Im in the process of designing a roof structure for a house I am building in Mt Crested Butte , Co. Altitude 9500ft. The house is a modern design with a low slope roof that will be carrying a lot of snow load. Its on a steep slope so building will be challenging. Im trying to build it using the greenest building material possible but also am willing to compromise for materials that last longer, perform better, or are easier to work with. The site will have 2 structures a detached garage with an apt below and the main 3 level house. For the detached garage I want to go with the least expensive option since the roof will be primarily over the garage. For the house I want a steel or exposed wood beam on the main level (2nd floor) but may go with a wood T&G ceiling or even drywall on the first and 3rd floors to save cost. The ground floor is a walk out basement so I like the idea of using drywall to reflect more light into the bedrooms that may be dark. Im considering SIP panels, conventional LVL beam, and other designs but also need to decide on what insulation I will be using. I like rock wool and dense pack cellulose and maybe some spray foam. Im also trying to decide how much insulation to put in. All lower walls will likely be poured concrete with foam. Upper stories will be double stud walls with dense pack cellulose.
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One important thing to consider is ice dams. Even if the structure is well insulated/ventilated, snow can collect behind, eg, a chimney and "dam up" meltwater during a sudden thaw. Such areas need carefully-installed waterproof membranes.
And, of course, the eaves and valleys need to be protected as well.
Do you want engineering advice from anonymous posters on the internet?
Please, hire an engineer
I do have a structural engineer already. Im mostly interested in thoughts on different roof designs i.e. SIPs vs LVLs. How best to insulate to achieve very high R values.
Nice design. It's going to look great. I'd check out green building adviser, maybe they will have some good info.
Thanks. I have already subscribed so I will.
You mention that you are willing to compromise for materials that will perform better or last longer, but you're insisting on a flat roof in snow country. I'd highly recommend putting some pitch to that roof to shed the snow so that you're minimizing the impact and risks to your structure from holding snow. Yes, you can build a low slope roof in snow country that is engineered to withstand the load, but the reality that will catch up to you eventually is the side effects of the snow sitting there...water getting back to other places and finding the tiniest of imperfections to exploit, snow weight that will pin doors closed in winter or crack drywall in spring, maintenance, removing snow over entries, etc.
Besides, building that low slope roof may wind up costing a lot more than a pitched roof even in the construction phase due to engineered loads. Tack on the costs over time of the snow that sits there and you could save a lot with a steeper roof.
There's a reason certain house styles are more common in certain regions. That's not to say you shouldn't build modern, just that you need to adapt that aesthetic to the very real needs of the location you're building in.