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  • Nik Gregg

Diary of an attempt at a sustainable home renovation

We have recently purchased a home that is our 'project' for renovation. Given my job is to promote household sustainability, I thought that this might be a worthy journey to share with others.

My key focus is energy sustainability, but I will also be sharing my journey regarding water and waste sustainability.

In this post, I want to give a bit of background as to 'the project' and the 'journey'. Then as time goes on - I'll seek to keep the posts up to date with how its all progressing.

The home: It was originally 1950's weatherboard timber home with a metal roof and then it was renovated in the 1970's, with a two story addition. The home now has four different cladding types: vertical cedar, fibrolite, timber weatherboard, vertical timber tongue & groove. The metal roof has been covered over with metal tiles. We have timber window joinery. 60% of the home is on timber piles and underfloor insulation has been strapped up, the other 40% is a concrete basement which houses a single car garage and a space we have made for an office. The basement walls are concrete brick. 50% of the home has a ceiling cavity with insulation measuring around 120mm and the other 50% is a skillion timber ceiling with no cavity and this appears to have some insulation from the original build. The home as you see it below, is north facing. It has little glazing on the west and south and a medium level of glazing to the east.

The home is approximately 187sqm, we have 4 bedrooms (no ensuite), one bathroom, one toilet, one dining room, a living room and a separate lounge. The kitchen is fairly compact (still 1950's style), one basement office space and a single car garage space (basically storage).

Heating / Cooling:

The home is meant to be heated by two open fires (spot the chimneys) and one 2kw panel heater in the dining area. Whilst the home has insulation, it is barely meeting NZ minimums and is below what it needs to be (I'll do some calculations on the heat loss in another blog). We moved in to the home in late Feb and the temperatures inside the home were very hot. The upstairs lounge was regularly over 26 and often between 28-30 degrees C.

For the past 3-4 months I have been measuring the temperature and humidity in 4 different points in the home. During March & April, the outdoor temperature has fluctuated between 8 degrees and 26 degrees C. The indoor temperature has fluctuated between 16 degrees and 30 degrees. At night, the temperature in the home did not drop down below 16 degrees despite a few 8 degree evenings, but we continued to have warm days above 20 degrees heating up the home passively. The upstairs lounge continued to heat up to 26 plus degrees even at the end of April.

In May the outdoor temperatures were a bit cooler in the evening, but still around 20ish during the days, in the home, the temperatures were between 15 degrees - 21 degrees.

In June the outdoor temperatures have dropped down regularly to between 5 degrees - 8 degrees overnight. The indoor temperatures are now regularly down to 11 degrees - 14 degrees overnight in the home. During the day, the home will passively heat up in the north facing rooms to 18 degrees - 24 degrees, the bedrooms will get up to around 16 degrees - 17 degrees. My office (in the basement) will hover around 16 degrees during the day but has not dropped below 14 degrees at night.

One of the open fire works, the other has some concerns, so we are only operating the one open fire. This provides good radiant heat and if we are lucky, we can get the living room and the kitchen up to 18 degrees, but basically, to get warm, you need to be close to the fire. Further away from the fire - its all about blankets and layers of clothes!

In the morning, we use a small fan heater in the kitchen to help take the chill off, and in my office I use a panel heater for a couple of hours in the mornings. My office does not take much to heat up, but it still only gets to 20 degrees.

The curtains in the home are either non-existent, light or old and poor. So we lose lots of heat.

Ventilation & moisture:

The home has no mechanical ventilation, but we have heaps of drafts and natural ventilation. The home has lots of louvers and these let a fair bit of draft in. The bathroom has no mechanical ventilation. The only way of venting the bathroom and kitchen is to open the windows. We do this regularly, every day for 15 minutes twice a day, except when its raining and moist outside.

The home does naturally ventilate and its also good really good cross flow when we open a few windows and doors.

The humidity in the bathroom is 65% at its lowest, but generally its between 80% - 100%+, suffice to say - we have mildew and mold that need removing regularly.

The humidity in the living areas is often 55% - 60%. The humidity in the bedrooms next to the bathroom is a bit higher at between 55% - 70%. The humidity in my office is 60% - 75%.

Condensation in the home is not large. The boys rooms have body condensation on the windows and a little bit of impact from the bathroom. Our main bedroom has very little condensation at all. The only area we have serious condensation is the bathroom and at this point, we are wiping this down and regularly tackling mold with our vinegar / water mix.


