DIY Roof: Steel Panels over OSB
  A "Big Hat" for Your Straw Bale House

Our DIY roof of enameled steel panels puts a “big hat” on our straw bale home. With a sturdy sub-roof of OSB and felt paper, we use 29 ga. steel panels and enjoy a durable, sturdy roof.

Once our trusses were up and braced, we installed our OSB sub-roof. With a crew of four, Barbara and Dave plus Dan and Anneke from the Whoadammit Ranch next door, we got the sheathing installed on both porch and house in one day.

DIY Roof: Flashing and Gable Ends with Vents

First in the logical sequence of installation were the gable ends with vents and flashing. Sturdy and comparatively inexpensive, T-111 panels were cut and nailed to the end trusses. A well-designed end truss provided a secure nailer for our end vent.

A made-to-measure vent was provided by the truss company and was easy to install. Don’t forget to caulk the flange before you fasten it to the wood.

Angled flashing secured the joint between the bottom of the end cap and porch roof. This joint is susceptible to leaking. Be sure to seal the flashing to the T-111. We used a good, durable caulking.

DIY Roof: Sheathing

As a compromise between strength and cost, we used 15/32 OSB (oriented strand board) as sheathing over our trusses and porch rafters. Because we were confident of the strength of our layered roof materials together, we did not join our OSB panels with H-clips.

We did stagger our seams, however, and believe this has added to the strength of our roof. We sheathed one complete side of the roof before cutting uniform overhangs. When we had our sheathing in place, a snapped chalk line and a power saw gave us an even overhang.

Excess OSB from the staged joins was used to sheath the smaller pieces on the porch hip roof. Very little material was wasted.

Now that we’ve lived in the house for a few years, we have found our layered roof to be strong and secure.

DIY Roof: Felt Paper and Roof Edge

The first layer over the OSB was #15  felt paper or tar paper. This material provided our primary moisture barrier on the roof. Galvanized drip edge attached over the felt paper and under the steel roofing secured our sandwiched coat of moisture protection.

There was a time, before oil prices went crazy, when #15 felt paper or tar paper meant that a 100 square foot section of this material weighed fifteen pounds. Since the oil crunch, this is not the case. Today, #15 paper might weigh from 7.5 to 12.5 pounds per “square” or 100 square feet of tar paper.

We were comfortable with the #15 because of the relatively low humidity here in the Arizona desert. Builders may want to check out heavier paper, even #30 in some areas. A builder today has many additional options. We liked the low cost and simplicity of rolled tar paper.

We began rolling out the paper at the low end of the roof and made substantial (6 inch) overlaps to “shingle” our roofing paper. We screwed in temporary battens of laths fastened with sheet rock screws to secure the paper as we moved up the roof. We removed the battens as we installed our roofing steel.

We used a staple hammer to fasten the paper to the OSB. The most secure fastening, of course, came when the steel roofing was installed.

Remember, we are sharing our experiences, our research, and our inclinations. We urge you to bear in mind that we are, perhaps like you, DIY builders. So, you might well come up with a more efficient and economical method.

DIY Roof: Steel Roofing

The final layer on our DIY roof was the 29 gauge steel. While this was the most expensive single material in our house, we felt it was well worth the money for a variety of reasons. Highest on the priority list was durability. We purchased a good quality steel with a baked-on enamel finish.

While a lighter color would have reflected heat better in the desert, we selected a green that blended with our surrounding mesquite. We wanted to make small visual “footprint” from the valley floor and live with a low maintenance roof for a number of years. Through our area builders' supply store, we were able to order sheets in custom lengths so our steel only had to be cut on site to cover the hip corners of the porch.

While there are a variety of blades, saws, shears, and so on available to cut roofing steel, we were not interested in gearing up for commercial roof installation. So we picked a shaded spot under our new porch and set up sawhorses with a sheet of 3/4" plywood as a table for cutting, predrilling, applying “bubble gum” aka butyl sealing tape.

To cut the steel sheets, we measured and snapped a chalk line on our cut. After clamping the steel to the sheet with the cut line elevated on 2” x 4” scrap pieces, we mounted an old, cheap saw blade BACKWARDS on our circular saw.

NOTE: If you do this, wear protective clothing, goggles, and ear protection.

The most important thing about this method for us was low cost and efficiency. The down side is rough cut edges with sharp points. There are many other blades available for cutting steel with a hand held power saw. Check them out. Be careful whichever method or saw configuration you use.

When the steel was delivered to our building site, the roofing was protected by a “throwaway” sheet of roofing to protect the finish of the top piece of steel. We used this sheet to drill guide holes for efficient installation. With the guide sheet above, we could clamp three or four sheets of good roofing steel below and use a hand drill to pre drill in a consistent pattern.

After the holes were drilled, butyl tape or “bubble gum” was put on the connecting edge that would be under the edge of the next sheet. This provided a wonderful seal for the sheets and gave us a waterproof DIY roof. Care should be taken to align the ends of the panels before putting pressure on the edge and sealing the panels together.

There are other systems available that don’t require “bubble gum”, but we have no experience with them. This worked well for us.

It is important to be consistent in your screwing pattern and your screw depth. We suggest setting your drill clutch tension to flatten the gasket on the screw without creating any distortion in the steel panel. This is especially important on the ridge connecting the panels. This should avoid any “drift” or irregular roofing alignment.

Besides the butyl “bubble gum” you will be installing foam gaskets, especially at the upper ends of your steel panels.

Once the panels were installed on the entire roof, we attached the roof caps. It is extremely important to get a good seal here. Foam gaskets are designed for every pattern of roofing and extras should be purchased.

We applied “butyl” bubble gum above and below each piece of gasketing and ensured that the end joins were secure. On the roof cap for the hip roof porch sections, we carefully squirted expanding foam in addition to the gaskets. Be careful here. Overzealous application will mean some really messy clean up.

Depending on your plans, your location, and your preference, now would be the time to install end trim and, after your fascia is sealed or painted, gutters.

This completed the DIY roof “Big Hat” for our straw bale house.

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