Sills and Foundations

Most of the braced timber frames in New England utilize compression bracing.  The role of the sill system in the function of compression braced frames is often overlooked or taken for granted.  We have had many requests to anchor post feet to dimensional lumber using metal fasteners instead the traditional heavy timbered sill with stub tenon mortises.  Thus far, we have denied them all and lost the occasional client over it.  The integrity of the sill system is critical to the longevity of the frame.  Strong connections to a rigid sill system can help to keep the braces in compression even with moderate shifting of the foundation.  Unevenness in the sills will cause braces to become unshouldered and allow the frame to move.

Most of the structures that we have restored have had either dry laid stone or granite foundations with no supplemental drainage.  Although we have seen many of these foundations shift, heave and sink leading to rot in the sill systems and unevenness in the frames we feel that stone and granite are still the best choice for a foundation.  The majority of the foundations that we have worked on have been from the pre-civil war era and held up remarkably well for their age.  Typically, we excavate the stones, remove loose and loamy soils, add crushed stone and drainage tiles, re-use the original material and re-grade around the structure.  We are often asked about the use of poured foundations and we strongly discourage it.  Although concrete can be sealed, the sealants don’t have much of a lifespan.  Concrete wicks moisture into timbers and accelerates decay.  The lifespan of a concrete foundation is significantly less than that of any given timbered structure.  It makes no sense to us to use a foundation that is sure to fail before the structure that it supports especially when it may actually damage the structure.  We have worked with poured foundations on only a few occasions at the request of homeowners but do not endorse it.  What we do like about stone foundations is that they can be reused or re-stacked for the life of the frame.  When the frame is gone there is no part of a stone foundation that needs to be hauled off to the landfill.

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