Comments: No comments yet
This weekend I finished fastening the sheathing to the roof (doing much better with heights now!) and Dad and I completed the house wrap. I chose Hydro Gap from Benjamin Obdyke, which is a “drainable” housewrap. It has little spacers on the surface to allow water that gets behind your siding to drain out. Sort of a mini rain-screen.
Useful tip: A belt sander with 36 grit sandpaper comes in real handy when you need to shave down the edge of a piece of plywood by 1/16”-1/8”. Just mark your cut line and grind away! The results are much cleaner than what you get from a circular saw.
Much could be written about each of these steps, but I’m tired… so here’s a bunch of pictures instead! That’s what everyone really wants to see anyway, right?
Comments: 2 Comments
After all framing was up, I started on two rows of blocking—pieces of 2x4 material fit between each stud and run horizontally along the length of each wall. Most codes specify that all edges of each panel of sheathing should land on solid blocking. This makes the structure much stronger. This will also give me solid backing to attach my interior plywood to. Because of the height of my walls, I determined that I would need two rows of blocking. I decided to run my blocking in a straight line, toe-nailing (well, screwing) one side of each block and face-nailing the other end. For the toe-nailing, I suggest using two screws, one coming up from below and the other down from above. This is much stronger than having both nails/screws pointing the same direction. I used a couple of pre-cut 2x4s to hold up each piece of blocking at the right height while I attached it to the studs.
I could have run my first row of sheathing vertically instead of horizontally, which would have allowed me to use a single row of blocking instead. However, for aesthetic reasons I would like to have my interior plywood run horizontally, which would have required adding additional blocking anyway, making the decision a bit of a wash.
Installing sheathing is a slow and awkward process: the panels are large, heavy, tough to position, and brutally unforgiving (if your structure isn’t quite square, now is the time you’ll find out).
Code requires nails/screws spaced 6” along panel edges and 12” along studs/plates “in the field” (i.e. all other wood members covered by the sheathing panel). What they don’t say is that this leaves very little room for nailing on edges where two panels meet up in the middle of a single stud. You want to make sure that you keep your nails/screws about 3/8” away from the edge of the panel, but you also want to make sure they’re secured well into the stud. To make this a strong connection, I suggest starting your screw at 3/8” from the panel edge and angling it into the stud at about a 10-20 degree angle. When fastening the adjacent panel, angle in the opposite direction and offset the screws by about 1/4” to avoid collisions with fasteners from the first panel. On the first couple of panels I staggered the screws half way between the screws on of the adjacent panel, but soon realized that this could cause issues later when I needed to drill through studs to run wiring. If you keep the screws closer together, you won’t have as much of a mine field of fasteners to work around later.
I also took to using an 8” spacing on horizontal edges where the panels landed on blocking, since this allowed me to attach every other screw directly to a stud, where it would have much better purchase than on the blocking itself (and could be fastened further away from the panel edge).
Traditional tiny house building wisdom suggests gluing all sheathing with construction adhesive. Now that I’ve gone through this process, I am not so sure that the pros outweigh the cons. For one thing, it is S-L-O-W. It requires dry-fitting your sheathing to make sure it fits correctly, starting a few screws, removing the sheathing, applying the glue, and re-applying the sheathing. Construction adhesive is messy and smelly stuff (Ideally, you should use gloves and a respirator), and it is frustrating to apply. However, once it is cured, it certainly does have the effect of solidifying the entire structure and helping to seal any cracks where air and bugs can get through.
Unfortunately, this also pretty much rules out making an alterations or corrections, or repairs in your framing—Not good for first-time DIY builders (see my dad’s last post detailing our wall straightening woes)! And given the quality of the structural screws I am using to attach the sheathing (GRK R4 #9 2-1/2”), I do not believe that the glue is really needed for strength.
That said, I have decided to continue gluing all wall sheathing, but will forego gluing the roof sheathing. (Applying glue to the rafters before laying down each sheet at 13 feet up in the air seems like it would be both difficult and dangerous).
If you do go the adhesive route, I have two helpful tips. One is to spring for the larger size caulk gun and canisters. You will save money and time, since the smaller ones will only cover about one sheet per canister. The other tip is to be aware that the caulk gun has a shut-off tab attached to the “plunger” which you can and should use between each bead of glue you lay down. This prevents the glue from continuing to be dispensed from the gun even after you’ve stopped applying pressure to the trigger. I didn’t know about this at first, and it nearly drove me crazy as it kept dispensing glue when I didn’t want it to (and wouldn’t dispense enough when I actually needed it!). Also, be sure you break the seal thoroughly before dispensing. Either way, it is a messy business.
