Choosing Best Airtight Options in Japan

What kind of materials are available in Japan, where are they found, are they safe, how are they installed….?

 

If you are looking to design, build or own a comfortable healthy house that consumes minimal amounts of energy then you may have searched and come across the following basic formula (no rocket science involved):

1. Airtight
2. Super insulated
3. Thermal bridge free (minimal moisture risk and heat or cooling energy loss at vulnerable spots in the assembly)
4. Optimal solar orientation (sun in winter and shade in summer)
5. Air ventilated (i.e., mechanically controlled fresh air!)

1    Passivhaus Consultants can help with this but of course, correct and healthy doses of the above cannot be achieved without the expertise of engineers, architects and builders or without the proper materials. 

Onto the topic of choosing the best airtight products (1 above) in Japan. First, let me start by showing an image of the effect on moisture infiltration of even a small (25mm or 1") hole in the airtight layer:

Thirty litres a year is a lot of moisture from one little hole, for example untaped seams or punctures from staples not covered up! It doesn't take much to imagine how this adds up and what the average home lets in these days, despite being more airtight than before. What does this cause? Mold, structural deterioration, and drafts which are not comfortable, conducive to build longevity, healthy, or energy efficient. Adequate and proper installation is paramount.

Next let's outline how these products should look in relation to a global society conscious of energy use and carbon footprint along with changing building codes around the world, such as the BC Step Code Canada.

 

Products should be VOC free, have a low carbon footprint, superior sticking properties where applicable in weather extremes, be robust during rigors of construction, smarter with regards to permeability in different directions, and have reputable certification that shows they meet the above conditions. Simply put, ones that are healthy and do a great job at keeping the energy and moisture where you want them. 

 

In my experience these sorts of products are difficult to find in Japan. For example, I recently did a search in Japan for foundation sealing tapes.

 

The first step was checking Japanese distributor sites based on known products readily available in Canadian, US, UK, and European markets—where Passivhaus is well established. What I found was 3M 8067 which hits a couple of the targets but not all. Beyond that not much else besides standard ¥599 rolls on the big sites and the same at local distributor’s shop. Translating and reading up on one "Eco" labelled product's JIS safety data sheet I was not convinced of its safety. So, what about tapes that ensure health, comfort, product longevity and energy reduction, aka lower energy bill? 

 

For products that deliver on the above I have turned my attention to one producer, Siga Swiss, for an upcoming Passive House project in Hokkaido. Why? Because they hit all of the above targets and more. The additional parts: Siga Swiss offers customizable solutions, transparent product info, computer simulated evaluations of your project followed by recommendations, and provide training on best methods of application. They are committed to doing their part globally and making sure it is done right.

 

These are the kinds of products we need to be using on our projects in Japan to get ahead and help push the world out of the dinosaur climate age. To do this, when speaking with suppliers, architects, and engineers ask whether a specific high performance product is available in Japan. like Siga Swiss for airtightness. This will get conversations started and ideas flowing as well as help toward a better educated industry along with comfier, cheaper, and better-built homes. Demand for better products can positively affect availability here in Japan. 

Of course, regarding any products that are pushing for similar goals already here in Japan please share and let’s discuss those too! Positive change works a lot better helping each other out. 

 

One final note. Alluding to traditional builds in a previous article on this site: “Yes we can!” If we keep these themes while blending traditional styles with new building techniques, technologies and products that make homes hit higher targets, specifically high-performance airtight tapes and membranes. These targets will be on the way to “2050 goals” rather than just words.

Squaring the Circle for Traditional Buildings

It often seems that there is a battle going on between traditional building techniques and high-insulation high-airtightness approaches such as Passive House. Advocates and practitioners of traditional buildings have a strong case that years of experience will show how and when buildings fail, and how they can be built to last. They claim natural materials can absorb and release moisture and are free from dangerous chemicals, so they are better for the building and more healthy for the inhabitants.

But traditional buildings do not use a lot of insulation and are not airtight, so here are two questions: 

How do you keep a traditional Japanese building warm in the winter? 

How does ventilation work in traditional Japanese buildings to ensure good air quality?

I'll get to the answers soon.

High airtightness is sometimes achieved with synthetic membranes, but concrete, plaster on stone or brick, and oriented strand board (OSB) can also play a part in a building's airtight layer. Insulation materials are often polymer-based, especially where a high performance is needed. To get the same insulation as ten centimetres of top-grade foam, you need over 30 centimetres of thatch, over 80 centimetres of wood, a similar thickness of clay mixed with straw, or over two metres of rammed earth. Cellulose fibre insulation is better than all those traditional alternatives, but you would still need over twice the thickness to match foam.

