Documenting the design and construction from start to finish of a Passivhaus (Passive House) in Ottawa, Canada. Insider info on what it's like working with an architect and costs associated with building.
Tagged with: framing
Yesterday was a big day. It started bright an early with the crane set-up on site. It was there to haul up and help install our roof trusses. Mark was in and out throughout the day and broadcast a few times with progress updates. Here they are:
The girls are happy (and toasty) in these walls.
At long last, our house has been framed in. (We still need a roof over our heads — a minor matter.) It feels good to have that massive task behind us. Our builders are, no doubt, also quite happy about this.
Our walls were no ordinary walls; they were an experiment/idea Mark had as to what they needed to be and how they needed to come together. This wall phase took a couple weeks longer than anticipated by Mark. There were bumps along the road, and a definite learning curve, but the team hit their groove, in spite of the bone-chilling temps, and put together one helluva house shell. We were fortunate to have such an open-minded and capable team, headed by Justin at Cornelis Grey.
We've rented a crane, for this coming Tues, to lift our roof trusses up so the roof can get going this week. Yay! And we're starting to line up tasks to follow. Windows, insulation, siding... Not to mention a whole slew of decisions requiring our attention, e.g. cabinetry, fixtures, flooring... There's no shortage of things to do.
And here are some shots of the shell from today.
Hello walls
Welcome inside
In the kitchen
The wander window in the 'void'. Only 19'10" high (HA!)
In the loft
Looking towards the back of the house
Rooftop patio
There's snow in the house. We always liked the idea of bringing the outside - in. But this is taking it too far. Wah-wah.
Our second floor (third if you include the walk-out basement) has been framed in. The cold temps have definitely come with challenges. We're using an adhesive on the edges of the wood fibre board that needs to be warm to be malleable. So we've rented space heaters to keep a small section of the basement warm for the adhesives. And there's snow on everything.
It's so bloody cold. Went out there for half an hour last week and my toes almost fell off. Props to construction workers in this city. It's unreal. And then I go sit in my cushy, warm office job, feeling slightly unworthy. Respect.
We took some friends on a tour of the house this past weekend. They had their children with them. The five year old said, "Mina's house looks like Elsa's* castle because it's tall and there was snow inside".
* For those of you who don't have a child, Elsa is a snow queen from Disney's film Frozen.
The third floor joists should be going in this week. In the meantime, Mark and I are trying to work out some design details for the inside, of which there are many. He's working on our kitchen & bath layouts so we can get them priced out to make decisions. We're agreeing on all the big picture items, so hopefully that bodes well for when we have to start selecting finishes.
He's also working on our HRV design. Where the fresh air and exhaust vents will be located. It's fascinating stuff. I'm working on a post with fancy visuals to help illustrate the concepts. I'm also doing a bit of research in to automated home technologies – ways to make the house smart. If anyone has any knowledge in this, please share! Just because the house is low-tech (crudely-speaking), doesn't mean other areas of the house have to be. Lights that learn? Maybe.
Dwindling winter daylight. Pano of the second floor.
Rear elevation.
Views of the city beyond the tree and rooftops.
The build has been frozen over the holidays, both literally and figuratively. So has my writing. Admittedly, I've been feeling frustrated that we weren't able to race ahead while the going was good (with the weather). I had hopes and dreams to be closed in before Christmas. Alas. There's a learning curve to be had with our wall system. And we've only had 2 or 3 guys out working most days. The second floor framing is coming along nicely now. We're full steam ahead in the new year. Whoooot! Attempting to stay warm and carry on.
This week our crew squared up the first floor walls, installed some LVLs (laminated veneer lumber) to support the floor above, framed some interior walls and started putting up floor joists for the floor above.
With the first floor framed in, it's starting to look and feel like a proper house :) Have a look at Mark's Periscope from this past Friday.
We can't believe our luck with the weather these past couple weeks. It has been positively balmy. If mother nature keeps this up, we can shave R-20 and a foot of insulation off our house. Just kidding...I have full confidence that Mother Nature will show up with a vengeance. As she always does for us here in Ottawah. We'll take what we can get.
Floor joists going in.
Our spectacular kitchen window. Deep walls = added counter top!
The sun sets over another week.
The last two walls went up this Monday. Here is a Periscope from the weekend with a special guest star appearance. Teaser: it was me. We put the final touches on the walls together.
We are counting our blessings lately for all this "warm" weather.
One of our wall sections being assembled and ready for lifting!
