Adding pole barn extension to existing metal building

[pclausen]

I currently have a 30x48 4 bay shop that I'm outgrowing, so I want to add another structure next too it. The existing building is a mix of steel and wood made by a now defunct company called Miracle Truss.

I want the add-on building to be 36' deep so that my 24' gooseneck trailer can be parked in it and stay dry.

Rear shot of existing building showing where I envision the extension going:

Another rear shot. Notice the grade. I'm thinking of building up the back corner using cinder blocks, but not sure how that would integrate with a pole barn?

And a series of front/side shots to get a better idea of what I got to work with:

I found this plan for a 36' pole barn:

http://www.public.iastate.edu/~mwps_dis/mwps_web/plans/72056.pdf

And from those drawings, here are some plans of various details of how it is constructed:

I was not planning on putting siding on the end that butts up against the existing building, just extend the existing sides out 3 feet on the existing end to meet the corner 6x6 posts of the addition. Not sure how to tie in the roof though?

As stated above, I'm also not sure how to best deal with the corner that will be below grade. Ideally, I would want to extend my lawn right up against the 2 side walls that will be below grade. I'm concerned with water/moisture as that is current an issue with the area where the trailer is parked. Eventually, I'd like to pour a slab under the extension, but for now I'll likely to go with gravel.

I thought about a lean on roof, but it would need to extend 3 feet on either side of the existing building to get my trailer covered. I need the extension to look well integrated with the existing shop (I'll be using white and green metal siding to help with that). Wife is pretty insistent that the view from the house on top of the hill needs to be pleasant and that the whole thing will integrate with the lawn/garden.

Here's what the existing end wall looks like from the inside (wall behind the tractor):

I think it will be difficult to add any type of structural support give the construction of the existing building (metal columns with wooden 2x4 girths).

How would you go about adding a 36' deep by 32' wide double bay extension to a structure like this?

 

[Zebrafive]

How tall are the walls of your existing building?
If you were to extend your current roof, what wall height would you end up with on each end with the 3' increase at the front and rear? It will be lower. Could you live with this wall height?
If not, and you move the addition rearward, so front wall is same height as current building could you live with the resulting lower rear wall height?
If not, I would build same height as your current building with a resulting higher roof, same style, pitch as your current building.
If by lean to roof you mean attaching to your current building and sloping to the new wall 32 away, I would not do this. The only way I would consider a lean to roof is if you were only making a parking stall for the trailer, 10' - 12'
wide, but not if 32' is the plan.

 

[pontiacman]

Try to keep the foundations similar to avoid movement due to frost (if you are in an area with frost). Non frost protected (slab) vs frost protected (frost wall) will move differently and could cause problems with the attachment point.

 

[pclausen]

Existing building is 12' tall (doors are 10x10 feet). My tractor is about 110" tall, so I think I could clear the front by maintaining existing roof line 3' front and back. However, I really like the idea of moving the addition back 3' so that the front lines up with the existing structure. I can live with a lower rear wall, and it would blend in better from the house. Would require custom trusses (my current quote was for regular 36' O.C. trusses with 1' overhang from Lowes). I guess I could draw up what I want and get Lowes (or some other supplier) to quite them for me? Or maybe make my own?

Front line around here is 24". Current structure has a foundation (frost wall?) around the entire perimeter with a 12" thick fiberglass reinforced slap. I was going to dig 24" diameter holes 30" deep and pour a 6" cement footer into each for resting my 6x6 main posts on. Then fill the rest of the way with cement once my initial framing was done. At a later date, I was going to come back and pour a cement slap inside the addition. Maybe I would be better off doing all the cement work up front?

 

[pclausen]

I started excavating for the extension this past weekend. This is what things looks like so far:

The plan right now is to put in a cinder block retaining wall up against the rear and right dirt side walls. I will install corrugated flexible drain tubes on the dirt side below slap level, and backfill with gravel to get proper drainage. I plan to use the "deep" cinder blocks and will drop in re-bar and fill then with concrete.

The retaining wall will be around 8 feet tall in the back corner, so there will probably be quite a bit of force in to, but being an inside corner like that should add a lot of strength, no?

This shot, before I had done much excavating shows what the challenge is. There will be all kinds of run off from the grade behind and to the right of the shop extension. I hope the precautions I take will be enough to keep the extension nice and dry.

I plan to coat the dirt side of the retaining wall with some sort of water barrier sealant before back-filling with gravel.

 

[Wnc3]

Maybe consider making it a free standing building. It sure eliminates the tie in problems and matching roof material, style and pitch. Even if it is only 1 foot away from the existing. Or if you have the room find a whole different area. It is not like you must have the trailer parked next to the shop and the money on the retaining wall could be put toward a concrete floor.

