Construction Principles in Antigua & Barbuda



As the theme of this session implies, this paper has been prepared to focus on the general principles adopted in the construction of buildings in Antigua and Barbuda.

It however examines these principles against a background which highlights the burning need to reduce the damage caused by hurricanes in a Caribbean Region that is caught up in the changes in global weather.

It examines various types of structures and materials and seeks to identify simple but effective ways to protect these structures.

Other necessary systems such as sewage collection and disposal and storm water control are briefly examined and their link with the local geology established.

The paper is brought to its conclusion by referring to the role that can be played by the appointed building inspectors of the Development Control Authority (DCA) in lifting the quality of our small and un-engineered buildings.


Every country is prone to some sort of natural hazard and in those places where the environment may be said to be particularly unfriendly, the country may fall under the influence of multiple natural hazards. In Antigua and Barbuda, our major areas of concern are restricted to Hurricanes and Earthquakes and these bring with them a following of other phenomena which may or may not occur. For instance depending upon the nature and intensity of a hurricane there may be flooding, coastal erosion, landslide or tornadoes. An earthquake may bring a tsunami or tidal wave with it or areas of soil liquefaction may develop with dramatic consequences.

When considering natural hazards there is a fundamental truth that must be accepted. Their frequency of occurrence, intensity and magnitude are all beyond our control. If we are to survive therefore, we must do what we can. We must put in place systems of mitigation designed to reduce their effects to manageable proportions realising that we cannot eliminate them completely.

The effects of these hazards are felt in several sectors of the life of the community. Their effect is felt in agriculture, public works and utilities, fisheries, international transportation, education, tourism, public and private buildings and the economy generally to name but some of these sectors. It would be inappropriate to address all of the sectors at this time and so this exercise will concern itself with small public and private buildings with particular reference to those in Antigua and Barbuda.

In recent years Antigua & Barbuda has been visited by hurricanes with an awesome regularity while the last destructive earthquake was experienced in October of 1974. It is not being suggested that the likelihood of the occurrence of another destructive earthquake should be ignored, but it is probably more likely that one of the several annual hurricanes will visit us. For this reason therefore this paper will concentrate on hurricanes and their effects.

In this age of advancing technology and because of the unprecedented acceleration in the dissemination of information there now exists the advantage of prior warning of the arrival of hurricanes. Although this does nothing to lessen their impact it does give valuable time to make preparations for mitigation. If this circumstance is to be most beneficial we must ensure that some of our mitigation systems are capable of being put in place in a relatively short time and are of a simplicity that will not require specialist involvement.


The first element to be considered is the soil at the site on which the building is to be constructed. In general terms, Antigua may be said to be geologically arranged into three basic soil type zones (Figure 1). In the north there are the limestones, across the middle is the clay belt and in the south the volcanic soils (Figure 1).

The limestones of Antigua are quite variable and may include water laid sedimentary deposits which are quite hard but have planes of weakness which allow the rock to be split into thin sheets. There is also soft limestone known locally as marl and used as good foundation material and widely utilised in compacted road bases. There is also around the village of Liberta a distinctive green limestone which is widely used as a decorative facing but when encountered below ground gives good bearing. There is also a white powdery limestone known as rock flour which is found in small pockets in hard rock. This is quite dangerous since it has little or no bearing capacity. Fortunately it is very rare.

The clays are by far the most interesting from an engineering point of view and must be handled with care in construction. Most of the clays tend to be what are known as swelling clays and these can exhibit enormous movements when their water content changes. Increases in the moisture content cause swelling and reductions cause shrinkage. Because of the high swelling pressures that develop (as high as 7.0 tons/ sq. ft have been recorded) buildings on these clays are likely to move and crack if their foundations are not carefully designed. Additionally there is a white clay found in a number of places including Marble Hill, Paradise View and Ottos. This behaves like marl when dry but quite embarrassingly shows itself to be a moderately soft clay when wet. Extreme care must be taken to identify this material and treat it appropriately.

The hard volcanic soils of the south are by far the most reliable foundation material only becoming problematical when heavily fractured or when interrupted by pockets of clay.

These properties of the soil all have to do with the ability of the soil to support the vertical load generated by the weight of the building. This ability to support is dependent upon what is known as the bearing capacity of the soil and is a parameter which is quantified by soil testing either in the laboratory or in place on the site.

