Can you tell me ...

A. This is a very broad subject area and it is difficult to give specific advice without being aware of the full details. Having said that, I would recommend you to make yourself familiar with the standard BS 8004, Code of Practice for Foundations, which gives detailed guidance on underpinning.

For safety reasons, underpinning is usually carried out in approximately 1m-wide bays, which should be excavated in stages to give the bases and their dry-packs time to strengthen before an adjoining underpin base is excavated.

While carrying out general inspection, ensure that the excavated area is safe from the risk of collapse. See if it appears to look adequately shored up for its depth. The HSE information sheet Safety in Excavations provides good information. Further information about underpinning can be obtained from various textbooks and other publications readily available from high street bookshops or libraries.

A word of caution: it is dangerous to rely on general information and therefore, always seek expert advice. A specialist should be able to offer various solutions after undertaking a full appraisal.

Q. We are building a shed for storage equipment and materials on our vehicle parking area, which is concrete slab construction. Moisture from the ground underneath does not appear to have caused any physical damage to the concrete slabs. Can you tell me if the floor and walls have to be protected against the damp in order to comply with building regulations?

A. Building regulations Approved Document C - Site Preparation and Resistance to Moisture allow a floor for storing goods or accommodating plant or machinery not to be protected from damp, providing that any persons habitually employed in the building are engaged only in storing, caring for or removing the goods, plant or machinery (C4 paragraph 3.2). As you are satisfied that the concrete slab floor is not damaged by moisture from the ground, you are not required to provide protection from damp. However, to be on the safe side, it would be prudent to consider the application of a liquid waterproof membrane.

The situation with the walls is different in view of the fact that the frost may damage most brick or block materials used in walls above the DPC (Damp Proof Course) level. Therefore, there is no similar exemption for walls. The building regulations - Approved Document C (paragraph 4.2) - clearly requires walls to have a damp proof membrane unless the wall is such that it would not be damaged by moisture rising up the wall.

Q. We are a subcontractor soon starting a refurbishment project in a busy city centre. We intend to provide protective barriers to all openings or excavations more than 1.5m deep. The main contractor is insisting that all openings or excavations must be covered or fenced off to avoid accidents. Is there any published information on this topic?

A. The HSE's Construction Information Sheet No 8 entitled Safety in Excavations states: "Take steps to prevent people falling into excavations. If the excavation is 2m or more deep, provide substantial barriers, e.g. guard rails and toe boards."

In the same document, under the heading 'Protecting the public', it states: "Fence off all excavations in public places to prevent pedestrians and vehicles falling into them.

"Where children might get onto the site out of hours, take precautions (e.g. backfilling or securely covering excavations) to reduce the chance of them being injured."

You can access the above HSE information sheet Safety in Excavations at www.hse.gov.uk/pubns/cis8r.htm

Because of the seriousness of the risks involved, these precautions should be confirmed by the HSE. You can access expert advice and guidance from the HSE's Infoline (08701 545500) or email hseinformationservices@natbrit.com