Figure 42. A peek into the installation, upper floor. View towards the east.
The first batch of wood elements were trucked to our site yesterday and the woodworkers started their work. This photo is from the end of the working day today, after the upper floor was mostly put together. This stage should be completed by Thursday.
No, I haven't abandoned this blog project despite the evidence so far. When I started the blog I wasn't working and I had lots of time to spend on the write-ups. But now that I'm gainfully employed, I can't seem to be able to find a decent chunk of time to work on this anymore. I'm going to try harder: let's see how it goes. So, here's a little report from our trip to Hecht in Sursee to check out the wall construction process.
Figure 34. The upstairs west wall can be seen in the back. The opening is where the door to the patio will be installed. The piece in the foreground is the downstairs south wall. More photos of it below.
Figure 35. One part of the downstairs south wall being loaded onto the trailer. At the bottom left of the photo you can see a wall element edge-on with one layer of insulation.
Figure 36. The same wall, seen from the other side. The rectangular openings are for the ventilation system, as are the round holes. When the thing is assembled, the round holes will be inside the floor and the vents for fresh air will be connected to them.
I was not completely satisfied with the wall discussion from three days ago so I spent a little more time looking through the PDF of the Bauteilekatalog I had linked to. The big challenge of calculating the U-value for the type of construction I've shown here is that the layers making up the sandwich don't extend uninterrupted through the entire length. There is a lattice made of wood that runs through the assembly holding things in place and providing stability. Wood is a better conductor of heat (λ in W/(m·K) is between 0.13 and 0.18) than insulating materials such as glass wool (λ in W/(m·K) runs from 0.031 to 0.048) and these areas where there's wood instead of insulation constitute a leak for heat flow (a thermal bridge) from the warm side to the cold side of the wall. In poorly insulated walls they don't make a big difference but in well insulated ones they do. Unless these regions are taken into account, the U-value that is calculated is lower than the true U-value (remember that a lower U-value is better).
The walls for our house are currently being designed. In the meantime let's consider a Minergie-certified wall module. There are a number of these units from different manufacturers that are guaranteed to satisfy the requirements. This one is made by Isover[1], a glass wool manufacturer. It has a total thickness of 35.75 cm and a thermal-bridge corrected U-value of 0.15 W/(m2·K). (According to the product description the non-corrected value is 0.12 W/(m2·K) though my own calculations give 0.13 W/(m2·K) – I must be using wrong λ values for some of the components). Anyway, the breakdown of the components is as follows. I've looked up the λ values when not provided by Isover (the numbers in red) :
[1] Here is the page where I found the information: Isover.ch 24-201
Figure 4. Two different above-ground wall constructions. Numbered elements are: 1 ‐ Interior wall surface. 2 ‐ Support structure. 3 ‐ Vapor retarder. 4 ‐ Insulation. 5 ‐ Post. 6 ‐ Wood fiberboard. 7 ‐ Ventilation gap. 8 ‐ Exterior cladding. 9 ‐ Exposed concrete.
In my last post I claimed that we were expecting the exterior walls of our house to be a minimum of 35 cm (14") thick to achieve the required heat transfer coefficient (U-value). I had also remarked that massive construction – masonry or concrete – would result in thicker walls, a few things being equal. Well, I ran some numbers through for a couple of wall types[1] I found in a compendium[2] of such things.
First I picked out the wall types seen in the figure. Then I chose the same material (Steinwolle[3] of the fiberglass persuasion) for insulation in both cases and I increased the thickness of this until the U-value dropped to 0.15 W/(m2 K). The total thickness of the wall in the case of the wood construction turned out to be 35.5 cm and 40.0 cm in the case of exposed concrete.
[1] There must be a couple of hundred wall element combinations possible! If you think I'm exaggerating, you can download a PDF of the Bauteilekatalog by clicking here.
[2] There are some decent free online tools with which one can calculate the U-values of different building components. I used this one here. Available in German and French. But wait, there's more! The tool also estimates the grey-energy embodied in the structures and 'environmental impact points' to help in the decision making process. More about these at some later date.
[3] Steinwolle is made from mostly natural mineral raw materials while Glaswolle has about a 70% recycled-glass content.