It is interesting to note that a mixture of clay and straw has a similar insulation level to wood, which means that a structure of wooden posts and pillars filled with traditional walls may have an even layer of insulation, avoiding cold spots. But a typical passive house wall has something like ten times higher insulation than a traditionally-built house, so for those walls to perform in the same way, they would need to be ten times thicker.

So how do you keep a traditional Japanese building warm in the winter?
Short answer: You don't. 

When it's cold outside, it gets cold inside. The walls are porous so moisture does not tend to build up. If you want the house to be warm you have to start burning stuff. Today that stuff is usually fossil fuel, either directly, or indirectly with electricity generated from fossil fuels. So you certainly can build with traditional, natural materials, but the inhabitants are only going to be comfortable with a steady flow of un-traditional, unnatural fossil fuels. 

Traditional Japanese heating is with wood burnt in an irori open fire or charcoal smouldering under a kotatsu table heater. Irori are open fireplaces in the middle of the room. Traditional Japanese buildings don't have chimneys, so the smoke finds its way up though the house, killing any bugs on the way, and then out through the ample gaps in the structure.

Traditonal kotatsu burn charcoal in a small irori pit, with a table over the top covered in quilts and blankets. The kotatsu just provides a warm space to sit in rather than warming the whole building, which in some ways is a very efficient use of fuel. This 1820 woodblock by Eisen Keisai also hints at other ways couples kept warm on long winter nights. 

Today people do not want open fires because of the risk of the house burning down, and the increased soot and extra cleaning. Charcoal-burning kotatsu are also a carbon monoxide risk so modern kotatsu use electric heating elements. They are still occasionally fatal because of the heat shock when elderly people get in or out of them. Many people in Japan love their kotatsu, but if they start living in an insulated house, they do not miss them!

Most Japanese homes do not have any central heating system, often relying on kerosene fan heaters, electric carpets, or air conditioners in heating mode. Some houses have underfloor heating, but there are frequent stories of people who use it for one year, see the electricity bill, then never switch it on again. None of these heating techniques is traditional or natural. 

Wood burning stoves may be a more natural method, and cast iron stoves from New England or the west coast of Ireland do look very nice in Japanese houses. The rituals of preparing wood and the cleaning and maintenance may not suit everyone's lifestyle, the smoke may not please the neighbours, and unless the house is in the middle of a forest the source of wood may not be sustainable. An increase in wood-burning stoves has been blamed for poor air quality in London, and since London is not a major producer of wood, you also have to wonder about the carbon footprint of transporting the fuel. 

Wood pellets are much more efficient than burning wood directly, which not only means less wood, but also less ash to clear from the stove and less pollution going through the chimney. The first wood pellets were made from sawdust waste from timber mills. However, as demand increases, and efficiency leads to less waste, trees need to be specially cut and grown for wood pellets. Economically speaking, pellets may have started off being made from a waste product with zero cost, but as and demand increases, the price may go up. The impact is not zero and while burning wood pellets may be better than burning fossil fuels, they do not provide a solution to the world's energy problems, and whatever you are burning, it's still better to burn less. Ideally some of the trees in our dwindling forests will be left as habitat, and end up falling to the ground and emerging in a few millennia as a carbon source for future inhabitants of the planet. But I may be digressing from the topic of traditional buildings. On the other hand, preservation of the environment may be exactly what advocates of traditional building want. 

If I may return to more urgent matters of survival, when a building is airtight, it must be ventilated. The solution used in most passive houses is a mechanical ventilation system with heat recovery. Advocates of traditional building techniques often have a visceral reaction to the idea of mechanical ventilation as it is clearly not a traditional way to ventilate buildings. It uses electricity, so how could that ever be natural?

It is not natural. But what exactly does "natural" mean? When people call for natural materials, what are they asking for? Asbestos occurs naturally in the ground, but I'm guessing you wouldn't want that in your natural building! Polyethylene and polypropylene are completely synthetic and harmless to taste and touch.

If you really want nature, you should go and live outside. Buildings are not natural. Rather than asking a binary question whether specific materials or techniques are natural or not, we need to look at health, comfort and energy use, over the lifetime of the building and make the least bad decisions to get the best health and most comfort for the least energy use and lowest environmental impact.

So how do you ventilate a traditional building? 

