I've got an existing 10'x12' shed sitting on a 4" thick slab of slightly larger
dimensions. I'd like to anchor the shed to the slab without moving or raising
The shed sits on several columns of pressure-treated 4x4's that are in mostly
good shape. These 4x4's only lie beneath the shed floor and do not extend
the exterior wall.
See the drawing at the link below:
I've been looking for a bracket (e.g. Simpson) that looks like the one I've drawn
in the link above that can be used to anchor the ends of the 4x4's to the slab.
I cannot find one of these in the Simpson catalog. Does anyone know where I can
find something like this or similar?
I took a look in the SST catalog but didn't find any connectors that
would slip onto a 4x4...... too small. :(
How about lagging a 4x4 "rim joist" to the ends of the existing 4x's
(both ends of them)
and then anchor these added "rim joists" to the slab with a simple
Use 1/2 lags x 8" long (6" seemed a bit short)
Check out the Simpson HL Heavy Angles
I think this will be the easiest way to anchor your shed.
Bob and others,
Thanks for your advice.
Looks like the SST HL37 angle bracket may work. I drew a new sketch of the
Questions I still have:
1) Should I use two HL37's per 4x4 end as shown in the sketch, or is one per 4x4
2) If I use two anchors per 4x4 end, one on each side, should I connect them
using a 1/2" bolt through the 4x4, instead of using lag screws?
3) Should I use concrete anchors in the concrete, or would a two 4" lag screws
per angle bracket be adequate? In either case I'd use concrete anchoring epoxy.
4) I was planning to anchor at each corner of the shed. Is that adequate?
The shed is a pre-fab shed with finished interior and electrical service. The
flooring is 5/8" or 3/4" plywood over 4x4 pretreated "joists" that are visible
underneath that lie directly upon the concrete slab, and to which I plan to
attach the anchors. The 4x4s are nailed from the inside to the plywood subfloor.
The shed cannot be moved or raised! And, I cannot drill concrete anchor holes
directly under the shed--not enough clearance to get a drill and bit underneath,
hence the need to offset the anchor holes from their attachment to the 4x4s. I
can drill horizontal holes into the 4x4s if the holes are at or near the center
of the 4x4s (which means I may not be able to drill straight through holes to
attach the HL37 anchors to both sides of a 4x4 and may have to use lag screws
into the wood, even if I anchor both sides).
The shed is located in the San Francisco Bay Area, so my primary concern is the
shed sliding or being thrown off the slab due to earthquake.
Thanks for any additional advice.
It's a shed. Drill straight down through interior floor and 4x4, squirt
some of the fancy epoxy down there, and screw in big lag bolts, with a
big washer or spreader plate on top so the bolt doesn't go through
floor. Threaded rod pounded in with a mallet, and big nuts on top, would
make it removable. Won't look any worse than toe-stubbers out in the
weather. And if you pick you spots carefully, it won't interfere with
the usability of the shed. One in each corner, tucked right against the
walls, should be plenty.
As to earthquake protection- unless you are near the edge of a cliff
where the shed could slide over, tying it down hard to the slab will
likely INCREASE the damage in a quake. Instead of just bouncing around
as a unit, any ground flex will be transmitted to the structure of the shed.
Upon reading aemeijers' suggestion, I'm inclined to agree with his
I think my original suggestion is a superior design but as aemeijers
says "it's just a shed".
And how much capacity do you really need?
Are we talking wind or earthquake restraint?
As aemeijers says....tying the shed down will transfer more load to
Yeah, after you're done.....the 4x4 are tied down.
What's the rest of the load path like?
Connection from the 4x4's to the shed sill & walls?
Shear capacity of the walls? Plywood?
Wood sheathing? MDF crap siding?
The whole shed doesn't weigh much (less than 2000lbs) so you don't
need much anchorage.
Simply your life....either use aemeijers' suggestion or
my 4x4 (or 2x4) "rim joist" lagged to the exsiting 4x4's and anchored
with heavy angles and an epoxied anchor.
Or forget the rim joist & just put a single angle on the end.
Your concept with multiple HL37's is way too complicated & too much
I'd install about 8 angles....two on each shed face
and that's probably 2x as many as you actually need.
When I anchored the walls of our shed to the slab I used a .22 calibre
gun-nailer. Then used it to toenail anything larger than a 2x4. Took about 2
hours, not counting moving all the crap out to make room to work and then
putting it back in. Use the rght size nails and locatoins and it's a breeze.
TEST beforehand in case the cement was a brittle mix done by some
neophyte. And be accurate; it's really tough to pull a cement-nail out of
cement once it's driven in. Wear ear protection; those 22 shells get really
loud inside a small building!
The 4x4's are nailed to the 5/8" subfloor that itself is connected to the walls.
The shearwall looks like 3/8" (or maybe 1/4") plywood with a decorative
exterior. It bears a slight resemblance to the base Tuff-Shed with the addition
of a side window, attic turbine vent, and drywall finished interior with
electrical outlets and lights, but I have no way to confirm that. (The shed was
installed by the house's prior owner.) I have boxes of stuff stored in the shed's
attic, so the shearwall would be tested under lateral motion.
Anchoring the shed, even if only one anchor at each of the four corners, entails
some expense and labor. IF/WHEN we get a strong enough earthquake to move the
shed, the most likely damage is to shear off the electrical service that comes
from underground at one of the outside walls and to move the shed such that I'd
nead to empty it, and then move it back onto it's pad and re-attach electrical
If I anchor the shed the floor may survive, but the building might collapse or
get tweaked so that it needs to be rebuilt or replaced. I assume that would be
far more expensive than moving the shed a foot or two and re-attaching
There is no nearby cliff. The pad extends at least a foot on each side, and the
side and rear property lines are about 4 feet from the shed walls.
I'll consider your suggestions. But, in the end doing nothing may be the most
Thank you, everyone, for your help.
Why the 4x4's? I would think the concrete slab would make a much better
and longer lasting floor than whatever junk flooring came with the shed?
Anchor the shed walls directly to the pad. If its made of wood it should
have a 2x4 sill plate and if metal the sides should be bent inward with
punched holes just for that purpose.
Drill holes, insert short sections of all thread into a mortar mix made
for the purpose and bolt the sucker down to the pad.
Not aware of anything that looks like that.
As an alternate choice I would just buy heavy gauge wall angles and use
three along each side.
If you are in a windy area use the perforated metal like garage door openers
are installed with and run an strip along each wall as far as your budget
allows. The same could be done along each end but you would not have a many
place to attach it to the runners.
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