Foundation fun-damental question

[jasong70]

ok - that was my attempt at being funny/witty. enough of that.

So I need a work area. My current oversized 1 car (20x15) is for cal parking only, and I like to keep it bare with just the essentials...so I need a new shed/garage.

I'm planning a 12x20 or 14x20 and the location of the building is critical. I need easy access and it needs to be out of the line of sight from the windows. That leaves me with only one choice. I'm on a 60x110 residential lot, backing onto a forest.

So here are a few pics of my dilema.

You can see some big trees I had the contractor leave there when we built the house. They're probably 75' tall and I think they're silver or sugar maples.

So, I know I need to take out 2 trees. I would like to do a slab on grade, 4" thick with a thickened edge, probably 12" or so.

Can I build close to the tree on the right? It would be about 2-3 feet away, well within the root zone. I'd really hate to remove the tree.

The alternative is a wood decking on piers or deck blocks. I'd really prefer concrete....did I mention that already?

 

[Falcon67]

A quick read on sugar maple indicates that it has a deep root system, so a slab on grade should not hurt the tree much, if at all. My slab is 12" from a 6" dia. Mesquite but only diesel kills them so that's not a good comparison. Those don't look like Silver Maples, which are considered trash trees around here - very shallow root system and weak wood. 14x20 on that lot size is going to be a squeeze, so good luck. Also note that most places have setback rules from property lines. Here, it'd be 5' off the side line and 3' off the rear.

 

[Chaznsc]

Based on the slope, it looks awful tight to me. And remember, you dont kill a tree overnight. It takes years for the death to come. Typically you want to stay at a minimum outside the drip line with fill or impervious cover. The roots covered will eventually die.

 

[pattenp]

If the tree on the right is the one with a slight lean it is not a very healthy tree by the looks of the base. If building close to it you should just take it down now because you'll be taking it down anyway in a few years.

 

[CJCar]

Also note that most places have setback rules from property lines. Here, it'd be 5' off the side line and 3' off the rear.

I'd add that this is where your planning needs to start. HERE, it would be 3' and 3' for a non permanent building, i.e. prefab shed. Put concrete under that prefab shed and it's now permanent, with 10' side and 30' rear setbacks.

 

[jasong70]

I'd add that this is where your planning needs to start. HERE, it would be 3' and 3' for a non permanent building, i.e. prefab shed. Put concrete under that prefab shed and it's now permanent, with 10' side and 30' rear setbacks.

We're lucky in that the setbacks are quite small. Just .5meters, which is slightly over a foot and a half. My goal is to push be building as close to the setbacks as possible.

I met with a builder today to discuss the project. He quoted my $950 for engineered plans and guesstimated the slab-on-grade to cost about $6k. I'm a pretty avid DIYer and I have friends that used to work in the trades (framing and one concrete guy)

He re-assured me that a slab foundation would be fine even with the trees. He did similar buildings for other clients.

The slope is gentle...in reality, it's ~16" on the 20' length, and it's because when I build the house, I didn't backfill that part of the yard.

For the foundation details, he proposed a thickened edge, 12" wide by 10" deep with 3 pieces of re-bar. 4" thick slab with wire mesh and fiber strands. The foundation would be proud of the ground about 8" or so for the drainage, all this on a cleared and compacted base. Does this sound right? It does to me from what I read here. The only thing not mentioned is the vapor barrier.

Thanks for the advice guys, I really appreciate this. I'll definitely do a build thread when I get started.

If the tree on the right is the one with a slight lean it is not a very healthy tree by the looks of the base. If building close to it you should just take it down now because you'll be taking it down anyway in a few years.

That tree that leans is coming out regardless, as well as the V shaped pair on the left. The ones being saved are the two right behind it (to the right of the white dog house)

 

[brownbagg]

if you build within five feet of the canopy of a tree, it will kill the tree

 

[Falcon67]

if you build within five feet of the canopy of a tree, it will kill the tree

FWIW - I work on a campus where we have a lot of oak, pecan and mesquite and misc other trees and many of those are surrounded on all sides by concrete, buildings, sidewalks, paved roads, parking lots, etc. Planting started in the 40s. Mesquite is especially good at chewing up a sidewalk.