I'm temped to say that you don't, but of course traditional buildings are ventilated—just not in a very systematic way. If there is a fire in the building then it is also working as a ventilation system by sending hot air up and out of the building while drawing air in through those thoughtfully provided gaps and porous surfaces. When there is no fire, air must find its way in and out through open windows and doors. The amount of natural ventilation then depends greatly on the outside temperature, wind speed and direction. So if a house is designed to always have fresh air, it will usually have too much ventilation. This will lead to uncomfortable drafts and a steady loss of heat. If it is designed to minimise drafts and heat loss, then there won't be enough ventilation for good air quality and control of moisture. 

The traditional builders will usually choose too much ventilation because that is the only way to guarantee there will be no moisture build up. So the house should not be airtight. If the builders do make the house airtight, they need to put in mechanical ventilation. They could ensure ventilation by providing a fire for you to keep stoked, but if they do that, they need to make sure there is no risk of carbon monoxide poisoning, which again will probably mean avoiding airtightness.

Mechanical ventilation does use electricity, but it provides fresh air, takes excess humidity out of the house, and keeps you warm very cheaply by recovering the heat from the expelled air. Heat recovery ventilation will only work if a building is airtight, making sure that air is coming in and out through the heat exchanger. Also, the insulation will only work effectively and without risk of condensation within the walls if the building is airtight. And if the building is airtight, active ventilation is needed because natural ventilation is unreliable.

Without active ventilation and airtightness, extra insulation is a risk as air leaking out of the house in winter drops in temperature and hits the dew point, producing condensation.

So the traditional builders are going to hand you a choice: 

Pay a lot for heating, or be cold. 

On the other hand, a traditional structure can be wrapped in an airtight insulating layer, and include a ventilation system. This will protect the structure and make it last longer, and will make it nice for the inhabitants, who probably do not want to live a traditional life that is not as comfortable and not as long.

In the fight for survival of traditional building, insulation, airtightness and active ventilation are not the enemy. They may be the saviour! 

References:

Pollutionwatch: wood burning worsening UK air quality, Guardian (2018, February 1st)

Steven Goodhew and Richard Griffiths (2004) Sustainable earth walls to meet the building

regulations

Emissions from Wood:

Roger Drouin (2015) Wood Pellets: Green Energy or New Source of CO2 Emissions?

Cool jets of air on a hot summer's day

It's very tempting to believe, when you stand next to an open window and feel the breeze on a hot summers day, that it's cooling you down. It may be cool as you stand there, but if the temperature outside is higher than inside, and you happen to be in a well-insulated, airtight house, and it's likely to be over 30 degrees every day for the next month with a chance of a few nights staying above 25 degrees, then you really don't want the windows open when it gets hotter. 

The heat exchanger in the ventilation system will do a much better job than the windows at keeping it cool. If it's 30 degrees outside and 25 degrees inside, the air coming in through the windows will be at 30 degrees, but the air coming in through the ventilation system will be a little over 25. It may be more humid, but that's another issue. Humidity could make it feel one or two degrees warmer, but not five.

Of course, the air coming in through the window may be cooling you down by helping evaporation and blowing heat away from your body, but even if it is, the heat is going into the house and will be there for you later.

Then there's the effect of air at velocity expanding into the room.

I remember this from the day of the first airtightness test, 9th August, 2011. It was a hot one, 31.6 degrees outside, according to the test report. It was 31.3 inside. The house was still being built then, so the windows were usually closed at night and left open during the day. We now do the opposite.

For the airtighness test, the windows had all been closed. They had fixed a fan to one of the windows, then blew a lot of air out until the pressure dropped about 50 pascals below the pressure outside. Then the fan switched off and the machine started to measure the pressure go up as the air leaked in again, and that was our chance to go around the house searching for places where air was getting in.

You could feel little jets of cold air coming in at the corners of some of the windows. I remember wondering at the time why the air should feel cold when it was hot outside, inside, and presumably in the wall between. Now I realise it was the air expanding. The same amount of heat. Bigger volume. Lower temperature.

So the same thing is probably happening, to a lesser extent, when the window is open and air is rushing in to a large room. But when the air stops moving and settles at the ambient pressure, which is very close to the atmospheric pressure, no coolth has been gained. Or rather no heat has been lost, since "coolth" is neither a word in English nor in science.

It would be nice if this effect could be used in some low tech way, with fresh air outside somehow increased in pressure so that it would come inside at a desirable temperature and pressure, and genuinely cool the house. Something more sophisticated than an open window but less than an air conditioner, which in fact uses the same principle but with a coolant rather than air.

