Here is a picture. Maybe I should have led with that instead of my novel. Hah!
What would you change? Thanks!
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.
Here is a picture. Maybe I should have led with that instead of my novel. Hah!
What would you change? Thanks!
One thing I'd change (before even looking at the pics) would be to change all XPS to foil-faced polyiso, since XPS has more shrinkage issues over time, is harder to air-seal, melts & shrinks with heat/fire, ignites at a lower kindling temp, and uses blowing agents with 100x the global warming potential of the pentane used for blowing polyisocyanurate. Purpose-made 2" FSK tape makes sealing the layers of foil facers very quick & reliable. The only real issue to look out for with polyiso is to keep exposed edges off the slab where it can wick up water.
Using rock wool batts rather than R13 fiberglass is more fireproof and higher R. In your climate the faced/unfaced is really irrelevant- air-tighness is key. Before insulating any of the pony wall bays it's important to first air seal the sheathing to the framing, either with can-foam/Froth-Pak or acoustic sealant type caulk, for both thermal an moisture performance reasons. Using foil faced iso on the interior of the studs puts a true vapor barrier on the interior side, which means if you ever wanted to add exterior insulating sheathing you'd be limited to EPS or rigid rock wool, but even an inch of polyiso improves the thermal performance of the assembly by more than a third, and 2" would cut heat loss in half.
Looking at the picture, if there's any space to add some rigid insulation between the duct and exterior wall as an air barrier and thermal break to the studs on that end it would be a real enhancement too. Air seal the ducts before boxing them in with duct mastic on every seam & joint, and if they're supply ducts rather than returns, insulating the ducts themselves to at least R6 is worth it. (an inch of closed cell spray foam works.)
The rim joist should be air sealed before insulating too. An inch of rigid foam cut'n'cobbled and foam-sealed onto the rim joist followed by batts is sufficient dew point control. Unlike R13 fiberglass, R15 rock wool is dense enough to not lose much performance to convection, and would not need an interior side air-barrier to work well, provided it's trimmed to a snug fit. Getting a good air seal to joists & subfloors with kraft facers is nearly impossible, but necessary to get the thermal performance out of fiberglass. (The big box store chains now carry Roxul rock wool batts in most US locations, but you may have to ask for it.)
Last edited by Dana; 07-10-2013 at 03:38 PM.
Dana, thanks so much for your reply. I've already benefited from all the great information you've shared on other topics and I really appreciate your efforts.
I'm a little surprised by the foil-faced polyiso. I already used 3/4" XPS under Advantech for the flooring, and was just sticking with the XPS for familiarity. However, I've seen that you often recommend EPS over XPS, and was kind of expecting that to come up instead. I do like all the polyiso benefits you mention, but isn't it a bad idea to put a vapor barrier on the interior? I thought one benefit of XPS and EPS was the ability to dry to the interior? I don't expect to ever add exterior insulating sheathing, since there is existing veneer brick over both the CMU and pony walls, so no problem there.
For the pony walls, I'm planning to remove existing drywall and batt insulation to air seal as you recommend. If the batts are in decent shape I'll likely throw them back in the exterior stud wall. If the new pony walls are built on the flat, there should be room between the two pony walls for at least 1" of foam, and maybe 2". I like the idea of covering the outer wall with foam and taping to seal it off completely. I should be able to squeeze at least a 1" layer of foam between the ducts and the existing exterior pony wall also, good idea.
The ducts are supply, and are completely in conditioned space. The shop and the upstairs are both fed from the ducts, though I could choose to seal off the shop supply - which is a major path for noise escaping the shop. I'm just not sure the shop will be comfortable without HVAC. Since the ducts are in conditioned space, is it still recommended to insulate them to R6?
Rim joist air sealing, got it. Thanks for confirming that 1" of foam on the rim joist is enough. The insulation in the rest of the ceiling wasn't for thermal benefits, since the shop and the space above are both conditioned. Assuming this doesn't change, the batts in the ceiling are there for soundproofing only (except the rim joist area). Given that, is rock wool still a good idea? The R13 fiberglass is in the plan because it's cheap and easy enough to add it, but it's not even the primary soundproofing strategy for the ceiling. The sound clips and green glue are really the first line of defense.
The advantage to polyiso is you get 50% more R/inch than with EPS. The downside to foil facers is that you have to be careful about where they are in the stackup due to their extreme vapor retardence.
For anything above-grade in an Atlanta climate putting it on the interior side of the assembly is fine, as long at the average summertime temp on the outer-most facer of the iso is above the average summertime outdoor dew point (which it is, in your stackup), and the outer layers are all reasonbly vapor permeable for drying toward the exterior.
For wintertime dew-point control, as long as the inner-most facer averages above 40F in January you're good to go too, so long as you don't put in another highly vapor retardent layer.
On the below grade sections I worry a lot less about putting vapor barriers against CMU than I do with poured concrete, since CMU has much lower capillary wicking power than concrete, and is more porous, drying more quickly at the above grade exterior. With poured concrete there is some concern about wicking moisture into the foundation sill & band joist if there isn't a really good sill gasket (or metal flashing) or EPDM membrane between the wood & concrete as a capillary break, but with CMU, not so much.
If you have the space/depth and want to use 1.5" of EPS instead of 1" XPS/iso that too will work. It'll be comparable to or slightly cheaper than foil faced iso, but it's harder to get a really great long term air seal on it due to the granular characteristic of the material, whereas getting a good seal taping foil facer seams with 2" aluminum FSK tape is dead easy. The primary issue is the space though- if you're conserving space, the higher R/inch of iso can tip the balance.
For the soundproofing layer R13 fiberglass is fine, but at the rim joist putting rock wool over the 1" foam is better. Air sealing both the subfloor above and ceiling gypsum is at least as important as the batts.
Supply ducts may run into condensation issues & dripping inside the soffit during the cooling season unless insulated. Air sealing the seams & joints is still more important though. IRC 2012 calls out R6 duct insulation for cucts in unconditioned or semi-conditioned space, R8 if routed in unconditioned attics. If you're fully conditioning the shop with it's own duct registers (both supply & return) you can skip the duct insulation, since there will be regular air exchanges keeping the dew point of the basement air sufficiently low to avoid the condensation issue. It doesn't take a huge air-flow to fully condition the basement, and it's cooling loads will be quite low relative to the upper floors, so if you have to add the registers be careful not to oversize them or it'll get pretty cold down there during the cooling season.
Again, thanks for the very thoughtful reply. Sorry it took me so long to get back to this thread, but I've been working out of town for a bit.
Based on the feedback so far, I've modified the drawing slightly. The modified version is below.