Building Defects Survey And Diagnosis Construction Essay

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Q1 - Explain the likely causes of the cracking and the movement within the external walls of the property as well as suggesting appropriate remedies.

After examining the cracking and movement on the exterior elevations of the property, it appears to be suffering from differential settlement on the rear elevation, and subsidence / differential movement on the side elevation.

The subsidence / differential movement on the side elevation of the property is shown by diagonal cracking this movement is widening the mortar beds horizontally.

The above could have been caused by seasonal movement, tree roots, poor workmanship during initial installation, broken drains or variable ground conditions to name a few.

Due to the limitations of the survey it would be virtually impossible to give a true diagnosis of the defect affecting the side elevation without undertaking a further investigation in the form of a trial pit for a more detailed inspection.

During the initial survey it was noted, that a rain water pipe was located on the corner of the rear elevation of the property that connects directly into the rain water gully otherwise known as a RWG.

This RWG could have been damaged by one of the reasons mentioned in one of the above paragraphs.

Any damage to this RWG would allow rainwater to leak from the RWG potentially causing subsidence / differential movement by washing the ground strata beneath the foundation away.

It is also thought that the differential settlement on the rear elevation of the property is directly linked to the damaged RWG as the ground strata supporting the foundations is being eroded away.

Another fault picked up in the survey was that the pointing had failed in several areas of the property allowing wind driven rain to enter the building potentially leading to cavity wall tie or lintel failure.

The property also appears to be bowing on the front & side elevations, this could have been caused by either the weight of the replacement concrete roofing tiles, lateral restraint issues, cavity wall tie failure or an insufficient amount of cavity wall ties installed during construction.

Remedial work

It is recommended that a reputable contractor be employed to run a CCTV drainage camera into the drain located by the damaged part of the property to see if there is any damage to the drain.

If the drain appears to be undamaged, then a trial pit will need to be excavated to determine the problem of underground movements at the rear and the western side of the property.

Once the trial pits are excavated and the level of damage to foundation and ground strata is determined, the contractor can then traditionally underpin the property.

Traditional underpinning is effectively a method of installing a foundation that is inadequate or where one doesn't exist.

The BRE states that, "Underpinning may be defined as the process of providing new permanent support beneath a structure without removing it, often so as to increase the capacity of the structure" (1991/P1)

The foundation is installed in sections, uninterrupted sections support the building until the newly installed reinforced concrete sections can take the load before moving onto to the next section of the foundation, this process reduces the vulnerability of the foundation during the remedial works.

It is recommended that a reputable contractor be employed, to remove the defective pointing from the property, and replace it with new pointing. This pointing is mixed with a water proofing additive, which ensures weather tightness is restored to the property.

As mentioned previously the property appears to bowing, it is recommended that a cavity wall inspection be undertaken to determine the condition and the number of installed cavity wall ties.

Once the inspection is complete the contractor can then install the replacement helical wall ties to the property, in accordance with the building regulations and manufactures guidelines.

After the helical wall ties have been installed the walls should then be strapped to floors using lateral restraint straps to ensure that no more movement takes places.

Q2 - Explain the cause of dampness evident around the windows and on the ceiling as well as suggesting appropriate remedies.

After viewing the interior of the property, it was evident that some of the rooms are suffering from a combination of condensation and dampness, this dampness is penetrating through the gaps between the property and the window jambs.

The reasons for damp penetrating through gaps between the property and the window jambs are as follows.

The mastic sealant that was installed around the window frames during the original installation, some 60 years ago, could have become perished over this period of time and failed.

This breakdown of the mastic sealant will allow wind driven rain to penetrate through the gaps between the frame and property into the interior window reveal. This could potentially lead to the window reveals becoming a cold surface which in turn could lead to surface condensation or more seriously interstitial condensation.

Another potential cause of the dampness could be with the age of the actual property itself as the property is some 60 years old. It is highly unlikely that any window jamb damp proof course, otherwise known as DPC was installed into the cavity wall during the original fitting of the windows.

If any window jamb DPC was installed during the original installation of the window frames then there is a possibility that they have failed over this period of time.

The BRE Good Repair Guide No8 states that, "Dampness at window reveals can indicate that window jamb dpcs are defective or absent" (1997/P2)

This window jamb DPC failure will allow damp to penetrate to the interior window reveal, potentially leading to the window reveal becoming a cold surface which in turn could lead to surface condition or more seriously interstitial condensation.

The patches of mold that are located on the ceiling are caused by condensation; condensation can form in a room given the right conditions some of the more common condition can be found below.

The lack of ventilation within the property stops it from breathing in a sense, high levels of humidity are generated from general household activities such as washing, cooking, bathing or even breathing.

This humid air remains trapped inside the property, with no means of natural or mechanical ventilation in the rooms the moist humid air will settle on any cold surfaces.

Cold surfaces can be created in a room, by not providing a sufficient amount of heat into the room or by only heating the room intermittently.

This situation can be exacerbated, by an absent or defective DPC in the window jambs or by no insulation on the internal window reveals. As well as poor quality mastic installation, during the original installation of the windows.

Remedial Work

It is recommended that reputable contractor be employed to install internal thermal insulation.

This internal insulation will provide an additional thermal barrier which will assist in keeping any heat generated locked within the room, and more importantly the property itself.

During the installation of the internal thermal insulation, the contractor will install additional insulation into the window reveals, this will insulation will stop condensation forming on the reveal.

