Flood Risk Assessment
The following Flood Risk Assessment was compiled to accompany the planning application for the proposed development at 14 Wardo-Avenue and was compiled with reference to the following documents:
- Preparing for Floods, Interim guidance for improving the flood resistance of domestic and small business properties (ODPM October 2003)
- Standing Advice Development and Flood Risk - England (Environment Agency March 2007)
- Planning Policy Statement 25: Development and Flood Risk (December 2006)
In consulting the Environment Agency Standing Advice Development and Flood Risk of March 2007, the Agency matrix classes the proposal as D2, being a residential extension of less than 250 sq.m. in a Flood Zone 3. No consultation is therefore required with the Agency. The following Flood Risk Assessment is proposed is in accordance with the Environment Agency’s advisory comments.
According to the Environment Agency options matrix we propose that the floor levels within the proposed development will be set no lower than existing levels and that flood proofing of the proposed development will be incorporated as follows:
- The finished floor level in the side extension shall be as per the existing internal floor level, approximately 100mm above existing ground level.
- Solid in-situ concrete floor construction with a screed over shall be used as it can provide an effective seal against water rising up through the floor. Solid concrete floors will suffer less damage than suspended floors and are less expensive and faster to restore following exposure to floodwater.
- Dense concrete blocks will be used to construct the dwarf walls below ground level which will reduce the amount of water penetration into the external walls
- External wall surfaces are to be treated with a water-resistant coating to help prevent floodwater soaking into the external face of the wall, thus allowing the wall to dry out more quickly. The coating will be applied to 500mm above the maximum expected level of flooding.
- Lime based plaster products have good water resistance properties and once installed over a water resistant render, such as sand/cement or proprietary sealant, will provide effective resistance to flooding. Following immersion in floodwater lime based plasters over a water resistant render should dry out quickly and should not deteriorate even if subjected to repeated exposure to floodwater. The water-resistant render beneath the plaster reduces water penetration into the underlying masonry, allowing the wall to dry out more quickly without the need to remove the plaster finish. Hence repair costs can be reduced. Hydraulic lime finishes with water resisting additives can also provide effective flood resistance for masonry walls, both internally and externally. As with lime based plaster, hydraulic lime coatings have good water resistance properties and can allow walls to dry out without the need for replacement following immersion in floodwater.
- Wherever used, wall accessories such as wall ties and screws will be specified as stainless steel in order to reduce corrosion.
- Where they occur, external cavity walls will be designed with a 50mm clear cavity in order to promote the free draining of water away from the internal face and insulation within the cavity will be specified as rigid board with impermeable foil facings that are resistant to the passage of water vapour.
- Internal plasterboard wall linings will be designed with horizontally laid boards so as to reduce the number of boards that will need replacing in the event of a flood.
- Kitchen units will be fitted 150mm above finished floor level on plastic legs.
- Electrical consumer units will be fitted at high level.
- Electrical sockets will be designed at 450mm above finished floor level in accordance with Part M of the Building Regulations.
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