SST_1807 – Creating And Managing Details

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For any construction project, details are an important part of the drawing set. It can take a long time to fully detail a project, so let’s look at how to draw a detail and some strategies for speeding up the drawings. We will look at importing details, applying the principles of detailing, creating details, creating multi-use details, and using details from your library.

Contents

 

Beginner Topics

Principles of Detailing – 4 D’s of Detailing

Deflection

Deflection, as its name implies, is where you prevent the water from entering a building by deflecting it. This can be accomplished by having roof overhangs, overlapping materials, or flashings (flashings, which are typically made of metal, help the water to deflect over other components).

You might be able to deflect water from a building by having a roof overhang. In the image below, you can see how much of the building is protected from the rain because of the roof overhang.

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You might be able to deflect water away from the building because the components overlap each other. In the image below, you can see how the cladding is deflecting water away from the foundation.

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A classic type of deflection is a flashing. These are essential for deflecting water away from a building.

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Drainage

If there is a chance of the water getting behind the cladding, drainage will allow the water out. Some cladding systems are specifically designed with the assumption that water will penetrate the cladding but will drain out of the wall assembly.

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Brick cladding often has small gaps or openings that allow some moisture through. Bricks are also permeable and can allow a small amount of moisture through in severe weather. Brick cladding systems are therefore designed specifically to allow the water to drain out through openings at the bottom (open vertical joints in the brickwork).

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Drying

Some wall assemblies are designed to allow airflow through the cavity to improve drying. Some systems, such as brick cladding, are designed based on how the sun and wind will dry the exterior skin of the brick.

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Durability

In terms of hierarchy, durability is the last stage. If the cladding system is such that deflection is not possible, drainage is not suitable, and drying is not available, then the product must be durable enough to withstand being occasionally wet.

Durability is an important lesson learned from leaks in buildings. The materials used in timber buildings cannot withstand being wet occasionally; the wood begins to rot.

The products that you use in your detailing must be durable. This might mean that you will need to check your timber treatment or that you might need to check the type of metal that you want to use.

 

Principles of Detailing – 5 Physics Principles

Gravity

Water ingress due to gravity occurs when the water moving down the face of the building finds a sloping path that allows the water into the building. This usually occurs because of the lack of a deflection device such as a flashing.

In the image below, you can see the water running down the face of the building. Because there is no flashing, the water continues to run down until it reaches the window joinery. At this point, it can find its way into the building and cause damage.

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The solution is to ensure that materials are correctly lapped and that flashings are correctly installed. Correctly installed deflecting devices such as roof eaves, water barriers, and flashings will prevent this. This image shows the same window joinery being protected from the water by a flashing (which causes the water to drain away).

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Pressure Differential

The pressure differential is the difference in air pressure between the inside and outside of the building. If the pressure on the outside of the building is higher than the pressure on the inside of the building, then this pressure differential can drive water up and into the building. This can occur even when there are very small gaps in the building cladding.

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The solution is to provide air seals, a wind barrier, or pressure equalization. In this case (window detail), the typical solution is an air seal.

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Kinetic Energy

Kinetic energy refers to the energy of wind-driven rain. The wind can drive rain a considerable distance into openings and even up roofs. A classic problem with wind-driven rain is when rain travels up a roof slope and into a building.

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In this image (0017), you can even see that rain is being driven up under a flashing and into the building. The flashing deflects falling water away from the building, but the wind can still blow the water up the trough of the roof and under the flashing. In this case, the flashing will help protect the junction from the wind, but not completely.

The solution for this particular problem is to use a stop-end on the roofing.

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Surface Tension

Surface tension is similar to capillary action. It occurs where the surface tension of water allows it to move horizontally on the underside of services. This often occurs in situations such as roof soffits, the underside of a window sill, or any surface of a building that changes from a vertical edge to a flat underside.

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To solve this problem, make sure that you have a break in the horizontal surface. This is often called a drip edge. The water will find it impossible to travel vertically upwards, so the drip edge will cause the water to fall away.

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Capillary Action

Capillary action is caused by water tension that allows water to pull itself upwards through small gaps in the building. Gaps less than 6mm wide are susceptible to capillary action.

In the image below, two areas have been highlighted as being susceptible to capillary action. On the weatherboards, capillary action can allow the water to travel upward where the boards are close together but not forming a sealed joint.

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In the second area, capillary action can allow the water to be drawn across the top of the window and inside the building.

The solution to capillary action is to ensure that your gaps are wider than 6mm. In many cases, an air gap will solve the problem, as shown in the image below. For the weatherboards, two overlapping gaps will prevent any capillary action. In the window detail, you’ll notice that there are gaps at the head of the window and a corresponding gap on the window joinery. The combination of these two gaps creates an area that is more than 6mm, thus preventing capillary action.

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Here is a summary of the ways in which water ingress can be controlled:

Water ingress caused by: Solution
Gravity Deflection

Overhangs

Sloped surfaces

Flashings

Drip edges

Cavity construction

Capillary Action Clearance between surfaces

Gaps

Weather grooves

Drip edges

Surface Tension Weather grooves

Drip edges

Rebates

Kinetic Energy Flashings

Facings

Seals and sealants

Deflection

Pressure Differential Air seals

Pressure equalization

Wind barrier

Air barrier

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