0.28 = 0.54, 0.26 = 0.38... Confused!

After another two-month wait, I got the results of the airtightness tests in a letter. I sent the insulation people a reminder by email on Friday and the letter came on Monday, with an apology that they had already sent the information to the architect and assumed he had sent it on to me.

The results, from a Passive House perspective, look very good. The standard we were aiming for was air leaking at a rate of 0.6 times the total volume of the house per hour, with a pressure difference of 50 Pascalls between inside and outside. The lower the figure, the less air is leaking and the better the airtightness.
The result back in August was 0.54. Unfortunately we didn't realise at the time that the result was this good. The result in December, after filling the hole under the front door, adding caulking around the windows and getting the big window to shut, was 0.38. This is 35% better. In the Passive House software, this reduces the performance of the house from 13.5 to 12.6 kWh/m2a (kWh of heating energy per square meter of floor space per year). That's a 7% saving on the house's heating requirement. Obviously airtightness affects thermal losses as leaking air will carry heat in or out of the house.
The Japanese measurement of airtightness, C, the number of square centimetres of gaps per square metre, was 0.28 in August, and 0.26 in December. An improvement of only 6%. Clearly the two figures don't have a linear relationship. We were apparently aiming for a C value of 0.2, although 0.3 seems to have been a closer target.

The C value seems to be based on on the air leakage at a pressure difference of 9.8 Pascals, and then goes through some exponential arithmetic. In reality, the pressure difference between inside and outside is surely going to be a lot less than 50 Pa, and probably even less than 9.8.

According to the results sheets (graphs for August above and December below, pressure on the y-axis, leakage rate along the x-axis), it looks like the leakage was measured at roughly 10 Pa intervals, from 10 to 50, and a line drawn on double logarithmic graph, deducing some exponential relationship between the pressure difference and rate of leakage. The Japanese and European standards are at different ends of the range of measurements, so neither estimate will be completely accurate.  This way of testing should give a very good estimate for the leakage at 30 Pa difference. 
I'm really interested to know how the C value is calculated, and the rationale for this. And how does the Passive House software calculate the effect from the figure for 50 Pa?

Japanese airtightness measurements suck

Apparently in Germany, when they do an airtightness test on a house, they test both over pressure and under pressure. In other words, they shut all the windows and doors, and put a blower on one of them to blow air into the building until the pressure gets to be higher than outside, then they measure how quickly the air starts leaking back in again. Next they blow air out so the pressure is lower inside, then they measure how quickly the air starts leaking in again. They take the average of the two values to get the airtightness of the house, which is measured, at least for Passive House certification, in the number of times the air will change per hour. The passive house standard is 0.6.
In Japan, they usually only have the equipment to do the under pressure measurement, which apparently is usually a little better. So, in a sense, Japanese airtightness measurements suck.
They did another airtightness test in December, which I'm still waiting for the results for. I should have done this months ago, but I've just now started looking carefully at the results from August. The experts said that we needed a C value of 0.2, but we only got 0.3 which was not good enough. They said that this was a reverse calculation, making it sound really difficult.
Never trust experts, especially if they make things sound really difficult and complicated. If they do that, it's a sign that they don't know what they're talking about. If they do know what they're talking about it, they should be able to explain it and make it simple.
Anyway, as a result of this 0.3 that should have been 0.2, we became very sceptical of the Compriband's effectiveness, and added caulking around each window to improve airtightness. We had previously planned to add a layer of insulation around the inside of the window frame, on the few centimetres of wall perpendicular to the window. This insulation would have reduced the thermal bridge effect of the window from something like 0.04 W/mK to 0.03 W/mK. This doesn't look like a lot, but when you think of all the windows in the house, and measure around each frame, there are something like 80 metres, and there are 70,000 degree hours temperature difference over the part of the year that needs heating, so it amounts to about 50 kWh per year.
Anyway, it was basically presented to me as a choice between putting caulking around the window frames, to improve the airtightness, which wasn't good enough, or carrying on with the plan to insulate around the frames and improve the thermal bridges. The caulking was going to work out more expensive than the insulation, but the builders offered to cover the extra cost, so it would make no difference to my pocket.
The decision had to be made quickly as other parts of the wall were about to go up, and the frames would no longer be accessible. I agreed to them adding the caulking, which the airtightness and insulation people went ahead and did.
But, while waiting for the results of the latest airtightness test, I started looking a little more closely at the figures of the last one. I should have done this ages ago, and in fact I've been waiting for an opportunity to talk with them and find out more details of this devilishly difficult conversion between the C value and the number of air changes per hour.
According to the figures the airtightness experts emailed me 4th October, almost two months after the test, the result was 259 cubic metres per hour at 50 Pa pressure difference. The bit of the form where the number of changes per hour should have been was blank, I guessed because they didn't have the figure for the volume of the house. According to the Passive House database, the volume was 500 cubic metres. Obviously this is not the exact volume, but it's close and serves as a design volume. Taking this, and the 259 cubic metres per hour, that looked to me like 0.52 times per hour, which meets the PH standard.
So, I surmised that either 1) my calculations are incorrect and it's much less straightforward than [volume per hour / total volume]; 2) the design volume of the house (500 cubic metres) is a lot more than the actual volume; or 3) the architect or airtightness experts were too lazy or too incompetent to perform a straightforward calculation. My money was on 3.　
I spoke to the architect on the phone, broken into two or three calls as he kept having to find information, or calls back because he had found more information. The figure he had was 0.542 exchanges per hour at 50 Pa. The actual volume of the house is 478.1 cubic metres. I'm beginning to wonder whether the airtightness people sent him a different copy of the results to the one they sent me... Why would they do that?
After first denying that the caulking had anything to do with the insulation and suggesting that the airtightness people had done it as an act of charity, he later came back and conceded that yes, the first airtightness test had met the standards, although they had told us that it had not, and that no there had been no need to add caulking on top of the Compriband, and yes, we could have had the extra insulation around the inside of the window frames and reduced the thermal bridge effects.
Another factor prejudicing them against extra insulation was that in some places the insulation would have stopped the windows from opening. As far as I was concerned though, it was a fairly straightforward choice.
Not sure exactly whether he's going to do anything about it, but he did at least say sorry, and not really related but he would get us a ventilation system with a bypass, and would cover the cost for it.
Maybe a complete coincidence but the airtightness and insulation people did the caulking work, and also did the airtightness tests.
There's something very satisfying about letting people know that they have done you wrong, but perhaps only relative to the much deeper dissatisfaction of feeling that you have been done wrong to.

