The problem with insulating from the inside

A couple of months ago Tikker asked me an interesting question about insulating houses. I was writing about our plans to insulate our house from the inside and she, basically, asked if that was such a good idea. That don't houses need to be insulated from the outside?

I replied very briefly. But today, for some reason, I felt I wanted to explain the theory behind insulation in a little more detail.

So here goes.

Generally (by which I mean "in cold climates") insulation is applied to the outside of buildings because it makes the entire structure of the building warmer than the surrounding air. When the structure is warmer, it doesn't get condensation on it - condensation only happens when warm air hits cold surfaces.

Think of it this way: you have two drink bottles on a table. One is filled with boiling water, the other is filled with ice. Which bottle gets condensation on it?

The answer is: cold, ice-filled bottle. As the warm air around the table hits the cold surface of the bottle, the water vapour in the air condenses onto the cold surface, creating drops of water.

The same mechanism (ie condensation) can take place inside a house structure if insulation is applied - for whatever reason - to the inside of the building, rather than outside.

It's hard to explain, but when insulation is on the inside of a wall, it, effectively, separates the rest of the structure from warm air inside a building. The exterior envelope of the structure ends up on the outside of the insulation layer - so the structure of the house becomes much colder than the interior air.

If the walls of the house are not perfectly airtight (and to be honest, most houses' walls aren't), the interior warm air can wind its way inside the building envelope - and condense there. And when it does... it's bad. Very. Very. Bad. That's how you get mould and mildew growing inside walls - through cracks and permeable materials warm air reaches the much colder elements of the building on the outside of the insulation layer (because insulation, on its own, is not airtight), and as soon as this warm air hits a cold surface, condensation happens. Most common places are where different elements of the building fabric meet: around window openings, in corners, at the junction of walls and ceilings, or walls and floors.

It is not to say that insulation should never be applied on the inside - because it does get done on the inside, and sometimes very successfully. But it's very, VERY difficult to do it well. In order to keep the interior warm air from passing through the insulation, there needs to be an airtight layer on the inside of the insulation layer, and it can have ABSOLUTELY NO GAPS IN IT.


If it is an airtight fabric such as Intello, every single joint has to be taped shut. Even things such as screw-holes and nailholes have to be thought through, because every hole in the airtightness layer creates a risk of air movement to the outside, and the resulting risk of condensation within that wall.

So that's why, if it can be helped at all, houses are always better to have insulated from the outside. It is an easier, more straightforward, less labour-intensive process which, even if someone makes a mistake whilst installing something, the problems that arise are not that bad.

If someone makes a mistake whilst installing internal insulation... Well. That can be rather, let's say, "more cumbersome". (F*cked up, I was going to say, but oh well.)

So, why are WE doing it then? Why are we wanting to install insulation on the inside?

The answer is: because our house does not have solid walls. We have a very "standard New Zealand" construction of what's known as "cavity wall". Basically, inside the walls of our house there's a gap: outside is brick, then there's 50mm gap, and then there's wood on the inside.

If we insulated our house from the outside, it... wouldn't work. We would be "heating" that gap inside the wall, basically, and from that gap the warm air would rise up into the roof structure and condense on the underside of our roof, condensing and potentially "raining" back down onto our ceiling insulation below.

And that is, basically, a very good example of why some houses get insulated from the inside. They are "retrofits", mostly - houses that are fixed up from something old, trying to fix old problems, rather than building a brand new house. It's a bit like having a second-best option: that, really, in an ideal world you'd be insulating on the outside. But sometimes you just... can't. To insulate a cavity wall from the outside requires re-engineering that wall so it becomes a "solid" wall instead (ie, a wall without a cavity) and to do that well... it kinda starts getting to a point where you need to think how much it's going to cost, versus what it would cost to just demolish the house and build anew.

So you choose a second-best option because you just have to. You don't want to - but you do it, because otherwise you'll be living with a non-insulated wall, and that's not good either.

I am thinking another day I may come back and share some ideas I have about our insulation, and how I am planning to tackle the airtightness problem. I have a couple of sketches I've made, just trying to get my head around all the corner details - that what is going to need to happen where walls meet with ceilings and floors, because we absolutely cannot leave any gaps.

But for the moment, I am going to go to sleep.

I handed in my very last assignment yesterday. I AM FINISHED!!!!

And also very tired. Good night!


If all goes well, I will have all my assignments finished by Thursday.

In fact, depending on how hard the last assignment is - it is being handed out today - I may have everything finished TODAY.

In less than a week, I will have, essentially, graduated.


Oh. My. God.

It is almost over.


When I realised I had been feeding our earthworms... polypropylene.

Earlier this year I discovered that teabags were made of polypropylene. I don't know why I hadn't known before. I had assumed that they were made of biodegradable fibres, so for years I put them in the compost bin.

Now, I have years forth of teabags to sift out of our compost soil. It'll happen gradually: I pick them out as I see them, gardening, weeding.

