Here in New England, we have to think about snow in relation to old barns and barn homes. In particular, we have to think about the tremendous weight that a sticky snowfall can deposit onto the roof of an old barn.
Snow weights a lot…
The expected snow load in Vermont can be as high as 65 pounds per square foot. On a giant old barn with a huge roof, that kind of weight can add up. We also live on the edge of the slate valley, so many of our barns have slate roofs. A slate roof adds eight to ten pounds to each square foot. That is some serious weight that the roof has to support!
Last weekend, we were blessed with 24 inches of snow in some areas and now we are getting heavy rain on top of that. So how did the master timber framers of the 1700s and 1800s build their roof systems strong enough to stay true in winter storm events?
The answer in many cases is the engineering brilliance of a queen system.
In the barn shown above, which dates from the early 1800s and that we restored last summer, the queen system is the two full-length timbers and the posts and braces that support them. This method of construction cuts the effective length of the rafters in half, keeping them ridged under the forces of gravity.
Roof loading, caused by the weight of the roof system itself, the roofing material and the snow that collects on it, leads to two types of force. The first is a load directly down that can lead to sag or failure of the rafters themselves. A queen system supports them in the middle, thereby cutting down on the possibility of sag.
The second force is an outward thrust, meaning that the weight pushes outward towards the eves of the building. In an inadequate frame, this can break the joinery that holds the building together. In order to help with this outward thrust, queen posts are braced down to the horizontal girts. When the rafters are pinned to the queen beam, it reduces the amount of outward force that they can exert on the eve walls.
Another way that timber framers keep the queen system and rafters from spreading under weight is the use of horizontal ties between the queen posts. This technique makes a ridged queen bent, and when the rafters are pegged down into it, they are held back from pushing the eves of the barn.
The photo above shows a beautiful frame that we will be restoring soon. The pre-1800s gunstock frame has a queen system that looks like a stand-alone timber frame structure that provides rigidity to the roof system.
Another common style of queen system has the posts angled to meet the rafters at a 90-degree angle. When the posts are angled like this, large braces are needed to withstand the outward force.
The barn pictured above is an 1850s barn that we restored and re-erected on Cape Cod. And here is a photo of a very large barn that we did restoration work on in place this past summer.
Let it snow!
And, as always, contact us if you have any questions about queen systems in antique barns.