Clay plaster in passive house

We are doing clay plaster in the middle of winter... here some video from the passive house under construction in Bratislava.



The load bearing walls and ceilings are made from massive wooden elements (Lignotrend). Before we put on the clay plaster, reed mats are fixed to the walls. Some partition walls are laid with clay bricks and will also be rendered later. All in all there will be over 15t of clay material in the building.

This will not only give the building some additional mass, but the clay will function as a humidity buffer. If there is too much humidity it will be absorbed, if there is little (below 50%RH), it will give off a humidity. This is very helpful in winter time, when ventilation causes a drop of relative humidity levels inside (due to temperature differences outside/inside).

The house is insulated with blown in cellulose (30cm), the windows are not built in yet and are just covered with the outer soft wood fibre boards (52mm) wrapping the whole building. We are heating inside and at the same time using a ventilator with 5000m3/h to keep the air exchange high. Very good drying potential.

Will come back to this building to show how things work out later...

Preliminary Blower Door Test on a Limestone building without inside plaster

Although the building did not have a final plaster layer inside (the airtight layer), I wanted to check how well this type of construction does with just the Polystyrene insulation glued to the outside. I expected a value around 1 for the Blower Door Test (BDT), but the first measurement was even better: n50 = 0,79!

Here is a short video I made with my iPhone and edited directly on the phone…


First, it is important to notice that the Polystyrene blocks (500x1000x300mm) were glued to the full surface. The plaster glue was troweled on the polystyrene blocks and then evenly distributed with a 10mm “comb” trowel. The Polystyrene was then pressed into that surface – a 5-6mm adjustment of the surface was possible. This was sufficient, because the walls from Limestone can be built very precise.

Of course the wall is still leaky – there are areas where we could not measure any leaks, but on other places some leakages were to expect. I presume there are areas where the Polystyrene connects to the glue and where there is still some air gaps in-between the troweled glue. Wall corners and some holes that were drilled to attach some connection elements from Dosteba were leaking. This will all easily be eliminated later by the inside plaster.

The electrical installation was without problem. Before mounting the electric boxes, the drilled holes were filled with gypsum, and then the plastic box pressed inside. The superfluous gypsum fills all gaps and does not crack.

Looking forward to the next BDT, I am confident we will get a result below n50 = 0,3.

Exceptional airtightness in PH in Jasenová

Because of the interest in the BDT results we achieved I am adding some more background information.

After taping of the last few areas around the window, the BDT could start. We soon realized that the result could not be bad, because the ventilator turned fairly slowly. So we created a low pressure and started checking out the envelope. There was a big disappointment when all the window hinges leaked. I usually take tight windows for granted... after calling the producer, we found the problem: They had forgotten to place small elastic strips over the hinges (the hinges are of a special construction) This can be done later as well, but no such material was available.

We then decided to go forward anyway. The measurement showed at low pressure 0.12 and at high pressure 0.00. The hinges nicely sealed up with the overpressure. With the elastic strips in the hinges I am certain we would have gotten the same 0.00 measurement with low pressure as well...:-)

After a good cheer at the builders the Testers wrapped up their equipment and left. i had some other customer to attend to but returned to the building site 3 hours later. To my big surprise the Testers were back...

They had called the mother company and they said a 0.00 measurement could not be analyzed - the data would display an error... (so much about software!) So they had to make some measurement, even if it meant to punch a hole in the airtight layer.

So we rigged up the equipment again, and now the measurement showed 0.12 at low pressure but 0,20 at over pressure!!! No I said, this can't be right, let's do it again. 3rd test 0.24 at low pressure and 0.20 at over pressure. Now we were really looking for what was wrong - some tape getting loose because of the over pressure? In the end we found the villain: A balloon tightening the oven air inlet had lost pressure and a big leak was fairly evident.

4th test: only overpressure tested, and again 0.00. So definitely the balloon - big relief!

5th test: A building pencil punched in on the side of the baloon, flat side - hoping a small opening will show a measurement 0.05... but again, only 0.00... (so much about precision measuring!)

6th test: The same pencil but standing high side - definitely a bigger gap but still just measuring 0.00...

Now we were really getting annoyed, we all wanted to leave for home, so I opened a 40mm drainage - we had to get some kind of measure. This time at overpressure we got 0.17. For a small house with only 349m3 for the BDT is a good proof that we had a really tight building!

Now we are waiting for the company to analyze the data and issue the BDT certificate - and I wonder what results they will use...?

So, don't make a house too tight, the BDT is a pain to do...!

Here are some pictures from the building site and especially the airtight details:

EPD Jasenová

Because we have a nice massive wooden ceiling for the 2nd floor, which we did not want to spoil, we are taking electricity and ventilation ducts OUT and then back IN trough the Airtight layer. The ducts will be covered with 60cm blown cellulose, so that should not be a problem. I was not sure we would get good airtighness, but the builders did a good job!