The soil is also important from another point of view since the Health Department requires the results of a percolation test. The results of this test indicate the ability of the soil to absorb water and provide guidance in the design of the sewage collection and disposal system.

Project Development

When a person in Antigua and Barbuda decides to construct a building the basic steps are as follows. For the purposes of this exercise these steps have been simplified by omitting matters of finance and legal requirements.

  1. An Architect is appointed to design the building to suit the site and the space and functional requirements of the Client.

  2. The Architect recommends the engagement of an Engineer if in his opinion necessary.

  3. Plans and other drawings as required are prepared by the Architect and the Engineer and submitted to the Development Control Authority for approval.

  4. Following the granting of such approval, the building is constructed.

The above is the system employed for larger buildings. For smaller buildings, the system remains essentially the same except that the "Architect" may be replaced by a "Designer" who might be a Draftsman and the Engineer may be omitted or replaced by a Technician. The approval of the DCA is however not subject to change and the requirements as to drawings and information must be satisfied. Since this exercise is geared towards small buildings the latter process is the one which will more specifically be addressed. It should be borne in mind that as the small, un-engineered building is more vulnerable to damage by natural hazard, particular attention must be paid to its protection. Because of the absence of professional inputs in its production, the required protection to reduce its vulnerability must come from elsewhere and so it is here that the vigilance of the Development Control Authority Inspectorate becomes crucial.

Development Control

The question that must now be asked is, "How is the DCA Inspectorate to provide the level of protection necessary to ensure the safety of buildings passing through their control machinery and carrying their official stamp of approval?" It now becomes obvious that the training of the Inspectors must be raised to such a level that it enables them to discharge this important responsibility with credible authority. Of course the proper training solves one problem but there are others. The number of Inspectors must be commensurate with the volume of work flowing through the Authority. There will also need to be a Chief Inspector to whom the Inspectors report and who in turn reports to the Town & Country Planner and attends the regularly held approval meetings. It is to be hoped that this workshop will produce suitable forms to make such reporting capable of providing the information and guidance needed for the granting of approval or otherwise where appropriate. Of course, suggestions such as these would require significant fine-tuning so that they fit into the intended functioning of the control authority unit.

At this point of Antigua and Barbuda’s development the demand for small housing and commercial units appears to be focussed on concrete and concrete block as the basic materials. Next would be a timber building on a concrete floor slab followed by a complete timber unit. It might therefore be prudent to first examine some of the pertinent concerns involved in the construction of a small concrete building. For completeness parallel references will also be made to timber construction.

Damage Caused by Recent Hurricanes

The main purpose of this exercise is to examine present practices within the construction industry, identify any shortcomings they may possess and devise appropriate ways to improve them so as to reduce the effects of hurricanes on buildings.

To assist in focusing on and identifying shortcomings it may be useful to examine some of the problems that were exposed by the latest hurricanes.

The various types of damage described above are so varied that it is clear that hurricane resistant design techniques need to be improved. Unfortunately, the improvement of the techniques is not the whole solution to the problem but systematic and rigorous implementation is also required.

The photographs included later show some of the devastation wrought in Antigua by the latest hurricanes.

Reconstruction Efforts

After the passage of a hurricane the immediate concern of the homeowner who has suffered significant damage is almost universally the same. After the shock of the event has somewhat abated, the damage is assessed and the question to be answered is how soon can the shelter once provided by this structure be restored?

It is that question which can lead to reconstruction being undertaken without the inclusion of some of the measures that would enhance the hurricane resistance of the buildings. In Antigua a number of buildings have been reconstructed in this way and some of the reasons cited are lack of financing, lack of alternative accommodation and a shortage of experienced workmen.

While these might be real enough reasons this state of affairs does not lead to mitigation during future events and it is a waste of what little resources were available.

The way forward must be, do whatever must be done to provide sufficient time to include in the reconstruction plans, elements designed to reduce future damage.

Recommendations for Safe Construction

In this section the various elements of a building are considered in turn and recommendations are made for the safe construction of each of these elements. The concept being used here is that if the component parts of a building are improved then the whole building is likewise improved.


