De-Water and Sub-Floors

Why is there water under my floor?

De-watering basements and sub floors

Surveys and reports

We cannot emphasize enough the importance of a having a technical survey carried out by an industry professional who is experienced, qualified and accredited in order to identify the root causes of the problem. The solution to standing water and associated issues such as dampness, decay and infestation in timber floors is rarely simple or a single source. We believe it makes sense to avoid costly mistakes of having works carried out which subsequently prove to be incorrect or inadequate simply because an accurate diagnosis has not been made at the outset. 

Our proprietor David Kerry BSc CSRT CSSW ICIOB is a degree qualified experienced quantity surveyor specialising in the remediation of damp and timber issues, qualified with the Property Care association to CSRT level.  David is also qualified with the Property Care association in structural waterproofing of underground structures (CSSW) such as basements and sub-floor voids. David is an incorporate member of the Chartered Institute of Building.  

Standing water under suspended ground floors is an all too common sight. Water may come and go depending on the seasons and amount of rainfall.

The source of water ingress could be any combination of the following:

  • Ground water due to high water table.
  • Water ingress due to falls of hard impermeable surfaces around the property incorrectly falling towards the house.
  • Defective rainwater gulleys and drains.
  • Water pipe leaks within the property.
  • Water leaks from local authority services outside the property.

 

Dry rot outbreak (image 1) with standing water in sub-floor void (image 2) exacerbating the problem. Dry rot found in right side top corner of the room shown in second image.

Suspended timber floors are commonly associated with older buildings and comprise generally of timber joists overlaid with floor boards with a space underneath the floor typically around 50cm deep but could be more or less.  

This form of floor construction allows for service runs under the floor such as electric cables and central heating water pipes.

In older properties the end bearings of timber joists are often sat on brickwork walls under the floor without a damp proof course to separate the joist end from damp brickwork. The joist end becomes damp and often starts to decay. Over time the decay and foot fall on the floor above leads to the floor dropping. In old terraced houses where the sub floor is most damp typically around the chimney breasts, the floor surface either side of the chimney breast is often seen to have dropped one or two centimetres which is usually due to decay in the joist ends.

Standing water in the sub floor leads to elevated levels of dampness in the walls and therefore, decay and infestation in the joist ends. Rots such as dry rot will spread faster over and through damp walls.

Also where there is a defective damp proof course the levels of dampness in the walls above the floor and the height to which damp travels above the floor will increase leading to unwanted problems such as unsightly damp stains, dilapidated plaster, spoiled decorations and powdery salt efflorescence.

In addition, standing water increases levels of humidity in the sub floor void with can diffuse through the floor structure. As timber is hygroscopic and vapour permeable this leads to increased levels of humidity in the rooms above and issues such as condensation and black mould occur especially in the winter months.

Standing water prevents access for services and repairs to cables and pipes.

At DRYabode we have various methods of dealing with standing water in sub floor voids. We treat the void and an underground structure similar to a basement.

Basement waterproofing is governed by British Standard BS8102 and our approach is waterproofing and de-watering sub-floor voids and other underground structures is the same.

David Kerry, our proprietor and surveyor holds the CSSW (Certified Surveyor in Structural Waterproofing) qualification having been trained and accredited by the Property Care Association (PCA). Dryabode Property Care are proud to be associated with the Property Care Association, the main governing body in the UK in this industry. 

 

Case studies

Case study 1

In this first example, our clients had been having problems with dry rot in the suspended timber floor of their home for years. In time of rainfall water entered and flooded the sub floor void causing increased levels of dampness in the timber floor and wall structure and flooding to a depth of approximately 75mm.

3

 

Invasive investigation of dry rot in sub floor void, timber joists and floor boards. Works are often complicated by presence of services such as electric cables.

 

 

 

Following a technical survey carried out by David, the root cause of water ingress and flooding was identified as coming from the following:

  • High water table and impermeable heavy clay sub soils.
  • Broken surface water gulley.
  • Broken surface and foul water drain.
  • Land drain from a neighbour’s property discharging ground water onto the land of our clients property near the building.
  • Patio at the rear of the property laid to incorrect falls directing surface water to the foundations.

 

2

 

Water ingress into sub-floor void caused by high water table, impermeable sub-soils and defective drainage. In this case the existing land drain has been installed by others many years ago at the incorrect height rendering it ineffective.

 

 

Having correctly identified the root causes, Dryabode produced a schedule of works and the project began. The main works which we considered critical to the success of the project were as follows:

 

  • The broken gulley and drain were repaired.
  • Path down the side of the house reduced in level to correct height below the damp proof course to comply with British standards.
  • New land drain scheme with silt traps installed around the house with the drain at the correct level back filled with correct drainage stone in compliance with BS8102.
  • Patio at the rear re-laid to falls away from the house incorporating a linear gully along the length of the patio.
  • Surface water drainage runs re-configured to provide a more efficient system.

The outcome has been successful with the sub floor void completely dry and the dry rot outbreak has been successfully addressed.

Case study 2 

During a damp proofing installation, we were asked to install a high quality real timber floor covering (engineered real timber laminate flooring). This type of flooring is sensitive to dampness and requires a dry, flat, level and stable substrate on which to be laid.

Prior to installation of the new timber flooring, David carried out a survey of the existing suspended timber floor. The hallway floor was found to be damp and out of level with excessive vertical movement (springy). David carried out some invasive investigation work, removing some floor boards and found the timber joists underneath to be wet and decayed. The end bearings had lost depth due to decay causing deformation of the floor surface.

There was approximately 10cm of standing water on the floor of the sub-floor void throughout the property which we considered was contributing to the damp and decay problem in the floor. In addition an incoming electrical supply main was submerged in the standing water causing some safety concerns.

David carried out some research with neighbours and found many properties in the area suffered similar problems.

1

 

Sump chamber and double pumps. This example is at the high end of the product range. Sump chamber is sub-floor voids are usually a lesser specification and lower cost.

 

 

 

DRYabode carried out the following works to deal with the problems we faced:

 

  • Installation of a sump chamber and automatic sump pump in the floor of the sub-floor void.
  • Removal of the existing floor joists and boards.
  • Installation of new pressure preservative treated joists with the bearings isolated from brickwork by wrapping the ends in plastic damp proof course.
  • Damp resistant tongue and groove floor boards with an access hatch providing maintenance access to the sump pump and chamber below.

 

We have now installed the high quality engineered beautiful timber laminate flooring successfully and our clients have the peace of mind that care has been taken in ensuring their new floor will provide many years of service. The damp proofing scheme has also been successful.