Truss Me, the Roof is Not as Hard as It Looks

Exterior Shell, The Roof

Now, I understand that what I’m about to describe is going to seem really overkill to people who are experienced in construction. Although building code varies from place to place, we kind of made an executive decision at the beginning of all this to follow our bought plans and blueprints as closely as possible – at least this time round. At this point in our tiny house build, we both agree that if we were to build another one there are some things we’d do differently. But we only got to this place of clarity by trying the methods we tried. If we had followed the plans for half the steps and improvised the other half, there’s a big possibility that somewhere down the line we would have ended up in hot water. This is because building is a big picture type of thing. Each step is connected, and sometimes that connection doesn’t make itself clear until 6 or 7 steps down the road, and you end up sitting there saying “ohhhhhhhhhh it all makes sense now”. I don’t think we are experienced enough just yet to have the foresight one needs to successfully alter plans and know for sure that it will pan out in the big picture.

IMG_9790With that said, I introduce you to our roof. The skeleton of any roof is the trusses, and ours called for twenty-one 4″ x 4″s , set on 16″ centres, that span the distance from the front wall to the back wall (8’1″ish long). Typically, people often buy their trusses because the angles can be tricky. Our plans came with instructions though and the roof isn’t peaked in the centre, so we made our own. Building a house on a small scale like this, I would highly recommend trying your hand at it yourself! But there is absolutely nothing wrong with hiring certain things out during your tiny house build. Doing a DIY project like this, with limited to no experience, is a balancing act between pushing your comfort zone and knowing when it’s time to ask for help. Take lots of time and draw lots of pictures!

IMG_9755IMG_9764Unfortunately, the hardware store didn’t have any 4″ x 4″s in stock, and we needed to start this work right away. On the bright side, they gave us a great solution – laminating two 2″ x 4″s together to form a slightly slimmer, but structurally stronger version of a 4″ x 4″. We used 2.5″ zinc coated deck screws every 12 inches (and a pair at each end) along with a thick bead of PL Premium between the two pieces to ensure a strong bond.

The following video gives an explanation of preparing each truss for installation.

This is a mock up of our roof framing I made in Microsoft Paint. The orange parts are the rim joists, and the green ones are the trusses. It's not to scale, and in reality there are way more trusses, but you get the picture!

This is a mock up of our roof framing I made in Microsoft Paint. The orange parts are the rim joists, and the green ones are the trusses. It’s not to scale, and in reality there are way more trusses, but you get the picture!

It took us a day or two to get all the trusses prepared and cut, but only one day to install them all! We used two 3.5″ galvanized nails (the same ones we used for wall framing) in each end of each truss to secure it to the rim joists on the front and back IMG_20151011_135639of the house. In the sketch, the trusses are the green parts and the rim joists are the orange parts. The rim joists basically form a box, the same dimensions as the perimeter of the house, and are toe nailed into the top plates of our walls. They provide a surface for the trusses to attach to. They are 2″ x 6″ boards, and we bevelled the tops of each one to reflect the appropriate 10° angle, sloping down from front to back.

IMG_9801Getting the roof components all up there and solid was a huge step, and it was just in time to race back to St. John’s for Thanksgiving turkey dinner 🙂 When we came back on Tuesday, October 13th, we beefed up the connections of the trusses to our walls with some hurricane clips – two per truss. The ones we used are called H-2.5 Simpson Strong Ties. We spoke to a friend of ours about our method and he told us that our house would be ready for the meteor that will strike Earth and cause another mass extinction.  Be that as it may, at least we don’t have to worry about heavy snow loads if we get some harsh winters in our future; which, let’s be honest, is pretty likely living in Newfoundland.

Top ends of our trusses with hurricane clips installed.

Top ends of our trusses with hurricane clips installed.

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Low end of a truss with hurricane clip installed.

We filled all the holes in the H-clips with 1 1/2″ roofing nails – they were a touch fatter than the holes, so when they were hammered in, they really bit into the metal and wood making it basically impossible for them to come out. These H-clips are designed for 2″ x 6″ boards, which meant the top two holes were not able to be nailed through in our situation; the top of each clip was sticking up proud of the top of each truss. So, we just bent them down over the top of the trusses with a hammer.

IMG_9810Next up was the upper layer of roof insulation. I say upper layer because, as you might have guessed, there is a lower layer! The lower layer will be composed of Roxul, and will fill the bays in between each truss. That won’t happen until we start the interior portion of the build. Anyway, we laid down 7 sheets of 2″ thick 4′ x 8′ rigid insulation on top of the trusses creating one continuous sheet, the size of the entire roof cavity, which brought everything flush with the rim joists. Using a few cans of expanding spray foam around the edges helped to prevent any gaps (aka heat leaks).

IMG_20151016_145742Then, we laid down small, 1 1/2″ x 1″ furring strips on top of the rigid insulation, directly above where each truss is located. We ripped 23 of these strips from 2″ x 6″ x 9′ boards, and fixed them into position with small pieces of tuck tape. The purpose of these furring strips is to act as spacers, creating a 1″ air cavity above the rigid insulation and below the roof sheathing.

Having an air cavity under your roof sheathing is important due to the condensation that occurs when cold outside air meets warm inside air rising up and out of your house through the roof. This condensation will form on the underside of the plywood roof sheathing and if it doesn’t have a way out, it will cause mould growth and rot. Creating a layer of air and installing vents along the front and back sides of our roof will allow fresh air to move into the roof cavity and out the other side, wicking and transporting the condensation along with it. In other words, we have a 1″ tiny attic! Lol.

IMG_9832With the furring strips on, we could then lay our 1/2″ plywood sheathing. This process was basically the same as the wall sheathing, with a few small differences. We bevelled the front end of the sheets of plywood along the highest part of the roof, and the back end of the sheets along the low part of the roof, to maintain our 10° angle throughout.

IMG_9838Also, we used screws instead of nails – 2 1/2″ yellow zinc construction screws around the perimeter where the sheets tied into the rim joists, and 5″ galvanized deck screws in the field. These were big screws! They had to go down through the 1/2″ plywood, 1″ furring strip, 2″ of rigid insulation, and anchor down into the trusses by 1 1/2″. We followed a pattern of every 6″ around the edges, and every 12″ in the field.

This is a whole lot of building talk – if you’ve made it this far into my writing, thank you so much! We’ve gotten so much support through the blog and it keeps me motivated to continue writing, and building! For the sake of not forgetting what we’ve done and for the benefit of any fellow tiny housers out there, I feel the need to lay it all out in detail. Hope it makes sense, drop me a line in the comments with any Qs or to let me know what you think!

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