You might have heard the acronym PUP applied to a house; though it might sound endearing (perhaps conjuring images of a playful puppy) it is in fact rather more prosaic and stands for Previously Underpinned Property; a building that has undergone the process of underpinning. Underpinning is the process of strengthening and stabilising part (or all) of an existing structure.
Previously Underpinned Properties (PUPs) are not necessarily synonymous with subsidence, though to an insurer they carry a similar risk. There are several reasons why underpinning may be required, usually stemming from the fact that the original foundation is simply not strong enough or stable enough.
This may be because the usage of the structure has been altered, or because the original foundations were simply insufficient. If the properties of the soil supporting the foundations alters, this could be as a result of subsidence, but can also be because the soil properties were wrongly classified during the design process. Underpinning can often prove more economical than complete rebuilding.
Properties built before the 1900s, despite enduring for so long, are at a slightly higher risk of subsidence than modern properties. Though old buildings were typically built using time tested techniques that new builds might benefit from emulating, they did not benefit from the modern mild steel and reinforced concrete that went into foundations after the turn of the century. This said, extensions to original buildings can also put more strain on existing foundations and may be another reason for underpinning to be sought.
Modern foundation systems
There are three main categories that most modern foundation systems fall into:
1. Shallow spread footings
These are used on surface soils with sufficient stability and load bearing capacity, where concrete pads or rafts are used to spread the structural load evenly across the ground. Typically, these types of foundations only penetrate the ground deep enough to avoid unstable topsoil, frost and other variations in temperature or moisture.
Where surface soils are too weak for a raft foundation, then piles are driven into the ground to reach stronger strata at greater depths. Piles are the second category of foundation types.
3. Basement or box foundations
Where a box of reinforced concrete is used to make a building "float" in the earth. This type works in a similar way to the cellars found in older buildings and is comparable to the way most boats are able to float in water, where the volume displaced compensates for the weight of the structure built.
Where underpinning should not take place
Underpinning should not be carried out in a couple of key situations, firstly if the cause for any damage causing ground movement has stopped and is unlikely to reoccur.
Secondly, where the rate and final extent of any damage is not likely to impair structural strength or integrity and will not threaten stability during the building's required life-span.
In both cases, repairing and redecorating after damage has occurred would be less expensive and less traumatic for the building's occupants. When ground movement is expected to affect a building on a structural level, there are some steps that should be considered before you need to consider underpinning. Pruning the upper branches of a tree and controlling tree roots can reduce subsidence danger from trees, as can repairing leaking drains and keeping drainage systems in a good state of repair.
Most home insurance companies will not even consider your property if it has been previously underpinned, but HomeProtect is different. We are unique in that we can provide you with a house insurance quote for your underpinned property online.
If you are selling your PUP, we may be able to transfer your cover to a new owner (subject to circumstance), which may be the key to closing a deal on an underpinned home.