One more detail about the sheathing. You will often see it recommended that a gap of 1/8” be left between panels at all edges to allow for expansion of the wood. 1/8” is actually quite a large gap. Ironically and inexplicably, most sheathing comes in full size, so following this rule means shaving 1/16-1/8” off of the edges of every panel(!) This is a tremendous amount of additional labor, which is why there are some sheets that are manufactured pre-cut and “sized for spacing”. I intentionally looked for plywood that was “sized for spacing”. Unfortunately, despite the the label on the sheets that I purchased (1/2” fir ply from Emerald Forestry Products), the plywood is, in fact, the FULL 4’x8’ dimensions! (It is possible that they were cut correctly but expanded due to moisture..?) I spoke to a couple local builders who hadn’t even heard of the 1/8” gap rule, so I probably shouldn’t be too concerned. Still, I’ve tried to leave a 1/16” gap, and have had to rip the edge of a few sheets to keep them from getting off the grid.
Comments: No comments yet
Although we had been very meticulous about checking the trailer and subfloor for squareness by measuring full-length diagonals across it, we didn’t - for whatever reasons - do likewise with the raised framing walls. I think we were lulled into some complacency by several things: (1) the fact that the floor kept appearing to be both remarkably flat and level in all directions - as far as we could tell from a 4-foot level and from shedding of rain water, (2) all the framing members were cut VERY precisely (my work) and fitted together tightly (Mikey’s), and (3) occasional checks for plumb (with our aging, cloudy, difficult to read 4 ft level) indicated that studs were vertical. Also, (4) when wall sections were raised, the top plate pieces met up with each other almost perfectly and did not either leave gaps or collide. What else could be more reassuring?
Well, our negligence became apparent when the 4x8 sheets of sheathing did not seem to fit together quite as tightly as we expected while mounting sheets around the back door, while trying to keep both the horizontal and vertical edges of each sheet in their proper places over corresponding framing members. The discrepancies noted were on the order of 1/4 of an inch or less, but they were mystifying nonetheless, and annoying because they were in a whole ballpark larger than the tolerances we had been trying to work to thus far.
So, a hiatus in construction was declared and a full investigation ensued, taking place over the last two days at least (with me doing measuring and texting Mikey at work with my curious and sometimes reversed findings). We had at first made a lot of ad hoc measurements with a long tape measure, inside and outside the framing, and concluded that the worst problem seemed to be that the 24’ back wall was not a true rectangle but instead was a very regular parallelogram, with opposite sides equal in length but apparently skewed somewhat in the direction of our (big) house. We couldn’t tell just how much the opposing, parallel sides were offset from each other, but measurements of the diagonals proved to be a full 1/2” different.
The fact that sheathing had already been applied with a very high quality, practically indestructible adhesive (PL Premium) - partially for the very purpose of ensuring that the wall would never become skewed out of square - now worked ironically and embarrassingly against us, as we contemplated in hindsight how best to correct a problem that would have been fairly easy to avoid earlier. (Another opportunity to demonstrate the appropriateness of Grandpa’s comment about more sense being shown getting out of a problem than getting into it.)
We thought quite a bit about doing whatever would have to be done to remove the five sheets of sheathing already in place, and we contacted Chris, our informal and unpaid consulting engineer about what to do. He spoke within a few hours to a contractor friend who described how to remove the glued plywood, and it did not sound like a process either rapid or pleasant. The plywood would not be re-usable, and the framing would be damaged if not treated carefully. A lot of sanding of leftover dried glue would have to be done.
Obsessed as I sometimes can be with any process of collecting lots of data both useful and useless, I hit upon an idea two days ago (Thursday, 9/1) for a good way to get some very accurate measurements by myself of all four walls and possibly the overhead framing that will be the roof before long. I proposed making measurements of the insides of various wall areas and openings, marking out the four corners of each area to be checked by using the inside corners where vertical and horizontal framing members - studs and plates - come together. To facilitate measuring accurately and without Mikey’s help (he being at his day job), I cut a bunch of short 1x4 stock pieces to tack tightly into the inside corners that I wanted to measure from. Measuring an inside dimension accurately and alone then became a simple matter of hooking my tape measure onto the protruding end of a 1x4 block and unrolling the tape to the protruding end of an opposite block (vertically, horizontally, or diagonally). The blocks were tacked in place with 6d nails, in holes pre-drilled at useful angles to make hammering in (just part way) and removal easier, without splitting the blocks.
I measured areas which corresponded closely to each of the four full walls; then Mikey suggested measuring the areas formed by various groups of several adjacent stud cavities to check on local distortions from squareness in specific smaller areas.
After compulsively recording lots of juicy numbers, I made a whole science out of analyzing the degree of distortion in each area measured. I hit upon determining (1) any difference between the two diagonal measurements of the area and (2) the horizontal run of the area, and then (3) the quotient of (1) by (2), which I multiplied by 1000 and dubbed the “distortion ratio.” Values of this parameter were calculated for each area measured and came out to numbers between 1.9 and 10.5, with lower numbers corresponding to less skewing. (A value of zero would indicate perfect squareness).
Then yesterday, at Mikey’s repeated urging, I ceased compulsive tape measurements and started checking what could be learned by suspending a plumb bob (which I dubbed Robert the Plumber) at various points on the framing. Wall area measurements, had, as mentioned above, indicated that the 24-foot back wall was a parallelogram leaning away from the Grove and toward our house, and its distortion ratio overall was about 2.0. The biggest finding of Robert, however, was that the vertical end of that wall was indeed just that - quite vertical!! That meant that for the whole back wall to be skewed, the FLOOR must not be level but must be sloped slightly away from the big house!
