GB2486463A

GB2486463A - Collecting water from a wall cavity

Info

Publication number: GB2486463A
Application number: GB201021323A
Authority: GB
Inventors: David William Beddoes
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-12-16
Filing date: 2010-12-16
Publication date: 2012-06-20
Also published as: GB201021323D0

Abstract

A retained height cavity wall used to collect water ingress and transfer it to a sump/pump unit for removal from the building. In the case of conventional strip foundations or to address residual risk the sump/pump unit is also used with a cavity membrane to remove rising groundwater from building floors.

Description

CavitvWall FloQ4 Protection

Background

This invention relates to the collection and management of storm water, floodwater and groundwater ingress to buildings with cavity walls.

One consequence of global warming has been an increase in flooding events over recent years. It is now accepted by the overwhelming majority of climate scientists that man made greenhouse gases are causing climate change (IPCC, 2009). Summer rainfall is more intense leading to inter-urban and flash flooding. Winter precipitation is becoming heavier and more frequent, casing more flooding. The wetter winters and storm surges combined with a continuing rise in sea levels will increase flood risk in the UK. Having realised that community level flood protection measures cannot be provided for everyone, the 15K Government is now providing grant aid for the property level flood protection of homes at significant risk of flooding. Currently this grant aid is being distributed by local authorities who must decide on how to spend the funding. The local authorities are allocating funds for the installation of external door guards and air brick covers in the belief that these measures can protect homes from flooding. however, floodwater can still enter a building as groundwater from below the floor or seepage through party and external wall construction. Conventional wall and floor construction methods are not waterproof, water seeps through the materials used and also leaks through the joins.

There are already a great many modem homes that have been built on floodplains and unfortunately many more are to follow e.g. the Thames Gateway development. These new homes are all built with cavity walls and a solution is needed to protect them from floodwater.

Statement of invention

To overcome this problem this invention proposes to use the resistance of the external cavity walls of the building and then in addition install a modified cavity membrane waterproofing system.

Advantages The outer masonry skin or leaf of the cavity wall is used as a first flood protection measure, the structural stability needed to resist hydrostatic pressure in the event of a flood being provided by the stainless steel wall ties that join the two leaves together.

A weak point for cavity walls in a flood situation is the retained height cavity which is the section of wall cavity between the DPC level and the external ground level as shown Building Regulations 2000 Approved Documents A -diagram 11.1. Within this retained height cavity there are weepholes that are positioned in the outer leaf at the bottom of the retained height cavity, typically in the third course below damp proof course (DPC). To prevent floodwater from entering through these weepholes and hence into the retained height cavity they need to be filled and then any storm water from driving rain that may find its way into the cavity will collect in the retained height cavity and be transferred via a link drain to a sump/pump unit for removal from the building. An alternitive is to fit automatic weepholes into the outer leaf that act as a one way valve, allowing water out of the retained height cavity into the soil but do not allow floodwater in. In the event of a flood, the retained height cavity can then also be used to collect the floodwater that enters through the porous bricks or through cracks between mortar and bricks for transfer via the same link drain and removal by the sump/pump.

Floodwater that* finds its way past the outer masonry leaf will pass into this retained height cavity that runs the perimeter of the building and the water will flow around the retained height cavity until it reaches the link drain when it transfers to the sump/pump, this means that no additional internal perimeter drains are required as the already installed retained height cavity acts as the perimeter collector.

Collection of the, floodwater from the retained height cavity stops any build up of water within the cavity itself which means that the insulation within the cavity is kept dry.

Collection of floodwater within the retained cavity also keeps the inner leaf of the cavity wall dry so there is no water damage to internal finishes.

Keeping the inner leaf of the cavity wall dry means that the building does not have to be dried out after a flood event, the drying out of a building after a flood can take up to a year and is a major cause of stress for the homeowner who is prevented from reoccupation during the lengthy period of drying.

In a flood event the floodwater will find its way under the building foundations and begin to rise under the concrete floor slab, using the retained height cavity as a collector will allow some of this water to enter the retained height cavity through the inner leaf of blocks below DPC for transfer to the link drain and sump/pump. My remaining floodwater then passes through joins in the floor slab or through the wall to floor join and will emerge inside the building onto the floors. The installation of a floor cavity membrane will collect this water ingress and transfer it into the sump/pump unit to keep internal floors and walls dry.