With the wood framed walls well underway now, I thought it was high time that I sat down to write a post about the design and theory behind the wall system we are using. When we set out to build our project, I spent a lot of time thinking about double stud wall construction. For those unfamiliar, a double stud wall is a wall made up of two seperately framed walls, one inside of the other, usually seperated by a space for insulation. The beauty of the double stud wall is that the overall thickness of the wall is very flexible: by moving the two stud walls further apart you can add insulation and increase the effective R-value of the whole assembly. The continuous insulation is also a great thermal break preventing thermal bridging through studs.
Still, there are a couple of challenges that the traditional double stud wall presents. First of all, the exterior wall is usually built first, and the interior wall much later once the house is enclosed. The main drawback of this is that the exterior wall necessarily becomes the load bearing structural wall. I'm a big fan of keeping structure as much to the inside of the thermal envelope as possible for two reasons: first, it keeps the structural elements warm and dry and protected from cycles of expansion and contraction, and second, it reduces the number of structural penetrations or complex structural details that interfere with a good air barrier.
When designing the system for our project, I set some key goals for myself. I wanted to have a system that hit all of these key points:
As discussed above, this is just the right place for structure to be. It also facilitates the next point below...
I wanted to use OSB with taped joints for the primary air barrier. In order to keep from having a messy transition at floors, the idea was to come up with a way to run the air barrier up straight past the floors without joist cavities to contend with
With all walls, and especially with high R-value walls, it is crucial that the wall has good drying potential, and that no opportunities for condensation are created within the assembly.
This could have been the first point. Super-insulated is Passive House's alternate code name.
I wanted to avoid insulation that would require scaffolding or lifts for installation, partly because of the limitations of the site, and partly for cost and labour savings. In terms of insulation type, I'm a big fan of mineral wool insulation. What's not to love? It's water resistant, mould-proof, fire-proof, high in recycled content, and has a good R-value that actually improves as it gets colder outside.
Wall section: Click to enlarge
Many hours of sketching and head scratching and I came up with the idea of creating a hybrid system. Taking some cues from Swedish platform framing, and some from the double stud wall approach, I designed a system using thermally broken wall trusses with wood fibreboard exterior insulation and 20" deep cavities for filling with Roxul. Here is how this system meets the design criteria from above:
The wall trusses are composed of a 2x6 stud and a 2x4 stud held together by a series of 5/8" plywood gusset plates. The 2x6 stud is the interior layer of the stud, and behaves very much like a standard 2x6 wall. The gussets support the 2x4 layer through shear resistance, and are engineered to support the siding and wood fibreboard insulation. These trusses align with the foundation below: the 2x6s bears down on the concrete, and the 2x4s are cantilevered out over the EPS foam. By building with these wall trusses, we end up with a double stud wall with an interior structural element, and the whole assembly goes together in one shot.
After the walls are stood up and insulated, the interior gets clad with OSB sheathing. At the top of the walls, the floors are installed on hangers that mount to the face of the OSB and through to the floor header installed into precut notches in the 2x6 layer. The hangers will use a self-sealing nail tape during install. The result is that the OSB air barrier runs in a perfectly straight line from the foundation up to the roof (with window and door openings being the only exceptions). Easy to tape, easy to seal.
The entire assembly to this point is extremely vapour open. The OSB is the most vapour resistant element so far, and it is on the warm side of all of the insulation. The mineral wool and wood fibreboard both allow water vapour to move through and dry to the exterior. This was one of the main reasons we chose to use the wood fibreboard exterior cladding over a foam material.
With a 20" deep cavity and 2-5/8" of wood fibreboard on the exterior, the nominal R-value of the wall is roughly R-96!
As the walls are framed, they are squared and stabilized with let-in t-braces on the exterior 2x4 layer. Coupled with temporary bracing, we are able to frame all of the exterior walls, floors, and roof prior to installing the OSB sheathing. This leaves the wall cavities open to the interior for easy installation of batt insulation. Adding the OSB after insulation is complete adds the final permanent racking strength to the house where it belongs, right against the structural framing.
We had all of the wall trusses manufactured off-site, and delivered pre-cut and labeled as a complete framing package. We have framed and lifted three wall segments so far, and although progress is slower that hoped for as we figure out the nuances, things seem to be working well! We rented a set of wall jacks to help lift the walls into place, as they are far too heavy to lift safely by hand. Here's today's timelapse showing the process.
We are starting to pick up some steam as we go. Three more sections to go on the main floor and we will be almost ready to install the second floor deck. It is really exciting to watch as the rooms of our home take shape!
There are many other details and considerations that went into this and all of the other construction methods being used in the house, so I welcome any questions or comments!
Mark's broadcast from site this morning.
Periscope removes the videos after 24 hours, so I'll start posting them up here for those who may have missed them. (You won't see the questions and comments from viewers, but the content is still all-good).