 

[rambler]

I plan to coat the dirt side of the retaining wall with some sort of water barrier sealant before back-filling with gravel.

That is a troubling comment to me. I would not want to try holding back water with an outdoor block wall, holding back the dirt is hard enough.

If you get over 4 feet or so, I hope you plan on doing a step-back type of wall, not a vertical one but each layer of block is set back.

Tile lower than the bottom level of the blocks a foot or 2 into the hill, with drainage outlet to somewhere, and a layer of gravel vertically over the tile so any water coming out of that sidehill will drain down and out and be away. You don't want any water pressure on the blocks, and you sure don't want them sealed to hold up water? Sidehills bleed water out of them, you need to get it down and gone, you sure won't hold it back successfully.

I see many sheds with an addition like you prepose, I'd do the same foundation type the original has, if the 'offset' truss proves to be spendy you just get traditional trusses and line up the front of the building, let the back of the building be offset, and you have a funny little seam and roof sliver that has to be sided, takes a lot of cutting of tin, but tends to look ok when you are done.

--->Paul

 

[pclausen]

Appreciate the feedback. The more I think about it, the more a separate retaining wall a few feet away from the stop extension might the the safe/wise way to go. I was having a hard time envisioning how to transition from block to metal siding on the rear and right walls, especially as the blocks steps down following the grade.

I was looking at the Keystone Retaining wall installation manual, and if I went that route, the retaining wall would like this:

I think my soil type is silt/lean clay as opposed to sand/gravel or silty sand, which unfortunately put me in the most challenging category for engineering a retaining wall as I need to use this chart:

So it looks like Keystone recommends consulting an engineer for case 3 for anything taller than ~6 feet.

Here's another page from the manual with a picture showing more or less how my retaining wall would look when completed, if I get up going that route. The only difference would be that the back wall would slope down as it extended to the left instead of remaining at full height.

 

[pclausen]

It's been a while since I have provided an update, so here goes.

First of all, once I looked into the price of a Keystone retaining wall, I decided that was way out of the budget I have for adding this extension.

Things have been moving along nicely. Here are some pics of the excavation for the pole barn extension. Site is leveled to within half a foot now with an average depth of 10" from where the floor will be to allow for 6" of gravel and 4" of concrete.

My main concern is the access from the front as the driveway coming in is quite a bit higher than where the apron will be.

I drilled out the 6 24" holes for the 6x6 posts. Ground was extremely hard and I ended up breaking the hydraulic downforce bracket on my pto auger the 6th hole.

Here's a shot of the 6 completed holes:

I then added a few inches of gravel to the bottom of each hole.

Bottom of holes are about 45" below where the finished floor will be.

Then it was off to Lowes to pick up a pallet of cement, 6 6x6x16 posts, lag bolts and misc lumber for bracing.

I then installed 5/8" x 6" lag bolts at the bottom of the posts.

Getting ready to raise the first post.

And it's standing.

Posts closest to shop have been plumed and braced.

Time to start mixing the cement.

1st pole took 13 80# bags.

2nd pole took 14 bags.

Now it was time to setup the batter boards in the rear.

And late afternoon mixing cement for the final post:

And a shot after cleaning everything up:

Had a friend help stand up and brace the 4 posts, but otherwise it was a solo affair. Had to make a trip to Lowes for a 2nd pallet of cement. I ended up using a total of 76 bags, so almost 13 bags per hole on average. So I mixed a little over 6000 lbs worth! Those 80# bags sure did start feeling heavy towards the end of the day.

I plant to install a French drain along the side and back and along the back of the existing shop as seen here:

As can be seen, the challenge will be dealing with the 400A service line entering the shop. I think it is down a full 36", so I should clear over top of it. There is also a buried water line in the foreground of the picture I need to deal with as well.

Last night I removed the supports from the posts, and I think things turned out nice and true. Here's a shot down the front of the building.

And down the back side.

I put blue masking tape on each pole to shop the level that the poured floor will be at (bottom edge of tape). I cut a little further into the bank that I should have. I'm at 11" at the shop wall, and 18" at the bank. Will be good for putting in the French drain though I think.

I plan to cut these to length and put around each pole and pour to bring concrete up to floor level. Should prevent any of the posts from ever seeing water (assuming the newly poured cement will join/seal with what I poured this past weekend).

I got 6 yards of crusher run being delivered on Friday and I'm picking up a plate compactor. Should make for another fun filled weekend.

 

[Zebrafive]

Have you changed size to match your current building to 30'?