Building site appraisal

Its impact on the design of a building

Site appraisal

• All building sites are different• The site for a new building needs

to be thoroughly appraised• Appraisal generally follows a two

stage process:1. Desk top appraisal

• Find out everything that is documented about the site, before visiting it

2. Physical site appraisal• Direct investigation of the site itself

Desk top appraisal

• Site location– Geography

• Elevation• Slope • Aspect• Flood risk

– Climate• Temperature range• Wind direction and

strength• Insolation (solar

energy)• Rainfall

Site specific problems: e.g. wind direction related to orientation

Sources of location information

• Ordnance survey maps, current and historical– Gives topographical information such as

height, slope, relation of site to roads and rivers

• Environment agency maps of flood risk• Meteorological office for local climate

information• Local authority map

collections for geological maps, soil maps, zoning maps, local area plans

External influences on a building site

• Covenants and easements– Rights of way– Rights to light from neighbouring properties– Rights of access– Leasehold restrictions

• Services– What’s under/over

the site?– What’s near

the site?– What’s far

from the site?

Typical inner city underground service plan

On completion of desk top appraisal…

• You will have studied many documents and maps

• You will have consulted many legal, statutory and service providing organisations

• You should now have a knowledge of all of the external influences on the site

• Now you need to get on the site itself.

Physical site appraisal

• First, measured site survey– To determine its true size and extent– To identify ill defined boundaries– Never rely on published documents

for this information• Direct site inspection

– Checking for signs of previous development (bricks and tiles on the surface are indicative)

– Checking for unmapped risks such as springs

Wind farm site on apparently undisturbed farmland

There will be power cables somewhere under this land

Building site in Berlin, 1,000 years of development & disturbance

Sub-surface inspection: Trial holes

• Dig a hole: a trial hole or inspection pit

• Can be dug by hand, but more economic to hire a digger

• Max depth 2 metres• More than one hole should be

dug on a site• Very dangerous to get in the hole

Site boundary

Trial hole

Proposed building

What are you looking for in a trial hole?

• Depth of top soil and nature of sub-soil– Clay, potential problems.– Sand, potential problems.– Gravel, fairly reassuring.

• Signs of disturbance from previous building

• Level of water table• Soil samples for testing

Trial hole results

• Soil samples for testing can be taken for– Chemical analysis– Structural testing

• Maximum realistic depth is about 2 metres

• If you are not satisfied that there is a suitable bearing layer in the depth of the trial hole, then boreholes are needed.

Boreholes: expensive but reassuring

• No practical limit to depth

• Drilled in a grid across the site

• Core samples taken right down to bedrock

Old buried landfill, not detected by trial holes

Borehole record

• Record for each borehole

• Gives depth and nature of every soil encountered

• Variation in depth of underground strata can be interpolated right across the site

Completion of site appraisal

• On completion of desktop and physical appraisal you should know– Exact size and shape of site– Previous history– Reasonable knowledge of subsurface

conditions– All service restrictions– All legal constraints– All special risks such as flood or

contamination• You are ready to start designing