We have gone 100% onto loose leaf tea. Peppermint we are already getting from our garden. Others we buy in large bags, partially imported, partially New Zealand grown, mixed together in Nelson - kawakawa and lemongrass, ginger, feijoa green tea, chamomile and lemongrass.

Bit by bit, less plastic. Bit by bit, changes in our consumption. Grow a garden, plant a tree.

Once an understanding grows of sustainability and the ecosystem and the pollution, it's not possible to go back, only forward. When my children eat a banana in town, I carry the peels home, "for the worms". We have "adopted" a stretch of street and pick up rubbish when we see it. Glass and aluminium cans, we carry home so we can put them in recycling bin. The school uniform "second hand shop" I have set up at our primary school, I think we've already diverted a dozen uniforms from landfill - by replacing the broken zips, they have gone to be worn by more kids, rather than into rubbish where they did not belong in the first place.

Gradually, as these changes become my new "norm", I find new things to reduce and reuse and repurpose and recycle. Wanting to take up less space in the world, not more. I volunteer at school, my husband at the toy library. He has helped them fix up old furniture to keep it going.

Bit by bit.

Russian-speaking community in Invercargill

Did you know that Invercargill has a sizable Russian community? I was saying to a friend the other day that, at the moment, I speak Russian on a weekly basis here - and not because of speaking to the same people, but because of meeting a variety of Russian-speaking people in public spaces.

Mostly, I meet them in the sauna! Local swimming pool has a small public sauna which, I find, is quite a common place to overhear someone talk in Russian or with a very Slavic-sounding English accent that, when I ask the person where they're from, turns out to be from Russia. Or maybe if not from Russia, then from Russian-speaking ex-Soviet countries such as Ukraine, Belarus, Usbekistan etc.

No official count exists, but by my estimate there are about 80 Russian-speaking people in Invercargill. Some Russians I have asked have agreed, guessing it to be about 75-100. I have personally met about 35.

A group of women meets every few weeks for a Russian brunch - a weekend meal at a cafe someplace for an hour of Russian chattering. I've attended one: my brain felt absolutely "fried" afterwards! Not having talked Russian for years, it is linguistically very challenging to put thoughts forward. I can understand everything - but I can't talk back effectively. Words are garbled, or not accessible at all.

My daughter's classmate is from Russia, so I talk to his parents at school, or when they've come for a visit. My son's therapist is an Usbek. I often hear and meet Russian speakers at public events in park - just last weekend I met a homeschooling mom of 2 who's originally from Belarus - or at the library.

Several Russian women have New Zealand passports and New Zealand husbands they've met whilst working in Europe, London mostly. A number of students from Russia is studying engineering, IT and management at SIT (Southern Institute of Technology), our local polytech.

It's a touchy subject I haven't dared to dig too deeply in, but my impression is that Russians I've met here do not take kindly to the current Russian political climate. It's small, off-hand remarks. "Russia's not... well." "You're familiar with what's going on, aren't you." "I did not want to live in a place like that." "I'm a lucky one, I had money to get out. Others aren't as lucky." As much as I would like to ask people, hey, what do you think of Putin?, it's not really a good question to ask, I don't think. (Would probably sound very similar to meeting an American and enquiring if they're Republican, or support Trump.)

I enquired from one of the enrolment clerks at SIT if there had, indeed, been a rise in Russian student numbers in Invercargill. She said yes. Apparently, New Zealand has started promoting overseas tertiary education options on the Russian market, and Invercargill is considerably cheaper to study at than other New Zealand cities.  Invercargill, basically, subsidises every foreign student's tuition fees because it recognises that people who move here to study contribute a lot of money towards the local economy (accommodation, food etc), without requiring many public services because, normally, foreign students do not have access to New Zealand's publicly funded healthcare or social benefits. That, basically, even after contributing towards foreign students' tuition fees, Invercargill is still earning enough tax revenue off it to make it worthwhile.

So, to Russian students who can be - but aren't always - cash-strapped, studying in Invercargill is more affordable than elsewhere in New Zealand, and the recent marketing campaigns have brought increasing numbers of them here.

What it means to me, a trilingual European "import"? I speak English the most. I speak Russian a little. I speak Estonian the least.

I've even started to notice a marked increase in my Russian speaking ability since making these Russian acquiantances, and have heard two Russian ladies say that I seem to speak better now than I did a year ago.

Looking into the future, it'll be interesting to see if speaking Russian will become more comfortable than speaking Estonian for me. After 10 years of speaking mostly English, my Estonian syntax has started to deteriorate. I can no longer write well in Estonian and when I speak, although I can recognise that Estonian sentences are "off" - they're composed of Estonian words, but arranged in a way English words would be in English syntax - I cannot fix them. I recognise mistakes, but I no longer know how to fix them.

Sure, my Estonian is still much better than Russian at this point, but I wonder for how long if I keep up speaking Russian on a weekly basis. We'll see.