Nothing is impossible!
How to build on a slope in French Polynesia
Slopes are an integral part of the Polynesian landscape. Living on
offers a number of advantages, including peace and quiet, unobstructed views
freshness and lush greenery. These plots of land, often on slopes
are becoming increasingly popular.
But what do you need to know before building on a sloping plot?
Three important steps are recommended before building
First step: the topographical survey
To obtain this, you need to call in a topographical surveyor.
This survey describes the exact shape of the land and provides information on the percentage of
slope, i.e. the ratio of the height between two points on
the horizontal. (slope 10%=10cm/100cm)
The topographical survey is used to determine the best possible location
construction.
Second stage: the geotechnical study
This provides a better understanding of the terrain. For example, to determine
whether it’s in an area at risk of movement. Or to detect
cavities. It also enables us to determine the nature of the foundation soil, on the surface
and at depth, according to the tests previously chosen with the structural design office,
to determine the foundation method.
The geotechnical study must comply with standard NF P 94 500. Which ensures that
calculations and justifications concerning settlement and bearing capacity
in the vicinity of foundations are respected.
These are not recommendations, but justifications to be found
in the reports. Beware of the types of tests recommended!
In mainland France, a G2-AVP/PRO report has been the minimum required
since the ELAN law was introduced, and it’s up to the seller to provide it, since it provides information
on the quality of the soil being sold. After all, the cost to the buyer is not the same depending
on the quality of the soil.
In Polynesia, there is as yet no law on this subject, and some professionals
think it would be useful to pass one to protect those involved in
the construction industry.
Normative recommendations remain recommendations: you have to adapt
to the terrain, so each project requires a recommendation, and discussions
with the various technicians (in particular the structural engineer and the geotechnician).
The third stage involves the expertise of the structural design office and the architect.
Together, they will design the best possible framework to
suit the terrain and optimize construction costs.
The last two steps are crucial.
And these studies, carried out by professionals, can significantly reduce the cost of insurance.
Choosing the contractor.
Once you’ve completed these three steps, it’s time to choose a contractor, a decision not to
be taken lightly. The price of construction per square metre should not be the
only criterion for selecting a builder. Above all, be sure of his credibility,
reliability and experience.
They should have a good reputation, and preferably have been working in the area
for a long time. If possible, ask for references or to visit homes he
has designed. Ask about his company. It’s imperative that the builder
has already worked in the mountains: these sites require more
knowledge and practice than flat terrain.
These recommendations may seem obvious, but we
still hear unfortunate stories of people who put their trust in us and
whose homes were never finished.
Sometimes there are numerous defects that
can put them at risk.
And what should have been a lifelong dream becomes a
nightmare. So take your time and choose the right one.
Once you’ve chosen your contractor, it’s time for construction. Here
again, there are several options open to you. It all depends on your budget and
your commitment to the environment.
The different building methods for a sloping site.
To limit additional costs, it’s advisable to adapt the house as much as possible
to the terrain, and not the other way around.
Design offices recommend the construction method best suited
to the nature of the terrain.
The first is semi-buried or recessed construction.
This allows earthworks to be carried out using a single platform, and integrates the construction
directly into the ground. The advantage is insulation: less heat enters the house,
keeping it cooler in hot weather.
The main disadvantage is the blind facade, offering less natural light.
For this type of construction, it’s important to prevent the earth from pushing against the walls
at the rear of the house. This allows better ventilation of the façade on the mountain side
and, above all, significant savings on foundations.
The second type, “restanque, staircase or stepped”.
When the slope is gentle, it enables villas to be built on variable levels
offering more natural light. The disadvantage of this type
of construction is the succession of levels, which hinders good
air circulation.
The third type, “belvedere, on stilts”.
This requires the least amount of earthwork, since the aim is to build one
or more platforms on posts. This type of construction is more
sensitive to the effects of wind, and often requires
two-way the height of the piles.
The advantages are numerous: panoramic views are unobstructed,
lower earthwork costs. And a more
environmentally friendly
The final option: complete earthworks.
This solution is the most expensive, because of the quantity of earth to be moved
in the backfill, which can be costly, not to mention the price of the retaining wall
or gunning.
Once again, this work should be entrusted to specialists.
Final tip
If you want to ensure that the recommendations made by the experts consulted in the initial
stages are respected, call in a building control firm.
This will cost you a little more initially, but will save you
from unpleasant surprises in the long run.
Thanks to André Chacra, Managing Director of ACI Aifaitoraa Concipio Ingénierie,
for his insights. And to a well-known contractor in Fenua, who did not
wish to be named.
Useful links :
The list of surveyors in French Polynesia :
www.service-public.pf/daf/wp-content/uploads/sites/42/2019/01/TABLEAU-OGPF-
06-juin-2018.pdf