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14 Building Pathology > Level 2 > Flashcards

Level 2 Flashcards

1
Q

Describe Sydenham school

A

Two-storey 1905 original school, extensively refurbished 5 years ago. Solid brick wall construction with pitched slate roof and flat inverted roofs.

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2
Q

What is a hipped roof?

A

Usually rectangular, has four sloping sides with no gable ends. All four sides of the hip slant downwards towards the wall at a consistent angle.

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3
Q

Are there any variations to a Hipped Roof?

A

1) Mansard Roof.
2) Dutch Gable Roof
3) Half-hip Roof.
4) Pyramid Hip Roof
5) Cross-hip roof

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4
Q

Advantages of a hip roof?

A

1) Self bracing v gable= more resistant to wind damage.
2) Aethetic and more live space.
3) Energy efficient (cool in summer) & weather protection.
4) Reliable drainage (on simpler designs).

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5
Q

Disadvantaged of hip roofs?

A

1) Less room than gable roof + Costlier.
2) Harder to ventilate.
3) More difficult to maintain.
4) No gable window/less natural light.

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6
Q

Typical defects to hip roofs?

A

1) Valley gutters can be more subsceptible to leaks. Replace lead flashing.
2) Must be specific pitch- to prevent wind uplift.
3) Poor ventilation- hip/ridge ventilation or vent fans.

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7
Q

What is the lifespan of a hip roof?

A

50 years (if well maintained)

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8
Q

Is there a British Standard for minimum roof pitch?

A

Originally BS 5534 (2014) however more recently and because BS 5534 stipulated that mortar cannot be the only means of fixing slates or tiles, BS 8612 (2018) was introduced for dry-fixed, hip and verge systems.

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9
Q

What is BS 5534?

A

Code of practice for installing slates and tiles to new-build pitched roofs and vertical cladding.

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10
Q

Is following British Standards a legal requirement?

A

Isn’t required by law, but its inclusion in a specification can be upheld in court if necessary and following its guidance aids compliance with building regulations.

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11
Q

What is a MEWP?

A

Mobile elevating work platforms (MEWPs)

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12
Q

What is the licence available?

A

Powered Access Licence (PAL)

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13
Q

How did you ensure a MEWP was safe to use?

A

Operators should have attended a recognised operator training course and received a certificate, card or ‘licence’, listing the categories of MEWP the bearer is trained to operate. The expiry date of the training licence or card should be checked.

Risk Assessment should be in place, and include things like weather conditions, ground conditions and harnessing.

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14
Q

What are the main hazards of MEWP’s

A

Entrapment, Overturning, Falling or Collision

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15
Q

What type of gutters were they?

A

They were aluminium gutters, a number were blocked

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16
Q

What are slipped slates?

A

When a slate has detached from the roof.

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17
Q

What causes slated to slip?

A 
Nail sickness (corrosion of nail), 
Decay of supporting timber battens/pegs) caused by rot or woodworm. Other defects include physical damage, poor quality slates that delaminate or poor workmanship. "
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18
Q

How long should slate last?

A

100 years.

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19
Q

What safety should you ensure when replacing roof slates?

A

Scaffolding or suitable tower.

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20
Q

What are the dangers of slipped slates?

A

Allow water penetration, risk of accident or blocking rainwater goods.

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21
Q

Is there a British Standard for Slating?

A

BS 5534 - Slating & Tiling of pitched roof

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22
Q

How do you remediate slipped slates?

A

Resecure with copper wire/lead tingles. If many tiles are defective, it may be nearing end of design life.

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23
Q

How long does synthetic slate last?

A

40 years

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24
Q

What is the purpose of chimney cowls?

A

“1) To improve draw (flue systems with weak draw can have rotating chimney cowl).

2) Anti-downdraught- CO is dangerous.
3) Animal-proofing
4) Weather-proofing- rain and snow”

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25
Q

What is buddleia and why is it a problem?

A

Large oval leaves with flowers that range from crimon to white (usually purple). Problem because extensive fibrous roots and seeds spread easily can cause structural instability. For large growths it is recommended to inject herbicide into stem and for smaller, then mechanical removal of plant and root.

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26
Q

How would the buddleia effect the chimney cowls if left to grow?

A

The plant could have grown further dislodging the chimney stack bricks, causing a blockage and effecting the ability of the cowl to draw air.

27
Q

What are Year 1 maintenance works?

A

Building elements considered poor and require remedial works.

28
Q

How did your findings assist with the clients Year 1 maintenance works?

A

It helped them identify building elements that require short term action, the client could then formulate a Specification or Schedule of Work.

29
Q

Describe the building (Whitehorse Lane, Selhurst)?

A

Typical mid-terrace 1990’s new build construction, cavity walls, pitched roof, two storey.

30
Q

What floor was the rear bedroom in the property?

A

It was the first floor bedroom to the rear of the property.

31
Q

What other areas did you look at for possible causes of the bad smell?

A

I took an initial work around the whole property to identify where the smell was the strongest. I had manhole keys so checked the external manhole, I also checked the bathrooms and toilets/sink. I also considered gas & smoke but located the source of the smell to the rear first floor bedroom. I also checked for mold and whether the owners had any pets.

32
Q

Why did the end-user have a professional clean before the inspection?

A

I requested a professional clean to be undertaken to elimate or reduce household smells such as pets.

33
Q

Who carried out the borescope inspection?

A

I instructed a Contractor who regularly dealt with borescope investigations on our behalf.

34
Q

How did you know it was a cavity wall?

A

The age of the property was a good indication, this was further confirmed by stretcher bond and weep holes. If I was uncertain I could measure the thickness.

35
Q

How thick is a solid wall compared to a cavity wall?

