Building a shed into a hillside

I am building a shed in this space cut into a hillside:



I have done extensive research and planning, and actually have already built the foundation and put it in place, on runners sitting on cinder blocks that are themselves on four inches of gravel. There is also ample space between where the side and back walls will be and the earth to put three to four inches of gravel for water runoff. In other words, I think I've got a pretty good plan for allowing water to run around and under the shed. Where I am hung up with my planning, however, is what to use for a water barrier on the portion of the walls that will be under ground. I was considering using OSB for the lower portion of the walls, with the rough side facing out, and coating it with truck bed liner. I've heard it adheres to wood well and a test run on a scrap of wood seemed to confirm this. I would like to know if this is a good idea or a stupid one, and if the latter what other material would be better to use, be it sprayed on, rolled on, or even some type of sheeting.

I would not recommend using wood or OSB for any portion of the wall that will be place against soil. (that's probably just the structural engineer in me talking).  I would make that portion of wall with cast-in-place concrete or CMU blocks.  As for a waterproof barrier I don't have a lot of experience with that, but most of the ones I have seen are done with some sort of elastomeric or bituminus membrane (such as the one in the link below).

http://buildingmaterials.cetco.com/Left-Side-Navigation/PRODUCTS/Waterproofing-Products/Envirosheet

Actually, the wood will not be against soil; there will be about four inches of gravel between the soil and the wood.  And if I coat the wood with truck bed liner there will also be material even stronger than the wood between the wood and the gravel.

I've considered pouring concrete, or even building a wall with cinder blocks and mortar, but the shed's foundation is already in place, and it cannot be moved as I cemented five 4x4 posts into the ground to act as anchors (the wind really gusts here sometimes) and bolted the foundation to it... under the flooring. It's not going anywhere without some demolition. With the foundation in place pouring a concrete wall is all but impossible, and while I could build a cinder block wall that would leave no space for gravel, which is essential for water run-off.  While it would be more work, and it would mean putting off finishing the shed until next Spring or Summer (a possibility anyhow), I could conceivably dig the walls out further, even with the foundation in place, thus giving me more room for a cement wall and still have room for gravel, but is it really worth that much work?  The terrace at the top of the hill isn't even four feet higher than the shed floor, and part of the plan next summer is to dig that down some. 

Just thinking out loud I guess. I was so looking forward to getting this shed done, and now it looks like I'll have more work to do "to do it right" (you aren't the only one to say I should pour concrete).

Any plywood/OSB sheets are going to disintegrate over time exposed to water no matter how well you coat it.

How about something like the cement sheets they use for tiling? Don't know much about them, but they are made for moist environs I believe.

Looks like you would want the one without the gypsum core. The only question I'd have is how to account for freezing/thawing? Perhaps predrill holes a little oversize? Of course, use treated screws, too.  
Cement board

It looks like from your pic that maybe a single sheet per side would be enough so you just need to figure out some kind of corner cover. Maybe caulk some plastic (ie, siding) or galvanized metal corner bead in place. Once the gravel is in place it won't move anyway and the caulk should allow movement. Oh, and don't kid yourself. It will be against soil after a couple years of rain. If you really want to ensure proper drainage you should do a french drain.

So you're suggesting cement board rather than OSB or treated plywood. As cement board is not really waterproof, I'd still need to put something on it, correct? Rather than truck bed liner I'm thinking something like this, then a sheet of this over that. Both of those should be available at a couple of places in town, but we'll have a Menard's by March and they for sure will have it, as well as cement board. I'm surprised that cement board is relatively inexpensive, somewhere between the cost of OSB and treated plywood.

Concerning the draining, I thought about doing a French drain, and still might. However, with my latest pseudo-plan i don't think it will be necessary. I am going to finish the foundation and floor today, then cover it with a tarp to protect it from snow and call it done for the year. I don't want to rush it, and we sometimes get that white crap by mid October. 

Then next Spring I'm going to dig the dirt walls out a bit further.  It will be a major PITA with the foundation there, but probably worth it, and it won't take much to dig 3 or 4 inches further out. Once I have enough room I'm going to pour a 3 or 4 inch thick cement wall, about 3.5 feet up in the back and sloping back to front on the sides. That will hold the earth back, and I can then probably get by with about two inches of crushed rock or gravel between the shed wall and the retaining wall.

Even if this isn't my final plan, I can let it percolate over the winter! LOL!

BearDad wrote:

As cement board is not really waterproof, I'd still need to put something on it, correct?

From the link, "There is a class of cement board strictly constructed of a Portland cement based core with glass fiber matt reinforcing at both faces. This type board is truly waterproof. These panels can be immersed in water without any degradation (excluding freeze thaw cycles). These panels do not require the sealing of edges and penetrations to maintain their structural integrity."

Not saying this was the best option (or even a good one), just what I thought of that may work.

