Main menu:
House Information > Content
These are questions that I have been asked over the years. I have removed any details that might identify people or properties.
1. I have been asked if an underground railway line might affect a property.
This is extrememly unlikely. Remember that, with the exception of the Jubilee Line extension (opened in 1999), all underground lines are at least 30 years old. Any damage would have become apparent before now. Generally they are deep enough not to cause any problems to a house.
Extensive condition surveys (about 1992-4) were carried out along the line of the Jubilee Line Extension to record the condition of properties before tunneling started so that any new damage could be identified. Similar action will be taken for any propeties where the anticipated settlement might cause damage.
The possible construction of High Speed 2 (HS2) is causing some discussion. There are obviously economic and other widescale issues but the only properties that might be affected are those in close proximity to a shaft or above a station tunnel. Station tunnels are constructed in a different way to the normal running tunnels and are of larger diameter so can cause significant effects at the surface. There are no station tunnels planned under West London for HS2.
Such a scheme will require an "enabling" Act of Parliament. A condition of this will be that, where any settlement is anticipated, mitigation measures will be planned and a compensation sceheme put in place.
I'd not worry at all about an underground running line under my property.
2. Someone asked about the foundations for a wall supporting a change in level.
This sort of wall (a retaining wall) must be designed taking into account the height to be retained, the amount of load from activiites above the wall, the type of soil and the potential water pressure. Brickwork (when constructed properly) is generally only suitable for walls up to about 1m high. Above this height, while brickwork is not out of the question (the Victorians did it all the time); a concrete wall, faced with brick if required, is probably more economic.
The foundations of the wall must be deep enough to be on good ground. Normally they will be a concrete strip for a brick wall. A concrete wall will normally have integrated foundations; a cross section will typically be "L" shaped.
3. I was asked about an end-of-terrace house with subsidence problems.
It was monitored for several years (and movement continued) and the insurers decided that they would not pay to underpin the house.
This is what I wrote:
Underpinning is not necessarily the correct solution to subsidence problems, if not carefully chosen it can make things worse. This is particularly true with terraced houses.
Underpinning will make the foundations of part of the property much more rigid than the rest. Buildings move naturally, especially when they are on clay. Usually this movement does not cause real problems. Houses of the age of most of the ones around here are more flexible than modern houses as they have softer mortar than the modern cement based materials. That's why problems often appear shortly after re-pointing with new, hard mortar.
If you make part of the foundations stiffer and the rest of the building - including the adjoining houses - continues to move, cracks can appear in new places and may be worse than the ones you started with.
It's better to look at other solutions first. To do that it's necessary to obtain a good understanding of what is causing the cracks and especially to determine if they are seasonal or are progressively getting wider. Many cracks are seasonal and grow and shrink as the water content of the soil changes. While cracks may be unsightly, very few actually endanger the fundamental stability of the property. Cracks became covered by insurance in 1972, before that, people were much less concerned.
If a tree is involved, it may be possible to reduce the shrinkage of the clay by reducing the water demand of the tree - by regular pruning or even some trimming of the roots. It may also be possible to introduce more water to the area around the tree. Many problems have been triggered by puting down hard paving on gardens so rainwater cannot percolate into the soil. One response of the tree in such circumstances is for the roots to move into new areas in search of water.
It's not just trees that demand water, a large hedge will have a similar effect.
Obviously the insurers are likely to seek to minimise their outlay but may have very valid reasons for their decision. In such a situation the house owner should always get advice from an independent Structural Engineer or Surveyor with experience of such situations.
4. Basement Construction.
I have no direct experience of this so you should take professional advice. There is a legal process, laid out in the Party Wall Act, which requires anyone proposing to carry out basement construction to inform their immediate neighbors. There is then a process of consultation and checking.
The following are some thoughts to get you started.
Basement construction raises three primary issues:
Noise and disruption during the works
The work itself causes noise, some of which will be carried through the structure, not just the air. There will also be parking restrictions because of the need to remove a large volume of soil.
Temporary stability
During the construction the existing foundations of the house being extended will be reduced in order to deepen them and a large hole is dug next to the foundations of the adjoining houses. The construction techniques must allow for this. This should not be a problem if the work is designed, planned and carried out by experienced professionals.
Long term effects
As discussed elsewhere, changes to the foundations of one property in a terrace can have longer term effects on adjoining properties. All buildings, especially on clay soils, move a bit but a house with a basement will move much less. It has been suggested that the people who might be affected by the work require the person carrying out the works to pay for long term insurance against any effects.