A

“Measured at a door/window.
A solid wall will be 23cm thick plus internal plastering and external rendering (if any)
Cavity wall 30cm plus plastering and rendering (if any).”

36
Q

What is the material used for cavity wall ties?

A

Modern=stainless steel, older properties galvanised steel and originally cast iron. CORROSION/FAILURE!

37
Q

How does cavity wall ties allow moisture to drop down into the cavity?

A

They have a drip detail in the middle, which accumulates water and drops into the cavity.

38
Q

What is the purpose of an insulation retaining clip?

A

Installed to the wall ties, 75mm disk that holds insulation back to the structure.

39
Q

Insulation placement in a cavity wall?

A

When different insulation types are specified (mineral wool/polysterene board), the least resistant to passage of water should be on the outer skin. Stops condensation forming.

40
Q

What could cause moisture to enter the inner leaf?

A

If mortar droppings build up on wall ties, it could bridge across water.

41
Q

What could occur if you render the outer leaf of a cavity wall? And how can you prevent this.

A

Render in two section, the first section above the DPC layer by installing a render bead. Otherwise you could have a bridging effect.

42
Q

What is the purpose of cavity walls?

A

Prevents water reaching the internal skin

Improves thermal efficiency - air is a good insulator and addition of cavity wall insulation improves this further

43
Q

Talk me through a cavity wall construction?

A

Outer leaf (i.e. facing bricks)
Cavity
Insulation board
Inner leaf (i.e. aerated blocks)
Wall ties
DPC (on each leaf, 150mm minimum from ground level)
Backfill (weak concrete mix below ground)

44
Q

Why would you backfill a cavity?

A

Prevents the inner and outer leaf being squeezed together when trenches are backfilled
Must stay well below DPC level and be struck away from the internal leaf so water falls to the outer leaf

45
Q

What are the main advantages of cavity walls?

A

1) Penetrating Damp- prevents moisture transferring from outer skin to inner skin. Water run down the inner surface of outer skin and collects in the cavity tray.
2) Insulation- better thermal performance than traditional (partial or filled).
3) Vapour Barrier- Positioned on warm side of the cavity insulation (insulation/inner masonry skin)- prevents warm moist air from penetrating to its dew point.

46
Q

What does U-Value in walls measure?

A

Thermal conductance.

47
Q

What tare the typical U Values for:

Solid Walls v Cavity Wall v Cavity Walls (No insulation)

A

Solid brick wall 2.0 W/m2K.
Cavity wall with no insulation 1.5 W/m2K.
Insulated cavity wall 0.3 W/m2K or less.

48
Q

What Building Regulation Approved Document sets out fabric standard for cavity walls?

A

Approved Document L- Conservation of fuel and power.

49
Q

What are the typical dimensions of a cavity wall?

A

102.5mm OS, 100mm cavity and 100mm internal skin plus plasterboard.

50
Q

Are you aware of any cavity wall defects?

A

Damp Penetration- Faulty DPC/ Bridging- ties coated with mortar/ unattached insulation. Poor weathering details such as coping, window cills.

Interstitial Condensation- Cold air

Wall tie failure- untied, or incorrect setting out or corrosion (horizontal cracks caused by expansion of rust).

51
Q

What is interstitial Condensation

A

Moisture heavy air disperses within a vapour-permeable materialsuch as cavity wall insulation. If this material is warm on one side and cold on the other side the moisture vapour will condense and deposit its liquid state within the material

52
Q

What is the standard wall tie spacing?

A

Spaced horizontally by 900mm and vertically by 450mm. - 300mm away from windows/ openings

53
Q

What is the minimum cavity in a cavity wall?

A

50mm (Approved Document C).

54
Q

According to BRE, what buildings are at risk of cavity wall tie failure?

A

Building cavity ties built before 1981, when the standards on cavity wall ties increased. Also, until 1970s wall ties were a twisted butterfly type

55
Q

What factors will affect wall tie corrosion?

A 
Humidity (interstitial condensation)
Rain fall (penetrating damp)
Chlorides
Sulphar dioxide
Changes in PH (carbonation, carbonic acid)
56
Q

What equipment would you use to detect the location of wall ties?

A

Wall tie detectors - hand held metal detectors

Borescope (to see within the cavity)

57
Q

What are the symptoms of cavity wall tie failure?

A

Bowed or cracked brickwork
Cracking that follows lines of wall ties (every 450mm horizontally)
Random bulges
Rust staining

58
Q

How can wall tie failure be rectified?

A

Resin/grouted - pre-drilled holes are filled with resin before new ties are pushed in, then more resin injected through the tie to fill around the end in the inner leaf (not suitable for porous masonry)

Mechanical - features a sleeve that expands when the tie is screwed up (only suitable when masonry is in a good condition)

Helical - long corkscrew with a wide thread is drilled trough both leaves

59
Q

What guidance is available for replacing cavity wall ties?

A

BRE 329 (Inserting Wall Ties in Existing Construction) contains further remedial guidance

60
Q

What was the deceased animal?

A

A house mouse (Light brown fur with lighter belly)

61
Q

What was the making good and how was it instructed?

A

I was not appointed to develop the works, only diagnose the defect. If I were to, I would first carry out further investigations such as Pest Control, and ensure that all possible routes of entry are sealed. I would then take down plasterboard wall, and remove any affected insulation and allow to replace.

62
Q

How did the rodent get in the cavity?

A

Few possible such as underneath foundations, drainage, air bricks. But most likely a redundant service penetration that had not been suitably sealed.

63
Q

What were the other possible causes for the smell that could have been a result?

A

1) Superficial substance on or beneath a surface.
2) Drainage- pipework connectings or venting to the soil pipe.
3) Fungal rot timber flooring/skirting (wet/dry rot)

14 Building Pathology (5 decks)

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