Designing the Dream: Up on the roof

Let’s talk about roofs. You want your roof to be as efficient as possible in conducting water away from the

house. Wood can stand to get wet, and dry off again, but it can’t get wet and stay wet without awakening dormant bacteria, mold, fungus and mildew—in a word, rot. Keep that water moving. Head it down, move it out.

There are different types of roof ventilation, which you can fi nd by Googling “roof ventilation”. Here I’ve shown soffi t/ridge ventilation.
As the hot air in the attic escapes through the ridge vent, fresh air is pulled in through the soffi t vent. I’m also showing here
the advantage of a cricket over the doorway, especially useful on the north side of the building in wintertime

Make your roof work for, not against you

Then, where the water from the roof reaches the ground, take into consideration how it will be directed away from the building. If the runoff drains onto a patio on the uphill side of the house, how will runoff escape? Ignoring that now can mean flooding during summer cloudbursts, and a formidable

glacier-cum-skating rink in the winter. On the other hand, you can take advantage of runoff by directing a gutter downspout to water your trees and shrubs. For every 2 sq. ft. of roof, 1” of rain will produce 1 gallon of water. It’s an amazing resource in this dry climate. Colorado law prohibits us from

catching water in a cistern, but we can redirect it as it runs off the roof, and the water police can’t do a thing about it. Your roof protects your home from the snow, hail, rain and in the San Luis Valley especially, the sun and wind. Metal roofs last a long time, shed the snow well, and stand up to our ferocious spring winds better than most other types of roofs. They will also shed embers in the event of wildfire. Composite roofs last almost as long, and come in a variety of styles. Asphalt shingles and rolled roofing are less expensive, but don’t last as long. “Flat” roofs (every roof has to have some slope, to drain), often used with southwest-style homes, have to be carefully and professionally designed and installed in order not to leak. Because snow can accumulate, they need to be structurally stronger than sloped roofs. For simplicity, durability and fi re-resistance, I’d go with metal on a sloped roof. Of course,

another option that will do double duty are the new solar shingles that will keep your home dry while producing electricity. I also recently read about green

(plant-covered) roofs that come as a pre-planted panel.

What’ll they think of next?

Put a little gable roof (called a cricket), or at least an angled snow diverter, over doors where the snow will dump, especially on the north side. They will save you a lot of snow shoveling by diverting snow to either side of the entry. Gutters won’t work on the north side; they’ll freeze up with ice and snow. It’s not as critical on the south, as the sun will often melt small amounts of snow in front of the entry during the course of the day, whereas on the north that dumped snow will melt & refreeze into an impenetrable barrier if it’s not removed. Another advantage of a little roof, if it extends out over an entry, is that it can provide overhead protection, so that you (or your visitors) don’t have to stand in the rain outside the door while looking for keys or waiting to be let in. Are you planning an addition for the future, when there’s more money? Plan it now, so that you can make all your roofs work together. At least you’ll become aware of where headroom, or ridge height, or slope might be a special concern, and you can plan for it now. A properly-designed roof overhang shades the windows from hot glaring sun in the summer and lets the house fi ll with warm sunshine during the winter. I’m sure you appreciate shade from an awning on a hot August afternoon. A well-vented roof, by shading the house, helps to keep it cool the same way. In the winter, a well-vented roof over a well-insulated living area will keep your house dry and warm by keeping escaping house heat from melting snow on the roof,

There are different types of roof ventilation, which you can find by Googling “roof ventilation”. Here I’ve shown soffit/ridge ventilation. As the hot air in the attic escapes through the ridge vent, fresh air is pulled in through the soffi t vent. I’m also showing here the advantage of a cricket over the doorway, especially useful on the north side of the building in wintertime. Designing the Dream

Up on the roof which can form ice dams when the runoff reaches cold eaves. That can cause ice to build up, back up under the roofing material, and cause leaks. The recommended amount of ventilation is 1:300 of net free air fl ow, that is, for every 300 sq. ft. of attic space you should have 1 sq. ft. of open air fl ow in both the intake and exhaust vent. (Net free air flow means the size of your vent minus any louvers, screening, etc.) It is vital to have both intake and exhaust vents. As with windows, if there’s nowhere for the old, stale air to escape, the new, fresh air can’t come in.

How will it look?

More complex roof styles are more expensive, true, but the size and slope of your roof will impact you aesthetically for as long as you live there. Once you’ve decided how your roof needs to drain and vent, look at it in elevation (side) view to see how it fi ts with the rest of the house. How do the proportions and slope of the roof work with the mass of the house and the heights of the walls? Bad proportion can make for an ugly house. Neither you nor your neighbors want that.

Roof slope is measured in rise:run. In other words, how many feet does it rise over a certain horizontal distance (usually 12’)? The house in our drawing has a slope of 10:12. Over a 12’ span, the roof rises 10’. The minimum slope for many roofi ng materials is 3:12, but check with the manufacturer of any roofing material for their recommended minimum slope – you don’t want water backing up under your roofi ng and getting into the house. Remember, head it down, move it out.

What’s the right choice?

I have to make note here that I haven’t done a careful study of the carbon footprint of various materials. My priorities for this house are that it be low-energy use, easy-access, suitable for the environment of the San Luis Valley, make the most of passive solar and views, be low-maintenance, and be of average price. The market price of materials still doesn’t accurately refl ect their carbon footprints, and the price of everything seems to be in fl ux. So I’m going for a solid house that will last me through the ups and downs of the near and extended future.