Apparently, if you are attempting to build a really square structure on a trailer, you need to be aware that the trailer itself is going to bend or bow somewhat in the middle, where the supporting wheels have springs which compress as the structure gradually becomes heavier. In our case (and likely in others) the four corners of the trailer are supported and stabilized by scissor jacks. Before construction began, Mikey adjusted those four jacks as well as possible to assure the trailer would be both level and flat, and as construction has progressed, we have occasionally “eyeballed” the trailer frame from front to rear to see if it is remaining straight. It has seemed to be very slightly bowed upward in the middle over the three axles.
Clearly, in order to avoid problems with sheathing and siding fitting properly (not to mention interior finish components) it is desirable to ensure continually that the floor stay as nearly as possible both level and flat. We have not tried but have thought it might help to work somehow with a 25 foot piece of clear plastic tubing and some water to make an effectively very long level and check the floor with it.
It would seem that when a full-sized house is built on a poured concrete foundation, the issue of ensuring that the foundation surface is level is resolved by the simple tendency of the semi-liquid concrete to level itself when poured. Then you could be confident that framing is square if vertical members are all kept perpendicular to the foundation; but in a house built on a trailer, things are more complicated.
We are probably going to go forward working with the discrepancies that exist now (they are really a long way from being showstoppers), but if we build another house sometime we will (1) keep checking the floor for level and flatness, (2) square up each wall section as it is assembled and put diagonal bracing on it before raising into position, where its fit at top plate level will verify whether the entire wall being put together is square, (3) take diagonal checks on each fully framed wall just before installing sheathing, and (4) buy a nice big level that can be easily read.
Comments: 3 Comments
We had an exciting tiny house adventure Sunday night. It was raining just a few drops in early evening, then developed into real rain. Around midnight, there was a waterfall-like sound and we were having a deluge nearly worthy of Noah himself.
Michael had gone to bed about 11:00. At 12:30, I was cleaning up dishes after an experiment with chocolate chip cookies (which actually came out pretty well). He drifted sleepily into the kitchen and confided that he was a bit worried whether the big tarp over the Tiny House would be shedding water OK.
It was still pouring heavily, but he went out to the site in slippers and a tee shirt (and pants, and an umbrella) and I followed very soon with two raincoats and more flashlights.
What he had found when I got there was a nightmare: about 2/3 of the length of the house was dry under the tarp where it was shedding water well from a temporary raised “ridgepole” we had put up under it, but the tarp over the rest of it had collected 2 bathtub-sized pools (“bags”) of rainwater that were hanging down between the newly-installed rafters and growing deeper by the minute as it continued to pour. The weight had begun to pull back the corners of the of the tarp so that a significant pool of water had already collected on the bathroom subfloor.
We pushed up on the hanging bags with what we had handy (a squeegee/broomstick), hoping to push the accumulated water up and over the ridge rafters of the house. No luck - they were just too heavy, even for two of us together. It really looked like something was going to give any second; I could not believe the tarp had not simply ripped under the enormous stress.
Michael yelled (had to - the downpour was so loud) “We have to pump!!!” I ran out into the huge puddle that was normally the yard and sloshed about trying to find the portable pump we use to clear small puddles off the tarp when rainstorms are over. Of course, it wasn’t where I expected, but I found it where I had actually left it; meanwhile, Michael brought our tallest ladder and climbed up on the side of the house near the deepest pool with an umbrella in one hand and pump in the other. I handed him the pump and he submerged it from above into the water, while I flailed a bit longer to locate an extension cord.
Amazingly enough, we got the pump running shortly and it shot a powerful stream out of its outlet hose onto the ground. We held our collective breath, hoping that the rate of outflow was exceeding the rate of continuing collection. Michael yelled that he could see the biggest pool shrinking, even though it didn’t look that way from underneath.
After he got the biggest pool drained to a more reasonable size, he moved on to the next, fearing that the tarp might not hold up long enough to finish pumping the first. Both pools were pumped dry, we pulled the tarp back into place and searched for another 10-foot 2x4 nearby to place overhead under the tarp where it did not have a ridge to keep water shedding rather than collecting. How to get it up above the rafters was a puzzle, which Michael solved quickly; and we finally got the tarp set up so that a repeat performance of the same horrendous event would be most unlikely. We used sponges and towels to start mopping up the floor, and the wet/dry shop vac to suck up what was left (an indispensable tool!). At this point the worst was over, and the rain was letting up.
As MY Dad said to me once that HIS father had said to HIM, “You showed a lot more sense getting out of that problem than you did getting into it!” I pass that on now to Michael, but with the disclaimer that the rain was more than we have seen in a very long time, and he had taken reasonable precautions to keep the rainwater from collecting into growing puddles. It just came down too fast and too hard. Also, the full extent of his foresight in planning minute details of the project is only just now beginning to become clear as the whole family watches him putting up sections of exterior wall sheathing.
Comments: No comments yet