Substructure Repair & Sill Replacement

“Sills may be the lowliest parts of a wood frame house but, like the keel of a boat, they form the base that supports all other structural members. When old house sills succumb to rot and insect damage, it takes technique and experience to replace them.”


Hydraulic jacks on carefully angled pads suspend walls while George Yonnone and Curtis Von Ruden maneuver 22 feet of new white oak sill.

George Yonnone Restorations has been replacing sills in antique homes and old barns for over 34 years. This experience is fundamental to the quality of every sill we replace.

The Sill Evaluation Process

Sill repair and replacement starts with assessing the present conditions. Sills tend to rot from the outside in. So while the sills may look good from the inside, in the basement, much of the outside wood can still be severely rotted.

Sounding the sills by tapping enables us to verify what sills need replacement. This makes sure you fix only what needs attention. And you avoid replacing a suspected sill only to find superficial damage upon removal.

The Sill Replacement Process

Setting up the jacks to lift the house and expose the sills is often the most time consuming phase of the project. At least it is for us. That’s because it’s the most important.


With timber framing studs, joists, and posts converge along the second story line – a structurally stable point to jack.

Simply jacking sections of your house sill by sill (as many inexperienced carpenters do) is incorrect. Plaster walls will almost certainly crack and the interior framing will likely buckle from this adverse stress. Jacking this way also pushes interior walls in at the bottom and ignores house settling issues present in the frame.

Keep in mind that merely replacing a sill with a new timber does not help you level the main frame. Part of the process of structural repair involves jacking and squaring the frame to level.

In simple terms, the object of jacking is to raise all low areas of the house to a predetermined benchmark. The new sills then realign the house based off of this main point of reference. When this is ignored, the frame remains stressed at all load-bearing members. This means the mortise and tenons, pegs and horizontal members are still in danger of breaking.

Also bear in mind that the most structurally stable point to jack is the second-story spanners. This method lifts the first-story walls without putting them under a heavy load from the weight of the house. This is the ideal way to avoid cracking historic plaster finishes.

Jacking up an antique house and replacing sills is a big job that needs to be done carefully. Sure, you can easily find a local carpenter who will give you a cheap price to do the job. Avoid this mistake. It will cost you later. This is the most important phase of the job where experience counts.

Putting in New Sills


An electric lag gun, similar to an auto mechanic’s lug gun, drives in the lag screws.

Before sills are replaced, all structural components are evaluated for damage including girder ends, joists, wall studs and post bottoms. These members are then repaired as necessary prior to sill replacement.

Once the house is sufficiently jacked and rotten sills are replaced, the new timers are lagged together. By using a sufficient lap joint and lagging the beams together, we are able to span long lengths without compromising strength.

With the new sills in place, the jacks are removed and the framing and floor joists are reattached to the sills.

The Art of Structural Repair

As artists, we understand the ability to conceptualize outside the box. It’s the dynamics of the structure that let the building tell us how to proceed during the process of jacking and squaring. Thirty four years of experience has taught us that anything is possible – even when architects, engineers and contractors say it can’t be done.

Clients often think they can open the phone book and find a contractor to make structural repairs to their colonial building. As a result, contractors trained in 20th century building methods are often hired to do something they are ill-equipped to handle. They typically employ fast and cheap construction methods inappropriate for 18th century structures.

Fifty percent of our work is repairing poorly done structural repairs, some of which were performed for resale prior to clients buying the property. Clients paid to have work done which then has to be torn out and rebuilt properly.

We Bring Our Experience to Your Project

Because we offer our services nationally, we are able to serve clients who are desperately trying to find someone to save their building. Clients have told me they have searched in their area for a year or more and were unable to find someone willing or able to do the project.

Contact us today to learn more about how we can do structural repairs and replace the sills of your house.