Basement Environmental Grades, An Easy to Understand Guide. #BS8102

 Easy as..

Environmental grades (1 to 3) are used to define levels of 'dryness', within a given basement or cellar, with a grade 1 environment essentially being more 'wet', than a grade 3 environment.

The first thing to understand is that these grades are defined within British Standard 8102 (2009)  Code of practice for protection of below ground structures against water from the ground.  As a 'code of practice' the British Standard is the primary waterproofing design guide which we and virtually all others refer to, where considering basements and their construction, and so it makes sense to understand and employ these definitions, which set the benchmark for appropriate waterproofing performance in relation to a given usage.

Grade 1.

Basement car park, not fit for purpose, degree of 'seepage' not appropriate.

Example uses of grade 1 environments are listed within BS8102 as 'Car parking; plant rooms (excluding electrical equipment) and workshops'.  The performance level is defined as: 'Some seepage and damp areas tolerable, dependent on the intended use, local drainage might be necessary to deal with seepage'.

In essence, and as per the example above, a basic car park which suffers minimal water seepage may be viewed as acceptable and compliant with grade 1, where the degree of penetration is not detrimental to the intended usage.

The question is often asked as to how you can quantify 'some seepage', and usually the measure is assessing whether a space remains 'fit for purpose' with a given level of penetration.

The same basement car park from another angle, part way through waterproofing works by Trace.

One of the key aspects to understand in respect of 'grade 1', is that it is the only grade which allows a degree of water penetration, whereas no water penetration is acceptable with grades 2 & 3.

If you are considering waterproofing to achieve grade 1, which in my experience most commonly relates to basement car parking, make sure that you consider store rooms, lift lobbies (plus associated plant rooms) and stairwells, because these will require higher grades and can be costly to remedy.

Grade 2.

BS 8102 provides examples for grade 2 'Plant rooms and workshops (requiring a drier environment than grade 1)'.  The performance level is defined as: 'No water penetration acceptable, damp areas tolerable; ventilation might be required'.

Condensation in a basement store room? Fit for purpose?

You may well ask how damp areas can be tolerable if no water penetration is acceptable?  This relates to airborne water vapour & condensation.  If we take the aforementioned example of a basement car park store room, or a workshop as per the BS8102 example, limited condensation related dampness may not be an issue (as long as generally 'fit for purpose', and depending on what it was designed to store), and it may be that the inclusion of ventilation (a mechanism for reducing condensation) as referred to in the standard, is enough to ensure that the space is as dry as it needs to be.

In such basic spaces, you would not ordinarily consider the inclusion of heating or dehumidification, which can be employed to prevent condensation, and this leads us on to...

Grade 3. 

This basement suffered no problems of water penetration past the waterproofing system, but was still damp because of poor insulation and insufficient environmental controls

BS 8102 provides examples for grade 3 of 'Ventilated residential and commercial areas, including offices, restaurants etc.'.

The performance level is defined as: 'No water penetration acceptable, dehumidification or air-conditioning necessary, appropriate to the intended use'.

As with grade 2, water penetration is not acceptable but in this case with the inclusion of residential space, this meaning fixtures, fittings, finishes and materials that do not react well with even limited dampness, AND greater vapour production via potential cooking/washing/cleaning/breathing, meaning greater potential condensation; it is necessary within grade 3 to include suitable environmental controls (heating/ventilation/dehumidification) so that  problems of condensation do not occur.

BS 8102 provides examples for grade 3 'Ventilated residential and commercial areas, including offices, restaurants etc.'.


BS 8102 environmental grades can be condensed into:

Grade 1: Some seepage acceptable as long as fit for purpose.

Grade 2: No water penetration whatsoever, condensation/vapour acceptable as long as fit for purpose.

Grade 3: No water penetration whatsoever, environmental controls necessary to prevent problems of condensation.

Easy as 1.. 2.. 3..

Some additional advice:

Examples of usage provided within BS8102, are just that (examples).  The key is identification of usage and ensuring that the environment created by the waterproofing system and environmental controls is appropriate.  For example, if a client is proposing to store textiles, books or delicate valuables which might be sensitive to vapour, and asks you to design appropriately, then while grade 2 might be sufficient for basic storage spaces, you'll need to provide grade 3 in this circumstance, even if this only means the addition of heating for example.

Tell clients what they're getting and use BS8102 environmental grades to explain/confirm it.  Ever heard the story of the retail basement car park designed to grade 1, which then allowed seepage, resulting in the client pursuing legally because the 'waterproofing' was not working?  In this case the designer had advised in writing that grade 1 was being provided, and thus protected themselves.  All of our designers always advise of the grade provided as a matter of course.

If you like this post, please click the +1 button at the top of the page, and as always we would recommend taking specialist advice where such considerations are concerned, and would be glad to assist you if so.

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