Recently I looked at a very old home with a stone foundation and what appeared to be stone supports around the exterior of a rear 2-story porch, which was not over the home’s basement or foundation. The stone had crumbled away and it appeared that there were telepost type supports underneath the porch, which I assume are newer than the original construction. The second story portion of the porch indicates that there has been a problem with sagging or shifting. I’m wondering if the telepost supports indicate that the problem has been addressed or if it’s likely that this could be a big problem? How is the sagging of these types of porches normally addressed?
Many older homes in various areas of the city have attached front and back porches that are not supported by the main foundation of the house. All of these additions, whether originally built with the home or not, settle and move over time. The movement you have observed is certainly normal, and appears to have been partially addressed.
The reason that there is movement in these building additions is that they have no continuity with the main stone foundation of the home. The stone supports you describe are likely stone columns that were originally designed to hold up the rear porch. These columns may sit on grade or may be embedded a metre or so into the soil, similar to the stone foundation of the home. These columns will be subject to frost heaving, movement and mortar deterioration, as will the house foundation, but will not withstand these forces nearly as well. This is due to the fact that all sides of the columns are exposed, are relatively small, and have no heat to minimize the effects of frost in the soil. Over time the columns will deteriorate, and will have to be extensively repaired or replaced. This is why you see teleposts installed.
As previously stated, all older porches will be subject to considerable settlement, unless they are supported on proper foundations or deep concrete piers. The settlement you noted in the 2 nd floor may not be as dramatic as it appears. Often, these rear additions started out as single story additions and the slope you observe in the floor structure, although now more dramatic, was done on purpose. This floor may have been the roof of the original porch, and was sloped away from the home to help shed water. This may also be the case if the second story was built originally as a screen porch. Wind blown rain and snow could accumulate in the porch and the floor may be slightly pitched to help remove this water and prevent rotting of the floor and walls. Often, small drains are seen in the bottom of the 2 nd floor porch walls, in this scenario.
The installation of teleposts for support of the rear porch addition is a good idea, as long as done properly, with attention to several factors. The teleposts may be installed over poured deep concrete piers, which is less likely, or large concrete foundation blocks. These blocks should be level and resting on a base of granular material, for better drainage. The blocks will have some seasonal movement, and may eventually settle or sink into the soil. In this situation, regular adjustment of the screw-jack tops of the teleposts will be required to maintain a relatively level and plumb addition. The original stone columns may have to be demolished and removed to prevent transferring of the bearing of the building from the teleposts, during settlement.
Adjustable steel teleposts are ideal for vertical support under load bearing beams, but have no mechanisms to prevent lateral movement. The majority of older porches have minimal beams, if any, and undersized or over-spanned floor joist systems. Normally, installation of a new main beam, or increasing the current beam size, is required for proper support of the addition. This may be done in conjunction with increasing the depth or number of floor joists below the main floor of the structure. Once this is completed and the new teleposts installed and adjustments made, additional framing or brackets may be required to prevent lateral movement of the teleposts and addition.
The movement of the porch and installation of the teleposts may be a major concern if the above modifications were not done along with the installation of the new supports. There may also be some concern if the addition has pulled away from the main building, or has sagged considerably, before being re-levelled with the new teleposts. This will be apparent if a significant gap is visible at the junction of the house wall and the porch walls or roof. If there is a gap that is quite small at either the top or bottom of the addition and much larger at the opposite end then there may be additional structural repairs required.
Proper support and structural integrity for additions and porches is very difficult to assess for the casual observer. Proper inspection by a professional Home Inspector or Structural Engineer should be done to ensure that the addition is safe for use, or to recommend proper repairs to stabilize the porch.