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Hemlock – Open Gap Rain Screen Siding

by LiveModern Webmaster last modified Nov 18, 2015 01:05 AM
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by bob last modified Nov 17, 2015

My use of eastern hemlock as a siding material has been generating interest. Hemlock is a common wood in Vermont but doesn’t get used a lot except in barns and outbuildings and sometimes for timber frames. My summer job during high school involved working in a small sawmill. We sometimes...



My use of eastern hemlock as a siding material has been generating interest. Hemlock is a common wood in Vermont but doesn’t get used a lot except in barns and outbuildings and sometimes for timber frames. My summer job during high school involved working in a small sawmill. We sometimes cut hemlock and I found the wood beautiful, but heavy. One summer, we cut some hemlock for a bridge. Fast forward um… lots of years and I ordered a bunch of hemlock for framing and decking when I built my barn. I learned a bit about how to work with hemlock, how it ages and weathers and I started thinking about how I could use it in my own work. I try to source materials as locally as possible and design within local builder’s abilities and interests – which is easy to do here where builders get together monthly to discuss building science related issues

Eastern hemlock in Vermont

In rural New England, buildings are often sided with pine siding in a vertical shiplap form – and often unfinished. It tends to develop a black mold that is relatively harmless but can be ugly. I found that hemlock is more resistant to this mold. It’s also harder and more rot resistant. It is nowhere near as rot resistant as cedar, a more common siding material however.

White pine siding on my own barn
white pine siding on a barn robert Swinburne Vermont Architect

A brief on open rainscreen siding: Good architect and builders are installing siding with a vented airspace between the siding and weather resistant barrier (WRB). This allows any moisture that gets behind the siding to dry out before it does damage. Modern materials (a better WRB) and the venting detail allow us to use different materials and different details for the siding itself. I have commonly seen the open gapped rainscreen detail used with ipe boards but Ipe is a tropical hardwood related to mahogany. Cement based boards are also used commonly but cement has fairly high embodied energy. Both of these are not locally sourced materials. The gap in the siding also reveals a view of the WRB (depending on the size of the gap) This means that damaging UV rays are also reaching the WRB. And bugs. Thus the need for a better (and black) WRB. There are several on the market designed for this. Both projects shown here use Mento and tapes from

It occurred to me that I could use narrow hemlock boards from local mills to create a very elegant (I hoped) rainscreen siding detail. It would use local and relatively inexpensive materials, it wouldn’t need paint or stain, installation could be simpler and faster if I got the details right, and if I installed it horizontally, the lowest courses could easily be replaced if the siding degraded due to splashback and snow banks. The damaged siding would not present a disposal concern – just toss it in the bushes and it becomes habitat for red backed salamanders.
I was lucky to have a client with a taste for modernism allow me to try my ideas out on his home. The results were rather spectacular and gave me a sense of the potential. Now I am doing my second project with hemlock siding. The builders for this project (Webster Construction of Marlboro, Vermont) are quite familiar with good building science and modern products and methods. They saw the potential and were happy to give it a try plus they were able to improve my detailing in several ways which I can then incorporate into drawings and specifications for the next time around.

modern ski house in vermont near Statton

The hemlock turns silvery gray within a year. The narrow boards create a woven, fabric-like aesthetic.

The hemlock is installed “green” with deck screws. This siding is all 1×3 so gaps will be quite small as the wood dries. Fiberglass bugscreen is installed directly behind the siding. strapping can be regular 1×3 strapping although coravent makes an excellent product for this purpose and should at least be used on any strapping set horizontally such as over and under windows.

hemlock siding installation

This is the corner trim detail the builder came up with and I really like. One side runs long and is cut after installation. The other side is held back for a crisp reveal – very architecty! Of note: the deck is white oak (local) and the post is European Larch which is from a harvest of a Vermont tree farm. European larch is used in Europe as a durable siding material that needs no treatment.

hemlock siding corner detail - Vermont architect Robert SwinburneHemlock siding in Vermont - Vermont architect Robert Swinburne

modern ski house in vermont near Statton with open gap rainscreen siding

detailing around windows is super simple. On the first house I used metal panels (installed by the roofer) to accentuate the windows and wrap corners. Here it is about as simple as it gets.

Eastern Hemlock siding detailVermont modern house by architect Robert Swinburne

A few of my minimal details:




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