In Antigua some builders are known to refer to what they call a "normal foundation". By this they mean a strip footing 2’ – 0" wide and 9" thick. It must be borne in mind that the dimensions of a foundation depend upon the load to be supported and the type of soil on which the foundation is constructed. It is therefore obvious that there is really no such thing as a normal foundation. Foundations have been dealt with adequately in the Building Guidelines and reference to the relevant sections of this document is urged. It may be useful to list a few pointers here.

When a timber house is being built with a concrete floor, the foundation arrangement may be the same as for a house with concrete walls, if strip footings are being considered.

Another common type of foundation being used for both concrete and timber buildings is the solid raft foundation. This type of foundation has the advantage of forming the floor and the foundation of the building at the same time (Figure 7). There are some conditions under which this type of foundation is more appropriate.

Condition No. 1 is necessary so that any settlement that takes place will be uniform and the building will not tilt.

Condition No. 2 is allowable since the entire floor area is being used to support the building thus reducing the contact pressure on the soil.

Condition No. 3 is important because the raft also forms the floor of the building and being a low lying element, could easily be flooded.


The floor of a house is an element that requires a significant percentage of the cost of construction and it is therefore important that it is protected and that it is used to improve the characteristics of the building. The general tendency here is to use a 4" concrete slab with BRC #66 somewhere in it. Welded wire mesh reinforcement is handled so badly on the local scene that it is sometimes seen penetrating the top of the slab and sometimes it penetrates the bottom. At other times it is in the middle. It is advisable to put the reinforcement where it does the best for the slab. If the ground floor slab is on polythene sheeting on a well compacted marl base then there should be little or no bending and the reinforcement may be put near the top of the slab to control any surface cracking that may take place and damage the tile finish. Where the base is soft, some settlement accompanied by bottom cracking is likely and the reinforcement may be more useful in the bottom controlling the width of bottom cracks. The more careful builders have hooks on hand when casting floors and these are used to lift the reinforcement to the required depth in the concrete after being trodden underfoot by the other workers. It might be useful here to say a bit about the placing of the concrete since an inspector who visits during the construction period may be able to make a useful input at this point.

It is important to remember that the workers have been in the sun all day and it eases their load if the concrete for the floor is soft and flows into place with little or no effort. This is good for the worker but bad for the concrete since too wet concrete tends to crack as it dries out during curing.

Remember also that it is good to vibrate or rod the concrete thoroughly since this produces a good dense concrete. Concrete is not a waterproof material but by compaction its porosity is reduced thus inhibiting the phenomenon of rising damp.

Where timber floors are being used the most important factor to consider is the rigidity of the floor. A bouncing floor does not promote confidence in the occupants of the building. Care should be taken to ensure that the floor joists are provided with adequate intermediate supports. This rigidity also protects inflexible floor finishes from cracking and loosening. The Building Guidelines provide adequate guidance on the location of intermediate supports and the safe spans of certain joist sizes and spacings.


Although the walls of a building are so located that they bear the full lateral force of a hurricane’s winds they usually suffer relatively few collapses during hurricanes. In earthquakes also, the walls are exposed to significant lateral loads especially where roofs are of very heavy construction. Since an earthquake is an acceleration, a heavy roof imposes a heavy lateral load on the top of the wall. If the connection between the roof and the wall is poor then the connection fails. If the connection is good, the lateral load is transmitted to the wall, which must be strong enough to withstand it. In both of these perils therefore the walls are a very important element¼ . so important in fact that if you lose a wall you will most probably lose your building in a hurricane or an earthquake.

For concrete walls the tradition is to use vertical ½" or 3/8" vertical rod reinforcement at about 4’ – 0" centres (Figure 5). The intention is that the reinforced cores of the blocks should be filled solid with concrete. Unfortunately very often this is not consistently done and cracking usually develops in the missed areas. The way to avoid this is to see to it that block cores are filled after every three courses. The filling should stop 2" below the top of the block so that joints in the filling do not coincide with the block joints. To enhance wall performance we would like to suggest that horizontal wall reinforcement be introduced at 24" c/c (every 3rd course). This helps to maintain wall integrity in cracked walls and so gives protection against falling masonry in an earthquake. To ensure the effectiveness of the vertical reinforcement it MUST be anchored at the foundation level AND at the ring beam level. (Figure 6)

Additional ½" diameter bars should be placed at corners, junctions and the jambs of doors and windows in the number and manner described by the Guidelines.

