Installing the Metal Roof

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We've decided to go with a metal roof for these reasons - cheap, doesn't leak, and long-lasting [the roof comes with a 40 year warranty]. It's also the choice most compatible with rainwater harvesting and a cistern, which will be placed on the NW side of the cabin.

Everyone in Tennessee, from builders to the actual metal roof vendors themselves, had told me I could use purlins to attach the metal to. These are basically boards [often 1x] laid horizontally across the rafters every 2', and they're what the metal sheets are screwed to. It sounded easy, cheap, and practical - I could actually install the sheets from the comfort of the loft because I could stand and reach through the rafters between the purlins.

We'd actually ordered all the 1x material for the purlins and had it delivered. But literally the day before I put the purlins in, my wife did some research on how metal roofs should be installed, and told me to STOP! Every single authority on the internet, sites like This Old House, contractor sites, metal roof sites - all recommended going with a conventional roof approach - which means sheathing, tarpaper [30lb roofing felt], then metal. The reason? Sheathing makes the roof stable and strong, it won't dent if something falls on it or someone walks on it, it's a must if you plan on insulating the roof, and the tarpaper stops condensation. Apparently a metal roof drips underneath from condensation when only purlins are used. My next door neighbor has installed a metal roof over his barn, with only purlins, and he says it drips all the time from condensation.

I called back the metal roof people I'd ordered my sheets from, and asked if you could use sheathing and roofing felt. They said that you could, that that was the best way to do it . . . and I wondered, why didn't you tell me the best way in the first place? Apparently for the average owner-builder, what's cheapest and easiest is what they do, especially in a land of no codes. I'm happy there're no codes, but . . . things should be done the right way, especially by the 'experts'. They shouldn't be giving out half-baked advice.

So now that I know my roof is going to be much heavier with all that sheathing, I first beef up the frame. I do a little preliminary wall framing, essentially a picture frame with 2x6's to create a lower and upper story all around the building - I don't want to be putting in 13' studs.

So I put in 2x6's up against the posts on the lower story, to support a top plate [to be doubled later] of 2x6's at 7.5' in height - where the bottom of the loft joists is. And all the 1x4's I now have no use for, I attach to the building as a temporary diagonal bracing until the wall sheathing goes in. Here's a pic:

The thick dark horizontal boards are old roughsawn 2x4's from the barn - they are also temporary.

The first step in installing the 7/16ths sheathing is to straighten the rafters across the middle with furring strips. Once this is done I nail up bumpers to the tails of the rafters, so that when I set the sheathing up there, it won't slide off the roof. I put in sheathing at the outside first, then move towards the peak, staggering the joints on different rafters.

On the first row of sheathing, I measure from the peak down to get the exact location for the sheets. I clamp the sheet and bump it around with a mallet a little to get it right where it needs to be. I then tighten the clamps and hammer in ringshank nails, which have a great permanent hold, but can be somewhat of a pain to get in, as they want to bend.

Here's me working on the first sheets:

Here's a shot of the barn (a.k.a. Tent City), where we're living as we build:

And a shot of the fireplace. I've removed that horrible ramshackle wall I'd put up last year with old boards to keep the gales from destroying our screened-in tent. The screened-in tent is now in the barn as you can see above. The fireplace is actually usable again!

Here half of the sheathing is in:

The most daunting prospect at first was how I was going to get the sheathing up there in the first place. But it was actually easy. I shoved it up on to the loft, then from the loft shoved it halfway through the rafters, then got up on the roof and pulled it through the rafters. The 7/16ths is very strong with a lot of flex - none of the sheets snapped.

Here are the girls with the stray dog Annie that showed up and we've been feeding. She keeps me up all night barking at shadows - I'm not too thrilled about her company. She's also got a game leg. A lot of people dump off dogs back here:

Here's the garden, with many plants taking off:

Here most of the sheathing is in - you can see the stakes I'd used as bumpers attached to the rafter tails:

Here's a shot from below:

Another:

After almost all the sheathing is in (I leave a little 'manhole' space at the peak for me to go through and to bring up materials), I roll out the felt. I start at the bottom, and do a large overlap for each successive layer going up towards the peak. I attach the felt with a staplegun till it jams up, then use buttoncap nails.

