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| Skill Level:
2-3 (Basic to Intermediate) |
Time Taken:
4-8 hours per wall. |
By
Bruce W. Maki,
Editor
Once the old siding was removed we spent a few hours doing some
important preparation work. The main purpose of this work is to
improve the insulation value of the walls and prevent water damage
if rain should penetrate behind the siding.
Improving the insulation has two components: Increasing the R-value
of the total wall assembly, and reducing the amount of air
infiltration, which is commonly known as draftiness.
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After the siding had been stripped the
house looked completely different. Like many older
houses, this house has solid wood sheathing nailed
across the studs.
This house is different from most older homes because
it has awnings over the windows. These added some
complication to the siding replacement job. |
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| We removed the siding all the way down to
the water table trim, which is the 2-part
white-painted set of boards just above the foundation. I
think the original purpose of the water table was to
kick the rain water outward and keep it from getting
near the foundation. Or maybe it's strictly decorative.
I've seen people leave the water-table attached to
the house during siding replacement, but we intend to
increase the thickness of the wall (by adding foam
insulation), so we removed the trim. |
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Many years ago, probably during the
1970's, somebody had blown-in insulation installed. This
operation involves drilling holes through the siding and
sheathing, then inserting a nozzle to inject expanding
foam into the space between the studs.
The holes in the siding are plugged afterwards, but
these plugs don't always stay put.
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| These holes are pretty big, about 2½
inches in diameter. We have found old bird's nests, and
bird skeletons, in other wall cavities.
If a plug becomes loose it creates a perfect home for
critters.
If you look in the hole, you can see the back of the
lath and the plaster that oozes between the lath boards.
This is supposed to be an insulated wall. Why is
there so much insulation missing? |
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When you consider that the only material on top of the sheathing
was a layer of paper and the clapboard siding, it becomes obvious
why this old house was so drafty. And that blown-in formaldehyde
insulation was terribly lame because it shrank after curing, leaving
half-inch gaps all around it. That stuff did nothing to reduce air
infiltration, I suspect it actually increased draftiness because of
the holes and the ill-fitting plugs.
At this stage many builders would apply a house wrap, such as
Tyvek or Typar, to reduce air infiltration and form a barrier to
water droplets that get past the siding. I've read about some
problems with those materials, because they can stop water droplets
from going anywhere, which can cause all sorts of problems such as
water damage to siding and trim.
 |
Here's a problem:
Notice the complex millwork (red arrow) where the
soffit corner meets the vertical corner trim. We would
like to remove the corner trim, install ½" thick
foam insulation, and then replace the corner trim.
But... this curvaceous soffit board prevented easy
relocation of the vertical boards. |
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| A view of the other side. This board
encloses the soffit where it meets the gable-end of the
house.
We could have removed that board and cut it 1/2 inch
narrower. But that amount of trouble, plus the effort in
replacing the corner trim, was not worth the outcome...
gaining a narrow strip of additional insulation. |
 |
|
By adding a layer of foam we are causing the siding and some of
the trim to "stand off" the wall by a fraction of an
inch... the thickness of the insulation. There are several factors
that limit how thick this new insulation can be. We used ½ inch
foam. I'll discuss the reasons later.
I have worked on many old houses, and I've noticed that over the
years nails become loose. This isn't necessarily a problem, but it
does allow more structural twisting and flexing during strong winds.
This movement is called racking, and it doesn't help
anything. Racking can be noticed by all the creaking sounds during
windy weather.
I've also noticed a lot of badly rusted nails around the exterior
parts of old houses. Sometimes these nails have corroded down to
nearly nothing. That can't be good.
When I see a wall or roof that has been stripped down to the
sheathing, I see a big opportunity... a chance to make
repairs and improvements at minimal cost and effort. Most carpenters
I've known just hammer in any loose nails and proceed with the job.
I have read about studies that show that wall sheathing secured with
deck screws can be up to 3 times stronger than sheathing secured
with nails. My experience in construction and demolition agrees with
that conclusion, so I figure... why not add a little extra holding
power.
 |
After hammering in the loose nails, we
used a collated screw gun to drive 1¾" deck
screws through the sheathing into the studs. This tool
made short work of fastening the sheathing to the wall. |
|
A closer view. This is actually two tools:
- The yellow and black part is a Dewalt DW257
deck/drywall screw gun, about $90.
- The silver part in front is a Senco DuraSpin DS200
collated screw feeder attachment, about $50.
When combined with a drywall or deck screw gun, the
DS200 can drive a lot of screws in a hurry. For fifty
bucks this thing is amazing, and it fits MANY popular
screw guns. |
 |
|
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Sometimes the screws didn't go all the way
in, so we had to finish driving them with a cordless
drill/driver. This happens because the operator
momentarily stops pushing on the screw gun which causes
the bit to stop spinning.
