This document provides guidelines for securing pitched roofs in coastal areas prone to cyclones and flooding. It recommends using hipped roofs instead of gable roofs to reduce wind uplift. Roofs should have a pitch of 30-40 degrees and overhangs less than 2 feet 6 inches. Roof elements like rafters and sheets should be securely connected to the building structure using metal straps and bolts. Regular maintenance is needed to replace weakened members and tightly secure roofing materials that can uplift during strong winds.

1. An assignment on
Pitch roof for
coastal area

2. The basic principles should be followed to protect the pitched roofs
against uplift:
Aerodynamic roof form:
• Roof pitch 30º- 40° to reduce effects of suction and uplift.
• Hipped instead of gable roof. If gable, then ends tied down firmly to rest of
structure. Lean-to should be avoided.
• Overhang <2’ -6” , vents in roof and masonry parapet.
• RCC roof provides superior protection, but heavy in earthquake. Need for
adequately braced vertical structure.
Roof connected to structure:
• Rafters at recommended spacing.
• Cross-bracing in plane of roof and ceiling, and also for openings, if any.
Openings restricted in size.
• Strong connections between roof and vertical structure. Metal straps,
bolts with washers on both ends instead of simple nails.
Well-fixed roof covering:
• CI sheet screwed at every corrugation. Tiles fastened individually.
• Use of J-hook bolts and threaded/ twisted roofing nails.
Pitched roof is very common in Bangladesh. Specially in the rural area.
But our country is located in the humid tropics between the Himalayas in
the north and the Bay of Bengal in the south. This geographical position
provides this region with life-giving monsoons, but also exposes it to
catastrophic natural calamities like floods, cyclones, and tidal surge. For that
reason the traditional pitched roof is hampered .
That’s why we need to know the method to secure pitched roofs.

3. Every sheet to be fixed to purlins with hook bolts or twisted nails at each
corrugation. More frequent fixings at edges to prevent uplift.
Adequate connections should be made with nylon rope or good quality
galvanized wire (instead of jute rope).
Roofing elements should be connected properly: purlin to rafter, rafter to
wall plate, wall plate to posts.
Even though more expensive than lean-to (akchala) and gable (dochala)
roofing, hipped roofing (chouchala) is more resistant to wind and protects
gable end walls from exposure to rain and water penetration.
Fig. Basic features of wind-resistant roofing

4. Hipped roof
This is the strongest type with all sides of the roof sloped. There are no
gable ends in this roof. Instead, rafters come across diagonally from the
corner and meet the ridge board a short distance from the ends of the
house. These are the hip rafters. Other shorter rafters go from the wall
plate to the hip rafter and are called jack rafters. After the ridge is firmly in
position, the rafters are attached to fit neatly onto the wall plate.
As the corners and the roof edges are zones of higher local wind suctions and
the connections of cladding/sheeting to the truss need to be designed for the
increased forces.

5. Overhangs, patios and verandahs experience high wind pressures and
should be kept short and small
• Avoid large overhangs as high wind force build up under them.
• Overhangs should not be more than 18 inches at verges or eaves.
• Build verandah and patio roofs as separate structures rather than extensions of
the main building.
• They may blow off without damaging the rest of the house.
Restrict unsupported eaves overhangs to not more than 800mm from the
wall and do not notch rafters over walls by more than one-quarter of the
rafters depth.

6. Securing the Ridge
• If the rafters are not
secure, the ridge can fall
apart when strong wind
passes over the roof.
The ridge can be secured by
using:-
(i) COLLAR TIES - Timbers
connecting the rafters. Nail them
to the side of the rafters.
(ii) GUSSETS - Usually made of
steel/plywood. This is used at the
ridge.
(iii)METAL STRAPS over the top
of the rafters.
Nowadays people use metal roof structure. MS or GI roof
structure can be made typically with 1½ inch x 1½ inch x /8
inch section. It is advisable to make trusses for better strength,

7. Rainwater Gutter
• Rainwater gutters prevent creation of furrows around plinth by rain
falling down from roof eaves.
• They also prevent rainwater splashing on walls.
• Arsenic-free rainwater can be collected for household use by keeping
a container where the water drains down.
• 4 inch diameter PVC (polyvinyl chloride, i.e. plastic) pipe can be cut
into half lengthwise using a saw.
• MS (mild steel) flat bar brackets can be screwed to rafters or wall
plate to hold gutter.
• If brackets prove too difficult or expensive to make, GI (galvanized
iron) wire or nylon rope can also be used for attaching gutter.
Fig. PVC pipe rainwater gutter detail and house being built with a gutter
Regular maintenance:
• Should make regular checks, especially around ridge and corners.
• Should replace weakened members, repair loose members.
• CI sheet should be tied strongly to structural frame to resist uplift by
strong wind. To further increase wind-resistance, number of purlins
should be increased near eaves, ridge and corners.

8. References:
1. Building construction- Sushil Kumar
2. Building construction- dr. B. C. Punmia, Ashok & Arun
kumar Jain
3. https://www.sheltercluster.org/sites/default/files/doc
s/Cyclone-resistant-housing-BRE.pdf
4. http://climatecolab.org/plans/-
/plans/contestId/1301502/planId/1320001
5. http://www.unisdr.org/files/11711_CycloneArchitectu
re1.pdf
6. http://www.sheltercentre.org/sites/default/files/Battli
ng%20the%20Storm.pdf
7. http://www.adpc.net/igo/category/ID189/doc/2013-
p74Wob-ADPC-handbook_complete-b.pdf