Why are specifications important for a roof to last?
With proper specification, the roof will be suited for the site. If it is particularly exposed or near an airport more fixings and better materials should be used to uphold against the increased wind. If an under spec roof was built in this area over time it would fail as fixings or covering could not withstand the prolonged forces.
What British standards and guidance are there for roofs?
BS 5534 - new build slated and tiles on pitched roofs
BS 5250 - code of practice for control of condensation in buildings, so proper ventilation to roof spaces to stop condensation
BS 8612 - dry fixed systems
BS 8000 - workmanship on construction sites, which covers the laying and fixing of tiles and slates
How do mortar fixings fail and cause water ingress?
Mortar has a limited lifespan and over time degrades with exposure and moisture. This then creates cracks allowing water ingress.
How does wind damage affect a roof?
Excessive wind can cause stress points where coverings may not be secured sufficiently and could lift tiles, it has a pulling affect on the roof. Even debris from surrounding trees could impact the roof and break the covering.
Why does improper fixings to covering cause defects to a roof?
If there are either not enough or not the correct type of fixing to coverings they are susceptible to wind damage as it will be easier to lift the covering. This could be to poor workmanship where they haven’t installed all fixings or poor specification of lesser strength systems installed in exposed areas.
How can you identify damp?
First visually check the area for discoloured decorations, depending on location you can discount rising damp if it is above 1.1m. You can use a protimeter to roughly determine how damp the area is.
Generally, if it is more random patches it may be penetrating and should investigate the surrounding area, if it is all throughout a room or property and just surface it is likely condensation (high relative humidity can help confirm this). And if it is rising damp, a carbide test can be carried out on low level brick to determine the cause.
What are the types of damp?
Rising damp, which comes from ground level to around the one metre marks due to capillary action. Often from failed or bridged DPC.
Penetrating damp, which is water infiltration from part of the building, often linked with other building defects such as cracked brickwork or failed roofs.
Condensation, when moisture in the air comes into contact with cold surfaces. Often linked with high moisture levels and lack of ventilation.
What are the limitations of a protimeter?
They are made for timber so testing on plaster will not provide accurate results but give a general idea of moisture content. A high level of salts in the wall can also impact the measurement, as it measures resistance different materials have different resistances so could give a damp reading when it is wet. But paired with good judgement and subsequent testing it is a good tool to help identify damp.
How do you carry out a carbide test and how can you determine what damp is present from the test results?
Drill into the area that is ‘damp’ ensuring you drill past the plaster, once you get to brick, collect 6g of dust. Mix with two scoops of calcium carbide in the test chamber and the gauge will give you a % of moisture.
If the brick dust has a high moisture reading, further investigation should be done to find the cause of the damp, you can look into the cavity to see if there is anything bridging or the surrounding area to ensure it is not penetrating.
If it is a low moisture reading it is likely that the damp patch may be condensation affecting the decorative finish and plaster and is not within the brick, then work for better ventilation or heating can follow depending on situation.
What is BRE digest 245?
It is Rising Damp in Walls, the diagnoses and treatment.
It gives an overview of what rising damp is, and guidance of diagnoses. Potential defects to look at for your case such as the different ways a DPC could be bridged (earth, rendering, floor).
Then information about how to carry out a carbide test properly and interpret results.
What are two types of wood rot?
Dry and wet rot.
Dry is found where moisture content is around 20% and is less common due to specific conditions required.
Wet rot is where there is higher moisture content between 30-50%.
How can you identify the different types of rot?
Wet rot has a dark appearance and may have black fungus growing, the timber will be spongy and soft. And a high moisture content.
Dry rot has a white/yellow whispy fungus growing, the timber will be brown in colour and a lower moisture content.
What problems does wood rot cause?
Either type eats away at the timber and that looses the strength of the material which will cause structural problems to where the timbers are in the building.
How can you treat wood rot?
Repair & Dry
Depending on the severity it can change, if caught early you can remove the moisture source and let it dry out. If not, you will need to likely remove the area and replace with new timber and protect the new and surrounding areas.
If it wasn’t caused from a leak for example and was due to inadequate ventilation further work should be done to ensure to does not happen again.
What are the limitations of a carbide test?
Calcium carbide reacts with any type of moisture in the sample, this could include hydroscopic salts which could indicate a higher reading, therefor to establish an accurate reading you should carry out salt analysis to the area as well and deduct the salts from the moisture result to obtain a more accurate result. However carbide tests are a much better indication than a protimeter.
What is carbonation?
It’s when alkaline elements in concrete react with carbon dioxide in the air creating calcium carbide which lowers the PH of the concrete, this lowers the passivity, which then if there is insufficient coverage to steel reinforcements carbon dioxide can react with the steel and it will start to corrode, expanding and cracking surrounding areas.
What is sulphate attack?
It’s a chemical reaction affecting concrete which causes it to expand and crack. Externally this can be from penetration of sulphates, such as water or internally gypsum or aggregates in the mix of concrete will react over time.
What are common defects to flat roofs?
Blistering, splitting or sagging of coverings, ponding, damage to flashings, solar decay, thermal movement splits and people or lose debris damage.
What is damp?
A building is considered damp when moisture can be seen visibly through staining or discolouration of finishes or causes mould growth, sulphate attack, frost damage or even drips and puddles.
What is a cold bridge?
Where materials with poor thermal insulators come into contact allowing a path for heat to ‘escape’.
What is / How would you identify condensation?
It’s when moisture in the air hits cold surfaces and condensates. The colder the air the less moisture it can hold. It often causes staining at cold bridges, peeling wallpaper and mould growth.
What are the causes of condensation?
Lack in insulation, ventilation, un-heated areas and excessive moisture in the air.
What are the remedies to condensation?
Reduce the moisture generation, provide adequate ventilation and heating and improve the insulation.
What could be causes of cracking in walls?
Subsidence, heave, settlement, thermal movement, lintel failure, wall tie failure, sulphate attack.
How would you identify wall tie failure?
You would generally see horizontal cracking at every 4-5 courses of brickwork and there could be bugling to the wall.
How would you identify sulphate attack?
The horizontal cracking could be every mortar course and could have some areas that are vertical going between mortar joints.
How would you tell the difference between lintel failure cracking or corrosion?
Lintel failure means the lintel is dropping and often creates a triangular cracking pattern above, where corrosion will expand the lintel and will crack at the corners diagonally, where it is lifting.
Why should you not use bleach products to clean black mould?
Bleach is formulated with chloride based products, continuously cleaning plaster with it can load it with chlorides which are hygroscopic, so during high relative humidity it can actually absorb more moisture and damp can occur.