It is also recommended that the contractor remove the perished mastic sealant from the window frames, and then reseal them with weather proof mastic, thus ensuring weather tightness between the frame and building.

Adequate levels of ventilation should be installed into the property, in order to allow the rooms breathe. As well as ensuring that there are a sufficient amount of air changes within the property.

The BRE Good Repair Guide No21 states that, "Buildings need ventilation to get rid of the water vapour generated in the home by washing, cooking and just plain breathing, in order to avoid condensation and consequent mould growth" (1998/P1)

Recommend that the owner / occupier runs the gas central heating system more often to raise the internal core temperature of the building, this increase in temperature will assist in protecting the property from condensation.

Q3 - Looking at the photo of the rear elevation with the man looking into the cavity. The ground level appears to have been raised and is almost level with the surface of the step.

What damp problems are likely, especially if there are mortar blockages near the ground floor? What remedies are required?

After viewing the rear elevation of the property it was evident that the property has a drilled chemical injection damp proof course otherwise known as a DPC.

However the tarmac finish in the backyard has reduced the distance between the DPC and the ground level, anything less than the required 150mm splash zone could result in the DPC being breached and potentially leading to rising damp.

Any surface water that pools either on the hard tarmac surface, or against the external wall of the property will over a period of time, cause the masonry brickwork to become saturated.

The above problem is exacerbated when rainwater splashes up beyond the DPC off the tarmac, or any remaining lodged water potentially causing further localised saturation of the masonry brickwork as well as increasing the potential risk of rising damp and frost attack.

Once the external masonry brickwork becomes saturated above the DPC, the moisture in the brickwork will travel upwards through capillary action.

As the moisture travels up through the brickwork, it will come into contact with the cavity wall ties. Cavity wall constructions can be bridged by many things such as mortar that has fallen onto the cavity wall ties, or any construction debris that might have fallen into the cavity during the construction of the property.

The BRE Good Repair Guide No5 states that, "in a cavity wall, the cavity could be bridged by a build-up of mortar droppings" (1997/P2)

Depending on the level of mortar droppings on the cavity wall ties and the amount of construction debris in the cavity, this will determine the amount of damp that will penetrate through to the internal wall and concrete floor of the property, as well as the level of potential damage.

Remedial work

In order to remedy this, it is recommended that a reputable groundwork contractor be employed to reduce the ground level in any areas around the property to the recommended distance of 150mm between the DPC and ground level.

It is also recommended that a reputable DPC contractor be employed to replace the existing DPC with a physical DPC membrane.

An additional recommendation would be to employ a reputable cavity wall contractor, to undertake a cavity wall survey, in order to ascertain level of mortar on the cavity wall ties as well as the amount of debris in the cavity.

Any mortar droppings or construction debris found during the survey will be removed eliminating the risk of bridging from the cavity.

Q4 - What may be the cause of the pyramid shape cracking above the front door?

The pyramid cracking above the front door of the property would generally indicate that the lintel has failed above the front door.

A possible reason for the failure of this lintel might have something to do with the age of the property itself. The property was constructed in the 1950's giving the lintel an age of around 60 years.

Depending on the construction and quality of the original installation, and also the environment that it has been subjected to, then any defective pointing will allow wind driven rain to enter the property. This may have caused the lintel to rot or weaken over this period of time.

It is also a possibility that over the past 60 years, the property may have moved through settlement, this could potentially cause the lintel to fail, which in turn would cause the outer leaf of the property to drop.

It was also noted that the roof of the property is covered with concrete roofing tiles; these tiles add a considerable amount of extra weight and load for the property to withstand. This increase in weight and load could also cause other issues such as lintel failure.

Remedial work

In order to remedy this it recommended that a reputable building contractor be employed to replace the defective lintel above the front door.

The building contractor will install two strong boy acro props above the damaged lintel. These strong boy acro props will support the inner and outer walls of the property allowing the building contactor to remove the defective brickwork and lintel.

As soon as these components have been removed, the replacement catnic steel lintel and exterior brickwork can be installed a long with the slate packers.

Once the brickwork has set, the strong boy acro props can be removed allowing the remaining brickwork to be repaired and pointed. After this has been completed the exterior wall will be completely weather proof.

For further information on lintel replacement please refer to the BRE good building guide issue No1 Repairing or replacing lintels.

Q5 - Looking at the rear elevation showing the chimney stack. Why is dampness likely to get into the roof space?

As the chimney stack is positioned on the ridge of the roof it will normally require two bossed front aprons and two side flashings. These ensure that the chimney stack and house connection are weather tight.

After viewing the chimney stack from the rear elevation of the property, there appears to be a front apron and two side flashings and missing from the chimney stack. These missing pieces of flashing are allowing rain to enter the roof freely via the spaces between the roofing tiles and the chimney stack.

If left over a period of time this rain will cause the chimney breast, ceiling joists, plaster boards as well as any services located in the area will become damp or even saturated causing a host of potential other issues.

Remedial work

It is recommended that a reputable specialist roofing contractor be employed to install the missing bossed front apron and two side flashings.

During the installation of these new pieces of flashing, the existing bossed front apron and side flashings located on the front elevation of the chimney stack should be examined for any damage and replaced where required.

Once the missing front apron and two side flashings have been installed, and the existing front apron and side flashings have been inspected, and/or repaired if required. Then these remedial actions will stop any rain entering the roof via the spaces between the roofing tiles and the chimney stack.