Of course for both timber and concrete walls, window and door installations are of the utmost importance. If a house looses a window or door during a hurricane it will almost certainly lose its roof as well because of the build up of internal pressure. Try at all times to provide fixing on all four sides of a window and a closed door.

In many cases of severe hurricane damage, the point of weakness has been in the window. Not usually the window strength, but its installation. The loss of a window or door provides what is called a dominant opening on one side of the building. Wind entering through it cannot leave and so a build-up of internal pressure takes place. It is therefore very important to protect the windows and doors and it is gratifying to see the tremendous number of houses now being fitted with hung timber shutters. This is an easily retrofitted element. A much neglected aspect of wall construction is the door or window lintel (Figure 8). Most lintels are constructed like normal vertical load carrying beams without realising that the lintel is subjected to horizontal wind load transferred to it by the window or door as well as by the wall above the lintel. Because several buildings have very wide windows and multi-leaf doors leading onto patios and terraces their lintels must be capable of resisting these horizontal loads over such wide spans and so the arrangement of the reinforcement must be altered.

Also, to avoid diagonal cracking of the walls at the corners of door and window openings, the lintel should be given not less than 8" bearing at each end.

The traditional timber wall in Antigua also seems to have fared well. This is usually a frame of 2" x 4" studs at 16"c/c with plates of double 2" x 4". Wall coverings are usually T-111 plywood but ship-lap siding seems to be increasing in popularity again.


It should be considered that the roof of a building starts at the ring beam because it is here that its main support is established. The traditional roof in Antigua provided a deliberate eaves fastening but unfortunately it only utilised a portion of the rafter depth. This has largely now been replaced by the over rafter U-bar fixing which is a great improvement (Figure 9).

It would be true to say that because of the almost annual occurrence of hurricanes in Antigua builders are now much more concerned about roof vulnerability. Roofs are steeper, overhangs are shorter, eave fastening is better and sheeting is screwed down rather than nailed down.

What has not yet been fully appreciated is that the uplift at the eaves is roughly the same as that at the ridge and yet the ridge end of rafters is left un-reinforced. We have been recommending a galvanised strap across pairs of rafters (Figure 10). Simpler yet and available as a retro fit technique is a rafter tie which also stops the roof from being split apart at the ridge. Because this tie is rigid it can also act as a rafter strut and reduce the flexibility of the roof by shortening the effective span of the rafters (Figure 11).

Although roof coverings are being screwed down rather than being nailed down, some attention must be paid to the spacing of the fasteners. Because of the distribution of wind pressures over the roof surface, every corrugation along the eaves and ridge should be fastened, with wider spacing being used over the rest of the roof.

In Antigua roofs are traditionally gable and hip roofs. Over the years however it has been found that the hip roof performs better in a hurricane. With our heightened hurricane awareness the trend is towards the ideal which is a steeper hip roof with little or no eaves overhang. Where there are existing roofs with moderate to generous overhangs, strengthening has been effected using hurricane clips. This method of retrofit is used on concrete buildings as well as on timber buildings.

There is a tendency in Antigua to design houses with very complex roof structures. Although the basic roof unit is a hip, multiple roofs are so put together that several valley arrangements are formed. If these valleys are not well built there can be serious roof leaking and so simple roofs are recommended. The earlier traditional roofs utilised the truss to some extent with the bottom chord being used in the ceiling framing (Figure 12). The truss also has the advantage of exerting no thrust on the walls as un-tied rafters do.

A word should also be said about asphalt shingle roof covering which has been used with varying success. The most successful asphalt shingle roofs had increased nailing and used roof cement as an additional adhesive. This method of fixing is highly recommended.

Storm Water Drainage

This is an important element which does not usually receive due attention. Although Antigua may be described as a relatively dry island, it can and from time to time does experience heavy flooding rains. Because of the soil types present there is a large amount of run-off and little penetration by storm water. It is therefore necessary to make provision for the collection and safe disposal of storm water.

