Obsessed with roofs
Published on April 15, 2018
A recent email thread involving a group working on a video about ZNE design prompted me to raise one of my favorite subjects. Say I, “Will you talk about the critical importance of roof design?” Queried Steve Mann in reply, “Do you have something more specific in mind?”
I’m so glad he asked! It gave me an opportunity to vent (pun intended) about this topic, which I find is absent from far too many conversations about ZNE home design. Here’s what rolled off the keyboard.
- You need to know your (approximate) energy loads early on, so that you have an idea how much solar-appropriate roof area you’re going to need. [That requires a calculation — for example, using NREL’s PVWatts.]
- You need to factor in code-required clearances around the solar array, and depending on the size/shape/proportions of the roof plane(s) in question, those margins can eat up a hefty fraction of the total area(s).
- You need to NOT have vent stacks and other obstructions interrupt that oh-so-critical PV roof area.
- All of the above — to those who are realistic and paying attention — dictate the simplest practicable roof form.
- The less attention you pay to the above considerations, the harder you will have to work on the enclosure and other efficiency measures to achieve ZNE — e.g., adding in more and more expensive measures, such as imported windows.
- Conversely, the MORE attention you pay to (simplifying) the roof, the more flexibility you will have with other building features.
- The simpler the roof:
- the more money you’ll have for other features;
- the less it will cost to develop elaborate architectural details to ensure thermal & moisture integrity;
- the easier it will be to air-seal and insulate the whole building;
- the more likely that the air-sealing & insulation will be done well;
- the better the building will perform; and
- the less the risk of later thermal, moisture, condensation, and rot problems.
So a simple roof is an all-around win: save money, improve thermal and moisture performance, get to ZNE more easily.
It’s time that we rekindle a time-tested aesthetic, one that finds beauty in simple, elegant, well-proportioned forms, robust materials, and quality of craft. One of my favorite architects who has complete mastery of this approach is Steve Baczek. Not coincidentally, Steve spent many years working with Joe Lstiburek and Betsy Pettit at Building Science Corporation — he’s also thoroughly conversant with building science. Take a look at Steve’s portfolio for inspiration!