I live in a small wooden 1927 railway cottage in Moera (New Zealand). In
improve it's energy efficiency I've insulated the roof (with one layer
Pink Batts, and a second layer of used Batts), and insulated under the floor
layer of polystyrene blocks plus a layer of aluminium-foil sisalation). Next
on the list was wall insulation (followed by pelmets above the curtains
and more attention on stopping drafts).
I didn't want to dismantle the walls in order to install batts so I was
limited in my options. AirFoam (www.airfoam.co.nz)
an insulation service where
they inject low density (4 psi) expanding foam into the walls from
the outside. The job would take them a day or two and require them to drill
holes between each pair of studs (bottom, middle an top) all around the
house. They quoted just over $4100 for my
house which was a bit too much for my budget (we're saving to redo the
So what you see below is my cheaper, but much slower, DIY wall insulation.
I should first explain that my house has no dwangs (horizontal braces
between the studs) because it has sarking (horizontal
wood planks) on the inside face of the walls - then we have standard
interior Gib over
the sarking. This makes the following approach much more do-able.
We're also lucky that almost all our electrical wiring runs down through the interior walls of the house. This is important because polystyrene reacts with the plastic around electrical wires - it effectively "melts" it. Which would be a very bad thing. In the three places were there is wiring in our outside walls I've left those empty (I may inject something harless at some later stage.)
Briefly the process is:
buy a lot of fire retardant polystyrene beads
build a polystyrene blower from an old hair dryer, plumbing
bits and ventilation hose
drill a hole between each stud pair, at the top of the
blow polystyrene into wall
plug the hole
repeat for whole house.
Now here's the process in detail:
28 Dec 2007
1. Buy the beads
in Porirua sell used polystyrene from Peter
movie sets like King Kong. They "mulch" them back into individual
beads, then reform them into underfloor insulation blocks.
I bought a 2 cubic meter bag (to start with) of the polystyrene beads -
for $40, plus $10
delivery. It was about 2 meters tall when full.
2. Build a blower
I went to Cash Converters to look for a vacuum cleaner that could be
used as a blower, but found the hair dryer section first. I'd heard
that vacuum cleaners can be tricky because they generate too much
The vacuum cleaners they did have were cheap ones without a blower
feature. So I went for a $7 hair dryer instead.
I dismantled the hair dryer and removed the electronics and heating
elements. Normally the blower function has two speeds. This is achieved
by supplying either 12 or 24 volts DC to the motor. I decided to switch
to using a 12volt battery to drive the blower motor rather than mains -
it's much safer. (And getting the
blower to work without the heating elements would have been too much
the resistance of the elements provides the voltage drop from 230 volt
So I can use one or two 12 volt batteries to run the blower.
For the front of the blower I bought some plumbing bits to funnel the
output down to a 35mm hole. The last section is a short piece of 32mm
(32 is the inside diameter)
plastic pipe with an outside diameter of about 35mm which I sanded
it down to 35mm.
The back of the blower consists of a clear plastic Chinese takeaways
container and a 3 meter long ventilation hose (100mm diameter). This is
then attached to a short bit of 90mm storm pipe which gives me
something firm to tie the bag opening to.
The finished blower connected to the bag. The black thing is the
Here's the blower fitted into the hole in the wall.
The 30 degree bend allows the blower to be plugged in right up under
the eve. This allowed me to drill the holes as high as possible. This
has the benefit that the hole is out of the weather (so that if my plug
is not 100% water tight it wont matter so much). Plus it's
further out of the line of sight.
Here's a short movie of the hair dryer in action.
3. Drill hole
I selected 35mm because I could buy plastic pipe with a 35mm
outside diameter, a 35 mm drill bit and 35mm diameter doweling (which
I've slicing into 20mm plugs).
4. Blow the beads
Here's the blower switched on and blowing beads into the wall. This is
a relatively low flow.
And here's a higher flow.
The amount of flow depends on several factors:
12 or 24 volts. I found 24 volts usually produced so much
that the beads would clog the back of the fan, so most of the time I
use 12 volts only. However - when it all seemed to be taking
way too long I tried 24 volts and ran it until the fan clogged or the
Which sent me back to 12 volts.
The shape and angle of the ventilation hose. If there are
or kinks in the hose the flow is usually good. You can use this feature
to adjust the flow to be the maximum possible without clogging the fan.
The height difference between the top of the bag and the
As the bag reduces in size the elevation the beads need to gain
increases. You can raise the bag by sitting it on a cardboard box or
When the blower seems to have trouble picking up beads it may mean the
wall segment is full. Pull the blower out carefully to check. If it's
windy the beads in the wall and blower may fly about - so have your
ready in your other hand.