A single sumplpump unit is being used to collect water from three different sources, water entering the cavity from driving rain, floodwater that passes initial external resistance and groundwater that enters from below the floor slab.

The protection measures initially use resistance of the external masonry but once the water enters the building structure it is no longer resisted but instead it is collected and managed, the advantage of this is that no stress is placed on the building structure e.g. water pressure is not allowed to build up under the floor slab as this can cause cracks and slab failure instead the water is allowed to seep in around the floor perimeter and is then collected by the floor membrane before being pumped out The measures adopted cannot be seen by occupiers, there is no stigma attached to the property by visual flood resilience measures e.g. ceramic tiled internal wall fmishes.

The deployment of aperture guards to doorways and the combined set of measures as described above can protect against all routes of floodwater ingress including water ingress through internal walls and party walls.

The system is cost effective as using the retained height cavity as a perimeter collector saves the installation costs associated with internal perimeter floor drain collectors.

The system can be installed with a minimum of disruption for the homeowner as no re.

plastering is required.

The system can be installed at any time and the homeowner does not have to wait to install as part of reinstatement works after an actual flood event in order for the work to be cost effective.

The retained height cavity collection channel can be regularly maintained from outside the building, capped inspection points situated in the outer masonry leaf at building corners can be used at any time for inspection and drain rodding without disturbance of occupiers.

The system can be fitted to existing buildings with cavity walls or installed at very little additional cost to a new build property, also incorporating closed cell insulation fitted below the floor slab to meet latest building regulations.

As the combined measures collect water from all ingress routes i.e. walls, cavity, wall to floor join and cracks in floor slab the installation will be equally as effective if installed as a suite of measures to collect and dispose of ground gas, using a gas extraction pump fitted in the sump/pump unit.

Introduction, to drawings

An example of the invention will now be described by referring to the accompanying drawings: Figure 1 is a cross sectional drawing to show the invention as installed to a building with concrete strip foundations and external cavity walls.

Figure 2 is a cross sectional drawing to show the invention as installed to a building with a raft foundation and cavity walls.

Detaile desçjption Figure 1 is a cross section of a building with external cavity walls. The outer leaf of the cavity wall A is shown in brickwork and the inner leaf H is typically concrete or thermal blocks, both the leaves are built off a concrete foundation G. The inner leaf can also be built with common bricks or be timber framed, the flood protection measures described here will still function. The internal wall or party wall T is shown here as concrete blocks built on a concrete foundation U. The DPC of the cavity wall is shown as C and below DPC the cavity wall is typically built in concrete blocks with concrete cavity fill F to within three course of the DPC as required in building regulations. The cavity wall construction up to the three brickwork courses (225mm) below the DPC can also be in trench fill blocks or mass concrete fill either way it will not affect the measures described here. One of the functions of the cavity in a wall is to prevent water from reaching the inner leaf and in general any water that passes the outer leaf A will fall within the retained height cavity D to the concrete cavity fill F at three courses below the DPC where it can exit the cavity via weepholes which are small apertures left out in perps' (brickwork vertical joints) along the third brickwork course below DPC. The weepholes are recommended for installation every 900mm by Building Regulations 2000 Approved Document C -5.5. C. Rainwater passing down the wall cavity and into the retained height cavity would normally pass through these weepholes into soil E and they create a problem in a flood event as they allow floodwater to quickly enter the retained height cavity and flood the interior of the building. However, as part of this installation the weepholes are filled and any water that gets into the cavity e. g. from driving rain is collected in the retained height cavity 1) on top of the cavity fill F and then passes through the link drain N to the sump/pump unit V set into the building floor slab W. The pump P then removes the water to outside the building via the exit pipe R. The drawing shows the top surface of the cavity fill F angled towards the outer leaf A to deflect any water in the retained height cavity D to the weep holes in the outer skin and this is typical of existing construction details, in a new build installation the surface of the cavity fill F could be formed in the shape of a drain invert to help the flow of water around the retained height cavity as it moves towards the link drain N. Most rain water that passes through the outer leaf A and falls to the bottom of the retained height cavity D will seep through concrete F and concrete blocks of inner leaf below the DPC but any excess will flow around the retained height cavity to link drain N for passage to sump V. An alternative to filling of the weepholes is to fit automatic weepholes every 900mm that let water out of the retained height cavity but will not let floodwater from outside the outer leaf to enter the retained height cavity, the automatic weephole is a one way valve.

