5 Pitfalls of Basement Drainage - Ben Norman

For those wanting to extend a property in an area of prime real-estate, where land is at a premium and extensions have already gone back, front and up, they have only one course left ... down.

Basement extensions are popular to add further dimensions to valuable urban property, adding a study, reading room, music room, perhaps a playroom or bedroom.

There are effectively three types of basement: converting an existing basement into a useable, ventilated, well lit and drained room(s), retrofitting a basement, excavating one below an existing property; and adding one to the plans of a new build.

We’re looking particularly at the middle option here.

Before embarking on such a retrofit basement project, please, please seek professional advice. Basement excavations do need Planning Permission, mainly relating to the installation of a means of escape or light wells as these affect the exterior appearance of the property.

As well as the obvious considerations: access, party walls, existing infrastructure etc, two major considerations are waterproofing and drainage.

 In assessing the viability of the project, consideration must be made for the following:

• Accessibility and affects on neighbouring properties.
• Geology, topography and the water table.
• The proposed use of the basement.
• Access from existing the property.
• Ventilation and light.
• Existing drainage.

There are different ways to make basements dry which is one of the most critical aspects of a successful basement. The waterproofing falls into 2 main areas, cementitious tanking and cavity drain membranes.

Tanking, layers waterproof material directly to basement walls, ceiling and floor, encapsulating the space in a waterproof ceil. A cementitious waterproof render system is applied in several layers, linked to a waterproof screed on the floor.

Alternatively membranes are used to create an inner waterproof structure with a cavity (created by the membranes studded profile) behind it that is fully drained. The constant draining reduces any pressure build up on the exterior structure.

The pitfalls:

1. Failure to check the location of existing drainage and services - Quite often existing sewers run across the rear of properties, particularly terrace housing.  Typically these sewers are around 1.5m deep, just about head height in the proposed basement.

2. Following on from number 1, owners naturally want to maximise basement space and extend right up to the plot boundary. This offers a bigger new 'family room' but leaves no space to divert the sewer. Manholes and drainage would now have to be located outside the plot boundary, perhaps even on neighbouring land.

3. Following on from 2 regarding sewers. The sewer may already be adopted by the water authority.  Therefore any works on or close to it would require a formal legal agreement of acceptance to be put in place. Without it, building control may not sign it off.

4. Make sure the basement is fully waterproofed with a membrane and sump pump system to drain anything low level including light wells.

5. More of a tip to avoid a pit in which to fall, bathrooms and WC's in a new basement require pumping. Installing pumping systems further reduces usable space, so avoid using the basement for this purpose. Keep them above ground level and with some careful planning they can discharge via gravity. 

A bonus pitfall:  There is sometimes a risk of sewers surcharging. A non-return valve is sometime a good idea to prevent flooding. 

Click the image and enjoy the link.

 
To avoid these pitfalls and many more, take professional advice, 
contact Ben Norman and the team at
 JMS Engineers on 01473 487047 

We add value to every project we have been,
are, and will be equally proud to support.

Rural view, plus inspired artist, plus creative structural engineering, equals 'dynamic loadbearing'.

Designed by JMS, fabricated by Artfabs.

Tim Ward is a truly inspired and inspiring artist operating from his public arts and landscape design practice 'Circling the Square' in Buckhurst Hill, Essex. His core mantra is to enable the 'application of artistic principles to urban design', the results of which can be seen across Essex and beyond.

But this is just partly a story about Tim, his concept and his design.

This is also an example of what can be achieved when two pieces of a jigsaw fit so well together, where the breathtaking inspiration of the artist's origination and design is transported into a practical, sustainable 'thing' by the creativity, innovation and skill of the consulting Structural Engineer - JMS.

Above right and below are two examples of Tim's work. Below is a cross section of his involvement in the Stockport Interchange, a project for which he was appointed by Transport for Greater Manchester.

Moving back into Essex, south of Colchester and we find the delightful surrounding areas and views of Rowhedge Wharf. What could possibly make the enjoyment of such views better than to create and install a walkway and watchtower.

Tim's design is as creative as the concept itself. We are as proud to work with him as we are to take our hats off to him.

The platform and tower comprise a spiral staircase, 'mast' feature, observation platform, base support and concrete foundation.  Each component requires different engineering dynamics to converge as one.

The Spiral Staircase is a 4 meters tall and over 2 meters in diameter staircase, mounted on a central support column with steps and a steel plate stringer. The 20 steps are formed of 12 per full turn with a hand rail and vertical bar infill to the steel spiral staircase.



The 'Mast' Feature is a bespoke tapering steel mast, 6 meters tall but only 35 centimeters diameter at the base where it is connected to a central support column. For special occasions, flag and bunting attachments can be nautically attached to the mast.

As for the Observation Platform, this is a dodecagon (12 sided to mere mortals) shaped platform 4.5 meters in diameter with a 1.2 meter barrier mounted on a steel rail and supports with a steel handrail.

The 'Rowhedge Recollections' durable photographic frieze feature (pictured below) and clear Perspex panels will be integrated within the handrail.

At the center of the platform is the 2.1 meter staircase access/egress with its handrail and vertical bar surround. The observation walkway is a 1.2 meter 360 degree platform.

These are some of Tom Jeffcoat's 3D drawings (JMS) which help define the detailed engineering and specification of the steelwork.

The Base Support and Concrete Foundation clearly have to support this lot in the ebb and flow of the River Colne.

The central base column descends into the specially built round section of the 1.9 meter high retaining wall.

It will be further supported by an additional steel framework and base plate in a concrete foundation.

The Rowhedge Recollections (below) is an anthology of photographs, diary comment and articles illustrating life at the turn of the 19th, 20th Century.

Much of the memorabilia centers on the Rowhedge Ironworks, which formed in 1904 changing its name from Donyland Shipbuilders.




From this time until 1964, Rowhedge claimed the successful launching of over 900 vessels. If the Rowhedge Watchtower could look back in time, what views must it see and tales to tell.

We add value to every project we have been,
are, and will be equally proud to support.