Planning and Laying your Foundations

An article Penni wrote for “Your Build” magazine

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So you’ve decided to self-build?

No doubt you’ve spent hours deciding on every detail of the functionality, aesthetics and technical specifications of your house. But, what about the footings and foundations? “Whilst the house itself may be the exciting bit, it’s essential to get the foundations spot on for any build, and especially if you’re opting for a pre-manufactured house in which case, the foundations must be precision engineered”, explained Penni Brooks of P&P Groundworks.

How much are your groundworks likely to cost?

You can use the area in square metres of the ground floor of your new home to calculate the total estimated price for your groundworks, please contact us for our current prices. You should also be aware that there are also some variable costs which cannot be quantified in advance as they are dependent on factors which can only be identified later in the process. Typically the most common item in this category is the depth of the footings. The footings are the main structural component of the foundation slab and their depth can only be finalised based on the result of a soil survey (costing between £1000 – £2000) and after examination of the actual excavation by the building inspector”, explained Penni. Step-by-step guide to planning & laying your foundations from P&P Groundworks.

This step-by-step guide explains everything any self-builder needs to know about the process of planning and laying foundations:

Step 1: Soil sample and topographical The details of this are required in order for the structural engineer to get the foundation design produced.

Step 2: Excavation (minimum 1m deep) The excavation must be carried out to the requirements / design of the structural engineer, and also to the satisfaction of the building inspector.

Step 3: Footings The footings must be concreted, according to structural design.

Step 4: Blockwork Blockwork to be carried out to all walls, as designed by the structural engineer and drains and services laid into footings where applicable.

Step 5: Hardcore to required level. (N.B. must be a certificated hardcore). 5a. Insulation, if required, to be installed. 5b. Clayboard, if required, to be installed.

Step 6: Concrete slab A precision-engineered concrete slab (to a depth of 200mm) is laid, together with power floating where required.

Step 7: Ducting The ducting for gas and electricity is typically laid to the edge of the slab as your energy supplier(s) will require their meter boxes to be on the outside wall of your property. If services are already on-site then the ducting will be laid to the point of reconnection on your property. Ducting for the phone line and water pipe are typically laid into and through the slab. The water pipe is laid in the ducting, typically 32mm in diameter. The gas pipe, mains electricity cable and phone line are provided and installed in the ducting by your energy and phone suppliers respectively.

Step 8: Drains and manholes must be fitted to handle waste from house (typically called ‘foul water’) and rainwater. Foul water drains are laid through the slab and connect to your drains via manholes. Manholes are inserted at each drain junction and where the drain run has to make a significant change in direction (typically more than 45° in the horizontal plane). Groundworkers will carry out the excavation, laying and joining the drains and subsequent backfill. If there is a suitable existing domestic manhole already connected to the main sewer then your drains will be connected to this. Otherwise your drains will be laid to the perimeter of your property where they will be connected to the main sewer by your local water authority. N.B. Any new connection to the main sewer must be undertaken by your local water authority.

Rainwater drains, which are an additional expense, are connected to a soak-away or rainwater collection tank. If you plan to use the rainwater in your house or garden, the rainwater collection tank is an extra expense, as is connection to a septic tank with a separate soak away, although rainwater drains to soak away are included.

Step 9: Site preparation for construction This comprises a hardcore finish, 1-2metre wide, around the slab to provide a safe base on which scaffolding will be erected, an additional hardcore finish for the crane to sit on whilst the house is being constructed (sometimes called a ‘crane-mat’ and also a hardcore finish of the driveway to allow practical access to the site during the construction process for the crane and other vehicles)