I won't comment on my power use yet, but I will do this another day. I am monitoring my power and am gathering information on this and where I am using it.


At this point, we have not done much to the home, because we want to get a handle on its performance and to see how it goes over winter.

We have however put a ground vapour barrier down on the soil in the underfloor cavity.

And I have just started to change over our old incandescent bulbs to LED's.

At this point, that's it.

Ok - will now try to write more later and more regularly.


Tues 28th June

The last week has been really quite wet and I've noticed through my monitors in the home, that the humidity is now regularly between 65% - 75%, the bathroom is almost exclusively above 80%, and outside it's been over 80%. Yep, we are regularly cleaning mold off the bathroom roof. I'm sitting in my office (down below the moist ground level) and it was 79% and 15.5 degree's when I came in, I've opened the door and windows and it's now 72% and 16.8 degrees.

The night temperatures on the south of the home have been between 10 degree's to 12 degree's, so not too cold. But interestingly, we have seen little condensation on the windows in the home all winter (so far).

I've just given the home a full airing (opened all the windows and doors) and tried to change out the air, the temperature has not dropped greatly and the humidity has not changed markedly (due to the high outside humidity). Have now closed the windows and am trying to capture the sun's heat.

Am looking to bubble wrap my office windows shortly - to see if I can retain more heat in the office present, I loose any heat gained during the day, to end up being about 2-5 degree's different from the outside temperature.

Friday 1st July

Cold night last night - outside south temperature dropped to 5 degrees. Inside temperature dropped to 10.2 degrees in the bathroom (open window), 12.4 degrees in the boys bedrooms and 13.4 degrees in our bedroom and the lounge. Very low levels of condensation - more like a mist.

Power use - measured microwave use for past 16 days. We have a 700w output microwave (small). On standby it was using 1.85w. At peak use, it was using 1.229kw. We use it mainly for re-heating, very little for cooking. Over the 16 days we used 2.180kwh, on average 136wh per day. This would equate to 49.64kwh per year, or an approximate cost of $14 per year.

Update - bright sunny day but a cold southerly blowing. On the south side, it's 9 degrees. Home got up to 18 degrees in the lounge and 16 in the bedrooms. Humidity was 73% around the home. Opened all the windows. Forgot about them for 40 minutes (oops), and have just closed them all. Temperature has dropped down to 15 degrees in the lounge and 11 degree's in the bedrooms, but humidity has fallen to 50 percent. Yah. Even got the bathroom humidity down to 58%.

Monday 4th July

It's been down to 1 degree outside (was below zero yesterday), the bedrooms are down to 6.5 degrees and 68% relative humidity and the lounge is down to 10.5 degrees at 58% relative humidity. Got our first lot of condensation in the lounge and the boys room is a bit worse, but not really bad. The bathroom was below 6 degrees and 70% relative humidity. I was up at 5am to heat the lounge with the open fire. Got it going and had it going for 2 hours and all I gained was an increase to 12.1 degrees. A lot of firewood for very little temperature gain. Once the boys got up, I measure the condensation on their window. The southern room had a light dusting of moisture on two glass panes and I collected 2.5mm of moisture - not much. The western room had slightly heavier dusting on 4 panes and I collected 25mm. I then went in to the bathroom. One shower had been taken, the bathroom was at 87% humidity, and I collected 45mm of condensation from two large panes.

The sun has come up, and in the space of 1 hour, the house is improved to 14 degree's and rising. My office is still sitting at 12 degrees and I have a panel heater on low.


The other day I updated a bunch of our lightbulbs. I converted 9 incandescent bulbs and 2 halogen over to LED equivalents. We have already noticed the superior light difference. We had a lighting load of 628w and I now have a load of 83.5w. I still have around 10 other lights to change over. I'm now drawing 13% of the energy of my previous lights.

Friday 5th August

It's been slightly warmer over the past couple of weeks...around 15 outside during the day and down to 8 at nights, no really cold nights. Condensation hasn't been noticeable. The home has generally dropped down to around 12-13 degrees at night. During a good sunny day, it's been back up to 20 plus degrees. On a cloudy day, it sits at 13-14 degrees.