Wall segment jam-packed full of polystyrene beads.
5. Plug the hole
Here's the plug glued in place.
6. Finish off
Next I'll sand it back, add filler if needed, and paint.
I added a screw to each plug so that it was easier to
If you run the blower constantly for two-and-a-half hours
you'll burn the motor out.
If you are feeling reckless and choose to run at 24 volts
need to nurse the ventilation hose to prevent the fan sucking up so
much polystyrene that it jams the fan blade. But it's faster.
With a fresh motor at 12 volts it takes well over
an hour to fill a full height
Try to keep the top of the bag no more than 1 meter below
the hole. More than that will reduce your flow rate.
How good is it?
I've been keeping indoor/outdoor temperature data for the last three
years. I'm hoping to see some reduction in heating usage next
year. Other than that I have no qualitative measurement of how good
insulation is or will be. It's a punt.
Under floor polystyrene block insulation is quoted as being
"better than R1.3". So I shouldn't expect more than R1. We'll see how
it feels next winter.
My first blower was based on a hair dryer. It worked really
well for a
while, but requires a lot of attention - running it from 12 volt
batteries is slow. At 24 volts it works
much faster but eventually over heats the motor so much that the
propeller drops off the motors metal shaft.
So now I'm trying a vacuum cleaner blower.
The Vacuum cleaner version
Here's an old Electrolux vacuum cleaner with a blow option.
Here's the nozzle which utilizes the venturi effect. The blower hose is
the one on the right. The polystyrene beads are sucked up the clear
tube on the left, and into the wall. That's a 32mm "y" join as used by
plumbers (this one's from Mitre-10 hardware store).
Here's the general concept. The blower from the vacuum cleaner blows
air through the top of the Y intersection. As it passes over the tube
coming from the bag of polystyrene it sucks air (and polystyrene) up
and into the wall cavity.
The "Y" join needed an extra plastic sleeve (cut from an ice-cream container)
inside to enhance the venturi effect.
Here's the clear hose coming out of the top of the bag full of white
beads being sucked up.
It's really good having a clear tube as you see the polystyrene being
The suck starts out very strong, but as the wall space fills up the air
space in the wall gets smaller - this reduces the venturi effect - so
less suction. To combat this I'm going to try adding some extra air
venting near the tip using a piece of breathable sponge (so air can
enter/escape without losing any polystyrene.
The vent holes didn't work for me. I wasn't able
to get enough air in without letting polystyrene out. I tried a
permeable sponge around the holes I'd drilled but that reduced the
airflow too much. If I had better engineering skills, and more time,
I might be able to get something working.
I'm now using both the hair dryer and the vacuum cleaner. The vacuum
cleaner works well for the first 80% of the space, then the reduced
airspace means the venturi effect is reduced. So then I switch
to the hair dryer blower to finish the job.
I've done the south wall and half the west wall.
Drilling the 35mm holes is still quite slow. The weather boards are
pretty hard - possibly rimu or kauri or something like that. So each
lasts about 8-10 holes. It looks like I might need as many as 10 drill
bits to do the whole house. I've tried sharpening them, without
success, they are a fiendish shape. They cost about $17 each.
Yesterday I went back to check some of the early sections that I'd
filled three weeks ago to see if any settling had occurred - nope. So
from now on I'll glue the plug in as soon as I've filled each section.
I've started sanding and puttying over the plugs. I'm supposed to leave
the putty for two weeks before painting.
You can see the paint under the bottom edge of the weatherboard has
separated. This may have happened over the last year as a result of the
ceiling and underfloor insulation warming and drying the house more
than it's used to. If you have a better theory give me an email.
One issue which my system creates - if someone wants to drill a hole in
the wall later on - like if I wanted to install an extractor fan over
the oven - it'll be messy! Commercial systems which inject
balls also add a slow drying glue to solve this. The only possible
"solution" to this problem I can think of is to drill the hole and
spray glue into the wall - very carefully. [Yes, this plan is
half-baked. If you can think of a better idea email
me - please!]
I finished the second wall yesterday. And just finished off the first 2
cubic meter bag.
I've improved the flow of the vacuum cleaner by streamlining the
where the hose joins the venturi chamber. So - if you have a go at
building one yourself make
sure there are a minimum of obstructions or diameter changes. With the
new changes the inflow has improved dramatically. I still have to use
the hair dryer blower to finish off though.
I've been busy with other work the last few weeks so haven't been able
to finished the last 2 meters of the north wall. After that I've got
small sections under three windows to do.
