Pre-Fab Amish Workshop foundation question

jaydbalt · October 07, 2013, 09:33:55 PM

I need some help. I am limited to 18' total height where I live on an accessory building. This is for a 14' x 24' two story woodworking shop with a plywood floor. I do not want to stand on concrete all the time. So I would like to go with a sono-tube/concrete and beam based foundation.

The building is 18' tall by itself so I need to get a foundation built. The site is on a gentle slope left to right on the front 14' side. I am thinking to do some excavation into the hill to give me room to do a pier and beam foundation below grade. I would put a short retaining wall on the high side of the slope. The inspector would measure the height of the building from the high side of that slope.

My problem is I want to build the framing for the building as low as possible. The inspector I spoke with today said it would require 2 2x12's on the 24' side. But I was planning on going with four piers on the long side and three for the 14' (short side). So my floor joists could be 2x6. Can I just nail up 4 2x6's for the equivalent of 2 2x12's? This is hurting my brain, and I really do not want to go to a structural engineer just for this foundation/frame.

Any help would be much appreciated.

MountainDon · October 07, 2013, 09:52:18 PM

QuoteCan I just nail up 4 2x6's for the equivalent of 2 2x12's?

Quick answer: No. It does not add up.

Longer answer:
* If you mean 4 - 2x6 laminated side by side to equal a built up beam 6" wide x 5.5" tall. Nope. A deeper (11.25" vs. 5.5" is always proportionally much stronger than increasing width.
* If you mean 4 - 2x6 with two laminated and then one on top of each other, to be a built up 3 x 11. nope. Stacked does not equal one solid 2x12. They flex different.

If the inspector is okay with piers and beams and you want to use something less than 2 - 2x12 ask the inspector what the spacing should be for using multiple 2x8's or whatever. He may tell you; he may not as his job description is "inspector", not "designer". But ask to find out, some are more helpful than others.

OR, go to this section of the IRC and see what other beam materials could work with various spacing of piers. The tables start at 20 ft width, but it is fine to extrapolate. You need to know snow load and what all the beam is holding up, as in how is the inspector counting the loft?

October 07, 2013, 11:08:14 PM

If you might want concrete you might look a the mats that are available. They are warmer in the winter. They are a lot easier on the knees and feet year around than about anything including wood if you plan on a lot of shop time as it sounds as if you might be. By the way

from Idaho......

hpinson · October 08, 2013, 12:24:33 AM

What about: a concrete slab, a moisture barrier, and a lattice of 2x4 sleepers laid sideways. 16" centers, foam insulation in the spaces in-between, and your plywood floor floating on top of that - screwed/glued to the sleepers. I've seen that done in a woodshop. It made cabling and electrical outlets in the floor easy too. It was a very nice floor, warm, easy to sweep, and supported some very heavy machines well.

Squirl · October 08, 2013, 05:41:15 AM

As in the chart don posted, 4-2x8s is close to 2-2x12s. Taller is better when handling load. I-beams are tall and skinny. You can reduce size, by reducing span (more piers).

Also there are more complications when you go with a raised floor vs. slab. I can't remember the code section right now, but IIRC, there must be a minimum clearance between non pressure treated wood and the ground. I believe it is 16-18". You also usually need 18" of space under the floor joists anyway.

If they are enforcing height restrictions, I would assume they are going to enforce most aspects of the building code.

October 08, 2013, 06:05:14 AM

Thank you so much. I'm pretty pissed at myself because I got a variance for a height over 15'. But I only got it for 18'. Many of the buildings are 18' high. So I am in a pickle. All I can do is shorten the height of the first floor to like 7'5, excavate down a foot to give me room for the joist/framing. I can avoid the 18' crawl space by using pressure treated lumber. I did speak to the chief inspector yesterday and he said that was fine. One thing I am trying to avoid is a lot of cost. I have an estimate for $8000 for a monolithic concrete floor, which digs deep into my budget.

I can shorten the span of the beams by adding more piers. I guess I could also dig footers and have cinder block foundation built right up to grade, and keep the sill plate and rim joist as 2'x'6. I would have to have a center set of pilings to use 2x6 for floor joists.

I think this is going to come down to me doing another freaking variance, or shelling out for a concrete floor. I do use 1" thick rubber mats right where I work. I make hardwood boxes and musical instruments. I finish with French polish which can be slick because of the oil. Dropping a box on the floor tends to diminish the quality of the final product.... So the mats protect my knees and my clumsiness of dropping things.

Again, I really appreciate your help here.

Squirl · October 08, 2013, 07:45:50 AM

In most markets that I know of, $8,000 is very high for a 336 square foot slab for an auxiliary building. Around me it would probably be about $1,500 in materials and the rest labor. $6,500 in labor for 1 day of work is a lot.

Would you mind if I asked the general location? Geography effects many options and aspects.

jaydbalt · October 08, 2013, 10:44:08 AM

Baltimore

Squirl · October 08, 2013, 11:56:03 AM

Thanks. I know that in the IRC there are exceptions for accessory structures under a certain square foot are not required to have a frost line footing (although they are usually a good idea). Even though Maryland is under the IBC (very similar to the IRC), I found the answer I was looking for.

http://www.baltimorecountymd.gov/Agencies/permits/pdmfaq/pdmfaq_bldginsp.html

QuoteQ. What size accessory structure requires a footing?

A. Those exceeding 400 square feet require frost-line footings.

$8,000 for a 336 square foot slab is high even for an east coast city. You might want to call around for other quotes. If you are at all close to the city, there should be a ton of sidewalk contractors. 14x24 isn't much larger than a large sidewalk. Find one with a decent reputation. If you were going to excavate a hill side and install a retaining, leveling the site for a slab seems about the same amount of trouble.