I've been tracking my condensation (on the days when it is noticeable). Today was one such day. The night temperature wasn't too bad, 8 - 9 degrees outside (13-14 degrees inside), but it's been still and misty outside, the relative humidity yesterday was above 80% for most of the day yesterday and this morning it was 96%, so lots of moisture around.

I've been using my Karcher moisture vacuum to measure condensation on our windows and over a few measurements I've concluded that on a medium sized window (600mm x 800mm)ish, a light misting of condensation is around 2.5ml - 5ml of moisture, a clouding is around 5ml - 7.5ml of moisture, a crying window is 15ml plus of moisture. Doesn't take a lot to make a window cry! Doesn't take much to have mould grow.

I also measured my bathroom. Interestingly, after one shower (our bathroom has no extraction fan - yet), I collected 250ml of water off the windows and shower walls, after another shower, I collected 500ml of water off the same surfaces. It is said that a shower can generate 500ml - 1l of moisture. I'd believe that. No sooner had I collected the moisture, than the air was dumping more on the windows (our bathroom is constantly above 80% relative humidity). Therefore it takes less than 2% of the shower moisture to create a problem on the surface of a mid sized window. When I open the bathroom door, I can see the moist air immediately go out in to the hallway.

Up in our upstairs lounge - we have not had any moisture on the windows previously, however, recently we put up some heavy curtains. This morning I had a light misting on the windows. The curtains had trapped the moist air, where-as previously, because the house is drafty, the air was moving (we have leaking louvers). The curtains didn't cause the moisture - as the room had a relative humidity of 70% yesterday, so we already had a high moisture content - so it's no surprise that once the air got trapped it released its moisture as it cooled.


I've been tracking the energy use of my toaster. We are a family of 5, with 4 of us at home, two teenage boys, my wife and myself. At least one of us uses the toaster each morning, and the toaster is used at least twice more during the day. I measured the toaster for two weeks. The low was 1.3w, the high was 1441 watts. The average use was 13.8wh or 330wh per day, a daily cost of 9c.

Saturday 6th August

Feel a bit happier, I insulated my office windows with bubble wrap a week ago and put up a curtain over the main glass doors, with the somewhat milder temperatures (only down to 8 degrees at night), I wasn't really seeing any difference between my office (which is an enclosed space underneath the home) and our home, which is wide open, lots of louvers and lots of drafts. However, this morning it was down to 4.8 degrees outside, the house temperatures ranged between 9 degrees and 11 degrees, and my office was up at 13.2 degrees, so a wee bit warmer, having retained a bit more of yesterdays heat. Also, in the home, there is a bit of condensation on various windows (not much - a clouding on some, misting on others - no weeping), but in the office (which has similar humidity levels to the main house - 70%), no condensation forming. See my pic below.

Saturday 13th August

Been an interesting week. The week started out very cold. External temperatures down to below zero degrees. The internal temperatures dropped down to 8-9 degrees in the bedrooms, 9-11 degrees in the lounge area (where the fire is), 6-8 degrees in the bathroom, where the window has no covering and is left slightly open as we are trying to remove moisture from the late night showers.


With these cold temperatures, a couple of days were nice and sunny and the external relative humidity (RH) was below 50%. On these days, I opened up the house in the colder mornings and was able to reduce the RH from the mid 60% to mid 50%. Whilst the days were fine and cold, we have had a cold house with 8-12 degree temperatures overnight, but lower RH at between 50% - 60%.

Over the last 24 hours, warmer night time temperatures have returned (6-8 degrees) along with the rain, the internal temperatures are at 12-15 degrees, but the RH is back above 65%, between 65% - 75%. The external RH is over 85%.

Whilst our internal activity is contributing towards higher moisture content in the home, without any doubt, the external humidity is also impacting our home, as our home lets in a lot of external air!

However, with the warmer temperatures overnight, whilst there is much moisture in the air, our condensation levels remain low. Additionally, my office has no internal moisture source, but its RH is high when the external RH is high. Presently it is 68%, outside it is 88%, but I have not had any condensation on my windows either before or after placing bubble wrap on them....

Saturday 10th September

Been a while since I have had the chance to update. Weather has been a mixture of mild(ish), wet, and cold.

