Shop floor load question

[Damon McLaughlin]

I am in the planning stages for having a shop built by a well know custom shed/shop/garage building. I am looking at a 14' by 30' building. The standard floor construction is 2x8 joists on six 4x4 skids, the joists are 16" on center and the floor is 3/4" tongue and grove boards (not sure yet which ones). I have the option of having the joists 12" on center and I could double up on the 3/4" boards for a 1.5" thick floor but I'm wondering if this is even necessary. The heaviest piece of equipment in my shop will be my Powermatic 3520 lathe which weighs about 750 pounds.

Is the standard floor sufficient for the load? The cost to go 12" on center is minimal so I'll probably do that. The cost to double up the floor with two layers of 3/4" boards is $540, the cost to upgrade one layer of 3/4" to 1" thick boards is $225.

While I'm at it, are double pane windows worth the extra cost of $61 per window? ( have six windows planned).

Thanks for your input.

[Jim Becker]

3/4" flooring over 12" OC will be pretty sturdy I would think...

[Bryan Lisowski]

I would do the 12"oc and just the single layer of plywood. Use the floor savings to do the double pane window upgrade. If down the road you feel some bounce by the lathe you could glue and screw another sheet you get from the home center.

[Bill Dufour]

With metal lathes it is very common to put a large plate under each leg to spread the load. Save your money for the windows. If they lathe ends up needing more support throw down a sheet of plywood under it. I am surprised you can buy single pane windows. Are they special order?
Bil lD.

[Tim Bueler]

Damon, I'm more or less in your neck of the woods. Believe me, in Spokane you will want double pane windows and lots of insulation if you plan to use your shop during the winter.

[David Gutierrez]

need more info, what is the joist span? what is the footprint of the lath? the weight of the lath divided by the area it covers will give you the pounds per square of floor load. this in conjunction with the span and spacing of the joists will provide enough info to check the floor joist.

[Todd Mason-Darnell]

I just ran the span calculator at:

http://www.awc.org/codes-standards/calculators-software/spancalc

You will have no issues with 2 x * on 12" centers. The max span at 100 psi live load is 9' 9"--way more than you will have in the shop with woodworking equipment.

[Lee Schierer]

You can determine whether the 2 x 8 lumber on 16" centers is sufficient for your anticipated load with the joist span calculator (http://www.awc.org/codes-standards/calculators-software/spancalc).

With regard to your windows, Yes sealed thermopane type windows are well worth their cost. Be sure the window frames are also insulated. Energy costs for heating and cooling are not likely to go down.

[Damon McLaughlin]

Damon, I'm more or less in your neck of the woods. Believe me, in Spokane you will want double pane windows and lots of insulation if you plan to use your shop during the winter.

I agree with both points. My current shop (12x20) is nicely insulated though it only has single pane windows. This past winter I kept it at 69 degrees 24/7 and my monthly electric bill only went up $50. My larger shop will be insulated and the builder is also insulating the floor, my current shop's floor isn't insulated and my feet were cold all winter.

[Damon McLaughlin]

Thank you everyone for your thoughts and suggestions. I'm meeting with the builder next week so that I can get blue prints to submit with my permit application. Will be nice to have a little more space and a warmer floor.

I decided to go with 12" on center floor joists and keep with the standard 3/4" flooring. The extra money will go to upgrading the windows to double pane.

Now one more question. I want to insulate the roof. My current shop has 2x4 construction and I used batten insulation so there is no air gap between the insulation and roofing boards. I learned after that one should have air space between the two. I can pay $350 to have the roof upgraded to 2x6 construction which would allow me to use batten insulation which would leave a one or two inch gap for air circulation between the insulation and the roofing boards. Or I can keep the 2x4 construction and use 2" rigid foam board to cover the ceiling. I believe I this would provide for a lower R value but it would be easier to do. Suggestions on what worked for you when insulation the ceiling of your stick built or portable building shed?

[Bryan Lisowski]

I would use blown in insulation after you finish the ceiling. If you want to leave exposed I guess disregard my previous.

