Raised Floor

[Ted Jay]

The first thing I think about is having to spend the extra money for the concrete your going to put a floor over. Concrete is expensive nowadays. I would opt to have a concrete grade beam around the perimeter of the shop area and down the middle, and spanning between those with either I-Joists or 2x12's. (I don't have the span table in front of me for a 15 foot wood span.) If your ground is frozen right now I can imagine how much heat it is going to take to warm up the shop and any issues with condensation between that cold concrete floor and raised wood floor. But I would at least spray in some expandable foam in the floor joist after the duct work install to keep as much of that cold in the concrete, and away from the floor.
Ted

[Allan Daskam]

Alot of good ideas ,good or bad this is mine . I built my shop 4 years ago. I live in north Iowa. have radiant heat in the cocrete,first a heavy mil plastic than 2 inch foam made to go under concrete, tubing, rebar, and concrete. but if i had taken your route i would go heavy mil plastic, concrete. than for the raised floor, all wood in contact with the concrete would be treated, that would be the 2x10's. put 2x10's around the perimiter fastend to the poles. If the poles are on 8 ft. centers you may want to put a 2x4 flat between the poles to keep the 2x10's strait, but don't think this is a must do. now there is a solid box. than the stringers can go in with 2" or more of rigged foam between the stringers and down on the concrete. leave a break or two in the stringers to run duct work acorss the stringers. for 16" spacings cut the foam 14 1/2" or 10 1/2" for 12" spacings. Yes i am pushing for 12" spacings, just a few more 2x10's. Than lay the sub floor. With walls on 4 sides 2x10's with rigged foam at the base, for insulation and a spacer, subflooring screwed down to the 2x10's things can't tip or move in any direction, so no need to fasten to concrete at all. one side note you could get a squeak from the foam when things are moved around (maby, don't know).

[Matt Ocel]

William -

It seems there are a lot of cooks in the kitchen.

If you want your DC under the floor, why pour concrete?

You can run I joist full length (you can get them up to 60' if your lumber supplier gets them off the rail cars) add a center grade beam, you can go 24 oc they make a 7/8" t & g sub-floor but I would go 16" oc in a shop.
You local lumber supplier can calculate the live and dead loads for you usually at no cost.

You can bolt a ledger to you exterior post and frame the floor like a exterior deck.

With I 9 1/2" engineered I joist you would be able to cut 6" holes (As long as you follow the engineering guidlines) for DC so any extra framing is not needed.

To prep the ground just cover with 2" foam and by taping the seams that will be all you need to do for a moisture barrier.

If you choose to pour concrete underneath (alot of extra Cash) make sure you pour a grade beam(ie thickend slab, footing) for a mid point bearing.

A tip - either way you do it lay out your shop and pull all the appropriate wire needed to wire all machines and future machines.

My .02


Just remember -

If you have any questions on loads, mechanical fasteners, materials, procedures, go to your local Lumber company.
They are usually more than happy to help. Plus they have a preety good idea of local building codes.

[Ray Knight]

If you are going with framed wooden floor, concerned about how to have essentially floor joists connect to concrete slab, then the next question is why spend the money pouring a slab you won't use, and that gets in the way. Pour footers, and frame with floor joists and leave a crawl space. That way you can put your dust control, wiring, and what ever else you need where ever you need it, get to it later, move it. seems like the concrete slab is spending extra money and getting in the way of your plan to have raised floor joisted floor. If you want to convert to concrete later for next owner purposes, you tear out the joists, and pour the floor. Now if you already have the slab, have the extra headroom, want raised wooden floor, then you are back to the discussion you are having. wish I had those options. I have a slab, with a slope to it, and only 8ft of headroom, so my wood floor options are limited to thin overlay. Good luck Ray Knight

[Matt Hutchinson]

Concrete is getting to be ridiculously costly. I would have to agree with the above who think that pouring only footers, no slab, is best. Not only is it more costly, but you have annoying little issues when trying to install joists, like "where is the high point of the slab?".

