on center, and have not decided how much fiberglass to put up there, or whether to install it tight to the underside of the floor or instead in the lower part of the cavity. After the insulation, the plan right now is to use soundproofing clips and hat channel, such as those sold by the Green Glue company. I’ll probably go with two layers of 5/8” sheetrock, with Green Glue in between for further sound reduction. The first layer of sheetrock will be quickly taped and mudded to seal the joints, and then the second layer will be offset from the first and fully finished. The lighting in the shop will probably be fluorescent fixtures, surface mounted to the drywall ceiling and therefore still floating. Not sure yet whether the wiring will penetrate the ceiling, but probably not if electrical boxes are required – to prevent holes in the soundproofing. I have a dust filtration unit that will also hang from the ceiling, and I’ll likely substitute a 4’ x 4’ sheet of plywood for the first layer of sheetrock in this location so that the unit can be hung easily and securely. All the edges of the ceiling will be caulked before walls are installed. Finally, there are a few leaky ducts around the ceiling perimeter, supplying the shop and the room above. These will be sealed with mastic. I know they are leaky because the exploratory holes I cut in the ceiling feel like a new supply register when the AC is running, hah! I’ll have to build soffits for these in order to keep the noise in the shop, and likely cover with the same double layer of 5/8” sheetrock and Green Glue. Not sure if the sound clips and hat channel will be practical in constructing the soffits.
WALLS: Ugh. I thought I was doing pretty well so far, but here’s where I’m stuck. I’d like to preserve as much floor space as possible so I’m trying to avoid building an interior 2x4 wall. I’d like a layer of drywall for fire blocking, but this may not be needed on the lower portion of the walls since they are CMU. The final visible surface of the walls will be plywood for a couple reasons. One, because it makes it really convenient to hang things like cabinets and lumber racks. Two, because you should have wood on the walls of a woodworking shop. I’ll probably get some decent looking sheets of “A” faced plywood and rip them into 12” strips. I can attach these horizontally so that I get a “planked” effect – which should look nice when you squint your eyes and turn the lights off. Hey, it’s just a shop, right? For soundproofing, I plan to use Green Glue between the drywall and plywood to decouple them. Now, what’s behind the plywood and drywall? Hmmm.
For the masonry portion of the wall, there are two assemblies I’m considering: The simplest would be a 1” layer of XPS with seams caulked, followed by the final layer of ¾” plywood attached with tapcons. This would get me R-5 continuous which is consistent with what I’ve seen for Zone 3 recommendations. I think the plywood should be safe from rot, since it would fill the same role as furring strips in this option. Electrical would be run on the surface of the wall in conduit.
As an upgrade for the masonry walls, here is a more complex assembly: two layers of ¾” XPS, ¾” furring strips, ½” drywall, and finally ½” plywood (or maybe ¾”?). If I go with this option the final wall thickness of 3¼” to 3½” would allow me to run electrical in the wall, which is an upgrade in my opinion. I could run the electrical first, so that it lies in the same plane as the first layer of XPS. This layer could be trimmed to fit and foamed or caulked tightly around the electrical. The second layer of XPS would be continuous. The ¾” furring strips would be attached with tapcons, say 24” on center. With careful planning I can offset the vertical electrical “channels” and furring strips so that there is no overlap. I am wondering about adding a third layer of ¾” XPS between the furring strips. Two ¾” layers should be R7.5, except where the electrical “channels” are run vertically and of course where the boxes are. A third layer would get me to R11 or better, except of course where the electrical “channels” and furring strips are located.
How simple it would be if the masonry walls went all the way to the ceiling, but they don’t. The upper pony walls are framed with 2x4’s, and I assume they are 16” on center though I need to confirm after the existing sheetrock is demo’d. There is existing kraft faced batt insulation, but I don’t know how well it’s installed or if this type of insulation is desirable. The walls are sheathed in plywood, and it’s a mystery what may lie between this and the brick outer layer. There is about a 3” offset between the face of the CMU’s and the inner face of the 2x4 wall. I’m struggling with this ledge, trying to decide whether to keep it or frame another inner pony wall to make a single flat wall surface.
If the ledge stays, I think I’d go with fiberglass batt insulation (keep the faced or go unfaced?) in the 2x4 wall. Since the pony walls are mostly exterior walls, I think the soundproofing clips would be overkill – especially given the doors and windows. I’d stick with ½” drywall directly on the studs, a layer of Green Glue, and then my planked plywood finished layer. Given the “complex” buildup of the masonry walls, the final ledge depth could be as much as 5” between the upper and lower walls. In this option, would there be any benefit to adding a continuous layer of XPS across the pony walls? It would bring the total R value of the wall up, but I’m not sure about the impact on moisture control.
The other option for the upper walls would be to frame a new pony wall, using 2x4’s that are 24” on center. From a soundproofing viewpoint, the double framed wall and the 24” spacing would both be improvements. I would need to make sure the new inner pony wall could support some heavy loads (lumber racks), so it would be framed and secured all the way up to the existing ceiling joists if possible – though in some areas HVAC soffits might require me to tie back into the original exterior pony wall. The new pony walls would be built to bring the final layer of planked plywood into the same plane with the lower walls, which of course depends on which lower wall assembly I choose. If using the “simple” lower wall assembly, I’d likely need to build the new pony walls on the flat. Either way, my best guess is that the two stud walls would have 2” between them. Insulation would probably be two separate R-13 batts, keeping the gap between the walls clear. I am unsure of this insulation strategy, and I’m considering a layer of XPS on the original pony wall – either instead of the second batt or in addition. The surface of the wall would still be ½” drywall, Green Glue, and the planked plywood. I’m planning to use the Green Glue here to prevent sound from travelling up the wall and around the edges of the ceiling.
NOW WHAT? If you’re still reading, thank you so much for taking the time. If you have an opinion (other than “He’s nuts!”) or some advice, I’d love to hear it. As you can tell, I’ve put a lot of thought into this plan and I really want to get it right.