Once you get the hang of it, almost all of the screws
go in with no problem. |
|
| Along the edge of the vertical corner
boards there was a thick mess of old paint. When we
caulk between the edge of the new siding and that
vertical trim I wanted a clean wood surface for the
caulk to adhere to. This is important because if we
simply caulked to the old paint, and the paint later
breaks away, that will create a gap for rain to get
behind the siding or trim.
To scrape away this paint we used a narrow paint
scraper with a triangle-shaped carbide insert. Carbide
stays sharp for a long time and can tolerate hitting
nails. |
 |
|
Once the sheathing had been fastened we could start covering the
wall.
| The first covering was 15# felt, also
called tar paper. This is meant to act as a water
barrier. Since tar paper is a moisture retarder, and not
a true vapor barrier, water vapor can pass through it
slowly, over time. But if any rain gets behind the
siding and foam, this layer of protection should keep
liquid water from getting into the walls and causing
structural damage. |
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|
We installed the felt with a hammer tacker, which is a staple gun
that you swing like a hammer. An ordinary staple gun works too, but
it's a lot slower.
 |
We fastened a strip of ½" plywood at
the bottom of the wall. The bottom edge of this plywood
lies exactly at the bottom edge of the water table trim.
We snapped a chalk line first, stretching from the
existing water table boards at each corner. Later, the
new water table trim will be aligned with this plywood,
so accuracy here will affect the entire project. |
|
Why put plywood here? I wanted a good nailing base for the new
water table trim, but more important, I wanted the lower edge of the
wall assembly to be completely solid. I have heard of bugs (like
termites) and small animals digging through soft materials like foam
insulation, so I wanted a solid line of defense facing any critter
that crawls up the foundation wall looking for a warm home.
| We continued installing pieces of felt.
Since felt is only 3 feet wide, it's easier too handle
than housewrap, which is 9 or 10 feet wide and comes in
large, unwieldy rolls.
At this point there were three rows of felt
installed. Each sheet of felt needs to overlap the piece
below by at least 2 inches.
|
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|
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We installed ½" thick
polyisocyanurate foam insulation (also called rigid
foil-faced foam) over the felt. The foam was
fastened with 2" cap nails, which are ring-shank
nails with a plastic cap that resists tearing through
the foam.
In a pinch I have used roofing nails to install foam
insulation, but if a big windstorm comes along the foam
may go flying. |
|
Cutting foam insulation is easy... I just use a drywall T-square
(or a long straight-edge) and a sharp knife. But handling foam in
breezy weather can be tricky... the wind can easily fold a sheet in
half. I just hold it by a corner and let it flop like a flag.
| Here we've progressed farther up the wall.
There can be a lot of ladder lifting and moving when
doing siding work on a two-story house.
We used a couple of 8 foot step-ladders for the first
10 feet of height, and then progressed to extension
ladders for the remainder.
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We continued nailing up the foam
insulation.
We also applied that pink tape to the joints, which
prevents a lot of air infiltration. We are relying on
the foam to act as an air and water barrier, which is
the function of house wrap materials.
For the foam to work properly and prevent drafts, it
needs to be sealed tightly at the joints and where it
meets windows, trim, etc. |
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| We caulked the gap where the foam met the
corner trim boards.
Any spots where the foam gets damaged (like when you
miss the nail head) needs to be caulked or patched with
tape. No, not duct tape.
|
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|
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We applied foam all the way to the peak of
the gable, even though above that window awning the foam
is useless, since the attic lies behind that part of the
wall.
But we needed to put something on the wall to
maintain that ½" thickness all the way to the top.
Using the foam was the easiest method. |
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| More Felt:
After the foam had been installed we applied another
layer of 15 pound felt. Many people would say this felt
is not needed, but I have my reasons for using a second
layer. |
 |
|
It's cheap, it's fairly easy, I can't see any harm, and it will
form a very thin layer of slightly breathable material that might
help errant water dissipate. Maybe. And there is another reason I'll
explain in the article about
installing fiber-cement siding.
Why Did We Use Half-Inch Thick Foam Insulation?
It was a decision between ½" and ¾" foam.
Anything thicker would have made the new siding protrude
too far from the existing window and corner trim. I
would prefer the thicker insulation, but the available
length of nails for the fiber-cement siding limited how
much space we could put between the wall sheathing
and the siding.
Hardiplank® siding can be installed with roofing
nails and a coil roofing nail gun. This greatly speeds
up the siding installation process. But the longest
roofing nails our nail gun could accept was 1¾".
The siding is a little more than ¼" thick, I
want the nails to penetrate one inch into the wood. That
leaves an additional ½" of nail length... so
½" foam is the thickest we could use. |
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Tools
Used:
- Cordless Impact Driver
- Basic Carpentry Tools
- Deck Screw Gun With
Collated Screw Feeder
- Drywall T-Square
- Ladders, Heavy-Duty
|
Materials Used:
- Deck Screws, Collated
- Polyisocyanurate Foam
Insulation, ½" Thick
- Cap Nails
- 15# Roofing Felt (Tar
Paper)
|
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