0.3

The conditions for a passive house seem fairly simple, although they are by no means easy. As far as I can tell, they amount to three things.  Insulation: the Building must lose less the 15 kWh per square metre of floor space per year. Airtightness: the building must lose less the 60% of its volume with a pressure difference of 50 pascals. Energy use: the building must use less than 120 kWh of primary energy per square metre of floor space per year. These measurements seem fairly straightforward. In Japan, insulation (Q value) is measured relative to wall area rather than floor space, and draftproofing (C value) is measured in square cm per square metre, and indicates the area of cracks in the walls. Airtightness is tested the same way in both places: by sticking a blower on a door or window, dropping the pressure and seeing how much air leaks in.

The insulators tested the airtightness yesterday, and it came to 0.3 square cm per square metre.  Apparently this is a pretty good score. In Japan 2 square cm per square metre is considered good, and less than 1 is a target for super-insulated super airtigthness. Our builder's previous best score was 0.8, and the insulators have done better still. The Passive House standard corresponds roughly to a C value of 0.2 so at first sight it looks like something is wrong.

However, we know that something is wrong. We know that there are issues with gaps around some of the windows. We know there is a gap under the door. We know that the big window doesn't close properly.  Here, the front row of the building team are doing their best to keep it shut. While the test was taking place, we went around the building sticking fingers in corners, and feeling cold air coming in in various places. 

As we know that there are problems, and the value is this close, hopefully it should reach the target when the windows are all sealed, the door has no gap under it, and the big window is fixed.  

Compriband - Magical tape

For a house to have good thermal performance, you need insulation and airtightness. A company called Wuerth provides a magical component called Compriband, which we are using to seal our windows.

Regular Japanese window frames are the antithesis of this as the aluminium is a great conductor. Also, sliding windows, while great at saving space, defy airtightness. This is just looking at the window moving within the window frame; there must also be no gap between the frame and the house, and whatever is filling that gap should insulate.

The problem is what to do with this gap between the window frame and the house, and German manufacturers Weurth have come up with a tape called Compriband, which can be fitted around the window before it is installed, and it then expands after installation to fill the gap with foam and provide an airtight membrane on the inside.

The tape is passed around the whole window frame. It should be cut diagonally at the join, to ensure the seal. Also, at each corner, there needs to be some extra length.

