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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An Insulation Sandwich to Stand On.

Exterior Shell, Sub-floor

After we finished installing the flashing, we had to close up the seams between all the lengthwise sheets, as well as gaps around hangers and the tongue. To do this, we used a special kind of duct tape IMG_9245made by IPG that is typically used in duct work or on chimneys. It’s heat resistant, which I thought was an added bonus, and it came in a roll of about 45 m (omg, finally something in metric). It also came with a hefty price tag though- $15 per roll, so we bought just one to see how it went. Turned it to be perfect for our needs, and we were able to do the entire trailer with just the one roll! The ‘aggressive adhesive’ lived up to its hype and I feel very confident that we’ve been meticulous enough about moisture and tiny intruder prevention. As a side note, it’s miraculous how well the volume of our purchases have been working out. Little waste makes us happy campers.

There was something very oddly pleasing and enjoyable about peeling the backing off of each strip of this stuff and sticking it to our flashing. Smooth lines, and no more IMG_9266gaps! Simple joys 😀 There was a scattered spot (in the area where we first began our flashing, when we still sucked at it) where the flashing was bowed a bit extra – in those places we beefed up the closure using caulking; PL Premium, to be exact. This stuff worked really well, I’d recommend it. IMG_20150903_154529We also used this stuff all around the perimeter of the axle section, and the hangers belonging to the leaf springs and equalizers. If there’s anywhere on the trailer with a higher risk of water infiltration, we figure it will be around the wheels, so that’s why we did that.

Ready for insulation!

Ready for insulation!

Since the caulking takes a little time to dry, we had to space this out a bit, and did it over two days: September 3rd and 4th. We were going to head straight home for the weekend then to recharge our batteries, but we decided to spend the afternoon on Friday the 4th getting the subfloor insulation started. Now, since I did the post on insulation in the research phase, I’ve learned a good bit more about it all. You might recall that we had said we were planning on rigid board (also known as code board) throughout, but at that time I had no idea how expensive the stuff was. Turns out, a 2″ thick 4′ x 8′ sheet is around $50 a pop. So to cut down costs, we tried to come up with a compromise for our subfloor, since it is probably the lowest risk area for heat loss. A lot more research ensued, and to be honest, I wasn’t really able to get a straight answer on anything.

In the plans we bought, the instructions did not include the seam taping that we did on our flashing. They said to use one layer of 2″ thick rigid board, and another layer on top of the first, of 1.5″ thick rigid board with a radiant barrier (shiny silver backing) on the side facing upward. This would allow for the required air space between the radiant barrier and the plywood subfloor in order to properly reflect radiant heat back into the house. No vapour barrier was used in their method on either side. My issue with all of this was that not taping the seams left the underside of the trailer too vulnerable. Also, using a radiant barrier in the floor didn’t make a whole lot of sense since the majority of heat loss would be happening through the roof – I would consider it up there but not in the floor. And lastly of course, the cost of all the rigid was daunting. So we bought some Roxul mineral wool batts – really cool stuff! IMG_20150827_162456IMG_20150904_140455It’s made from volcanic rock (basalt) and steel slag, spun into a fibrous mass which is basically fireproof, highly moisture resistant, and much healthier and practical than fibreglass. It is recommended to install a vapour barrier with it though.

With all of this insulation research, my biggest concern was vapour barriers and if / when to use them. Theoretically, in a predominantly cold climate, you want to place a single vapour barrier on the warm side of your insulation (towards the inside) in order to block moist air moving from inside the house, into the wall / floor space and condensing on the insulation or exterior sheathing once it meets the cooler temperature towards the exterior. Since we had sealed the bottom, moisture and water vapour were effectively blocked from that side, so if any moisture got in, it would be kinda stuck with a vapour barrier on top as well. I was worried that putting that vapour barrier / retardant on the top would run the risk of turning our subfloor into a big ziplock bag of mould, if any vapour was able to sneak inside somehow. Oh the stresses… we decided against it in the end and went back to plan A to fill the entire trailer with rigid board. IMG_20150904_143856That way we don’t have to vapour barrier, and we’ll be adding extra structural integrity to our base. The rigid board is closed cell foam, and it is petroleum based of course, so it is intrinsically very adept at preventing moisture intrusion (and mould development). It’s printed on each board that at least 20% is recycled material, too. Our floor is going to be R-20!! Hooray for warm feet. The roxul won’t go to waste though because we are going to put it in all our walls 🙂

We have an account at the hardware store now, so we’re feeling very professional and important being able to say “Yes, put it on my account, please”! We bought our stack of insulation and the very nice people working in the yard offered to bring it over to our warehouse with their forklift! Gotta love rural Newfoundland. IMG_9276

Each (standard) bay in the trailer frame is 4″ thick, 23 3/4″ long, and 91″ wide. This meant we would get two pieces from each sheet of rigid board, and each bay would accommodate two pieces stacked on top of one another. There are a few exceptions to this, such as in the axle section, and the two end bays, so we adjusted measurements accordingly. We first started out cutting our pieces to size using our circular saw. This achieved very straight lines, and it was ok, but the IMG_20150904_163058blade spins so fast that it actually burns the foam a bit along the cut, and also, I find it a bit overkill / aggressive for this kind of material. The weight of the saw causes the sheet to bow in the centre along the axis where it is being cut, and this sometimes causes the blade to get pinched by the foam, resulting in the saw kicking from time to time. This is not fun. It is a pretty amazing machine though, I enjoyed using it when it was cutting smoothly, and it will be much better when using it on wood.

On day 2 of insulation, Tuesday September 9th, we incurred a power outage for the majority of the day, so we had to try a different method. As it turns out, using a utility knife blade to score the rigid board and snapping it along that cut works beautifully! I’d say even cleaner and faster than the circular saw, and safer as well. We kept this up even when the power came back on. Getting a really snug fit for these pieces of insulation is really important in order to block drafts and to have an efficient and economic subfloor. Why pay for heat if it’s going to escape out through gaps? I took a segmented video laying out the whole process of preparing a sheet of rigid board to place within the trailer frame- you can watch it below!

Using a regular handsaw works well too, and we used one for some of the smaller, thinner trimming we needed to do on certain pieces. And that bread knife… I gotta say, it was essential for those notches. If you’re a good hand at cutting homemade bread, you’ll be great at slicing insulation with the same knife. We finished insulating on September 9th, and bought our stack of 3/4″ 4′ x 8′ tongue and groove plywood for our subfloor as well. We’ll very soon have something to stand on!

Finished job!

Finished job!