Home improvements: 4 weeks ago we installed a heater to our bathroom. A 2kw fan heater. We wanted to install both a heater and an extractor fan, but we couldn't get an extraction unit in to our roof, as we are going to renovate the bathroom we didn't want to install one in to the outside wall and then just have to remove it when the bathroom gets renovated. So we only installed the heater. I was also interested to see, what impact will the heater have on its own? We also installed a new dishwasher. What impact will this have on our power bill? It should be less, because we have a deep sink and we were washing dishes 3 times per day, to stop the bench getting cluttered.

Bathroom: wow, what a difference the heater has made! Yes, we still have high moisture readings after showering. Our moisture readings are still above 85%, but, we have the heater on before showering, during showering and for 15 minutes after our showers. We also open the window fully after the shower. Our thinking; lets keep the air really warm so that it holds the moisture, then lets keep the heater on with the window open so that the moist air is more easily changed out. Result: our bathroom is much drier. We have been able to reduce the RH content down to below 50%, which we could never do without the heater. Also, the boys bedrooms have lower RH readings, they are now more regularly down below 60%. The bathroom ceilings and walls are noticeably dryer. Yes, our power bill will have taken a hit (still to see how large a hit), but the key thing, is that our bathroom and home is drier, less moisture and therefore less mould. We still need an extraction system, but the heater is a great start.

Heating trials: On the 24th August, it was another cold, grey day. Outside it was between 10 degrees and 14 degrees, with humidity between 70% - 80%. I put my heater on for 8 hours at maximum. It gave me 2hrs 47 minutes of heat, using 4.485kWh. I was able to improve my office temperature from 14.7 degrees to 20.9 degrees. It took 4 hours to get me close to 20 degrees. My RH dropped from 62% to 58%. Upstairs, there was no heating, and the house was at 16 degrees. So it took me 4 hours to get a reasonable temperature and it cost me $1.35.

On the 25th August, which was a cold grey day, it was damp outside with a humidity reading of 93% and an outdoor temperature that peaked at 13.8 degrees. I put my oil radiator on for 7 hours. I had it on the highest temperature. Over the 7 hours, it used 4.2kWh to heat my 12sqm office up to 21.5 degrees. My office temp started at 14.9 degrees in the morning, it took almost 4 hours to get to 20 degrees. The humidity started at 65% and dropped down to 61%. I could not ventilate the office, as the air outside was more moist than the air inside. So, in summary, it cost me $1.20 and over 4 hours to get my office up to a nice temperature, my humidity remained high. 4 hours after switching the heater off, my office had lost 1.5 degree's and was at 63% RH.

Thoughts: even in a small space, when it is cold outside and the room is poorly insulated, it takes a long time to heat. Heater thermostats compromised the ability of the heater to stay on constantly to heat the room up faster. It didn't cost me as much as it could've, but I was having to use blankets to stay the course. Humidity was not impacted as much as I would've like.

I've also been doing some night time bedroom trials - more on this later.

Saturday 17th September

Been a mild week, started out nice and sunny and then has got damper and wetter. During last week and the beginning of this week, we have been able to air the house out on the nice fine days (17 - 18 degrees) and to capture that low moisture air from the cooler night time temperatures (6-7 degrees). Our internal RH dropped down to 44% - 48%, and was regularly below 50%, which was really unusual for our house.

However, the last 3-4 days have brought rain, and the outdoor RH has been over 90%. Our internal humidity has been steadily rising and is now running at 65% plus. In my office, it is now up to 78%. If I open the doors to let new air in, the outdoor RH is 92%.

My office has no internal source of water or moisture, but it is easily the most damp area of the home, it is below ground level and the ground moisture seeps through the walls.

On Wednesday, it was raining / drizzling consistently in the morning. So I thought I'd try out the de-humidifier. My starting RH was 68%. After 3 hours, I reduced it down to 62%. It took 564wh of energy, so cost me around 15c. I've just turned it on now - its drizzling outside, and the outside RH is 93% and 15.3 degrees. My office RH is 78% and 17.2 degrees.......I'll be back soon.....see what my power use is over the next hour and the difference I, now it's been just over 7 hours. It's been raining pretty consistently outside all day, I've used 1.4kWh of energy to run the dehumidifier all day, which has cost me around 40c. The RH outside is up to 95% and is 15.5 degrees. I've not had a heater on at all. My indoor temperature has remained steady at close to 19 degrees and I have an indoor RH of 67%, which is down only a little bit from this morning! Wow, not much RH change but, now this is the scary part, whilst my RH didn't reduce much, I still collected during the day 2.5l of water in my dehumidifier!!

