DSJ - SoE - Building Pathology Flashcards
For your survey in Nannerch, detail the cause and mechanics of failure to the floor
The cracking and large hump in the floor suggested the concrete slab had expanded, which I suspected was due to Sulphate Attack. Chemical reaction between Sulphates and Tri Calcium Aluminate (contained within cement) in the presence of water and causes expansion and cracking. Potentially contamination to hardcore from old gypsum plaster or furnace waste. Lack of DPM in the floor slab, allowing sulphates and Tri Calcium aluminate to react in a solution. Expansion of the floor - base of walls fairly sturdy forcing slab upwards.
What is a Thermo-hygrometer?
The thermo hygrometer measures both humidity of the air and temperature of the air, which allows for calculation of the dew point - less than 10C
What is Dew Point?
The dew point is the temperature to which air must be cooled to become saturated with water vapor. When cooled further, the airborne water vapor will condense to form liquid water. When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface.
How do you calculate Dew Point?
Generally calculated within the Hygrometer’s software.
Td = T - ((100 - RH)/5.) where Td is dew point temperature (in degrees Celsius), T is observed temperature (in degrees Celsius), and RH is relative humidity (in percent). Apparently this relationship is fairly accurate for relative humidity values above 50%.
What is RH?
Relative humidity (RH) is defined as the actual amount of water vapor present in air expressed as a precent of the maximum quantity of water that that same air could hold at a given temperature.
What is roof spread?
When walls are pushed out of vertical at eaves height .
What caused the roof spread in Tarvin?
There are a number of potential causes:
Poorly triangulated roofs or heavy roof coverings cause rafter feet to spread and push out the top of the wall.
What remedies are available for roof spread?
Hip ties
Ridge beam or stronger purlins
Tie bars
During your survey in Liverpool, what defects did you find?
Structural movement in the walls - Buddlea growth
Buddleia can cause structural damage if it gets a foothold in the smallest cracks and crevices of buildings. The roots of the Buddleia plant have the strength to force buildings apart - leading to damp.
Decay to purlin
Leak around rear chimney stack - loose flashing
Part of the chimney breast had been removed
What advice did you give in your Liverpool Building Survey Report?
I recommended replacement of the decaying section of the of purlin and secure to the remaining section of the purlin using a scarf joint / repair plate.
Either, rebuild chimney breast, support using gallows brackets or remove stack altogether.
Specialist to poison the buddleia. Mechanical removal may lead to further damage. Then undertake brickwork repairs.
Renew lead flashings around the chimney
What is a Scarf joint?
A scarf joint is a method of joining two members end to end in woodworking or metalworking.
Scarf joints are commonly used where the ends of timbers have decayed, for example in a damp exterior wall. This approach, which enables the decayed timber to be cut out and replaced with sound material, depends on careful joint detailing for its structural integrity. Scarfe joints are usually fixed using stainless steel bolts or screws with traditional wedges or adhesives used between each timber surface.
Height of the timber x 3 = the joint length
Interlocking scarf joints, such as a hooked, keyed, and nibbed scarves, offer varying degrees of tensile and compressive strength, though most still depend on mechanical fastening to keep the joint closed (e.g. reinforced with fish plates and through bolts).
What code of lead did you suggest for the flashing replacement in your Liverpool Building Survey?
Code 4. 25 mm turn in, secured with clips or wedges @ 450mm centres. 75mm upstand. 150mm overlap onto slates. Should terminate on the slate not a joint. Min 100mm overlap between sheets.
What do you think caused the bulging to the walls to the Knutsford terraced properties and what did you recommend?
Lack of lateral restraint to the walls at mid height. I suggested installing a series of steel straps into the wall secured by at least three joists and casting L section of the steel strap into a pocket formed in the wall. Install noggins into gap between the joist and wall.
Strap 5mm thick, 30mm wide and the length variable - typically 1200mm to 1800mm.
Structural engineer to design tie bars. Outside my area of competence.
With the Liverpool survey, how did you know it was Bedlea?
The leaves of a buddleia plant are dark green with serrated edges. If you look closely, you will find very fine hairs on the underside of leaves and the stem. The flower heads of mature buddleia plants grow in long tapered clusters, typically purple or violet in colour.
With your survey in Macclesfield, what made you consider condensation?
Decay to centre of joists and not to the bearing ends