The portion of water falling on the roof is usually collected in a cistern or a number of water tanks (Figure 13). The water falling on the rest of the site must be directed by the adjustment of the ground levels to the roadside edge of the site where it is hoped that a roadside drain will be found. Again because of the soil types present care must be taken to drain storm water away from the building so that seepage to the foundation material is minimised to reduce the possibility of swelling which can cause damage to a building or its floor.

Sanitary Waste Collection & Disposal

In Antigua, because there is no coral limestone, sewage is collected in a two-chamber septic tank and the effluent that issues from the other end must be disposed of safely (Figure 2). Traditionally this is piped to a large hole in the ground that has been filled with graded stones called a soak-away (Figure 3). The intention is that the stones scatter or break up the flow of the effluent thus distributing it over the surface of the walls of the hole where it is absorbed. If the soil has a high clay content very little absorption will take place and the soakaway does not function well and soon becomes filled with health endangering effluent. In such situations a drain field may be used (Figure 4). This may consist of perforated PVC pipes laid level in a stone filled trench at a depth of about 12". These pipes spread the effluent over a large area of the site where it may be absorbed by the dry topsoil, transpired by the vegetation and evaporated by the sun and wind.

Recommendations for Effective Development Control

It might be said that the building practices used for the construction of small buildings in Antigua today are close to satisfactory. It is extremely gratifying to note that because of the regularity of our hurricane events there has been a marked heightening of awareness among owners and builders alike. There is hardly an adult in Antigua today who has not experienced a hurricane first hand. Who has not ventured outside for the first time after a hurricane to see what damage has been inflicted on their property. Antiguans are now fully aware of the awesome power that there is in a full-blown hurricane.

Note that the descriptive phrase used is "close to satisfactory" and we need to examine why such qualifying word as "close" is necessary. Some home owners have not suffered severe damage and so they are not fully awake. Perhaps their time will come. But the problem to be dealt with concerns those builders who are not fully sensitized. In recent years the number of "Contractors" in Antigua has increased alarmingly and there is no regulating body in place to say who is or is not qualified to claim the name. Because of this state of affairs the DCA can now play a very important role by shifting focus. Since there is no body in place to regulate the builder let the DCA regulate the quality of buildings they approve for construction. To ensure the effectiveness of this new approach a number of questions must be answered.

These questions touch on the fundamental issues that must be explored if the DCA is to be capable of lifting the standard of the country’s building stock and indeed if they are the body to do so.

To ensure this capability, the Building Inspectors who review submitted plans as well as construction on site must realise that the Laws of Antigua require that buildings comply fully with the "Antigua & Barbuda Building Guidelines". Therefore they are simply ensuring compliance with the law when they base their reviews on the clauses of the Building Guidelines.


Having followed the development of this exercise it should have led to certain logically formulated conclusions.

Firstly, it must be recognised that the forces of nature will, as they have in the past combined to produce hurricanes, continue to do so in the future. These organized structures of wind, moisture and energy that sweep across the Atlantic from the coast of Africa to the coast of North America will continue to adversely affect the islands of the Caribbean Archipelago which lies in their path. Hurricanes are here to stay and so steps must be taken to lessen the damage they inflict on buildings and other engineering installations.

Since the power of the hurricanes cannot be reduced, then the resistance of building structures to the forces they exert must be increased.

The way to do this is by paying careful attention to the construction principles that have traditionally been in use throughout the region and improve upon them by the addition of well designed and proven systems of mitigation.

Several of these systems have been examined in this exercise and they have been fully described in the Building Guidelines.

The use of the Building Guidelines therefore, which is now mandated by law, is crucial to the achievement of the building strengthening that is sought.

The vehicle for the implementation of the Guidelines is the Development Control Authority and the training of their Inspectors will equip them to guide the designers and builders in paths that lead to the mitigation that is so desirable.

So what generalised statements can be made about mitigation? One statement is that a building that is to survive a hurricane must be a "fully tied building".

If all of these ties are maintained the chances of survival will be greatly enhanced. It is therefore important to examine houses not only while they are under construction but also houses that have been built years ago. During construction ensure that these ties are being incorporated and with existing houses undertake programmes of retrofitting to install any missing ties. Remember that money spent in installing mitigating features is money well spent. It is less costly to repair a damaged house than it is to replace a destroyed one.

USAID/OAS Post-Georges Disaster Mitigation:

Page last updated on 05 Jun 2001