It's only a few hours to put in the felt. Here're a couple shots of it in:

The next step is the metal itself. It took us a while to decide on the color, but ultimately we went with crimson. We wanted something that really stood out and popped. If over time we hate it we can always paint it - in fact it's recommended to paint your metal roof every 5 years to increase its lifespan. It's only the paint finish that keeps the metal from rusting and decaying.

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The sheets come in standard 3' widths. It's the length that is cut to order. I measure down from the peak, substract 3" for ventilation at the top, then add 3" for covering the fascia and overhanging it - I come up with a length of 9'4". The metal roof installers typically order the metal for the length of the rafter, because the overhang and ventilation gap are equal.

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I get the sheets up to the roof by rolling them up and attaching a bungee cord. I then shove this up through the rafters, and pull it through from above.

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I have to remove my bumpers because the metal overhangs the rafters. So when I get the first sheet in place I have to hold it with quick-grip clamps.

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I'd previously run a line from one edge of the peak to the other, then measured down 3" for where my metal should start. The gap allows for ventilation out the ridge cap.

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As far as laying down successive sheets, I find that if I run sealant tape (really a sticky putty) down the rib which will be overlapped with the next sheet, the sheet I'm laying down sort of sticks to the putty and doesn't want to slide down and off the roof. The sealant tape also guarantees water won't wick up under the rib and leak in - it's recommended on any pitch shallower than 1/3.

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Once the metal sheet is right where it needs to be, I predrill and fasten with screws. The screws I got from the metal manufacturer - they are painted and come with rubber gaskets. I'd had to buy a drill with a clutch for this step [Hitachi/corded/$50/awesome], so the screws don't get overdriven and cut the gasket. They have to seat just right . . . as soon as the gasket begins to flatten out, you stop driving. When the drill's got a clutch it does this automatically.

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I predrill with a 1/8" bit every 2' down a rib - this was recommended by the manufacturer. Every bit I have breaks except the short double-tipped bit the metal guy had given me. It just barely sticks out of the drill, so the bit won't snap. The bit just sticks out enough to punch a hole in the metal - and that's all I need.
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Here one side of the roof is done:
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I then lay down 'gutter guard' (a plastic mesh) to keep critters from getting in through the ventilation gap at the peak:

This is what the metal roof installers use.

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I'd forgotten to mention that before I even put the sheathing in, I put blocking between all the rafters above the ridge beams. The blocking at the eaves is a little short, made with 2x4's, so there's a gap above it before the sheathing. This is for ventilation up through the soffits and out the ridge cap. Here's a pic:

Since my 'manhole' between the rafters must now be closed to roof the other side of the building, I put in boards to get up to the roof for the final sheets. I first shove the last materials up through the hole, then seal it with sheathing and felt. For my improvised ladder up to the top, I cantilever 16' boards out the side of the building. They work great:

The last metal sheet on the first side I'd put in incorrectly. I actually have to remove it one dewy morning, and the roof is so slippery I begin tying myself in. I quadruple up some rope, and tie it from my waist to the frame inside the building. It's somewhat of a nuissance avoiding stepping on the rope, but it gives me a great sense of security, that if I fall, at least I won't go off the roof - I'll have the rope to hold on to. At one point I make the very dumb error of trying to move one sheet over a little with my foot, and I start skiiing down the roof on the sheet. But I jump off and the metal stops and everything's okay.

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The final hours of installing the metal roof are brutal. It's a hot day, and the metal magnifies that a thousand times. I've basically locked myself up on the roof with the last of the materials to get it done. After the last sheets, there's the ridge cap to put in, 3 lengths of 10' each, somewhat overlapped. I use a longer screw for the ridge cap so that the screw actually catches the sheathing and bites in. It is brutal, endless, and when I get off I drink a quart of water straight, and go throw myself in the pool. But it's now finished, we have a roof! That's something to celebrate:

Here's a look at it from inside:

We get a heavy rain, and I notice a drip drip drip on the loft floor. I calm down when I realize rain is collecting on the cantilevered boards, flowing down them and dripping off. The roof is watertight. The roof does pop though, when it gets extremely hot. The metal actually expands and contracts (that's why rubber gaskets are used with the screws), and when it does it pops just like a metal can. Bong! But it's not that often, and it's something you get used to.

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A final shot of the roof in:
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