Quote :

Once I have enough room I'm going to pour a 3 or 4 inch thick cement wall, about 3.5 feet up in the back and sloping back to front on the sides. That will hold the earth back, and I can then probably get by with about two inches of crushed rock or gravel between the shed wall and the retaining wall.

If you're going to go to the trouble of a concrete wall then why don't you just make that the shed wall? Just need to extend the floor over to it. Now you have more room for more stuff!

Can't wait to see it when it is done. Then you can come to my backyard and build one for me, and it will be very easy for you since there are no hills in Florida.

Very cool ! Definitely want to see pix during the progress and completion !

Guilty/Forgiven wrote:

Very cool ! Definitely want to see pix during the progress and completion !

Shed Pix

1 - the hill before attacking it ... sort - of. This pic is actually a few feet south of where I dug out, and actually after I started digging. But it shows how overgrown the hill is. The previous owners had a fence at the base of the hill, but when we learned that our yard extended clear to the top we enlarged the fence and have been trying to take the yard back from nature ever since.  I make a little progress every summer, but it will be a couple of years before I win the battle.

2 - the location; you've seen this one.

3 - part of the dirt pile. I dug it all out by hand and transferred the dirt to our driveway a wheelbarrow at a time.

4 - the full pile ... sort-of.  At one point I put out an ad saying "free dirt" and someone hauled away about 1/3 of what I had. This pic is after I finished digging and had built up the pile again.

5 - separating the dirt. My plan was to put gravel under and behind the shed, and when I saw how much gravel was in the dirt I was removing I decided I would separate it out rather than throw it away and pay someone to bring me gravel.  I would spend several hours each week standing over a home-made straining table, working the dirt a couple of shovelfuls at a time, putting the gravel in a pile and the clean dirt in my truck. I would then haul the dirt to anyone that needed it for fill,, gardens, whatever. Got a lot of strange looks from people while I was working the dirt; some asked me if I was looking for gold! I just kept working it though, and I completely finished about 2 or 3 weeks ago. I then started washing the gravel, as it was still very dirty and I didn't want to put dirt back into my hole. I just finished cleaning the gravel today and put it all under the shed's foundation.

6 - a cinder block. Not sure why I took the picture. LOL.  The foundation sits on runners which themselves sit on cinder blocks.

7 through 9 - the foundation, complete and in place.

10 - one of the corners. I anchored the four corners and even the exact center in cement; don't want the shed blowing away!

Shed Pix

11 - Floor Down. Lesson learned too late: don’t use tongue-in-groove OSB; the groove is smaller than the tongue, leaving a 1/8” space between the board tops. I'm sure this is by design, but grrr. I wish I had known that.

BearDad wrote:

Shed Pix

11 - Floor Down. Lesson learned too late: don’t use tongue-in-groove OSB; the groove is smaller than the tongue, leaving a 1/8” space between the board tops. I'm sure this is by design, but grrr. I wish I had known that.

The gap is by design, it is done so that when the board swells (which it will when it get's wet) hopefully it will not exert so much force that it causes the outer walls to "bow out".

Looking good !  Man I love me a project like that... I'm at that stage where I can no longer do any major woodworking, only smaller projects... cuz of my back and surgeries and pain. Kinda sucks for someone who's passionate about building things. But I am enjoying watching your progress on this. Keep up the awesome work !

https://www.dropbox.com/sh/nnirsdtmniwil4p/AAD8Zi2CfGL02A_ALac1Be9Ha?dl=0

12 - 15, rockin' the rafters

Everything is now are tarped up for the winter, although I left the lumber in the garage as I plan to build the walls during the winter.

BearDad wrote:

https://www.dropbox.com/sh/nnirsdtmniwil4p/AAD8Zi2CfGL02A_ALac1Be9Ha?dl=0

12 - 15, rockin' the rafters

Everything is now are tarped up for the winter, although I left the lumber in the garage as I plan to build the walls during the winter.

That's the first time I've seen rafters put together like that, with the exception of actual trusses. Are you doing this by yourself with no help? If so, then I could see why you did them this way.

Yes I am, but that's no why I chose to do it this way. Doing it with the OSB gussets, and the notches on the bottom to sit on the walls, allows me to put the rafters together before building the walls. I used the following video for a guide:

https://www.youtube.com/watch?v=h7fRanWeoUc

the other common way to do shed rafters is like this guy does in this video:

https://www.youtube.com/watch?v=jlAj-pLksMg

With boards extending up to the peak and then a board going the length of the roof. I thought all his computations to figure out the cuts was a bit more complicated than it needs to be, and then there is the manner of attaching the rafters the center board, no doubt with hurricane brackets or some such. The main reason I didn't do it this way, besides what seemed like extra complications, is because my shed is tucked into a hill, making access to the rafters difficult (at least before they are up. The way I did it I can pretty much just raise them into place, as shown here:

https://www.youtube.com/watch?v=8GMukEPSMmg

I sloped the rafters at 5 inches, and although we are in SD we really don't get a lot of heavy snow fall where I live, so I'm not worried about the rafters needing to hold a lot of weight.