If there is one fundamental flaw with older wood-framed buildings, it's the
fact that ordinary lumber was used adjacent to masonry. Concrete, brick,
stone and mortar are porous and absorbent materials that are capable of wicking
moisture upward from the ground. And since the ground in many areas is usually
damp, this means that any wood placed next to masonry could be continually damp.
A common problem with older buildings is decay (rot) that attacks the lower-most
The lowest structural component on many wood-frame buildings is the sill
plate. There are regional variations in terminology, so in some places this
piece may be known by another name, such as the mudsill. The term sill
plate normally means a piece of wood that is attached to the top of a foundation
wall. Floor joists would normally rest on the sill plate, then floor sheathing
on top of the joists.
|This garage was built on a concrete slab, a fairly
common method of construction.
It's also common to find the walls resting directly on a short
foundation wall, with the floor slab perhaps a few inches below the top of
In either case, it's typical to find the bottom plate of the
stud wall (also called the sole plate) directly above concrete. In
these cases the bottom plate could be considered to be a "sill
plate", though it may not be perfect use of the term.
||Some sections of the bottom plate were visibly crumbling (red
arrows), while other areas appeared to be intact because the wood
was hard on the upper surface.
|But when I struck these intact-looking sections with the
claw of a hammer, they broke up easily. Not a good sign.
Somebody had poured a topping slab (an additional layer of
concrete) over the original slab, perhaps because the first slab was badly
cracked or pitted. The smooth edge of the slab had been formed by the
bottom plate of the wall.
There was this suspicious tapered gap between the wall and the concrete
topping slab. (Red arrows)
It appeared that the garage wall had moved outward over time. The space
between the red arrows was about 1½ inches. Movement like this is
consistent with a rotted bottom plate (a common problem) or broken anchor
|There was evidence of this topping slab being
done in two pours.
Arrow 1 points to the clean edge from the older-looking concrete, and
arrow 2 points to the rough edge on the newer concrete, at the rear of the
garage. Perhaps the previous owner (who, ironically, is a local
contractor) had broken up the rear section of an earlier topping slab and
poured more concrete to replace it.
Whatever the story, someone did a sloppy job. There was excess concrete on top of
the bottom plate, which only helps to hold moisture in.
Arrow 3 points to the edge of the "really bad rot".
But Where To Start?
The first step before lifting a small structure is to remove or disconnect
any anchor bolts. I couldn't find any in the bottom plate. Many older structures
don't have anchor bolts.
||The next thing I did was install at least one steel
connector between the top plates and each stud.
I'm going to be lifting the top plate and without some serious
connectors, the studs will stay put while the top plates lift
away... not good.
|I used a diamond blade in a circular saw to trim away the
excess concrete from the rear (newer) topping slab. The material would
interfere with placing the new bottom plate back into the proper location.
I just snapped a chalk line from the inside corner to the smooth edge
of the front topping slab, to create one long straight line.
||The red arrows indicate the wedge of concrete that I
Note how the concrete dust covers everything. It's a good idea
to remove things from the area to prevent dust damage. This dust can be
rinsed off but should not be wiped off, because it is so abrasive.
I've ruined safety goggles by simply wiping concrete dust from them.
Getting A Lift:
I used a 6-ton hydraulic bottle jack and a heavy-duty steel lally
column to do all the lifting of this garage, and it was more than
adequate. I also brought along a 12-ton jack, but it was overkill.
I always place the jack on a sturdy base of wood blocks.
On top of the jack was a piece of ¼" steel plate. This is heavier
than the steel plates that come with the lally columns.
Note: If there was bare dirt
instead of a concrete slab in this garage, I would have needed to make a large
base of several blocks of wood or solid concrete blocks. Soil will be
compacted when a heavy load is placed on it, and the weight must be spread over
a large area, perhaps as big as 2 feet by 2 feet. The size of the load bearing
area depends on:
- The type of soil, as some soils can only withstand
about 1,000 pounds per square foot,
- The weight of the structure, and
- The number of columns being used to temporarily support the structure.
I use a piece of duct tape to keep the top steel plate (one that comes
with the lally column) from falling on my head.
I positioned the top end of the lally column under the top plate, just
beside a stud.
Then I pumped the bottle jack to raise the structure a fraction of an
Listening to the structure is very important here. When a building is
raised you will hear lots of snaps, crackles, and pops. These are roughly
the same sounds that you will hear when a building creaks and groans during a
strong windstorm, but the sounds are a little louder and much more frequent. Very loud popping or
snapping sounds should be cause for concern.
|After raising part of the structure by about 3/4 inch, I
place a light-duty lally column next to the jack.
||This light-duty column (the nearer column) supported the
underside of the top plate, but on the opposite side of the stud.
||I used a wrench to tighten the adjuster screw. Caution is
required here because the end of the screw tends to "walk
around" and drift away from the center of the steel plate.
A steel plate must be used, or else the screw could dig into the
|After a few minutes I had raised the corner of the garage
and placed two lally columns under the top plate.
I could push on the lower part of the wall and it would move in and out
about an inch. This told me that the bottom plate was free of the concrete
The sequence of lifting could be important. I usually start by lifting
near a corner. Sometimes I've lifted a small structure in the middle of a
wall and the entire wall was picked up, to my surprise.
|After about an hour of work I had lifted the entire side
wall of the garage. The red arrows point to the temporary support columns,
which are steel lally columns or 4x4 posts.
||It's hard to see here, but the bottom plate has been lifted off the concrete by at least half an
Originally the gap between the concrete and the bottom plate was filled
with dead grass and debris. Now you can see a gap between that debris and
|The lowest piece of siding also had some rot damage, and I
needed to remove it. Even without that damage, I would have needed to
remove some siding so I could get a new piece of wood into place.
