Guest article, by ‘NRP’…
The following article covers aspects of the roof – including structure, sheathing, underlayment, materials, and roof life…
“‘Ruff’, No Blue, I said ‘Roof'”.
In my opinion the second most important part of a house, first being a good foundation/footing, is the Roof-System. I say Roof-System because all of the combination of all of the components.
You MUST have a good structure to support all of the loads.
Dead load; is the weight of the Roof-System in of itself; Trusses (supporting structure), Sheathing, Underlayment, Roofing (Clay-Tile, Shingles, Metal, Shakes) and all weight added such as the Drywall ceiling, Insulation, Equipment that may be on the roof, and so-on.
Live Load; is the loads from Snow, Ice, Rain-Build-Up, any weight that is not a permanent weight on the roof. And yes even this old “fat-boy” walking on the roof.
Uplift; the Uplift is a MAJOR factor when designing a roof system in a windy area. When wind passes over a structure (house) the wind actually pulls up on the house/roof.
A Note on Live/Dead/Uplift loads; Where I live we have a standard Dead-Load of 8 pounds per SqFt (PSF) and a Live-Load of 25 PSF. I personally take the Live-Load and double it. The house I currently have is 50PSF plus the 8PSF in an area that “requires” a Live-Load of 25#. I HATE to shovel snow off a roof if I get a freak storm that dumps 3 feet of wet snow. Every year there are dozens of stories about buildings collapsing from “heavy snow”, do not let your house be one of those stories. Normally a house is designed for a 75 MPH Wind Load causing Up-Lift. But again NRP being the nutcase that he is always builds for a minimal of 150MPH. I know that in places like Hurricane/Tornado Alley 150MPH will not be enough, so build to your area. Make sure you fasten the roof to the walls/foundations very very well. Sunlight is actually one of the hardest things on a roof; the UV’s can literally destroy the finishes on a cheap metal roof or decompose the asphalt shingles. Choose roofing that will stand the test of time.
The framing of a roof can be done in many different ways, but ALL roofs must be designed or “stamped” by a Structural Engineer. Wood Trusses are the most common style of a roof structure. Steel Trusses are also common in areas where Termites and moisture can be a problem. Red-Iron structure is becoming popular also; personally I use a combination of Red-Iron and Steel Trusses.
This usually is a layer of either Plywood, OSB (Oriented strand board), or Steel that spans the structural members (Trusses). Standard “code” is 7/16” OSB, again I use 5/8” for two reasons. One I’m a fat guy and I hate a “spongy” roof when I need to access the roof. Second if you use Shingles, Shakes, or Tile you will be nailing the materials to the roof sheathing, the thicker sheathing the better to hold the roof down. Nothing worse that shingles blowing across the yard in a wind/rain storm
Most homes use 30# Felt, or “Tar-Paper” I prefer using a product called “Titanium® UDL25 – InterWrap”. It’s a LOT stronger than Tar-Paper and will last uncovered, if needed, for quite a while. Whatever product you use be sure to think of this layer as the “roof”, meaning it should withstand the weather (rain, snow, sun, wind) without the final roofing. Its purpose is many fold, it acts as a “slip sheet” between the roofing and the OSB, it acts as a secondary water barrier.
There are literally dozens upon dozens of different materials on the market to choose from. Asphalt Shingles, Wood Shakes, Single Ply, TPO, PVC, EDPM, Asphalt-Built-Up, Clay or Concrete Tile, Metal roofing in many different styles.
Personally I will be choosing a good “Standing Seam” metal roof, here is why. ALL roofs will move around a LOT from the extreme temperature changes, a normal roof will expand and contract around .5 to 2% on a normal day. If you have a black or dark colored roof you may have even more movement. Additionally this movement may not be uniform, when the sun hits a roof and there is a tree shading one part, the roof will not expand evenly. Amazingly the amount of movement does not tear a roof to shreds.
The “life” of a roof, Asphalt roof may MAY last 10 years, even with a 30 year warranty they will NOT last that long and just try to get a company to repair a roof after 10 years, good luck. Tile and Clay, well lets just say…. NO. Metal “R” panel style roofs are fastened with screws through the face to the underlayment below. Is putting holes in a roof a good idea? Then take into account the moving of the roofing, the holes WILL become elongated and leak, period. A Standing Seam Roof (SSR) has a clip that is fastened directly to the structural member below the sheathing, making the fastening of the roof much stronger, this clip stands from 3-5” above the sheathing, than the metal roofing is crimped or snapped to the clip with no penetrations in the roofing. This is a very watertight roof membrane. And has a very high uplift resistance.
I always have a tendency to “over-build”, there is a reason for that. I don’t care for making weather related repairs on my home, it’s costly and foolish if I did not build it correctly in the first place. In my opinion the extra cost in building or over building correctly is money gained in the long run. The roof is NOT a place to skimp on building or cost.
What experiences have y-all have with Roof-Systems? Anyone have a roof blow off during a wind-storm? Maybe a very bad leaking roof? Dry-Rot on a poorly installed roof? All can be very expensive to repair/replace. My thoughts are to build very well once and avoided the repairs if possible.
Building your home should be a good experience. If you do it yourself or have a contractor, make sure to relax, remember it’s a house, NOT a home, you and your family are the difference, it takes more than a pile of wood and concrete to make it so.