In the event of a flood the floodwater will be outside the building and against the outer leaf A, the level Z indicates the level of water represented by a flood 750mm or ten brickwork courses deep from level of floodwater Z to outside ground level E. A typical cavity wall as shown can structurally withstand this depth of floodwater. When floodwater is at level Z the water will start to seep through bricks and leak through any cracks between mortar and bricks, the most water ingress is always at the bottom of the wall three course below the DPC where the hydrostatic pressure is the greatest.

Floodwater that enters the wall cavity will pass down to area D which is the retained height cavity that is the section of wall cavity between the DPC and the external ground level where it will flow around the cavity on top of the cavity fill F until it passes through the link drain N into the swnp V for removal via pump P and exit pipe R. Continuous removal of floodwater that passes the resistance of the outer masonry leaf A will prevent any build up of water in the retained height cavity D and keep both the cavity insulation 13 and the inner leaf H dry. Keeping the insulation and inner leaf dry will allow immediate reoccupation of the dwelling after the floodwater has receded.

Dependent on materials used in building construction, foundation depth and soil type under the building the floodwater will, usually after about two or three hours, begin to fmd its way under the concrete floor slab, some of this water will pass through the inner leaf blocks below DPC and be collected by the retained height cavity, link drain and sumpipump for removal from the building. My remaining water will then begin to rise through the wall floor join and flood across the building floor. A floor cavity membrane M is laid onto the floor slab to collect this water ingress which then flows under the cavity membrane and into the sump V with lid S which is positioned within the floor slab W. The cavity membrane M will also collect water ingress through cracks in floor slab, construction joints in floor slab, through wall floor joins at internal and party walls. All water collected under M passes to sump V for removal from building via pump P and exit pipe R. Floor finish L is laid over membrane M and hollow skirting K is fitted between floor membrane M and wall plaster J. Dependent on rates of water ingress and the floor area of the building more than one swnp/pump unit may be required but each is available to perform any or all of three different functions i.e. to remove rainwater from the retained height cavity, remove floodwater from the retained height cavity and remove floodwater from under the floor cavity membrane.

Figure 2 is a cross sectional drawing to show the invention as installed to abuilding with a raft foundation and cavity wails. This form of construction could be used for new build on a flood plain. The simple reinforced raft foundation is commonly used for buildings on poor soils and has the advantage that a high quality concrete raft will resist the passage of water, the concrete raft X is shown with a toe beam to carry the external cavity wall.

The outer masonry leaf A sits on the raft toe beam and as in Fig us the initial resistance to the floodwater. The retained height cavity is formed by the outer leaf of the wall, the concrete toe beam at external ground level and the DPC level of the external wail C. The weepholes normally positioned in the retained height cavity are filled or automatic weepholes are installed. My water that gets into the retained height cavity will flow around the retained height cavity and then into link drain N for transfer to sump V and pump P and removal from building via exit pipe R. The waterproof properties of high quality concrete and the raft construction that eliminates the vulnerable wall to floor join should prevent any floodwater from entering onto the floors of the building, however it is always best to have a solution for any residual risk which may occur if aperture guards are not deployed, a power cut stops the pump or the floodwater reaches a very high level and must be let into the building for reasons of structural damage. The drawing therefore shows an optional cavity membrane system M and hollow skirting K that can collect and manage any water ingress onto the building floors, using the same sump V and pump P. If a flood risk assessment of the building indicates that the residual risk is minimal then the decision may be made to omit an internal cavity membrane that discharges into the sump and external location of the sump pump unit may be possible, with the water collected by the retained height cavity being passed to an external sump and pump unit.

Claims

Claims 1 A cavity wall below damp proof course and above external ground level to collect water ingress, the cavity being linked to a sump/pump unit.
2 A cavity wall according to claim 1, in which the wall has automatic weepholes.
3 A cavity wall according to preceding claims in which the sumpipump unit collects water ingress collected by a floor cavity membrane.
4 A cavity retained height cavity wall substantially as herein described above and illustrated in the accompanying drawings.