[Peter Christensen]

My shop is 24’ x 28’ with 2 x 6 walls, R20 fiberglass bats. Roof is a scissor truss with R40 fiberglass bats. Even with the 4/12 pitch roof the scissor truss gives about 30” more along the peak than the 9’ high walls. The raised heal of the truss allows for the insulation and lots of extra room to the sheathing for good airflow. If your contractor is getting trusses then getting scissor trusses won’t cost a lot more but will give you more headroom. Worth looking into. Windows are triple pane pvc but we get -40 temps in the winter. They cut a lot of outside noise so likely keep your noise in if you have neighbors close.

[Bill Dufour]

My power company will pay the difference so you can buy the foil faced roof sheathing for the same cost as the regular wood only stuff.
Bil lD

[Frank Pratt]

Even if you fill 2x6 cavities with fiberglass batts, it's pretty minimal. What's code in your area? I wouldn't go less than R20 in the walls & R40 - R60 in the ceiling.

[Jim Becker]

Now one more question. I want to insulate the roof. My current shop has 2x4 construction and I used batten insulation so there is no air gap between the insulation and roofing boards. I learned after that one should have air space between the two. I can pay $350 to have the roof upgraded to 2x6 construction which would allow me to use batten insulation which would leave a one or two inch gap for air circulation between the insulation and the roofing boards. Or I can keep the 2x4 construction and use 2" rigid foam board to cover the ceiling. I believe I this would provide for a lower R value but it would be easier to do. Suggestions on what worked for you when insulation the ceiling of your stick built or portable building shed?

You are correct that it's important to have an air space between the insulation and the roof sheathing and that's typically maintained by styrene "baffles" that get stapled to the bottom of the roof desk. This is for most types of insulation, but isn't necessary for closed cell spray foam unless a particular local jurisdiction requires it. Spray foam gives you the best insulation for the available space. With a 3.5" deep bay, closed cell foam will provide about R21. (open cell will be about R12 or so) with a 5.5" deep bay (2x6 construction), closed cell will give you about R38 as compared to R20 for fiberglass bats. You have to figure out the best combination of structural cost plus insulation for your particular needs and budget. Lowest cost is likely 2x6 with R20 batts, but you never know...

[Damon McLaughlin]

You all have been very helpful. I decided to wait on the insulation as I will be doing that myself and its something that I won't be doing until the shop is complete. The encapsulated fiberglass insulation is twice the R value of rigid 2" boards and within my budget, at least for the walls. For the ceiling I may go with what I put in my current small shop which is denim insulation. All this could change by the time my shop is completed, I have a few months before finalizing what to go with.

I talked with the builder today, I decided to go with five windows instead of six to eight to keep cost down and because I'm not sure yet if I need the other windows. The builder will rough in for the windows at no cost so if I decide later that I want them it will be easy to do.

[Tom Bender]

Insulation is over rated!

Jim is right on (as usual) about the styrene baffles. Install them and 3 1/2" batts in the ceiling. Install something in the walls. It will be fine. Then spend your money and effort on the more important parts of the heating load.

I have run a number of load calculations on a variety of buildings. Priorities are almost always;

1. air infiltration
2. window and door transmission
3. ceiling transmission
4. wall transmission

Typically windows get framed an inch oversize, the windows installed, siding and drywall and trim. The insulator is supposed to stuff the gap around the windows loosely with fiberglass. If he stuffs it too tight the windows jam. often this is just skipped and you get a lot of leakage. Doors, same.

Fireplaces and sliding glass doors and terrible energy hogs. If you install a vehicle door, get a good one.

Congratulations on the new shop.

[Alex Zeller]

I would use 3/4" advantec sheeting. The stuff is strong and dense. For the small extra charge you could go 12" on center but I doubt you'll notice a difference. My 2nd floor in my garage is 2x10" 16" on center that span 16' to an I-beam that runs down the center of the garage (it's 32 x 36). I have all sorts of heavy stuff up there with no bounce at all. When I was building my house I was worried that particle board flooring wouldn't be as good as plywood but the lumber store talked me into it. I'm sold on the stuff now. It's denser, stronger, and it's pretty much waterproof.