Getting into the corners

One piece of advice the manager of Pazen gave to me was to look into the corners. When the Compriband tape is applied, each corner needs a little extra length, so that the tape can expand to fill the corner, and the insulation is complete and the airtightness maintained. The picture above is what the corners should look like, with the Compriband filling the gap. In one case, it looks like no extra length was given at the corner.

In another case, although it looks like extra length was given, there is some daylight visible at the corner, so the Compriband has not filled its gap.

You can follow Wuerth Japan's blog here
And see a range of their products from their Japanese website here.

Windows going in

They were starting to load the windows from their storage half an hour away in Hotaka at 8:30 and supposed to arrive at the site around 10. Kentaro from Wuerth turned up around 10:30 to show them how to use the compriband.

I heard the crane go past my house at 8.30. Presumably they can only hire cranes for whole days. Crane drivers must be used to sitting in the cabs for hours waiting for something to happen. Perhaps a career worth considering, although it may be a bit late for me to switch.

The windows started arriving after 11:30, which did not surprise me. Kentaro had another appointment later, so could only comfortably stay till 12:00. In the end he stayed a bit longer and showed them how to install the compriband around one of the smaller windows. He reassured me later that he made his next appointment on time. It's a shame that most of the time he was here was spent waiting and listening to my rants on energy efficiency and its enemies in the Japanse building industry, rather than watching and advising on the application of his product.

As of the morning, nobody seemed to know how the large fixed upstairs windows were going to be installed. The fixed windows are triply tricky because they are going upstairs, they are heavy because the glass cannot be removed from them, and they cannot be fixed to the pillars in the same way as the other windows, from inside the frame.  The moving windows can be taken out of the frames and screws put through the frame into the pillars on each side. Small strips of wood and a crowbar are used to adjust the windows when they are installed, and a spirit level to check they are horizontal and vertical. This makes a big difference to windows that swing open, and in the case of the concertina door, another adjustment is needed for each wing of the window. Yesterday I spoke over the telephone to  the manager of Pazen, the German manufacturers. He plans to be in Japan in September and offered to make final adjustments then.  

In the case of the fixed windows, obviously the glass cannot be opened and removed, so the frames must be fixed from the outside. As this is impossible, or at least very difficult with the wall construction and 120 mm thick pillars, they are using metal strips, which they first screwed onto the window, then after putting the window into the building, screwed onto the pillars. 

Just as I could have predicted that the windows would have arrived an hour and a half late, I should also have been able to predict that they would try to get these difficult windows in as quickly as they could, while the crane was still there, with decisions made on the site, and an attitude of "it'll be right". Although I shouldn't have been surprised, I was shocked to see that the three south-facing upstairs windows had all been installed when I got back from teaching my afternoon lessons a couple of hours later.

When I first saw these metal strips sticking out beside the windows, they started ringing alarm bells as thermal bridges. Especially these ones, on the opening window upstairs on the South East. Obviously the assembled window is heavy, and they wanted to get it in when the crane was there, but each glazed wing could be removed, and the three parts could be lifted and put into place. In this case the metal strips are unnecessary. I spoke to the window importer who did not seem terribly interested in thermal bridges. I also contacted someone at Passive House Institue in Germany who seemed much more interested, although has not got back to me yet. I've since calculated them at 0.0009 W/K per strip. 

The manager of Pazen in Germany was also interested but seemed confident the thermal bridge effects were negligible. He was more concerned that the window in this picture was moving, and so did not need to be fixed with steel strips. He had sent the right number of steel strips for the two fixed windows, so he was worried that we hadn't used enough on the big heavy fixed windows to keep them in the house.

In the case of the large window in the middle, the metal strips have been screwed onto the frame after the compriband was added. This means that the compriband has not been able to expand to fill the gap between frame and wall, doing its job of insulator and airtightener. You can see a bit of daylight. If we can see daylight, the air will be able to see daylight too, and the airtightness will drop. I need to find out what they are going to do about this. The carpenter and site foreman seem to think the job is done. The architect thinks that they have been temporarily put into place and will all be reinstalled. The insulation and airtighntess contractors are on site at the moment, and I think airtightness issues are in their ballpark. Perhaps they will be going around with a needle later checking the corners.

The smaller window to the west (on the right looking out of the house) seems to be fitted correctly, at least if we can really ignore the steel strip thermal bridge effect, and if two strips on each side is going to hold it in place.

So that's one out of three. 

The house feels really good with windows, and it may make it a bit cooler over the summer, but with the vapour barrier almost completed, they will have to keep the windows open to avoid suffocation.