Here's a screen shot from my weather station which shows indoor and
temperature. It's still a bit too warm for me to tell if the insulation
has had any effect. It's warm inside and out. But at least you can see
the way the inside temperature is a lot steadier than the outside temp.
You can see my
weather data live. The web
cam is looking at our
front yard and the sky to the north (and the house across the street).
OK - finished blowing all the walls. Phew! It took a while but now its
I've glued and puttied all the holes.
Next step is to sand and paint over those and I'm done.
Now that the job is done I can look back and ask was it worth it? At
this stage (summer) it's too soon to tell. I'll report again in mid
winter (that's July for us here in New Zealand).
Would I do it
again? I think - yes. Now that I've got the tools and techniques worked
out it will be much quicker to do next time. If there is a next time.
Before I forget here's a few bits I've learned (of interest only to those who might try this at your home):
All hair dryers are virtually identical inside. I pulled apart 8
hair dryers (some look like they came from the early 1980's) and
they all contain the same basic bits; switch(s), heating elements,
motor, rectifier, and a few capacitors.
The first hair dryer I bought was the best design for my purpose
- it was wide at the back and narrow at the front with a smooth
transition funnel. The gaps between the fan blades were big enough to
allow the larger pieces of polystyrene through.
I ground down the outside edge of the fan to prevent large
(10mm) bits of polystyrene gettign stuck between the edge of the blade
and the inside wall.
If you run the hair dryer for half-an-hour then stop it - you may
find it does not start again. You'll need to either wiggle the fan
blades a bit (to dislodge a buildup of polystyrene dust in or around
the motor. Also - if the motor doesn't restart don't leave it on for
more than a second or you'll burn out the motor. Sometimes it was
enough to just jiggle the fan blades a bit with a stick down the front
of the blower nozzle.
My vacuum cleaner blower used a 38mm diameter clear hose which
was great for seeing what was going on - but sometimes it clogged up.
When that happens you can, without turning off the vacuum, pull the
nozzle out of the home in the wall and put your hand over the end of
the nozzle - thus turning the blown air back down the clear hose. With
a bit of wiggling this will clear the hose. Then you bung the nozzle
back into the wall and carry on.
If the vacuum blower clogs repeatedly - you've probably reached
the 75% limit for that cavity. I put a plug in the hole and moved to
the next hole. Or you could switch to the hair dryer.
It's easier to drill all the holes in a wall. Put plugs in the
holes (with a screw handle in each one so you can get it out later).
Then vacuum blow the whole wall. Then hair dryer each segment. Glue in
the plug (I used PVA). Move on to the next segment. When the wall is
done putty the holes. Then move on to the next wall.
When removing unglued plugs you may find they have stuck. I used
the nail pulling end of a hammer, as if I was pulling a nail, but
tapped the hammer handle gently to nudge the plug out.
The perfect blower would be made of clear plastic so you could
always see what was going on. Have a clear section before and after the
motor is the next best set-up.
I didn't have to wait long for a cold snap.
Screenshot of my weather station showing a sudden 5 degree drop. By
10pm the temperature difference bewtween indoor and outside temp was
about 10 degrees. The slight upswing in indoor temperature at 7pm was
when we closed the blinds and cooked dinner.
It's now three months later and time for a look back.
My power bills are down. Although it was the warmest May on record, so... they would be anyway.
June is not being quite so kind. It looks like we might end up averaging 20 daily Units for the month of June.
I've had several people email asking a few questions:
1. What about electrical wires - doesn't the polystyrene react with the plastic around the wires?
I'm lucky that our house has almost all it's wiring on the internal
walls. There are about 4 spots with wires - so I just left those empty.
At some later stage I'll think about filling those with something
non-reactive, like wool fibre.
2. Is it fire retardant?
Yep. Poly Palace only use fire retardant polystyrene in their
underfloor products (so I made sure they gave me fire retardant beads).
I still haven't sanded and painted over the puttied plugs. The putty is such a close match to the existing wall colour that I haven't prioritised it.
My power usage - particularly heating - has gone waaaaay up! Back in October my wife and I had a baby (Adam) who is lovely - but we are using an extra heater in his room now and washing a lot of nappies). And Michelle is home most of the day - so it looks like we may exceed our 2004 power usage of 6542 kWh. I'm guessing we'll be around 7000 kWh, but still well under the 8000 kWh that qualifies us for the "low user" charging rate.
I've had the house rated with HERS (Home Energy Rating Scheme) - we got 6.5 which is pretty good for a 1927 house. Apparently one of the key positives in our house was the double layer of batts in the ceiling.
I spent the last summer installing four 1000 litre rainwater collection tanks in behind our garage - for use on the garden next summer.