Wednesday 26th October

It's been over a month since I last reported. Not too much has happened of note. The temperatures haven't dropped down below 6 at night and have largely been above 8/9 degrees, so not too cold. The bedrooms inside the home have remained above 14 degrees. Our moisture levels have largely fluctuated with the weather - on rainy days, the moisture in the house is generally between 60% RH - 68% RH, on these same days, the moisture in my office (basement below ground level) is usually between 70% RH - 80% RH. Today for example, there has been rain overnight, it's fine, sunny and clear, but the ground is wet. The house is reading between 62% RH and 65% RH. My office is reading 71% RH and outside is 77% RH. Already, over the past hour, the outside RH has dropped from 88% RH to 77%. But the office has not changed. When I tracked this the other day, outside the RH dropped from 93% - 64%, but the office stayed at 72% despite opening windows and doors. I've got the doors wide open today, it's 9am. Lets see how we go. It's 19.4 degrees inside (no heating at all), and its 17.3 degrees outside. I'll come back to this in an hour.

Just on the bathroom. Wow, that little heater is making a huge difference. We run it during and after each shower (for around 10 minutes). Then we open the window and close the door and wait for the hot air with moisture to escape. The bathroom has been much, much, much drier! The RH drops down pretty quickly, to be in line with the house at around 60%. We have far less mold growth on the walls and ceiling and we have heaps less moisture building on the ceiling. I used to go in to the bathroom, and it was almost permanently above 75% RH., despite having the window open a huge amount of time. Now, the bathroom moisture reflects that of the home at 60% (ish).

It's now 10:30, it's 19.7 degrees inside, the RH has fallen slightly to 68%, outside the temperature is 17.7 degrees and the RH had fallen to 71%, but now it's on it's way back up and the rain is coming in. In short, airing out my office did help a wee bit.

Wednesday 16th November

The last few weeks have had a good number of rainy days and a few really sunny days. Whilst the evening have been relatively warm (15-18 degrees), the days have been average (17-20 degrees). There has been little to no condensation (as you would expect with warmer evening temperatures), but the humidity in the home has been between 65% - 80%, it has been very hard to reduce it. Outside the humidity has been 80% - 90% on most days, even when it hasn't been raining. We have not really noticed the high levels of humidity in the home - if it was winter, we would notice it through condensation, but in these warmer conditions, the moisture either stays in the air or beds down in the furnishings. BUT, in the office, unless I 'air out' the office, the humidity very quickly starts to show in all the paper that I have in the office, my books and paper are curling and becoming damp. I have two choices, put the heaters on to try and dry things out, or ensure doors and windows are opened regularly to get some form of air movement. Observation: even on days when it is raining, we need air movement and air change, otherwise the moist air settles and makes things damp and musty in a closed environment.

Monday 5th December

Well, in today's update, I've got a bit of power information and a continued observation around humidity.

Humidity: It's been much warmer outside (18 - 25 degrees) and the nights have been pretty warm as well (15-18 degrees). A number of sunny days in a row. Interestingly, upstairs in our home, the RH has dropped down to 45% - 55% and it has stayed in this range for both day and night. But my office, has stuck consistently at around 62% - 67%. At night it nearly always moves back up to 67% - 69%, during the day it drops down to 62%. Once or twice it dropped down to below 60%, when it was really dry outside. Most days the outside humidity has been between 55% - 65%. The difference between my office and the house, is that my office: a) gets no sun, b) is surrounded by earth on two sides. Without sun, I'm not drying it out, I'm just changing the air and then the moisture comes through the walls from the earth. The office is below 22 degrees, and is much cooler than the outside temperatures - makes it nice to work in, but the RH is not decreasing. Will be interesting to see what happens over summer.

Power use: I've been tracking my office power use for the past 75 days. Over this time, I have a laptop on for 8-10 hours a day, a printer on, and a second screen for my work. I also used the heater to stay warm over the winter period. My average use was 2.57 kWh per day, or 107 watts per hour.

Fridge / Freezer: I also tracked my fridge over winter. The fridge is over 10 years old. At it's peak, it was drawing 1085kw. On average over the week I measured it, it was using 2.54kWh per day, which equates to a daily running cost of around 71c, or an annual use of 927kWh. A good modern fridge would use 1/3 of this.


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