I used a reciprocating saw to cut the nails that held the siding to the
||Once all the nails were cut I went outside and pried the
|At the end of the black pry bar you can see more rot damage
on the bottom plate. This rot was not noticeable from inside the garage.
||The view from inside the garage.
Since the extra-thick concrete slab was in the way, the only way I
could remove the old wood was by pushing it towards the outside.
|I snipped the nails that held the bottom plate to the studs.
Many of these were badly rusted.
||I pushed the old bottom plate outside. It didn't put up a
|Then I discovered some anchor bolts. Since the wood had
rotted so badly, these never got in the way
||Towards the back of the garage the bottom plate seemed to be
much sturdier. I pried on it and it didn't crumble.
|My initial plan was to only replace the rotted sections of
the bottom plate, so I proceeded to cut the plate where it seemed intact.
||This was another anchor bolt. It was hidden beneath a stud.
After cutting the bottom plate, I discovered that there was rot on the
underside and center of the board. So the I decided to replace the bottom plate on
the entire wall.
|I had to remove the old anchor bolts before I could install
any new wood. It would be almost impossible to reuse these anchor bolts.
A couple of the bolts were simply cut off with a metal-cutting blade in my
||This anchor bolt became loose, so I dug it out of the
concrete. It appeared to be some sort of discarded piece of hardware.
|I swept the concrete clean.
||I slid a 12-foot long pressure treated 2x6 into
position. Since I had removed that lowest piece of siding, it was easy to
get this board in place.
If there hadn't been a topping slab in my way, I might have been able
to slide this new board in place from the inside.
I also slid an 8-foot 2x6 board into place to complete the 20-foot bottom
Elevator... Going Down
Once the new wood was in position, I lowered the structure back down.
- Placing the bottle jack next to a temporary support.
- Raising the building a bit more.
- Removing the temporary support.
- Slowly lowering the bottle jack.
I had to do this 5 times, once for each of the temporary supports.
While lowering the building, I used a hammer to tap the bottom of the studs
inward or outward, whatever it took to make them line up with the bottom plate.
|I used some of these angle brackets to help hold the studs
to the new bottom plate.
||The ends of the bracket can be bent over.
I used Simpson Strong-Drive Screws in some places here, mostly to
prevent splitting the wood. Nails are better because they have greater
|Once the bottom plate was securely attached to the studs, I
drilled some holes for anchor bolts.
I used my fancy and expensive hammer-drill to drill through the wood
and into the concrete.
||I placed 3/8" lag shields into the holes. These
are made from lead, which is soft and conforms to the threads of
the lag screw.
|I used a punch to drive the lag shield all the way down into
||I threaded a 3/8" lag screw into the hole and tightened
it with a socket wrench. It's easy to over tighten this type of fastener
and strip the soft lead. I think next time I'll use big Tapcon screws or
I installed 3 anchors along the 20-foot wall.
|I fastened some treated 2x4 blocking between the studs,
resting on the bottom plate.
The main reason I did this was to keep a certain chipmunk out of
the garage. I knew it would take a couple of weeks before I could get
around to installing replacement siding (because I had to custom-mill the
||A closer view of the new bottom plate, or sill plate. The
red arrow points to one of several deck screws that I used to fasten each
piece of blocking to the bottom plate.
I also used metal angle brackets to hold things in place. This prevents
the stud or block from shifting while nails or screws are driven at an
Most sill replacement projects would not require these extra blocks of
wood, though they do improve the structure somewhat.
A Bit About Rot:
Ordinary wood will rot if:
- The moisture content is 20 per cent or higher.
- The temperature is above 35 to 40 degrees Fahrenheit.
- There is adequate oxygen surrounding the wood.
The decay process is caused by fungi that are everywhere. The fungi use
the cellulose in wood as a food source. Keeping the fungi spores away from
wood is impossible. Keeping oxygen away from wood is impractical. The key
to prevention of decay is to keep the wood dry, or at least provide a
quick drying time for wood that gets damp or wet.
It's my understanding that fungi spores go dormant if conditions are
not right. Under favorable conditions the fungi cells will consume the
wood. Since these are single-cell organisms, they reproduce by dividing in two. But this process takes time.
If wood is wet only for brief periods (a few hours at a time), the
fungi do not have adequate time to undergo their cell-division process, so
the fungal colony doesn't grow. If the fungi are exposed to sunlight, the
ultraviolet light will kill them. Lots of old houses and barns have wood
siding with almost no paint. The wood gets wet during rainstorms but dries
out quickly, so it never rots (but there are other problems, such as
warping and splitting).
If wood structures can be designed and built to provide adequate
drainage for stray water (such as the rain that gets driven behind the
siding by strong winds) and adequate airflow around moisture-prone
areas, then the structure may survive indefinitely. It's been my
experience that most carpenters and builders have little concern for such
details. In many cases it seems that only building codes and building
inspectors have any real power to enforce good building practices.
Masonry tends to act like a sponge, remaining damp for long periods of
time. Masonry can also wick the moisture upwards from the soil, so
even if concrete appears dry on the surface, it may be damp just below the
wood wall structure. Today, building codes state that any wood placed next
to concrete must be treated to prevent decay. This typically means using
CCA-treated lumber (the greenish-tinted lumber sold for decks).
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