Airtightness revealed

Here comes a short explanation how we went about planning construction for the small passive house. First, I created a box without windows with the expected floor area, optimized it for maximum use of existing board materials without need for cutting and calculated PHPP without any windows. I then added windows to optimize the gains. And experimented with airtightness and ventilation systems...

Obviously, sealing the envelope (as I mentioned before in my blog) played an important role. We have achieved n50=0,17 1/h before, so our target to get below 0,3 every time we build should be realistic. A visible airtight surface during construction should enable that.

This surface could not be on the outside. The building should be possible to build any time of the year, and tape doesn't stick well at low temperatures. So it had to be on the inside of insulated, ready-made elements.

The airtightness layer should never be completely inside, there should always be space for installation in front of it. No penetration of the layer should be necessary except for a few.

So what we ended up with is an insulated envelop, with panels going over two stories, capped of by roof elements. With elements made with TJI's and an airtightness layer from OSB, it should be strong enough to hold up a few days by itself. We will tape this empty box from the inside and achieve airtightness straight away (windows are preassembled).

The next days we build the inner load bearing structure as a stud wall, assemble the floor and the load bearing dividing wall. All inside a cosy and warm (airtight) shell. This stud wall will also function as an installation layer for cables/tubes and as support for dry wall.

We can't wait testing it out in practice, going to be a major revolution if it works out the way we expect.

Cradle to cradle

Passive houses are about energy efficiency and comfort. But as a juror in the re:design award I again became aware of how important it is to take a closer look at material life cycles.

Solving the problem by reusing our trash is not the way forward - it does not give us less trash, but just extends the life cycle of the material.

Energy efficiency and curbing CO2 emissions is todays trend. With so much free energy (there is 40000 times more solar energy hitting the earth than we need, we just have to figure out how to reap it's benefits more efficiently) the future will be how to deal with what is really scarce on this planet - materials - and how to avoid pollution in the confined space we live in.

One way forward is to put limits on consumption and tell everybody that we should be satisfied with less. If anybody believes restricting themselves voluntarily is the true nature of human kind, think again. It will never happen.

We always want more. Passive houses are a good example how energy efficiency (less consumption) can be achieved by more comfort and a better living experience. People want passive houses because it gives them more - with the benefit of using less. That is why the passive house movement is so exceptionally successful, even with slow or no government support.

The only reasonable approach to long term sustainability I have found is the Cradle to Cradle approach. Compared to energy conservation a less known, but similarly important concept. A simple concept but with very complex implementation - probably the reason for not making the news headlines today. But I am in no doubt, that when the have solved the efficiency and green energy problems of today, this is going to be the next Big Thing.

As a student I created a design of a dustpan and brush called "JAMES", that to a large degree fulfills the Cradle to Cradle concept, although at that time I did not know. It just felt the right thing to do. The Dustpan is made of one piece of highly recyclable aluminum (long before any unibody design from Apple :-)) and the brush is made purely from natural materials. The aluminum can be recycled without the loss of quality in a technical cycle and the brush can be given to rot and nurtures new life.

Targeted for ALESSI, the design unfortunately never made it into production, but they added it to their ALESSI Museum. Well, for a student that was success enough.

How about a small passive house?

This is my first blog and I will continue to add some insights that will hopefully be valuable to other architects and builders of passive houses.

First about a new project we are working on - a very small passive house to be built repeatedly (mass production would be a too optimistic term :-)

Size

Building costs are usually estimated by floor space or building volume. A smaller house should be cheaper than a bigger house. But many costs do not grow linear, so half as big does unfortunately not mean half the price.

Costs are not only influenced by size, but for example design, efficiency of construction, technical installations and much more.

Our solution has been to completely rethink how to construct and assemble the house. We had two main goals, first: build quickly and anytime of the year, and two: achieve standard airtightness of n50 < 0,3 1/h.

Ventilation

This is where size meets passive house: without a very good airtightness, it is much harder to achieve the passive house standard (anybody using PHPP knows that this is valid for bigger buildings as well). For this small PH, going from 0,2 to 0,6 means a hike of the annual heat demand from 14,9 kWh/m2 to 18,1 kWh/m2, monthly method.

The air flow volume for a small house is also critical: A sufficient air exchange of 74m3/h corresponds to an exchange rate of 0,34 1/h, a higher rate can easily lead to dry air in winter time. So choosing a system that can provide high efficiency at low volumes has been critical.

Our first thought to install a compact unit failed just on this point: the smallest unit on the market still needs an air exchange rate of 105 m3/h to be able to extract enough heat. Not only does the compact unit have a lower heat recovery efficiency, but increasing the ventilation to 105 m3/h would lead to an air exchange rate of 0,47 1/h and combined increase the annual heat demand by 2,4 kWh/m2/a.

(All calculations are based on climate conditions in Žilina, the most difficult to achieve conditions in Slovakia)

More on other topics next time... maybe you've  figured out our buiding system by then :-)