News item 6 - Conservatory Foundation Construction Advise
Foundations are an essential part of the conservatory project to take time over and get right. It is easy to understand the consequences of getting it wrong - so my philosophy like a structural engineer is to build to a higher standard than required if conditions are unpredictable.
It has taken a long while historically to get to the present position as far as depths of strip foundations are concerned. Depths have been shallower for conventional extension builds until relatively recently - with conventional extension strip foundations now at 1m ( British Standard 8004 ) or deeper for conventional extensions depending on ground conditions and tree proximity etc - so if you are building a 2.1m high wall and not trench filling with concrete - would 600mm deep for a dwarf wall be adequate for this part of the conservatory if building regs are not required - I would say not - so it is always necessary to adjust the foundation depths to suit the heights of wall and loadings and stick with the building regs recommendation if in doubt. It is also important to avoid frost damage in extremes of cold so do not skimp and try to avoid hard graft by digging trenches too shallow.
- It is always important to look at the ground conditions and see what it looks like when digging the first part of your trench and adjust your depth downwards to suit. if the ground is soft and crumbly at a trench depth of 600mm , then it will be necessary to keep going downwards until hard ground is found ( this is also open to interpritation as to what is hard ground ) - ground conditions can vary at various points of your foundations so it can be possible to step the foundations to suit or just dig further down for all of it - which is my preferred method. 750mm is deep enough to avoid frost damage in most areas if this is a consideration.
- Rain and wet conditions are not ideal for foundation digging as this will affect the base of the trench requiring more work later to remove wet soil and shore up the sides or the foundations can sink or move when dry conditions arrive.
- Hot conditions are also not ideal for foundations as ground can shrink and dry out quickly and then swell when water returns after the foundations are infilled with concrete, causing heave and pressure on the foundations. It is important to get the concrete into the ground quickly after digging if weather conditions are hot , wet or unpredictable.
- If it is minus degrees then an additive may be required to allow the concrete to cure properly. 5.
- If it is hot then a retarder may be required to allow time to barrow it to the rear from your drive if delivered in a large amount.
- Trench filling is a more practical solution in my opinion in bad conditions because the disruption to the ground is kept to a minimum avoiding heave and shrinkage and allows the over ground part to proceed more quickly.
- Sloping ground requires special care to make sure again that depths are correct and foundations stepped to suit.
- Drainage channels are required around the conservatory if ground levels slope towards the conservatory - to deal with run off water . Retaining walls need to be added when level changes are larger and there is the potential for land slippage.
- Drains and manholes if moved require building regs approval or local water authority permission depending on who owns them.
- Drains that require building over require bridging with a lintel and infilling with pea gravel or sand to avoid downward pressure on the pipes.
- Manholes can be built over but require a double sealed lid to avoid smells if inside the conservatory and access will need to be provided ( important and essential )
- Gulleys require sealed lids if smells are to be avoided even with dirt traps present so make sure you have looked at and sourced the components for your clay or plastic pipe system before starting your build.
- There are special requirements when building close to neighbours buildings and exposing their foundations during your build so you will need to look carefully at the regulations to see what is required.
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