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Cheap wall insulation with polystyrene beads and a hair dryer

How to insulate into your walls for under NZ$400 (US$300).

Jump to:
28 Dec 2006 Start with hair dryer
10 Jan 2007 The venturi effect
21 Jan 2007 Refinements
4 Feb 2007 Half way
10 Feb 2007 Speeding up
17 Feb 2007 Costs and tools
7 March 2007 Temperature
10 March 2007 Finished blowing
19 June 2007 3 months later
19 June 2008 1 year later
13 Jan 2010 IR thermal imaging
25 Mar 2011 Compressed air system

By Paul Kennett 2006-2011

Your Questions and Answers

See my latest: compressed air powered insulation blower (my version 3 setup)


I live in a small wooden 1927 railway cottage in Moera (New Zealand). In order to improve it's energy efficiency I've insulated the roof (with one layer of new Pink Batts, and a second layer of used Batts), and insulated under the floor (a 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) provide 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 three 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 roof).

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:

Now here's the process in detail:

28 Dec 2007

1. Buy the beads

Poly Palace in Porirua sell used polystyrene from Peter Jackson movie sets like King Kong. They "mulch" them back into individual beads, then reform them into underfloor insulation blocks.

A 2 cubic meter bag of polystyrene balls
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 force. 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 hassle because the resistance of the elements provides the voltage drop from 230 volt mains.)

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 blower on top of the bag
The finished blower connected to the bag. The black thing is the battery.

The blower stuck in the hole in the wall.
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

35mm hole in external wall
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

Blower on with low flow
Here's the blower switched on and blowing beads into the wall. This is a relatively low flow.

Blower on with high flow
And here's a higher flow.

The amount of flow depends on several factors:
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 plug ready in your other hand.

Wall segment full
Wall segment jam-packed full of polystyrene beads.

5. Plug the hole

Plug glued in place
Here's the plug glued in place.

6. Finish off

Next I'll sand it back, add filler if needed, and paint.

Other hints

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 this 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.


10 Jan 2007

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 plastic fan propeller drops off the motors metal shaft.

So now I'm trying a vacuum cleaner blower. 

The Vacuum cleaner version

Electrolux vacuum cleaner with blower option
Here's an old Electrolux vacuum cleaner with a blow option.

Nozzle utilizing the venture effect
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).

Overview of venturi blower design.
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.

Sleeve inside Y tube to enhance venturi effect.
The "Y" join needed an extra plastic sleeve (cut from an ice-cream container) inside to enhance the venturi effect.

Clear hose with beads being cukced up.
Here's the clear hose coming out of the top of the bag full of white polystyrene beads being sucked up.


It's really good having a clear tube as you see the polystyrene being sucked up.

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 there's 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.


21 Jan 2007

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 drill bit 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.

Plugs sanded and puttyed
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 polystyrene 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!]


4 Feb 2007

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 section 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.


10 Feb 2007

I'm now making much faster progress. Each column takes about 20-30 minutes to fill 80% with the vacuum blower. Then another 15-20 minutes with the hair dryer blower.

Here's a 10 second video of the vacuum blower going on the eastern wall.


17 Feb 2007


In New Zealand dollars.

Part Unit cost Quantity Cost
Hair dryer 5 5 25
Ventilation duct 3m (plastic) 1
Polystyrene beads (2 cubic m bag - delivered) 50 2 100
Wires for hair dryer 0 3 m 0
35mm drill bits 17 8 136
38mm clear tubing 5 3 m 15
Vacuum cleaner (with blower function) 0 1 0
45mm to 32mm plastic reducer (plumbing) 1
32mm x 1m pipe 1
32mm plastic bend (115 degree) 1
32mm plastic Y joint
Can of spray glue (to block thin gaps) .5
No More Gaps (to plug bigger wholes/gaps - or you could use putty) .5
Putty (500g tub) .5
Batteries (12 volt rechargeable) 2
35mm doweling (1.8m length) 1
PVA .5
Duct tape 1 roll
Electrical tape 1 roll
Zip/cable tie 1
Sandpaper 1
Development time mucking about with hair dryers and plumbing bits 20
Time (roughly 1 hour per column) ? 60 ?


Links to polystyrene bead insulation info


7 March 2007

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.

Temperature data for 7 March 2007.
Here's a screen shot from my weather station which shows indoor and outdoor 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).

10 March 2007

OK - finished blowing all the walls. Phew! It took a while but now its done.

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):


13 March 2007

I didn't have to wait long for a cold snap.Weather data for 13 March 2007.
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.

19 June 2007 - Three months later

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.
Monthly Power Units - average daily Units used

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).

3. In the UK polystyrene wall insulation is blown in with a glue. Why is that?

My quess is (1) it means the next time you drill a hole in the wall you don't have a lot of beads dribble out, and (2) it stops/reduces the polystyrene from settling.

I don't have an answer to either of these issues with what I've done.

4. What's next?

Windows. See my insulation blog; http://www.kennett.co.nz/paul/myonlinediary/


19 June 2008 - a year later

It's now mid winter just over a year later...


13 Jan 2010 - IR thermal imaging

I've just had a my walls insulation assessed with a infrared thermal imaging camera.


25 March 2011 - Compressed air system

Over the last year I've been working with a friend on "better" systems. We've played with a Ryobi leaf blower system which never quite worked well enough to be considered "better".

Then we switched to a compressed air powered insulation blower - which is the best of the three setups I've tried.

Positives are:

Negatives are:

Please email me if you have any questions, ideas or suggestions.


If you live in the Wellington area and would like to borrow the blowers or have a look at how it all turned out send me an email.

Cheers, Paul