So here's my vote: floor joists on 16" centers resting on concrete or block that is poured/layed between footers. This is low cost, but there are a few things to work out that the contracters would have solutions for. I would call someone (a contractor or two) and have them come out to your place and discuss the options. Any person in constuction worth a darn will be able to give you the pros and cons, and likely will have solutions based on factors that some of us may be forgetting.

Hutch

[Jim Becker]

I will attest to the fact that concrete has gone through the roof, figuratively speaking, relative to cost...there is over 30 yards of 'crete in our addition, not including the patios and walkways and that was one budget item that was way over from the original figures. There is a lot of merit in just pouring an appropriate footing and perimeter arrangement and then using piers to support a joist system for your floor.

BTW, one of the issues with putting your wood structure directly on the concrete is ventilation. Like any "crawl space", even if it's only a few inches deep, proper ventilation is important to avoid mold and other issues around moisture, etc. Using a poured sill and piers to support your wood floor will make it easy to maintain air flow through the space for proper ventilation.

As to engineered joists, my shop ceiling in build with them. (Supports the second floor) They are awesome products. They do cost a little more than traditional lumber but as you surmise you can get them in almost any length you need. That cuts labor costs for installation. They also carry a lot of weight for a given size and are easy to route utilities through without compromising strength.

[William Parks]

I want to thank everyone for their helpful advice. I have taken your suggestions and currently in conversation with our contractor about not pouring concrete in the shop area and putting in piers for floor joists. Grading should start sometime this week so I suspect soon we'll be moving at break-neck speed. I can see where this project is going to be a real challenge/learing experience about building construction versus making furniture, but I'm excited to get started on my new shop.

[Jim Becker]

William...one word: PICTURES! (When you get going, that is... )

[Pat Germain]

Anyone know why concrete has become so expensive? As far as I know, they aren't mixing rice, flour eggs or gasoline into it. Perhaps it's the cost of transporting the raw materials, then the final product?

[Bryan Rocker]

One quick comment about ventilated crawl spaces. If you look at some of the recent houses built on crawl spaces you will find they do not have any vents. If you ensure you have the moisture/water issues controlled, as in removing them either via drain or sump pump you can seal up the walls of the crawl space. The key here is moisture control. One common addition in sealed crawl spaces is a small fan that monitors moisture levels, turns itself on to blow moisture air outside the crawl space until the moisture back within limits.

[Jim Becker]

Bryan, in this area, a crawl space can be sealed as long as it's properly insulated to control moisture, etc. In most cases, that's spray foam. I know this because we went through it for our addition...there was no place to do any ventilation anyway due to the grade (wells would have cause all kinds of issues with the back patio) But what I referred to earlier in this thread was insuring that there was good air flow in and around the joist system itself which would have been a more complicated issues with the joists sitting on a concrete pad.

[Matt Ocel]

Code calls for crawl space to be ventilated wether it be active or passive.

Concrete is becoming so expensive because of the Portland cement.

[Jason Roehl]

Matt, "code" is a pretty nebulous term--it varies greatly from area to area, state to state, and even town to town. What may be code requirements in your area isn't even on the radar elsewhere. I read a few construction journals, and there is an ongoing debate about various ventilation/insulation issues, be it crawlspaces, wall, roofs, etc. Add in all the different climate zones in this country, and it becomes difficult to codify consistent weather-tight/insulation practices nationwide.

[Matt Ocel]

Jason -

You are correct. I was in a hurry this morning and on my way to work I thought to myself - I should have been more specific and wrote "IRC" code or "typically".

I stand corrected!

[Matt Ocel]

Jason -

There is and will always be ongoing debates on insulation/ventalation issues simply for the fact that building materials and building practices are always changing and usually for the better.

P.S. Lafayette IN. flies under the IRC code which under section R408 requires Ventilation in Under-Floor Space (aka. crawl space)