Design Considerations
Tapered Insulation provides lots of flexibility in installation, regardless of insulation type the product is generally considered easy to handle and cut on site where necessary.
Options for the scheme configuration (the layout in plan view) are numerous. It could be said that there is no right or wrong layout, only the end result of positive drainage being the desired outcome… But consideration should be made to the theme of the tapered scheme!
This decision can be influenced by adjoining or abutment details, the use of the roof or the roofing contractor’s preference. The required U.Value and the distance of fall will also impact the decision on scheme configuration, often numerous scheme layouts need to be presented to fully consider the best option.
Design consideration & Impact of Scheme Design
There are several parameters to consider when designing a tapered insulation scheme that could have a significant impact on the rest of the build.
- Design Fall of Insulation
- Direction of Fall
- Quantity of drainage points
- Position and distance between drainage points
- Upstand Heights
- Intended use of Roof Area, i.e. a Terrace.
The table shows the variance in Insulation thickness, area of flat board zones and the heat loss at the minimum thickness of insulation (the flat gutter/ sump zones).
As you can see, there can be huge difference on each parameter compared to other design variations; some of which may be viable, others not.
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Falls:
1:60
Gutter Falls:
1:60
Min Thickness (mm):
50
Max Thickness (mm):
250
Heat Loss at Min thickness (W/m2K):
0.73
Area of gutter/sump (m2):
2.88
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SELECT A DESIGN TO SEE THE DIFFERENCES IN PERFORMANCE | |||||||||||
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Design | Fall | Gutter Falls | Min Thickness (mm) | Max Thickness (mm) | Heat Loss at Min Thickness (W/m2K) | Area of gutter/sump (m2) | Notes | ||||
1:60 | Flat | 170 | 230 | 0.19 | 23.1 | Short Fall Distance | |||||
1:40 | Flat | 150 | 240 | 0.19 | 23.1 | Short Fall Distance | |||||
1:60 | 1:60 | 50 | 250 | 0.73 | 2.88 | ||||||
1:40 | 1:40 | 30 | 330 | 0.73 | 2.88 | ||||||
1:60 | 1:80 | 60 | 230 | 0.4 | 2.88 | U Value achieved 0.11W/m2K | |||||
1:40 | 1:80 | 30 | 270 | 0.73 | 2.88 | ||||||
1:60 | Flat Sump | 130 | 270 | 0.24 | 2.88 | Mitred | |||||
1:40 | Flat Sump | 120 | 330 | 0.4 | 2.88 | Mitred | |||||
1:60 | Flat | 130 | 290 | 0.24 | 10.1 | Longer Fall Distance | |||||
1:40 | Flat | 90 | 330 | 0.35 | 10.1 | Longer Fall Distance |
Based upon the roof achieving 0.13 W/m2K (BSENISO6946:2017 Annex E)
150mm Medium density concrete deck
No void/fixed ceiling
PIR Insulation, suitable for adhered single ply/bitminous felt system
BS6229:2018 states U Value of 0.35W/m2K or better should be achieved by the minimum thickness of insulation. On the examples, where 0.35W/m2k is not achieved the minimum thickness of insulation will increase further
Summary |
Differences | |
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Thinnest Min Thickness | 30mm | |
Thickest Min Thickness | 170mm | 140mm |
Thinnest Max Thickness | 230mm | |
Thickest Max Thickness | 330mm | 100mm |
Smallest Area of Gutter | 2.88m2 | |
Largest Area of Gutter | 23.1m2 | 20.22m2 |
Worst heat loss at min thickness | 0.73W/m2K | |
Best heat loss at min thickness | 0.19W/m2K | 0.54W/m2k |
Oatking Resource Hub
Our resource hub contains useful product data and technical information for a wide range of insulation types, along with industry standards and guidance from roofing affiliates.
-
Falls:
1:60
Gutter Falls:
1:60
Min Thickness (mm):
50
Max Thickness (mm):
250
Heat Loss at Min thickness (W/m2K):
0.73
Area of gutter/sump (m2):
2.88
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- 3
- 4
- 5
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SELECT A DESIGN TO SEE THE DIFFERENCES IN PERFORMANCE | |||||||||||
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Design | Fall | Gutter Falls | Min Thickness (mm) | Max Thickness (mm) | Heat Loss at Min Thickness (W/m2K) | Area of gutter/sump (m2) | Notes | ||||
1:60 | Flat | 170 | 230 | 0.19 | 23.1 | Short Fall Distance | |||||
1:40 | Flat | 150 | 240 | 0.19 | 23.1 | Short Fall Distance | |||||
1:60 | 1:60 | 50 | 250 | 0.73 | 2.88 | ||||||
1:40 | 1:40 | 30 | 330 | 0.73 | 2.88 | ||||||
1:60 | 1:80 | 60 | 230 | 0.4 | 2.88 | U Value achieved 0.11W/m2K | |||||
1:40 | 1:80 | 30 | 270 | 0.73 | 2.88 | ||||||
1:60 | Flat Sump | 130 | 270 | 0.24 | 2.88 | Mitred | |||||
1:40 | Flat Sump | 120 | 330 | 0.4 | 2.88 | Mitred | |||||
1:60 | Flat | 130 | 290 | 0.24 | 10.1 | Longer Fall Distance | |||||
1:40 | Flat | 90 | 330 | 0.35 | 10.1 | Longer Fall Distance |